G
Guest
·I want to get extended upper and lower trailing arms, but I don't know if I should get adjustable uppers or not. What is the purpose of getting adjustable? Is it worth it? Any advice? I have a '96 caprice.
Adjustable upper arms... yea or nay?
1 - 20 of 36 Posts
G
Guest
·It is necessary to also extend the upper control arms when extended lowers are installed. This is in order to maintain proper driveline angle. Not doing so will result in abnormal wear of the U-joint(s), vibration, and potential excess wear to the trans tailshaft bushing and can even lead to transmission failure.
Unfortunately, there are no "extended" upper control arms that are fixed length with the same characteristics as the OE stamped steel upper arms, which are designed to flex, and which seem to provide the best overall axle control without any real downside, as long as the bushings are in good condition. There is an exception, and that is cars that are lowered significantly. The flexibility of the OE arms masks the fact that at the extreme of travel the B-body rear suspension, as designed, is in a "bind" condition. Lowered cars operate with the suspension alot closer to the "edge" of rear suspension bind and often suffer problems with bushing wear, increased tendencty to incur wheel hop, harsher ride, etc.
The aftermarket does have adjustable rear upper arms. None of them have any flex designed in as do the stock upper arms, and many use polyurethane bushings, which have less compliance than the stock rubber, which was the OE choice for many years, though newer OE applications are now seeing use of more sophisticated materials, including urethanes.
Depending on the source, there are a number of available upper arms that use a spherical bearing at one end or at both ends instead of bushings. The use of bearings can eliminate most of the bind, however a price is usually paid--cost, bearing wear, driveline noise in the chassis/body/passenger compartment, and increased ride harshness are a few potential issues.
With adjustable arms, the biggest issue probably comes down to getting the ride height set where you intend to run it and then adjusting the arms to provide/restore the proper driveline angles.
A second issue is that WHEN the rear axle is placed in extended position, the mounting positions on the frame and rear axle housing for the upper control arm are no longer aligned properly with each other. This actually FORCES any regular rubber or poly bushing into static bind, with the car sitting still at normal ride height. This leads to problems typically seen when there are bushings at BOTH ends, such as torn bushings--a spherical bearing at one end does help but is not 100% effective at resolving this issue. I have not yet seen an adjustable upper arm that compensates for this misalignment--BUT I believe that something will eventually be produced that does.
There is an entire section in the Factory Service Manual devoted to driveline adjustment, and I will only suggest that anyone who plans to or has moved the rear axle become familiar with it.
Not to scare you away from the idea, but there are ancillary issues that go with moving the axle:
--exhaust system clearance, especially with aftermarket systems with larger pipe diameters
--change in relationship of upper/lower spring seats, thus rear spring angle/loading, much more critical with lowering springs
--change in shock absorber angle, and induced bind/wear on the mounts, which typically use a rubber or urethane bushing
--frame-to-axle brake hose length compensation--not usually a problem, but something to pay attention to
--rear axle pinion snubber contact location at top center of "nose" of differential, which may call for a longer bumper to contact sooner (especially if using a larger than stock driveshaft), or relocation of the bumper to avoid being chewed up by the pinion flange/deflector ring
--driveshaft slip yoke spline contact reduction which lowers overall torque capacity of the driveline (in reality it increases the area load on the slip yoke that is now LESS engaged with the trans output shaft = greater chance of twisting the splines). A longer slip yoke alone may or may not be sufficient to restore this to a "normal" or acceptable range, depending on the power level being applied. The act of moving the front U-joint away from its ideal location in relation to the tailshaft bushing of the transmission changes the loading that the transmission "sees" internally, and may eventually do harm. Bottom line, you have to consider a new driveshaft, regardless of what the extended arm supplier may tell you.
Unfortunately, there are no "extended" upper control arms that are fixed length with the same characteristics as the OE stamped steel upper arms, which are designed to flex, and which seem to provide the best overall axle control without any real downside, as long as the bushings are in good condition. There is an exception, and that is cars that are lowered significantly. The flexibility of the OE arms masks the fact that at the extreme of travel the B-body rear suspension, as designed, is in a "bind" condition. Lowered cars operate with the suspension alot closer to the "edge" of rear suspension bind and often suffer problems with bushing wear, increased tendencty to incur wheel hop, harsher ride, etc.
