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HARRYS91GTASLP 03-29-2007 08:47 PM

Bad vibration when down shifting
 
Hi everyone. First post for me.

I have a 1991 GTA with SLP options. Awhile ago i had a vibration when running at 70 mph, and when I dropped it into neutral, then back into drive, maintaing rpm the vibration would go away.

Well, my Goodyear felt the ujoints were the problem, and we felt a very slight bind in the rear ujoint, so I had him replace both front and rear.

The vibration at high speeds seem to be corrected, but now I have a worse problem.... During light acceleration a slight turbine whine appears when going into 3rd and 4th gears. and if I downshift from any gear there's a hellacious vibration.

I took the car to Driveshaft Service here in Marietta. By the way, the guys are great. Worked on the car all day, found a small balance issue, but couldn't correct the problem. They felt it might be a torque converter problem because the transmisson case vibration was off the charts.

One thought: I did have a loose SLP panhard bar, and the mechanic had tightened it before replacing the ujoints (should have stopped there :rolleyes: ). Could the panhard bar come loose before I bought the car, and after the bolts were sloppy-loose the vibration wasn't there? I see at Spohn where they sell both the standard and the adjustable panhard bars.

Bottom line: Could I have one or two new-defective ujoints, or need to get an adjustable panhard bar, since the problem started after tightening the panhard bar and replacing the ujoints?

I have an auto tranny of course.
Thanks in advance!!

Fred91GTA 03-29-2007 09:02 PM

Re: Bad vibration when down shifting
 
Well the adjustable panhard bars are there to correct the alignment of the rear end when the car is lowered. Using the stock length panhard bar on a lowered car would make the rear end sit more to one side.

Hmm... as for the vibration issue, I've never had that problem before. I also have an SLP GTA. Sorry I can't be of any help there. I was having several problems with vibration and clunking when putting the tranny in gear when I first got the car, but I replaced all the mounts and had the U-joints replaced all at the same time along with having someone check and balance the driveshaft. After all that and a couple of hundred bucks later, The car was as tight as a brand new 4th gen.

HARRYS91GTASLP 03-29-2007 09:10 PM

Re: Bad vibration when down shifting
 
Thanks for the reply.... The guys at Driveshaft Service took the driveshaft out to balance it, and I'm assuming that they know what they're doing when putting it back in, so that fact that the whine entering high gears at low rpm as well as the vibration is still there tells me that the problem may be the ujoints or the panhard bar, or the torque converter as he suggested, but I'm not a mechanic by any means so that's why I'm at a loss.

HARRYS91GTASLP 03-29-2007 09:14 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by Fred91GTA
Well the adjustable panhard bars are there to correct the alignment of the rear end when the car is lowered. Using the stock length panhard bar on a lowered car would make the rear end sit more to one side.

Hmm... as for the vibration issue, I've never had that problem before. I also have an SLP GTA. Sorry I can't be of any help there. I was having several problems with vibration and clunking when putting the tranny in gear when I first got the car, but I replaced all the mounts and had the U-joints replaced all at the same time along with having someone check and balance the driveshaft. After all that and a couple of hundred bucks later, The car was as tight as a brand new 4th gen.

YES!! The car has been lowered. It sits about 8 or 9 inches off the road. Does that mean that I need to get an adjustable panhard bar? Does a mechanic normally know how to adjust a panhard bar?

HARRYS91GTASLP 03-29-2007 09:24 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by HARRYS91GTASLP
YES!! The car has been lowered. It sits about 8 or 9 inches off the road. Does that mean that I need to get an adjustable panhard bar? Does a mechanic normally know how to adjust a panhard bar?

Also, how do you install a panhard bar...with the car on jackstands or on a lift? My guess on jackstands.

HARRYS91GTASLP 03-29-2007 09:26 PM

Re: Bad vibration when down shifting
 
Here's what Spohn says about their adjustable bar:

Replace the factory's weak, stamped steel, flexible panhard bar with one of our heavy duty set-ups! Allows for centering the rearend after lowering. The best component for serious handling performance. Allows alignment of the rear for clearance when running larger tires. Greatly increases rear's lateral stability.

