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Discussion Starter #1
Looking for info from people who have actually done this and not required a new DS.

Ive been reading threads... Pming with people who say they know what they are talking about... but have no actual experience.


I want to lower my 1996 Impala. Id rather not purchase a new driveshaft, but IT MUST have the rear wheels re-centered in the wheel openings, so I know that means adjustable lower control arms.

My question is, is there a certain amount of drop that will allow me to adjust the rear axle without requiring a new driveshaft. Like where is the the line in lowering between needing a DS or not but still having the rear axle centered?

I know this has been discussed before and Ive read so much... but its full of conflict.

Thanks in advance.

Popo

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My dad is on Eibachs (1.5-2" I think.) with C3 Fab Adjustable Centering arms with stock DS. No problems in the probably 3-4 years he's had it.

I've got ST's (2") and UMI extended adjustables, and while the stock DS worked fine, I did switch to a CVPI shaft over concerns about the T56 being just a hair shorter combined with the centered arms and my increased power levels.

-Brian
 

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Discussion Starter #3
My dad is on Eibachs (1.5-2" I think.) with C3 Fab Adjustable Centering arms with stock DS. No problems in the probably 3-4 years he's had it.

I've got ST's (2") and UMI extended adjustables, and while the stock DS worked fine, I did switch to a CVPI shaft over concerns about the T56 being just a hair shorter combined with the centered arms and my increased power levels.

-Brian
Thanku... by centering arms, do u mean adjustment from left to right?

Did he do any adjustable lower control arms that center the wheels in the wheel wells?

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By Centering Arms I mean they center the wheel in the wheel well.

Last fall my dad did airbag the rear axle of his car and as part of that he did move the spring perches fwd about 3/4" on the axle tube. While my springs seem to sit ok, I feel that this is on my list of things to do next in order to vertically line up the spring perches again.

-Brian
 

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Ok. I want to do a little 1" drop and if a new ds is not necessary, i dont want to waste the time or money. I do however need the rear wheels to sit centered in the openings to appease my ocd. Lol.

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..I want to lower my 1996 Impala. Id rather not purchase a new driveshaft, but IT MUST have the rear wheels re-centered in the wheel openings, so I know that means adjustable lower control arms...Popo
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I think you mean longer fixed LCA's and adjustable uppers.
I don't know of any LCA's with adjustment. Since those are in tension on launches, that would be a risky proposition. Lowers are fixed and the uppers (in tension) are adjustable to get the pinion angle correct.
Are you currently running the stock driveshaft? What gear ratio? I take it you already know about the stock shaft's 1st bending natural frequency falling into the mph range of a stock powered car with 3.73 and higher gears?
 

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I just centered my wheels with upper and lower control arms and installed the Hotchkiss springs at the same time. The lowering didn't really change the driveshaft length at all. I went with a Ford Crown Vic MMC driveshaft. It's about 1/2-3/4 inches longer and it's aluminum. It appeared as though the stock DS would have worked. It was just 1/2" further backed out of the tailshaft. There is still a ton of driveshaft yoke in the tailshaft housing.

I'd be tempted to just install the springs and mark the driveshaft with a magic marker where it goes into the tailshaft housing. Then, jack the rear of the car up using the frame and see how much more the driveshaft comes out of the tailshaft. Maximum suspension droop should be the minimum driveshaft engagement.
 

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UMI's are adjustable lowers and uppers. I've got them on my car along with a set of weld on lower attach point brackets. No issues with launching yet. I would be curious to see what the tension/compression limits of the threaded adjuster are compared to what my car can actually create in the arm.

-Brian
 

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UMI's are adjustable lowers and uppers. I've got them on my car along with a set of weld on lower attach point brackets. No issues with launching yet. I would be curious to see what the tension/compression limits of the threaded adjuster are compared to what my car can actually create in the arm.
-Brian
Learn something every day :)
Of all the B-bod's I've been around, I've never seen a set of those.
Of course they can be designed to resist buckling under compression loads; they'll just be beefier and heavier than the upper adjustment design has to be. It's probably only a risk from an OEM point of view; any damage/bend to the lower arms from a road hazard or incorrect jacking could make them fold up under load.
 