The aftermarket does have adjustable rear upper arms. None of them have any flex designed in as do the stock upper arms, and many use polyurethane bushings, which have less compliance than the stock rubber, which was the OE choice for many years, though newer OE applications are now seeing use of more sophisticated materials, including urethanes.
Depending on the source, there are a number of available upper arms that use a spherical bearing at one end or at both ends instead of bushings. The use of bearings can eliminate most of the bind, however a price is usually paid--cost, bearing wear, driveline noise in the chassis/body/passenger compartment, and increased ride harshness are a few potential issues.
With adjustable arms, the biggest issue probably comes down to getting the ride height set where you intend to run it and then adjusting the arms to provide/restore the proper driveline angles.
A second issue is that WHEN the rear axle is placed in extended position, the mounting positions on the frame and rear axle housing for the upper control arm are no longer aligned properly with each other. This actually FORCES any regular rubber or poly bushing into static bind, with the car sitting still at normal ride height. This leads to problems typically seen when there are bushings at BOTH ends, such as torn bushings--a spherical bearing at one end does help but is not 100% effective at resolving this issue. I have not yet seen an adjustable upper arm that compensates for this misalignment--BUT I believe that something will eventually be produced that does.
There is an entire section in the Factory Service Manual devoted to driveline adjustment, and I will only suggest that anyone who plans to or has moved the rear axle become familiar with it.
Not to scare you away from the idea, but there are ancillary issues that go with moving the axle:
--exhaust system clearance, especially with aftermarket systems with larger pipe diameters
--change in relationship of upper/lower spring seats, thus rear spring angle/loading, much more critical with lowering springs
--change in shock absorber angle, and induced bind/wear on the mounts, which typically use a rubber or urethane bushing
--frame-to-axle brake hose length compensation--not usually a problem, but something to pay attention to
--rear axle pinion snubber contact location at top center of "nose" of differential, which may call for a longer bumper to contact sooner (especially if using a larger than stock driveshaft), or relocation of the bumper to avoid being chewed up by the pinion flange/deflector ring
--driveshaft slip yoke spline contact reduction which lowers overall torque capacity of the driveline (in reality it increases the area load on the slip yoke that is now LESS engaged with the trans output shaft = greater chance of twisting the splines). A longer slip yoke alone may or may not be sufficient to restore this to a "normal" or acceptable range, depending on the power level being applied. The act of moving the front U-joint away from its ideal location in relation to the tailshaft bushing of the transmission changes the loading that the transmission "sees" internally, and may eventually do harm. Bottom line, you have to consider a new driveshaft, regardless of what the extended arm supplier may tell you.
G
Guest
·Well said 'Lifer!!!
The whole room just got a little brigther on my end.
Thanks for the enlightenment!
The whole room just got a little brigther on my end.
Thanks for the enlightenment!
G
Guest
·Just having a good day, I guess--thanks! 
G
Guest
·Can somebody PLEASE sticky this one to the top of the suspension forum?
Outstanding, Bill.
Edit-denkyubedymuch!
Outstanding, Bill.
Edit-denkyubedymuch!
G
Guest
·Wow! A lot of info here. I would like to get the BMR arms and an extended driveshaft but I don't know wheather to get adjustable or fixed arms. Are fixed less hassle than adjustable? What would be a better choice? I also plan to put stock impala springs and new shocks on my caprice. Any ideas for shocks and any other suspension mods I should do while I'm down there?
G
Guest
·The BMR fixed arms would certainly be less hassle than the adjustables. They don't address any of the issues I've mentioned very well, or make things worse, in my opinion, but they do move the axle back and should maintain pinion angle.
Nothing to offer on shocks or springs--too many choices!
Nothing to offer on shocks or springs--too many choices!
G
Guest
·We are very, very lucky to have assets like Bill!
Thanks!
Peter
Thanks!