Specifications:

* 1.25" x .095" wall mild steel tubing
* Stronger, yet lighter then stock
* Polyurethane bushings (fluted) with grease fittings for easy lubrication
* Right hand and left hand threaded CNC machined double male stud adjuster threads into 4130 chrome moly TIG welded threaded tube adapters
* Reuses OEM mounting hardware, no need to drill out your car's mounting brackets
* This is the highest quality, easiest to adjust on the car panhard bar on the market!
* Available powder coated your choice of bright red or gloss black

HARRYS91GTASLP 03-29-2007 09:50 PM

Re: Bad vibration when down shifting
 
I've been reading-up on panhard bars and found that it's used to center the rear-end to the body of the car, for racing to help in cornering in high speed turns, etc.. Question: Do I need a panhard bar on my 1991 GTA? One message board poster felt that if he didn't race his vehicle he wouldn't use a panhard bar, just use stiffer anti-sway bars.

What do you all think?

Fred91GTA 03-29-2007 11:20 PM

Re: Bad vibration when down shifting
 
How much is your car lowered? Mine is lowerd about an inch from stock using the Eibach Pro Kit. Crouch behind your car and look at the rear wheels. Does one side stick out more than the other? Or are they in the wheelwell at the same depth?

I got the adjustable one to center my rear end as well as the lower control arm relocation brackets. I just wanted the correct geometry for my rear suspension. If you have the stock panhard bar on a lowered car, it could make a significant difference in the rear suspension geometry. Not to mention that it's a weak piece and bends readily under load.

Also, how many miles are on your car and when did you buy it? I could've sworn I saw a red 91 GTA with the SLP Package that was lowered for sale on www.cars-on-line.com

I installed my panhard bar with the car parked on a New York City Street on jackstands with traffic passing by every minute. :)

HARRYS91GTASLP 03-29-2007 11:33 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by Fred91GTA
How much is your car lowered? Mine is lowerd about an inch from stock using the Eibach Pro Kit. Crouch behind your car and look at the rear wheels. Does one side stick out more than the other? Or are they in the wheelwell at the same depth?

I got the adjustable one to center my rear end as well as the lower control arm relocation brackets. I just wanted the correct geometry for my rear suspension. If you have the stock panhard bar on a lowered car, it could make a significant difference in the rear suspension geometry. Not to mention that it's a weak piece and bends readily under load.

Also, how many miles are on your car and when did you buy it? I could've sworn I saw a red 91 GTA with the SLP Package that was lowered for sale on www.cars-on-line.com

I installed my panhard bar with the car parked on a New York City Street on jackstands with traffic passing by every minute. :)

Yep, that's the one. Bought it from a guy in Washington state. Nice car. I'm hurtin though because the vibration is the only thing wrong about the car. I'll take a look at the tire clearance in a bit.

The panhard bar on the car now is the SLP option, the same one that Spohn sells. Set length, no adjustment. I do have the control arms, in fact most of the car has the SLP options, including the exhaust, runners, etc.

I guess my question is: Can a set-length panhard bar, installed on a car that has been lowered to about 8 inches off the pavement cause a vibration when down-shifting at low rpm, as well as when entering the higher gears on higher acceleration?

HARRYS91GTASLP 03-29-2007 11:47 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by HARRYS91GTASLP
Yep, that's the one. Bought it from a guy in Washington state. Nice car. I'm hurtin though because the vibration is the only thing wrong about the car. I'll take a look at the tire clearance in a bit.

The panhard bar on the car now is the SLP option, the same one that Spohn sells. Set length, no adjustment. I do have the control arms, in fact most of the car has the SLP options, including the exhaust, runners, etc.

I guess my question is: Can a set-length panhard bar, installed on a car that has been lowered to about 8 inches off the pavement cause a vibration when down-shifting at low rpm, as well as when entering the higher gears on higher acceleration?


