Rear end has mind of its own

[Dave M]

Hi there!
I have a 1979 Corvette that I recently rebuilt the engine and transmission for. The transmission has been transformed into (I am proud to say) a truly marvelous mechanical masterpiece, and the engine (I am even prouder to say) is simply sweet music to ones ears!
Unfortunately, in this great wide world that we live in, there is always a certain amount of hell that we must go through to find glory. As I always say, If there's hell on the horizon there's greater glory not far off! Mind you, on the Big Scale of Things, my little problem hardly rates a mention.
Unless your sick with Corvette Fever like I am!
Now to my problem. Since the engine + Transmission rebuild they seem to out perform the rear suspesion, the rear end of my Corvette has developed a mind of it's own!
The engine and transmission are now run in and are good for very spirited driving, unfortunately when the gas pedal is pressed quickly the rear of the Corvette pitches or throws to the left requiring a rather deft hand at the steering wheel. This produces a rather impressive effect, but not at the local shopping mall!
Inversely, When coming off the gas pedal the Corvette will pitch to the right, this becomes an ever eye widening experience as the faster the Corvette goes, the worse this effect is. As often is the requirement when travelling at speed, remove foot from gas pedal and you had better do it quickly! With my Corvette you have to be ready for the pitch, not only the driver of my Corvette, but pity those nearby! The other day when cruising home on the local tollway a person (in a lesser car) pulled out into the lane I was travelling in. They were travelling slowly so evassive action was required, my foot came off the gas pedal quickly, and you guessed it, the rear of my Corvette set up a tremendous wobble. I have rebuilt the brakes also and the Corvette pulls up nice, but what a process, the people in the car next to me thought it was an act of road rage! (These days I find witty one liners and rude hand gestures a little inappropriate!) Actually it is quite bad and breaks my heart that my favourite car is the worst handling car I have ever proudly owned. (I don't tell anybody this.) I expect there is a solution.
Anyhow hope this is not too long winded and you can understand what I am getting at.
All of you, take care,
Dave M

 

[1979toy]

Had the same problem with my '79. Unlike you though, I fixed mine before I did the engine work.
What I did was rebuild the trailing arms, rear wheel bearings and change the oil in the differantial. I found one rear wheel bearing really bad, I suspect that was the cause of my torque steer. The only way to tell for sure if the rear bearings are bad is to disconnect the half shaft, otherwise the shaft holds everything tight enoungh to give a false indication.

 

[69MyWay]

Dave,

Sounds like you have been having fun with the hobby. I agree with the whole "hell on the horizon" thing. In my case, I am dreading putting the replacement engine back in the 90 in a couple of weeks. Lining up the input shaft with the clutch in that limited amount of space is going to bust a few knuckles.

Back to your problem.

I think 1979 Toy nailed it pretty well. Not for sure your wheel bearings are bad, but at least the trailing arm bushings. These bushings are at the front end of the trailing arms right up under the lower back portion of the doors in the frame.

Here is the good and bad. The good is, they are not very expensive and are only one assembly per side. That bad is that you have to yank the entire trailing arm out which usually means fighting some pretty stubborn bolts on the shock mounts and a lot of work from underneath.

There are special tools available from most Corvette parts retailers to help press out and change them. However if you have a press, or a hacksaw and small torch you can heat and cut the old ones out.

A very wise fellow would take carefull note of the current amount and position of shims on either side of each trailing arm bushing. This is partially how the alignment is done on the rear of the car. Make sure you put it back the same way so it is pretty close to right before you go to the alignment shop.

You also want to check the bushings at either end of the rear strut arms that go from the differential out to the wheel area.

The best way to check all this is to jack the car up and support it on the frame. Grab one rear wheel at a time and pull on it and wrestle it around up, down, side to side. Have a spotter watch the suspension for movement and try to pin point the bad parts.

I also think you will be very pleased if you contact our local experts here Guldstrand performance. They know all about these suspensions and the best way to get them right. You can also check with www.vettebrakes to look into complete rear suspension kits.

 

[Yoda]

Dave,
.... . . . ..A very wise fellow would take carefull note of the current amount and position of shims on either side of each trailing arm bushing. This is partially how the alignment is done on the rear of the car. Make sure you put it back the same way so it is pretty close to right before you go to the alignment shop... .. ..

Very sage advice... from both 1979toy and 69myway.. Also one of our members "Brutus" is in the middle of doing his trailing arms bushing and live's in Sydney, Australia I don't have a clue if this is close to you or not, but he is doing his own bushing and trailing arm restoration.. (just type in "Brutus" in the members section under advanced search to get his bio..) He's a great guy and has one sweet Corvette too.

 

[vigman]

I agree with the info.

You state a 1979 Modified........