Peter
G
Guest
·If you go with extended uppers, I highly recommend you install the uppers first (ie. leave the lowers off). Due to the fact that the angle is offset from stock, the bolt holes in the uppers are very difficult to align. However, if you disconnect the brake lines from the axle housing and leave the lowers off you can easily manipulate the rear and get the holes to line up in mere minutes.
I did it the other way at first and it took me 3 nights cursing and swearing I'd never do it again.
Oh and Bill, thanks for your service to our contry!
I did it the other way at first and it took me 3 nights cursing and swearing I'd never do it again.
Oh and Bill, thanks for your service to our contry!
G
Guest
·Glen, it was a privilege and honor. Thank you, from ALL who have served.
G
Guest
·Bill:
Are you saying, for non extended control arms, it is better to leave the OEM uppers in because they "flex"?
Or is a Hotchkis or BMR better over OEM fixed length?
Roger
Are you saying, for non extended control arms, it is better to leave the OEM uppers in because they "flex"?
Or is a Hotchkis or BMR better over OEM fixed length?
Roger
G
Guest
·Roger,
What I'm saying is HOW the car is used will reveal the shortcomings of any design that doesn't accomodate axle motions that the stock arms take in stride through their flexible design.
As I know you put more "straight-line" stress on your car than other modes, you may not experience the downside of non-stock links that are most commonly used--lots of differnt brands with the same basic design.
Doesn't mean you won't ever see or feel the effect, as you still have to turn around at the end of the strip, and the suspension is going to be forced out of straightline mode then, and in just turning out of a driveway and lots of other normal road-going situations.
Many aftermarket uppers use polyurethane with a fabricated solid link, and if there is NO twist in the link, the normal ride motions, side forces, travel over uneven surfaces, etc, is putting alot of stress on the bushings that stock control arms deal with by their own ability to move/twist/flex in conjunction with the stock rubber bushings. Poly has a "cold flow" characteristic that will force it to change shape--rubber of the type used in bushings has better memory/resilience. Once poly is forced out of shape, the link point is no longer being captured in every direction--it can get sloppy, in other words. I emphasize that this happens over time, but usually more quickly than the stock rubber will deteriorate/wear.
For standard axle location/wheelbase, I'd stick with stock arms until a design similar to what Currie or Edelbrock makes (not specifically for B-body) does become available. Hotchkis is in the process of changing to a new design for their adjustable upper that will be fitted with a spherical bearing on the frame end--its been over a year in the making and should be available soon. I'd stick with rubber bushings on the axle, no matter what, unless going to a full-race setup, where I'd use bearings at both ends.
I know of at least one enterprising SS owner who has boxed the uppers and is using a spherical bearing/sleeve setup in place of the frame-end bushings and is happy with the result (stock axle location, of course). I think he's still using rubber on the axle side, too.
What I'm saying is HOW the car is used will reveal the shortcomings of any design that doesn't accomodate axle motions that the stock arms take in stride through their flexible design.
As I know you put more "straight-line" stress on your car than other modes, you may not experience the downside of non-stock links that are most commonly used--lots of differnt brands with the same basic design.
Doesn't mean you won't ever see or feel the effect, as you still have to turn around at the end of the strip, and the suspension is going to be forced out of straightline mode then, and in just turning out of a driveway and lots of other normal road-going situations.
Many aftermarket uppers use polyurethane with a fabricated solid link, and if there is NO twist in the link, the normal ride motions, side forces, travel over uneven surfaces, etc, is putting alot of stress on the bushings that stock control arms deal with by their own ability to move/twist/flex in conjunction with the stock rubber bushings. Poly has a "cold flow" characteristic that will force it to change shape--rubber of the type used in bushings has better memory/resilience. Once poly is forced out of shape, the link point is no longer being captured in every direction--it can get sloppy, in other words. I emphasize that this happens over time, but usually more quickly than the stock rubber will deteriorate/wear.
For standard axle location/wheelbase, I'd stick with stock arms until a design similar to what Currie or Edelbrock makes (not specifically for B-body) does become available. Hotchkis is in the process of changing to a new design for their adjustable upper that will be fitted with a spherical bearing on the frame end--its been over a year in the making and should be available soon. I'd stick with rubber bushings on the axle, no matter what, unless going to a full-race setup, where I'd use bearings at both ends.