Good find! Yes, the rear end is aligned more to the LEFT, about 1 1/2 inches!!

If the right-most end of the bar attaches to the body, then the other end attaches to the axle, correct? Then would I would need to EXTEND the length of the adjustable panhard bar so the same amount of tire extends out from the wheel wells?

FearThisGTA 03-30-2007 07:30 AM

Re: Bad vibration when down shifting
 
Welcome and nice car! As far as the vibration is concerned has the transmission ever been replaced or out or the car?

HARRYS91GTASLP 03-30-2007 10:17 AM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by fearthisgta
Welcome and nice car! As far as the vibration is concerned has the transmission ever been replaced or out or the car?

Good question. I don't know. It has a shift kit installed; does that involve dropping the transmission? The guys at Driveshaft Service mentioned that their equipment detected vibration off the chart off the transmission case. They felt it could be the torque converter, and suggested a guy in Woodstock look at it.

When you think about it, the fact that there's bad vibration when I drop into lower gears, and if I hold off on the rpm's the vibration isn't there...could be the transmission. Thanks for the help.

HARRYS91GTASLP 03-30-2007 10:24 AM

Re: Bad vibration when down shifting
 
By the way, here's a pic of the car:

<img src=http://i98.photobucket.com/albums/l268/ukharry/c084.jpg />

MunsonGTA 03-30-2007 10:54 AM

Re: Bad vibration when down shifting
 
car looks great, definitely get an adjustable panhard bar. if that doesn't fix the vibration, which i don't think it will, i'd look into the torque converter also. sounds like it might have an issue when it's locking up, or it might have become unbalanced.

HARRYS91GTASLP 03-30-2007 11:02 AM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by MunsonGTA
car looks great, definitely get an adjustable panhard bar. if that doesn't fix the vibration, which i don't think it will, i'd look into the torque converter also. sounds like it might have an issue when it's locking up, or it might have become unbalanced.

Thanks Munson. Could you tell me...if the car is up on jackstands, then the mechanic would EXTEND the length of the panhard bar to "move" the body to the right, correct? The car does pull to the right, and a REAL GOOD front-end man said that the alignment was PERFECT...could the offset in the rear cause the pull to the right?

As far as the torque converter is concerned, any suggestions as to the best unit to buy, and how much is involved, approximate cost for labor, etc... It would be worth the cost... I feel lucky to have found it, 64,000 miles, full Pontiac and SLP options, nice paint.

HARRYS91GTASLP 03-30-2007 11:06 AM

Re: Bad vibration when down shifting
 
More pic's:

<img src=http://i98.photobucket.com/albums/l268/ukharry/4388.jpg />

<img src=http://i98.photobucket.com/albums/l268/ukharry/baf1.jpg />

HARRYS91GTASLP 03-30-2007 11:30 AM

Re: Bad vibration when down shifting
 
Guys and Gals... I just looked under the car, and the panhard bar is RED and is threaded ON BOTH ENDS.... Saves me about $130 :snide:

FearThisGTA 03-30-2007 12:38 PM

Re: Bad vibration when down shifting
 
Thats one goooooooddddd lookin GTA ya got there. :drool: IMO, I have a TCI Breakaway conv and the stall speed is between 2200-2400 and its very streetable.

HARRYS91GTASLP 03-30-2007 02:08 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by fearthisgta
Thats one goooooooddddd lookin GTA ya got there. :drool: IMO, I have a TCI Breakaway conv and the stall speed is between 2200-2400 and its very streetable.

Summit is asking $400.00 for the TCI Breakaway. The Vigilante is about $800.00. Why the difference?

HARRYS91GTASLP 03-30-2007 02:10 PM

Re: Bad vibration when down shifting
 
Quote:

Originally Posted by fearthisgta
Thats one goooooooddddd lookin GTA ya got there. :drool: IMO, I have a TCI Breakaway conv and the stall speed is between 2200-2400 and its very streetable.

fearthisgta, could you post a link for the TCI Breakaway item you bought for yours? Thanks!


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