Rear Suspension Geometry ('85) - After Lowering
Thread Starter
Burning Brakes
Joined: Apr 2003
Posts: 1,071
Likes: 2
Rear Suspension Geometry ('85) - After Lowering
I just finished my suspension rebuild and lowering on my '85. I'm having it aligned on Friday and want to make sure I have everything the way I want it.
I was reading another thread about the measurements on a World Challenge car. Those measurements reported here Previous Thread state that the inner half shaft u-joint is higher than the outer by 1/2". My current setup is just the opposite, my half shaft is near horizontal with about 1/4" higher on the outer joint.
It seems that one would want the outer to be higher to promote negative camber gain, but the effect may be more complex than that.
Anyone have any insight??
Thanks in advance.
Ryan
I was reading another thread about the measurements on a World Challenge car. Those measurements reported here Previous Thread state that the inner half shaft u-joint is higher than the outer by 1/2". My current setup is just the opposite, my half shaft is near horizontal with about 1/4" higher on the outer joint.
It seems that one would want the outer to be higher to promote negative camber gain, but the effect may be more complex than that.
Anyone have any insight??
Thanks in advance.
Ryan
Thread Starter
Burning Brakes
Joined: Apr 2003
Posts: 1,071
Likes: 2
Well I just got off the phone with Doug Rippie. Looks like I'll be making a few changes tonight.
I started with a poor assumption on my part about the aftermarket lowering components - thought the geometry would be ok and I'd gain new spring bolts in the back and poly components in the front. Much to my dismay I now have a couple of difficulties.
1. 1" remaining in shock travel on all 4 corners (not enough)
2. Rear Suspension Geometry is incorrect, half shaft should be parallel to the floor.
I'm going to raise all 4 corners 1/2" tonight, requires pulling the front suspension apart again ... Joy!
Thought I'd let everyone know.
I started with a poor assumption on my part about the aftermarket lowering components - thought the geometry would be ok and I'd gain new spring bolts in the back and poly components in the front. Much to my dismay I now have a couple of difficulties.
1. 1" remaining in shock travel on all 4 corners (not enough)
2. Rear Suspension Geometry is incorrect, half shaft should be parallel to the floor.
I'm going to raise all 4 corners 1/2" tonight, requires pulling the front suspension apart again ... Joy!
Thought I'd let everyone know.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Inner rear ujoints higher will give you 'squat' on acceleration, which helps rear traction. The halfshafts try to straighten out on accel and thus, lift or lower the car.
Equal height is better for ujoint longevity, and less drivetrain loss (negligible).
Lower inners will reduce your squat, (you'll still have it from weight transfer).
I'm not sure how either will affect camber.
The squat effects the camber, but it all depends on which link is longer (and the angle of each, but I don't want to open that can o worms.)
Shorter upper links (halfshaft) should give you some good negative camber on squat.
Equal height is better for ujoint longevity, and less drivetrain loss (negligible).
Lower inners will reduce your squat, (you'll still have it from weight transfer).
I'm not sure how either will affect camber.
The squat effects the camber, but it all depends on which link is longer (and the angle of each, but I don't want to open that can o worms.)
Shorter upper links (halfshaft) should give you some good negative camber on squat.
Thread Starter
Burning Brakes
Joined: Apr 2003
Posts: 1,071
Likes: 2
I raised the ride height and corrected my Geometry problem.
Front shocks have about 3" of travel, rears have 2" maybe a little more. Half shaft is straight across the back.
Front suspension took 5 hours start to finish including machining a 3/4" thick spacer like the original 3/8" thick ones in the '85 - '87 vettes. Spacers took 1 hour to locate the material, machine, drill, deburr, chamfer and bead blast. Increased the length of the front spring retainer bolts from 3 1/2" to 4".
Went to alignment today, the results are in my Alignment thread in the Autocross and Road Racing Section.
Ryan
Front shocks have about 3" of travel, rears have 2" maybe a little more. Half shaft is straight across the back.
Front suspension took 5 hours start to finish including machining a 3/4" thick spacer like the original 3/8" thick ones in the '85 - '87 vettes. Spacers took 1 hour to locate the material, machine, drill, deburr, chamfer and bead blast. Increased the length of the front spring retainer bolts from 3 1/2" to 4".
Went to alignment today, the results are in my Alignment thread in the Autocross and Road Racing Section.
Ryan