I know of at least one enterprising SS owner who has boxed the uppers and is using a spherical bearing/sleeve setup in place of the frame-end bushings and is happy with the result (stock axle location, of course). I think he's still using rubber on the axle side, too.
G
Guest
·Bill:
thanks. The UCA's in the rear are stock and the lowers are Hotchkis. Want to replace the uppers but do not want a Polly bushing.
I have retired the SS from the 1/4 mi and will be putting the 3:42's back in for the LV run.
For some reason the BMR's are 1/2 the cost of Hotchkis. Both brands only offer polly bushings, IIRC. I have no interest in the extended version.
thanks again.
Roger
thanks. The UCA's in the rear are stock and the lowers are Hotchkis. Want to replace the uppers but do not want a Polly bushing.
I have retired the SS from the 1/4 mi and will be putting the 3:42's back in for the LV run.
For some reason the BMR's are 1/2 the cost of Hotchkis. Both brands only offer polly bushings, IIRC. I have no interest in the extended version.
thanks again.
Roger
G
Guest
·rosadod,
I ordered Global West's Rear Lower Control Arms with a 3/4" extension. For the upper arms, I made my own (see below)...
It was a real pleasure to finally meet Bill Harper at Las Vegas...
I have built a set of chrome moly adjustable rear upper control arms which Bill saw at Las Vegas.
![]()
I hope to install them this weekend (big maybe)on my 94 9C1. They have spherical joints on the front and an offset yoke on the rear to compensate for the 3/4" extension. With centered yokes, they can be used for stock length axles. (Actually, I should make a set of centered yokes for stock length and install them on my car before doing the extendeds. I currently have no issues and that makes my car a good test platform to ensure these arms work perfect. I'll be slapping on all the goodies for the extended set-up which will be rather full blown & complicated & might possibly cause issues of all sorts.)
Anyway, I designed these to use the stock GM 14mm & 12mm mounting bolts & use the stock GM rubber axle bushings. I'll post installation & road test results as soon as possible. They are a closed body turnbuckle style arm like the Edelbrock & Hotchkis arms for the GM A & G body cars and use the same 3/4"-16 threaded studs. Larger chrome moly studs are available in 7/8"-14 and monster 1 1/8"-16.
Bill might post something about what he saw and Iam hoping they work perfect & install without issues. The axle (either one of the rear wheels)can move over 8 inches before the sphericals reach bind & with the bump stops only 3 1/2" away from the frame, all "SHOULD" be OK except for the biggest & deepest New York Pot Hole..!<---- I bet the rear springs would fall out if you hit it..!
The spherical cartridges are UHMW plastic and since ISSCA Las Vegas, I have learned to lubricate them using non petroleum lubricants such as Teflon Grease. Petroleum lubricant causes UHMW to swell (causing bind)...
George
I ordered Global West's Rear Lower Control Arms with a 3/4" extension. For the upper arms, I made my own (see below)...
It was a real pleasure to finally meet Bill Harper at Las Vegas...
I have built a set of chrome moly adjustable rear upper control arms which Bill saw at Las Vegas.
I hope to install them this weekend (big maybe)on my 94 9C1. They have spherical joints on the front and an offset yoke on the rear to compensate for the 3/4" extension. With centered yokes, they can be used for stock length axles. (Actually, I should make a set of centered yokes for stock length and install them on my car before doing the extendeds. I currently have no issues and that makes my car a good test platform to ensure these arms work perfect. I'll be slapping on all the goodies for the extended set-up which will be rather full blown & complicated & might possibly cause issues of all sorts.)
Anyway, I designed these to use the stock GM 14mm & 12mm mounting bolts & use the stock GM rubber axle bushings. I'll post installation & road test results as soon as possible. They are a closed body turnbuckle style arm like the Edelbrock & Hotchkis arms for the GM A & G body cars and use the same 3/4"-16 threaded studs. Larger chrome moly studs are available in 7/8"-14 and monster 1 1/8"-16.
