Mixed signals, extended LCAs only? - Chevy Impala SS Forum
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post #1 of 30 (permalink) Old 05-28-2016, 02:19 PM Thread Starter
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Mixed signals, extended LCAs only?

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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post #2 of 30 (permalink) Old 05-28-2016, 02:22 PM
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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.

1996 BBB SS, 398ci Solid Roller LT4, TorqHead 24x Conversion


1995 DCM SS, LS3, Texas Speed 260cc PRC heads, Lingenfelter GT1-1 cam, V-max 90mm TB, Headman 1 7/8 LT Headers, 2 1/2" cat-back, 3200 Circle-D TC, 3.73 gears -- 493HP/434TQ @ the wheels (Daily Driver)


2014 Chevy SS; Low Lash Solid Roller 429ci LS3 -- 548HP/464TQ @ the wheels....


Last edited by KW Baraka; 05-28-2016 at 02:55 PM.
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post #3 of 30 (permalink) Old 05-28-2016, 02:26 PM Thread Starter
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Originally Posted by jcarl126 View Post
.......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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post #4 of 30 (permalink) Old 05-28-2016, 02:37 PM
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Experience with these cars over the past 20 years of having done a lot of things right.....and wrong

KW

1996 BBB SS, 398ci Solid Roller LT4, TorqHead 24x Conversion


1995 DCM SS, LS3, Texas Speed 260cc PRC heads, Lingenfelter GT1-1 cam, V-max 90mm TB, Headman 1 7/8 LT Headers, 2 1/2" cat-back, 3200 Circle-D TC, 3.73 gears -- 493HP/434TQ @ the wheels (Daily Driver)


2014 Chevy SS; Low Lash Solid Roller 429ci LS3 -- 548HP/464TQ @ the wheels....

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post #5 of 30 (permalink) Old 05-28-2016, 02:55 PM
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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.

KW
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post #6 of 30 (permalink) Old 05-28-2016, 04:18 PM Thread Starter
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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.

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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post #7 of 30 (permalink) Old 05-28-2016, 06:55 PM
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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

1996 BBB SS, 398ci Solid Roller LT4, TorqHead 24x Conversion


1995 DCM SS, LS3, Texas Speed 260cc PRC heads, Lingenfelter GT1-1 cam, V-max 90mm TB, Headman 1 7/8 LT Headers, 2 1/2" cat-back, 3200 Circle-D TC, 3.73 gears -- 493HP/434TQ @ the wheels (Daily Driver)


2014 Chevy SS; Low Lash Solid Roller 429ci LS3 -- 548HP/464TQ @ the wheels....

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post #8 of 30 (permalink) Old 05-28-2016, 07:48 PM
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Quote:
Originally Posted by jcarl126 View Post
....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/getFi...&TID=28&FN=PDF

Bill Harper
ISSCA #127
[email protected]

Last edited by Navy Lifer; 05-28-2016 at 07:54 PM.
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post #9 of 30 (permalink) Old 05-28-2016, 07:53 PM Thread Starter
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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!
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post #10 of 30 (permalink) Old 05-28-2016, 11:27 PM
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Quote:
Originally Posted by jcarl126 View Post
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?

1996 DGGM Impala SS
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