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Discussion Starter #1
Hey guys,

New to B-body's but not LT-1s.

Anyway, I see on UMI performance website saying you DON'T need adjustable rear Upper control arms to run their lower control arms only... But then I see from other people that the pinion angle will be way out of whack of you skip the uppers and only do extended lowers?

I have a p71 DS conversion all set up so that's a non-issue, I just need to hear from first hand experience if you need uppers and lower or just extended lowers are ok for centering those rear wheels.

(Spoke with a guy from one of the LCA fab companies but I wasn't impressed with the conversation to be honest so looking for unbiased and educated advice)

Thanks,
Jeff C
 

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.......Anyway, I see on UMI performance website saying you DON'T need adjustable rear Upper control arms to run their lower control arms only... But then I see from other people that the pinion angle will be way out of whack of you skip the uppers and only do extended lowers?.....
This may be true........but I had extended LCAs on my '96 Impala for about 17 years......

IJS.

KW




EDIT......see below.
 

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Discussion Starter #3
.......Anyway, I see on UMI performance website saying you DON'T need adjustable rear Upper control arms to run their lower control arms only... But then I see from other people that the pinion angle will be way out of whack of you skip the uppers and only do extended lowers?.....
This may be true........but I had extended LCAs on my '96 Impala for about 17 years......

IJS.

KW
KW,

Ok so you're running Only extended lowers and you're good to go?

This is what I was looking for. A reputable source , you seem to have a plethora of knowledge for all things GM.


Thank you,
Jeff C
 

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Experience with these cars over the past 20 years of having done a lot of things right.....and wrong :eek:

KW
 

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KW,

Ok so you're running Only extended lowers and you're good to go?.....

Damn.....talk about a massive brain fart!

No, Jeff....I do NOT have extended lower control arms....I have extended UPPER control arms!!!

Sorry 'bout that. cwm4

KW
 

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Discussion Starter #6
KW,

Ok so you're running Only extended lowers and you're good to go?.....

Damn.....talk about a massive brain fart!

No, Jeff....I do NOT have extended lower control arms....I have extended UPPER control arms!!!

Sorry 'bout that.


KW

Hahahah no worries! It IS an extended weekend, the relaxation has started early haha.

So only extended/adjustable uppers are required to relocate and center the rear axle?
 

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Hahahah no worries! It IS an extended weekend, the relaxation has started early haha.

So only extended/adjustable uppers are required to relocate and center the rear axle?
Yes.

Most are 3/4" extended and you'll REALLY want an extended driveshaft with them.

Hotchkis is 1/2" extended and you can use the stock driveshaft.....but I eventually went with a longer shaft.

KW
 

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....I see on UMI performance website saying you DON'T need adjustable rear Upper control arms to run their lower control arms only... But then I see from other people that the pinion angle will be way out of whack of you skip the uppers and only do extended lowers?
There is no free lunch--if you reposition the axle back to make the wheel look centered in the body opening, using longer rear lower control arms, you will also need adjustable uppers to correctly set the driveline angle(s)--strictly speaking, you're setting the U-joints up in a range of angle variation that is low enough to avoid excessive vibration due to oscillation/orbit of the joints as they rotate.

The factory has specific numbers (found in the Factory Service Manual/FSM) as far as what the front & rear U-joint angles should be....best to heed them.

Some reading suggestions:
Education Zone: Power Train Set Up Guide | Inland Empire Driveline Services
http://www.iedls.com/asp/admin/getFile.asp?RID=6&TID=28&FN=PDF
 

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Discussion Starter #9
KW and NavyLifter,

Thank you both, guys! Looks like I will just buck up and do both uppers and lowers.

I have the driveshaft (aluminum crown Vic p71 "police" marked DS) in the garage ready for conversion joints and install so that's taken car of... Full control arms next!
 

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KW and NavyLifter,

Thank you both, guys! Looks like I will just buck up and do both uppers and lowers.

I have the driveshaft (aluminum crown Vic p71 "police" marked DS) in the garage ready for conversion joints and install so that's taken car of... Full control arms next!

I think UMI offers both standard and extended lowers. Their standard wouldn't require anything to be changed on the uppers since you aren't changing anything in the rear end. Are you sure you weren't looking at those?
 

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Discussion Starter #11
KW and NavyLifter,

Thank you both, guys! Looks like I will just buck up and do both uppers and lowers.

I have the driveshaft (aluminum crown Vic p71 "police" marked DS) in the garage ready for conversion joints and install so that's taken car of... Full control arms next!

I think UMI offers both standard and extended lowers. Their standard wouldn't require anything to be changed on the uppers since you aren't changing anything in the rear end. Are you sure you weren't looking at those?

In retrospect I could have been, but thought i was looking only for extenders... Hmm. In any case I'm going to order extended uppers and lowers from BMR performance unless you guys have reason for other manufacturer? I used BMR on my fbodys and seemed well made when I did but companies change...