Bill might post something about what he saw and Iam hoping they work perfect & install without issues. The axle (either one of the rear wheels)can move over 8 inches before the sphericals reach bind & with the bump stops only 3 1/2" away from the frame, all "SHOULD" be OK except for the biggest & deepest New York Pot Hole..!<---- I bet the rear springs would fall out if you hit it..!
The spherical cartridges are UHMW plastic and since ISSCA Las Vegas, I have learned to lubricate them using non petroleum lubricants such as Teflon Grease. Petroleum lubricant causes UHMW to swell (causing bind)...
George
G
Guest
·Very nice looking upper!!!!! They look better than my Metco's
G
Guest
·edfromm,
Thank you for such a great compliment..!
![]()
It cost me a $140 in parts, machining & powder coating to make one set. If I sold them, the price would be $210 + shipping. For the larger sized studs, I would have to locate a machine shop capable of performing the tube swaging and I am sure the price would be more because I got a great deal from the shop doing 3/4 sizes...
Thanks again--George
Thank you for such a great compliment..!
Thanks again--George
G
Guest
·rosadod,
I think you should use adjustable upper control arms if you plan to extend the rear axle... You will most likely need pinion angle adjustment capability [if you extend the rear]. If the control arms are built as a perfect set of four arms then adjustment will not be a necessary feature. But, if you plan to race your car then having adjustable suspension components is a big plus especially in drag racing for traction.
So far, all the upper arms available by the major manufacturers do not properly compensate for extending the axle. In that, all the arms currently available are built as straight units with all the parts centered. Because the upper arms form a 90 degree "V" to help the lower arms keep the axle centered transversly; straight arms will not work properly.
Reason, when the axle is moved to a new location it also moves the two bolt up points on each side of the pumpkin. By bolting on straight control arms when two of the four bolt points has moved there will be a bind condition created. Reason, the forward chassis bolt points remain in the original position and the straight arms are still pointing to the original rear bolt up point. The only way to make the arms fit is to force them into the new rear bolt up point read stumpy's post above. This causes bind, torn bushings, etc... Bind is very bad because it can cause a tire to leave the road surface [very bad, especially in spirited driving]. Also, GM engineers are not stupid & neither are the other car makers; that is why the upper control arms are placed at a perfect 90 degrees to help the lower arms keep the wheels from moving to the left & right or worse..! The lower control arms on our cars also form an obtuse angle to help the upper arms control transverse axle movement.
I have built my first set of rear upper control arms that use Pythagorum's Theory to reach the new bolt up points created by moving the axle rearward yet the arms are straight and will not create bind.
In fact, I have included all the features I know of so these arms will eliminate most if not all bind with one exception. I purposely want to retain the GM original rubber bushings in the axle. Reason, the slight amount of bind remaining as a result of tightly bolting onto the rubber bushing is offset by the fact that a rubber bushing will control axle "Wrap-Up" better than stiffer bushings i.e. Delrin, Polyurethane, etc... Minimizing but NOT eliminating axle Wrap-Up greatly improves rear wheel traction especially when the throttle is opened quickly [drag racing]. Do an internet search for "Wrap-Up" and see how many rubber bushing snubber kits are on the market. If you remove all the rubber that GM installed then there is a chance you may need to buy axle snubbers to regain the original rear wheel traction capabilities of the car.
When the throttle is opened quickly the pinion gear tries to climb the ring gear because for every action there is an equal & opposite reaction. It comes about because the axles, wheels & tires are grabbing & rotating in one direction while the entire case of the rear axle is trying to rotate exactly opposite. This is called axle wrap-up a bad thing for tire to road surface friction but a small amount of controlled wrap-up is better than eliminating wrap-up. Think of how this works: The invention of thin sidewalls on drag slicks was a cure for most of wrap-up but it is still there...
I also wanted spherical bearing type bushings on the forward bolt up points to replace loosing the twist arm characteristics. I used 4 x 4 off road, high articulation type sphericals with advanced UHMW plastic...
I have a lot more to say about this subject but must close for now... I just hope like hell that my arms will fit the chassis... Hopefully, I'll be bolting them on very, very soon...
