More Poly Bushing Questions.....
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
More Poly Bushing Questions.....
SO, the FSM mentions "trim height" which I believe is normal ride height..... It says when replacing bushings to torque various bolts with the vehicle at trim height.... I can see where that would be important with rubber replacement bushings, which is what I think the FSM from 1990 is referring to.... BUT, is this also the case with poly bushings? Im working on the rear thrust rods at this point. I have replacements all set with the poly bushings inserted. I have the sway bar bushings also which I plan to do at the same time. Then the rear is complete. Dog bones already done!
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Trim height is as it sits. When car is dropped down off jacks, suspension will be bound a little. Car will need to roll 5 or 6 feet to settle. You could drive it a short distance on a less than perfect road so suspension "shakes" itself out. Then check your rear ride height and torque all the bolts. Alignment will need to be done afterwards. Car should be level and on its wheels when bolts are torqued.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
Trim height is as it sits. When car is dropped down off jacks, suspension will be bound a little. Car will need to roll 5 or 6 feet to settle. You could drive it a short distance on a less than perfect road so suspension "shakes" itself out. Then check your rear ride height and torque all the bolts. Alignment will need to be done afterwards. Car should be level and on its wheels when bolts are torqued.
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 764
Trim height is as it sits. When car is dropped down off jacks, suspension will be bound a little. Car will need to roll 5 or 6 feet to settle. You could drive it a short distance on a less than perfect road so suspension "shakes" itself out. Then check your rear ride height and torque all the bolts. Alignment will need to be done afterwards. Car should be level and on its wheels when bolts are torqued.
- by no means an expert on the subject, but that's the way I would approach things. drive it a bit, final torque at ride height, and alignment. 
Last edited by Joe C; Jun 25, 2018 at 11:02 AM.
Drifting
Joined: Aug 2009
Posts: 1,971
Likes: 243
I’ll put in a vote in for the other camp of thought - it doesn’t matter with all poly bushings. The poly bushings do not shear like the rubber bushings as the suspension moves through the range of motion. They rotate around an axle (the sleeve), they do not shear like rubber because they are both rigid (cannot flex like rubber) and they are not bonded to the inner or outer bore. They pivot like a bearing.
It won’t hurt at all to be at ride height when torquing. It also won’t matter. I didn’t bother. If you have significant binding you have overtorqued. The only place I noticed binding was the front control arms, for which the FSM doesn’t provide a torque spec. I backed the torque off until the binding was very minimal (this is without the front spring or shock installed so you can get a tactile feel of binding). If you have binding on the face of a poly bushings you will prematurely wear it as the bushings rotates - again, it would wear because it rotates and does not twist in shear like rubber. Use Loctite on the control arm bolts/nuts.
My car sits perfectly level and had zero issues at a Corvette alignment shop.
It won’t hurt at all to be at ride height when torquing. It also won’t matter. I didn’t bother. If you have significant binding you have overtorqued. The only place I noticed binding was the front control arms, for which the FSM doesn’t provide a torque spec. I backed the torque off until the binding was very minimal (this is without the front spring or shock installed so you can get a tactile feel of binding). If you have binding on the face of a poly bushings you will prematurely wear it as the bushings rotates - again, it would wear because it rotates and does not twist in shear like rubber. Use Loctite on the control arm bolts/nuts.
My car sits perfectly level and had zero issues at a Corvette alignment shop.
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
I’ll put in a vote in for the other camp of thought - it doesn’t matter with all poly bushings. The poly bushings do not shear like the rubber bushings as the suspension moves through the range of motion. They rotate around an axle (the sleeve), they do not shear like rubber because they are both rigid (cannot flex like rubber) and they are not bonded to the inner or outer bore. They pivot like a bearing.
It won’t hurt at all to be at ride height when torquing. It also won’t matter. I didn’t bother. If you have significant binding you have overtorqued. The only place I noticed binding was the front control arms, for which the FSM doesn’t provide a torque spec. I backed the torque off until the binding was very minimal (this is without the front spring or shock installed so you can get a tactile feel of binding). If you have binding on the face of a poly bushings you will prematurely wear it as the bushings rotates - again, it would wear because it rotates and does not twist in shear like rubber. Use Loctite on the control arm bolts/nuts.
My car sits perfectly level and had zero issues at a Corvette alignment shop.
It won’t hurt at all to be at ride height when torquing. It also won’t matter. I didn’t bother. If you have significant binding you have overtorqued. The only place I noticed binding was the front control arms, for which the FSM doesn’t provide a torque spec. I backed the torque off until the binding was very minimal (this is without the front spring or shock installed so you can get a tactile feel of binding). If you have binding on the face of a poly bushings you will prematurely wear it as the bushings rotates - again, it would wear because it rotates and does not twist in shear like rubber. Use Loctite on the control arm bolts/nuts.
My car sits perfectly level and had zero issues at a Corvette alignment shop.
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Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
I’ll put in a vote in for the other camp of thought - it doesn’t matter with all poly bushings. The poly bushings do not shear like the rubber bushings as the suspension moves through the range of motion. They rotate around an axle (the sleeve), they do not shear like rubber because they are both rigid (cannot flex like rubber) and they are not bonded to the inner or outer bore. They pivot like a bearing.
This is all exactly correct. It doesn't matter one bit, since the inner sleeve rotates inside the poly bushing, acting like a plain (bushed) bearing.
It won’t hurt at all to be at ride height when torquing. It also won’t matter. I didn’t bother. If you have significant binding you have overtorqued. The only place I noticed binding was the front control arms, for which the FSM doesn’t provide a torque spec. I backed the torque off until the binding was very minimal (this is without the front spring or shock installed so you can get a tactile feel of binding).
Drifting
Joined: Aug 2009
Posts: 1,971
Likes: 243
The sleeves and bushings are same length. The issue is that the steel tangs that capture the control arms are very thin and flex/collapse as you torque the bolt down. Sure, the greatest point of contact is on the sleeve and it does “capture” the sleeve but there’s really no avoiding it, the steel is going to contact the face of the bushings. How much drag they put on the bushings is entirely up to you and how much you tighten that bolt. For a rubber bushing that’s just fine because it’s designed to twist. For poly, you need that free-er range of motion. I used blue Loctite. I had considered red but if I needed to ever pull it apart it would take heat to do which would torch a poly bushing. Haven’t had no issues with loose hardware, wear, noise or binding to date...I believe about 1.5 years now.
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
I understand what you’re saying about the steel tangs and the poly material. The tangs are supposed to be thin and collapsible specifically so they can capture the steel sleeve of either the stock rubber bushings or the poly bushings. If it isn’t tightened down on the sleeve, then the sleeve will be rotating on the through-bolt. The tabs or tangs won’t be so tight in the bushing material that it will cause problems. And the faces of the rubber bushings are the same - they have to be able to rotate in the tangs too. And frankly, it will probably self-clearance the poly faces after a short time anyway. So the proper thing to do is tighten the nut so the sleeve doesn’t rotate on the bolt.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
Sway bar bushings, spring pad bushings and trailing arm bushings installed in the rear and so far, so good. No noise and the rear seems to have settled down a bit. (was a bit high in the rear at first) I have the thrust arms ready to go, but Im waiting until after the Rocky Mountain get together/ cruise. Ill put them in and all the rest of the front end bushings, then get it aligned.
Thanks to all who have added the good info.
Thanks to all who have added the good info.