Help! 1984 Coupe - Sway when de-accelarating

[AussieCorvetteNut]

Hi Guys,

Need a bit of help.
I have just purchased a 1984 Coupe, Doug Nash 4+3, low production light blue/ medium blue combo.
An original car that does need a bit of work after 30 years.

I have just had the mechanic fix some issues to get it past a roadworthy so that we can transfer the title and rego here in Australia. While she was there, I asked the mechanic to replace the half shaft universal joints.
He did this no problem and it cleared up the 105km/h vibration issue...he said the needle bearings where cactus and that the uni was on the way out.

On my trip home this arvo, while the drive-line is under heavy load/ acceleration, there is a vibration and I think it may be the differential carrier bushes and mounts.
There is also an issue when you back off on the gas, there is an alignment issue, where the back end gets a bit twitchy...scared the $@#t out of me...:ugh

I have only just got my Bendpak hoist delivered this week, so I haven't got it installed yet (another weekend job ).

Thought someone would know from their experience, what the problem could be and where I should target once I get her up on the hoist.

Appreciate your help...



Tony

 

[hcbph]

Issue

Having just replaced the u-joints in my 86, I have one or two suspicions. I'm wondering if all the pieces and parts were reassembled and aligned properly. One area is when the dogbone is removed, manual says to remove it at the bottom of the differential posing a potential alignment issue. If on the other hand it is removed from the bottom of the knuckle then that reduces the chance of alignment. The other item is the bushings, if they are worn they could allow the pieces and parts of the suspension to move.

Just some thoughts.

 

[AussieCorvetteNut]

Appreciate the help

Having just replaced the u-joints in my 86, I have one or two suspicions. I'm wondering if all the pieces and parts were reassembled and aligned properly. One area is when the dogbone is removed, manual says to remove it at the bottom of the differential posing a potential alignment issue. If on the other hand it is removed from the bottom of the knuckle then that reduces the chance of alignment. The other item is the bushings, if they are worn they could allow the pieces and parts of the suspension to move.

Just some thoughts.

Thanks for for the thoughts.

i have a Haynes Repair Manual ( will get the 1984 Workshop Manual as I had one of these for my previous 81 Coupe). This manual suggests to have the rear end aligned once the half shafts are re-installed.

I agree that it is an alignment issue as the car changes it's tracking when you back off the gas and it did not do that prior to changing over the drive- axle universal joints.

i will nurse her down to the alignment shop and have it checked.



Tony

 

[hcbph]

Thoughts

Tony

I know it's too late now but in case someone else reads this, there is a very good article here that I used when I did mine: C4 - Rear Hub Replacement - Corvette Forum : DigitalCorvettes.com Corvette Forums

thinking though all I removed and did to change out my U-joints, it's got to either be out of alignment, shot bushings or something not put back right. Being it wasn't doing it prior to the changeout on the u-joints I'm inclined to say either alignment or not reassembled right.
I'd seriously consider getting it up on jackstands and give it a good once-over on everthing relating to the half-shafts and knuckles to insure they're reassembled right and are tight. That's in addition to getting an alignment done.
Thing is, when I did mine I used the doc I noted and unhooked the dogbones from the bottom of the knuckles rather than from the differential end. Nothing changed there so I didn't even need to have a realignment done. The bushings etc in mine were still good and it's tracking just fine. Being the most likely culprit is the adjustment on that dogbone was affected, I'd look at that first thought it could be the tierod end on the toe bar also.
One other thought is if the ride height was misadjusted, don't know if that would do what you're experiencing.

Good luck and keep us posted on what you find.

Paul

One other thing I just thought of, the hubs. If the bearings are going or the spindle nut wasn't torqued tight enough, might do that. IIRC the manual say to do something like 160 ft pounds for the spindle nut, yet the info I've found says to torque them to around 200 ft pounds. That's what I used when I did mine and mines been just fine.

 

[AussieCorvetteNut]

The alignment fixed it

Tony

I know it's too late now but in case someone else reads this, there is a very good article here that I used when I did mine: C4 - Rear Hub Replacement - Corvette Forum : DigitalCorvettes.com Corvette Forums

thinking though all I removed and did to change out my U-joints, it's got to either be out of alignment, shot bushings or something not put back right. Being it wasn't doing it prior to the changeout on the u-joints I'm inclined to say either alignment or not reassembled right.
I'd seriously consider getting it up on jackstands and give it a good once-over on everthing relating to the half-shafts and knuckles to insure they're reassembled right and are tight. That's in addition to getting an alignment done.
Thing is, when I did mine I used the doc I noted and unhooked the dogbones from the bottom of the knuckles rather than from the differential end. Nothing changed there so I didn't even need to have a realignment done. The bushings etc in mine were still good and it's tracking just fine. Being the most likely culprit is the adjustment on that dogbone was affected, I'd look at that first thought it could be the tierod end on the toe bar also.
One other thought is if the ride height was misadjusted, don't know if that would do what you're experiencing.

Good luck and keep us posted on what you find.

Paul

One other thing I just thought of, the hubs. If the bearings are going or the spindle nut wasn't torqued tight enough, might do that. IIRC the manual say to do something like 160 ft pounds for the spindle nut, yet the info I've found says to torque them to around 200 ft pounds. That's what I used when I did mine and mines been just fine.

Thanks Paul,

i took her in for an alignment this arvo and saw the marks that were made before the dog bones were removed from the differential end. Checked the alignment and the left rear had serious toe-out, while the right rear had virtually none.
Took her for a drive after that and she seems fine now, so will keep this in mind as I have further driveline and suspension work planned.

Hey she is a 30 year old car with the original ball joints, so I have started a list of parts, some are on their way after the Ecklers sale on the weekend, while others I have to order.
Sounds funny, but it is cheaper to order from the U.S as opposed to buying the parts that are here...on some things.

Really appreciate your help.



Tony

 

[hcbph]

Next up

Tony

Glad to hear you got that taken care of. IMO do some serious checking on things like brake hoses as they can degrade internally over time, the age and condition of your tires, fluid levels including the O.D. of your 4+3 along with differential and hubs. Easy to overlook in the excitement of a NTY car but very important for your safety.

There's alot of good information out here and people willing to help someone with info and ideas on problems so don't be bashful.

Have a good one.

Paul