Thank you,
Jeff C
 

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....unless you guys have reason for other manufacturer? I used BMR on my fbodys and seemed well made when I did but companies change...
Thank you,
Jeff C
Search reviews of the several extendeds currently available, and compare with your experience. One maker just starting his line 15 years ago had problems but ironed them out. I looked for material and fabrication quality - choosing the names in my sig. I notice METCO new is up to ~$650 now. Yikes! I have your same DS and will be sticking it in sometime between soon and probably never. :cool:
 

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Discussion Starter #13 (Edited)
Search reviews of the several extendeds currently available, and compare with your experience. One maker just starting his line 15 years ago had problems but ironed them out. I looked for material and fabrication quality - choosing the names in my sig. I notice METCO new is up to ~$650 now. Yikes! I have your same DS and will be sticking it in sometime between soon and probably never. :cool:
The Metcos are truly awesome looking... But yea that leaves me hurting. UMIs and BMRs can be had for 300-350$ a set and The PMTS are boxed for $409 a set with hardware but make no mention of how far they actually extend.

I'm with you on the DS, I'm waiting on CIA headers to do next (arrive Wednesday a www yea) but am fearing those manifold holds as two broke off on my friends 94 caprice during a header install which lead to a last minute head/cam job lol
 

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In retrospect I could have been, but thought i was looking only for extenders... Hmm. In any case I'm going to order extended uppers and lowers from BMR performance unless you guys have reason for other manufacturer? I used BMR on my fbodys and seemed well made when I did but companies change...



Thank you,
Jeff C
I have the BMR extended set on mine and I think the quality is good. The BMR's are the bar style, as are the UMI. Others like Hotchkis use a boxed arm, but I don't think there is anything better or worse in this case...

I do have to say though, I kinda like the UMI rod ends...I know people have said they will offer a harsher and noisier ride, but I'm sure they offer a tad better performance?
 

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Discussion Starter #16
I have the BMR extended set on mine and I think the quality is good. The BMR's are the bar style, as are the UMI. Others like Hotchkis use a boxed arm, but I don't think there is anything better or worse in this case...

I do have to say though, I kinda like the UMI rod ends...I know people have said they will offer a harsher and noisier ride, but I'm sure they offer a tad better performance?
Interesting.... Less flex with the rod end, I'm assuming? That would make a metal-on-metal contact point between the rod end and the bolt, that wouldn't be an issue?
 

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Interesting.... Less flex with the rod end, I'm assuming? That would make a metal-on-metal contact point between the rod end and the bolt, that wouldn't be an issue?
The rod end would in theory allow for more suspension movement without binding up. When you move the rear back you actually end up pushing the brackets out of alignment a bit and the bushings can have a little tendency to bind, especially on the uppers which is why there is one manufacturer that does an offset axle side mount. In some ways I almost feel like the rod ends would help with this...

Yes, the metal to metal would give you more "feedback" from the road and could make it a little noisier.
 

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There is no free lunch--
Right there. there are many things you CAN do that aren't necessarily the right way, and many guys have been getting away with it for years, but it doesn't make it right.

FACT: when you run extended lower control arms to center the rear wheels, you will change the pinion angle if you do not account for this via adjustable uppers

FACT: if you run extended upper control arms, you will end up with a clevis that meets the axle bushings at a poor angle potentially causing bind/deflection and accelerated wear . The fix for this (aside from using a spherical joint at the axle end) is to use an offset clevis to meet the bushing squarely and only a few brands currently use one.

FACT: If you extend the rear end to center the wheels, you will be pulling the driveshaft out of the tailshaft further which could potentially cause issues if you don't run an extended driveshaft.

FACT: (and this is an often overlooked problem from what I have seen on these boards) If you extend the rear control arms to center the axle, you will be changing the angle at which the springs meet the lower axle perches. At 3/4's extended, it is actually scary seeing the angle the springs meet the perch. Ideally, you should be moving the spring perches forward the same distance you extended the rear. I have seen hardly anyone actually do this, but I did on mine and was happy with the result (and it looks much safer).
 

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Discussion Starter #19
Right there. there are many things you CAN do that aren't necessarily the right way, and many guys have been getting away with it for years, but it doesn't make it right.

FACT: when you run extended lower control arms to center the rear wheels, you will change the pinion angle if you do not account for this via adjustable uppers

FACT: if you run extended upper control arms, you will end up with a clevis that meets the axle bushings at a poor angle potentially causing bind/deflection and accelerated wear . The fix for this (aside from using a spherical joint at the axle end) is to use an offset clevis to meet the bushing squarely and only a few brands currently use one.

FACT: If you extend the rear end to center the wheels, you will be pulling the driveshaft out of the tailshaft further which could potentially cause issues if you don't run an extended driveshaft.

FACT: (and this is an often overlooked problem from what I have seen on these boards) If you extend the rear control arms to center the axle, you will be changing the angle at which the springs meet the lower axle perches. At 3/4's extended, it is actually scary seeing the angle the springs meet the perch. Ideally, you should be moving the spring perches forward the same distance you extended the rear. I have seen hardly anyone actually do this, but I did on mine and was happy with the result (and it looks much safer).

Ok, I'm all for buying uppers and lower....

Which company makes the offset clevis? 3c Fab only?

I see they are extended 5/8".... Can I use a stock driveshaft with 5/8" extended? Or can I use my P71 aluminum driveshaft with 5/8" extended or do those only fit for 3/4" extended? I know it's 1/8" but I also know that can make a big difference in things.

How did you go about moving the spring perches??
 

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Trying to wrap my head around this mod.

So the rear wheels do not appear to be positioned correctly from the factory because the body was mounted a little crooked?
Is that right?

And people are compensating for this by changing the rear axle position?

Or was the axle mounted incorrectly in the first place?
 
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