Help! 77 corvette sway.

[77coolvett]

Help please. My corvette has developed what I call the sway. When at highway speeds and you accelerate or let off the throttle the car seems to sway. I have read some things on this. My u joints,brakes, rotors, calipers, are all brand new and tight. There is no play where shafts to the wheels are connected to the diff. All the bolts are tight to the rear end, the spring appears to have no breaks in it. All the connecting points appear to be tight and I cannot get any play in any connecting point with a pry bar. I'm obviously overlooking something. What do I need to look at? What might be the problem?

 

[Tom Bryant]

Check your trailing arm bushings. If they are deteriorated and allowing the front of the arm to move around that will steer it all over the place. They will move one way under acceleration and the opposite under deceleration.

Tom

 

[77coolvett]

Thanks Tom. Stuped question but what am I looking for. They are hidden where they attach in the body? I see shims and the bolt with the castle nut that holds them in place but how do you check them?

 

[Tom Bryant]

There is a metal sleeved rubber bushing in that front eye where the bolt with the shims goes through. If that rubber is degraded that arm will move around on the bolt. If they are original, they probably are not is very good condition. The front trailing arm bolts and their respective shims align rear wheel toe in/toe out. Also there are rubber bushings in both ends of the strut rods that are used to align camber to the rear wheels. They must be in good condition too. Any excess movement in the trailing arm bushings, strut rod bushings, rear wheel bearings or those big bushings between the differential cross member and the frame will allow changes in alignment under power or braking that will adversely steer the rear of the car.

Tom

 

[77coolvett]

Thank you. I will look tonight. ok I took my rear end completely apart. I took the calipers, brake lines, shocks, strut rods, rear spring, and the trailing arm assemblies off. I noted where the shims go also. I took a lot of pics. I bought the car mainly restored. The bushings all look to be in good shape and most likely new. It took me 4 hours to get both sides apart. It all came apart fairly easily. The drive shafts I guess you would call them have 3/16 in and out movement. The shields that are very close to the rear end do not hit or contact the diff in any way. The u joints and all the brakes are all new. The wheel bearing is tight and has no play in it. How do I know that all the shims I took out were actually in the correct place? It was a body off the frame restoration so it was apart at one time. There was no forward to backward movement from the control arm assemblies but side to side there was slight movement. The strut rod bushings are clearly new. The way it looks everything was detailed and or replaced during the restoration. I'm not sure what to do now. The car all of the sudden developed this movement when steping on the gas than letting off at highway speeds. I could include pics but I don't know how to do it. I dont want to scratch anything as every piece was painted and or detailed so I was very careful taking it all apart. Putting it all back togather may be a trick. What else should I look for and or how do I measure the play? If the shims were incorrectly installed when the car was put back togather how would I straighten that out to get it right? I'm really lost here and any help would be very much appreciated. This is my first corvette and I love it but this funny movement from the car is scary and I really want to get it corrected.

 

[Tom Bryant]

I wasn't aware that the car had been restored. Taking it apart at least determines that no short cuts were taken. Check around and find an alignment shop that is experienced with Corvettes and take it in for a 4 wheel alignment. Reassemble everything just as you took it apart. It could be simply an alignment issue. No way to determine if the correct number and thickness of shims are installed without the right equipment. There are some ways to get it close from home so you can drive it to a shop. Also ask if they have the trailing arm shims in stock. Some shops do so little of these any more that they don't stock the shims. If that's the case you would want to order a selection of shims to take in with you. Last time I took the '81 in for tires and alignment they didn't have the shims. It was still in specs but the guy would have liked to make a very minor adjustment. It drives great though. If something is wrong the tech will be able to tell what part is causing it. This seems like your next step after reassembly.

Tom

 

[77coolvett]

Is there any chance the movement can be caused by the rear end? I'm this far into it. If there is I will take out the rear end now vs after it is all back togather. Thank you for all your advice so far.

 

[77coolvett]

I found the problem. This may help others that have the same issue. First thank you Tom for the advice without it I would not have found the problem. Upon taking the rear all apart noting the shims and locations. After Tom's suggestion I looked further and took some measurements. Here's what I found. 1 there was not enough shims on the dr side outside of the trailing arm. 2 the outside bushing was coming out. What I did to correct it. First I re installed the shims I took out to start with and in the same locations. 2 I have a assortment of shims so on the outside where there was only 1 shim I shimmied it so the bushing cannot come out again. This matches the pass side much more closely. My next step is to take it to a alignment shop for final adjustment and inspection. Again thanks Tom.

 

[Tom Bryant]

I can see that. There has to be enough shims on both sides so the trailing arm can't move back and forth on the bolt.To increase toe in you would have to remove a shim from the inside and install a shim on the outside. It looks like you found the problem and should be ok to drive it to the alignment shop. I wonder if the guy that restored it just didn't have enough shims and thought it would be ok?

Tom

 

[navy2kcoupe]

Maybe that's why the previous owner got rid of it...........
Couldn't figure out what he did wrong.
Good for you, for keeping on it to the conclusion, and for updating the thread and letting
us know what the final fix was!
Andy

 

[77coolvett]

Thank you all. Todd