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The amount of lowering does not have much impact the requirement of a new driveshaft or not. One can experience vibrations with the extended control arms at both stock ride height and at a lowered one. It really seems to depend upon the tolerance stack-up of each vehicle - some get a vibration right off the bat, others are OK up to a certain MPH (driveshaft RPM).

I had a set of 3/4" extended arms on a 2" lowered SS that was fine at regular cruising speeds, but did experience a vibe at higher speeds.

If you want to center the rear wheels, you must use BOTH extended upper and lower control arms. If you use only the lowers, it will screw up your pinion angle tremendously.
 

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Discussion Starter #11
I think you mean longer fixed LCA's and adjustable uppers.
I don't know of any LCA's with adjustment. Since those are in tension on launches, that would be a risky proposition. Lowers are fixed and the uppers (in tension) are adjustable to get the pinion angle correct.
Are you currently running the stock driveshaft? What gear ratio? I take it you already know about the stock shaft's 1st bending natural frequency falling into the mph range of a stock powered car with 3.73 and higher gears?
Im running everything stock in the susp right now. Just picked up a new posi carrier and 4.10s to go in. Wanna find a diff cover with girdle before install though.

Im not aware of the impala ds bemding. Im still learning b'bodies.

Also, i am pretty sure I was looking at adjustable lcas... i run adjustable lcas with rod ends on my camaro as well.

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Discussion Starter #12
Would a longer yoke do the job?

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The bending frequency is the natural resonance, its the rotational speed that can set up an almost sinusoidal wave response along the length of the DS if my physics is coming back to me correctly.

Even if that's an incorrect description I still know its not really something you want to have going on. Its a function of length, tube diameter and wall. And the only way to change any one of those things is to change the shaft. That's my take on it. Now some guys get away with it and some don't. I did for a while although the vibration around 75-78 got interesting, so I just avoided it. I've since switched to a Crown Vic shaft.

-Brian
 

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The bending frequency is the natural resonance, its the rotational speed that can set up an almost sinusoidal wave response along the length of the DS if my physics is coming back to me correctly.

Even if that's an incorrect description I still know its not really something you want to have going on. Its a function of length, tube diameter and wall. And the only way to change any one of those things is to change the shaft. That's my take on it. Now some guys get away with it and some don't. I did for a while although the vibration around 75-78 got interesting, so I just avoided it. I've since switched to a Crown Vic shaft.

-Brian
That's a pretty good description.
And the "1st bending mode" version of that sinusoidal wave response makes the driveshaft want to turn into a jumprope shape. And it doesn't just go round and round causing the imbalance. It oscillates back and forth, and THAT'S where the danger lies. With nothing do damp it, it will literally tear itself in half.
popo, There's no if's and but's. With 4.10 gears, you don't want to leave the stock shaft in there for any high speed hijinks.
 

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I too am curious about all this. I am at stock ride height, with hotchkis stock length lowers and a Dennys DS with a 6 speed swap. I want to do the same mod as well, and have been looking at the UMI products. I am under the impression I should be good to go with my current set-up, and have no plans to lower the car.

Mike
 

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Discussion Starter #16
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popo, There's no if's and but's. With 4.10 gears, you don't want to leave the stock shaft in there for any high speed hijinks.
Thats good to know. Thanku. Always learning. So i guess i will wait to do the gears for when i lower the car and center the wheels. Then i get a better DS at a longer length as well,??

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.. Then i get a better DS at a longer length as well,??

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Yes and Yes.

Where are you located?
I had a 4" shaft made locally for much less than what I could get from the popular vendors, plus you can't beat dealing locally!
4.88 gears, 530 hp, on the roadcourses.......smooth as silk :)
 

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Yes and Yes.

Where are you located?
I had a 4" shaft made locally for much less than what I could get from the popular vendors, plus you can't beat dealing locally!
4.88 gears, 530 hp, on the roadcourses.......smooth as silk :)
Im in PA, about 30 min outside of Philadelphia

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