Have there been any suspension mods (front or rear) done?

Any funny noises?

Check the back of the Differential where the spring mounts to and the Differential & the Differential hanger bushings...

A way to look at things under load.....
IF your emergency brakes work...

DO THIS ON A PROFESSIONAL LIFT AND NOT 4 JACKSTANDS!

Put the car on the lift, put somebody in the car.Apply LOW power ( I'm assuming automatic ) go from drive to reverse while you watch underneath
and watch for any KLUNK's or movement in the drive line.

Next.. release brakes, engine off, car in neutral.

Lower the car so you can grab the rear tire at the 12 & 6 O'clock position.

Rock the top away from you while pulling the bottom towards you then reverse the action.. if you feel ALOT of play (over 1/2 inch of travel) the bearings shot and needs replacement. This makes the car handle VERY funny and is the MOST common rear end failure.If your unsure how they should feel..try your front tire.

Typically those rear bearings on DAILY DRIVERS WITH NO MAINTAINCE go about 30K miles.

Oh yes check where the lower control arms bolt to the frame, sometimes the frame cracks a bit there.

All the A-ARM ( upper & lower ) bushings ok?

Mike

 

[75SHARK]

Oh, yeah! Fun driving that vette isn't it?! You're experiencing a thing called 'torque thrust'. As stated in above posts, your rear susp components are shot, and more than one I'll bet. Every time you accel/decel the alignment of the rear wheels shifts, changing the 'thrust line' of the vehicle sending you off in another direction. A vette guy who lives nearby had the same prob with his. We drove it most of last year to work out some engine probs, but got to enjoy the challenge of holding onto it. Just add a 4-spd, and you've got your hands full! We decided to put it up for repairs when a tree almost stepped out in front of me!
-Dave

 

[Dave M]

Torque steering huh?
I have always enjoyed the way one can steer a trail bike with the rear wheel but with my Corvette it is rediculous. But thanks for the suspension info all of ya. The jobs half done simply with a bit of moral support. I had suspected the control arm bushes but needed a little coaxing into believing it and who ever said "Don't fear the ghost in the machine" , it's pretty true.
It's all sound advice you have all given me, once I have sourced the control arm bushings the rattle gun is coming out!
And 79toy bag me out will you?! (I'm hanging my head saying this) You are absolutely right , the suspension is more important than the fury of a 350 on avgas. Atleast I had the good sense to rebuild the brake system with lots of new parts when I first got the Corvette! I know you're right mate.
69myway I bet you are, deep down, excited 'bout that replacement engine for that 90 of yours! I know I would be, and i'm looking foward to hearing about it. If I lived nearby I'd be straight round to give you a hand putting it in!

Rare81 Thanks for the tip to Brutus. And Brutus - Pest coming your way!

Vigman As far as I know there are no modifications to the rear suspension of my Corvette. I have replaced the strut rod bushes and spring hanger bushes and changed the diff oil. The wheel bearings, I think are ok. and yes! There is a noise coming from the rear end sometimes. Like , now that I think of it, I thought it was coming from the spare wheel carrier which is empty 'cause I've got no spare. When accelerating and turning from a standstill onto a highway a rattly noise does come from the rear. Usually full steering lock left or right , full acceleration, and from a stand still. The diff seems good, no, the diff works great but do not know much about how it is mounted. (I can hear the tinkle of chassis stands, and I know my lead light works).

And 75Shark There is nothing worse than a walking Corvette and that would have to be a walking tree!! RE- A tree almost stepped out in front of me. I love a good story, infact I kind of like the idea of "Never let truth stand in the way of a good story". A good friend of mine (Rob) recently bought a Honda VTR1000 SP and he lives in the country, you know, cows and fields and bush etc. He was riding his bike home from work one Friday afternoon. Rare for any traffic on the road he was on so a comfortable 110mph was ok. He was having a very good time until a flock of sheep was herded onto the road just as he crested a hill and pulled a lovely mono at um probably 100mph. 190 unsuspecting sheep, my friend superman dived off (he reckons) and landed on sheep and did not get a scratch on him. Surprised that he was ok turned to genuine concern for his brand new bike. Mean while the farmer, who owns the sheep turns up. Rob starts blubbering about his bike, and the farmer says "Stuff your bike mate I've got 18 dead sheep, and that 's all I've counted so far!"
How lucky we are.

And somebody tell me - am I doing this right ?
Why would I want to unsubscribe from a thread ? I do not understand.
If I am tired of a thread do I remove it?

and thanks to all those who have welcomed me to the CAC. Specially all the girls Anniversary78, Barb , Lemonpeel and others - love you.

I'm liking this n and while I am at it The community coordinators do a great job of keeping this show on the road.

All the best everyone.