P.S. Bill Harper: I showed an aircraft engineer my control arms in Seattle yesterday. He said they are strong enough to suspend the entire car off the ground. However, I know what Hotchkis is using and that some owners have high horsepower cars so I plan some 7/8"-14 models too.
George
I think you should use adjustable upper control arms if you plan to extend the rear axle... You will most likely need pinion angle adjustment capability [if you extend the rear]. If the control arms are built as a perfect set of four arms then adjustment will not be a necessary feature. But, if you plan to race your car then having adjustable suspension components is a big plus especially in drag racing for traction.
So far, all the upper arms available by the major manufacturers do not properly compensate for extending the axle. In that, all the arms currently available are built as straight units with all the parts centered. Because the upper arms form a 90 degree "V" to help the lower arms keep the axle centered transversly; straight arms will not work properly.
Reason, when the axle is moved to a new location it also moves the two bolt up points on each side of the pumpkin. By bolting on straight control arms when two of the four bolt points has moved there will be a bind condition created. Reason, the forward chassis bolt points remain in the original position and the straight arms are still pointing to the original rear bolt up point. The only way to make the arms fit is to force them into the new rear bolt up point read stumpy's post above. This causes bind, torn bushings, etc... Bind is very bad because it can cause a tire to leave the road surface [very bad, especially in spirited driving]. Also, GM engineers are not stupid & neither are the other car makers; that is why the upper control arms are placed at a perfect 90 degrees to help the lower arms keep the wheels from moving to the left & right or worse..! The lower control arms on our cars also form an obtuse angle to help the upper arms control transverse axle movement.
I have built my first set of rear upper control arms that use Pythagorum's Theory to reach the new bolt up points created by moving the axle rearward yet the arms are straight and will not create bind.
In fact, I have included all the features I know of so these arms will eliminate most if not all bind with one exception. I purposely want to retain the GM original rubber bushings in the axle. Reason, the slight amount of bind remaining as a result of tightly bolting onto the rubber bushing is offset by the fact that a rubber bushing will control axle "Wrap-Up" better than stiffer bushings i.e. Delrin, Polyurethane, etc... Minimizing but NOT eliminating axle Wrap-Up greatly improves rear wheel traction especially when the throttle is opened quickly [drag racing]. Do an internet search for "Wrap-Up" and see how many rubber bushing snubber kits are on the market. If you remove all the rubber that GM installed then there is a chance you may need to buy axle snubbers to regain the original rear wheel traction capabilities of the car.
When the throttle is opened quickly the pinion gear tries to climb the ring gear because for every action there is an equal & opposite reaction. It comes about because the axles, wheels & tires are grabbing & rotating in one direction while the entire case of the rear axle is trying to rotate exactly opposite. This is called axle wrap-up a bad thing for tire to road surface friction but a small amount of controlled wrap-up is better than eliminating wrap-up. Think of how this works: The invention of thin sidewalls on drag slicks was a cure for most of wrap-up but it is still there...
I also wanted spherical bearing type bushings on the forward bolt up points to replace loosing the twist arm characteristics. I used 4 x 4 off road, high articulation type sphericals with advanced UHMW plastic...
I have a lot more to say about this subject but must close for now... I just hope like hell that my arms will fit the chassis... Hopefully, I'll be bolting them on very, very soon...
P.S. Bill Harper: I showed an aircraft engineer my control arms in Seattle yesterday. He said they are strong enough to suspend the entire car off the ground. However, I know what Hotchkis is using and that some owners have high horsepower cars so I plan some 7/8"-14 models too.
George
G
Guest
·XBOX, what's the story? Did you ever get them installed, and how did they turn out? I might be interested in a set of stock length ones if you decide to produce and sell them. Let me know.
![]()
G
Guest
·What he saidOriginally posted by HEADSICK:
XBOX, what's the story? Did you ever get them installed, and how did they turn out? I might be interested in a set of stock length ones if you decide to produce and sell them. Let me know.![]()
G
Guest
·Great looking CA's--excellent work! I'd be interested in the extended length when they're available.
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