1989 Pontiac Firebird Vibration Problems HELP!! (Tulsa, OK)

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1989 Pontiac Firebird Vibration Problems HELP!! (Tulsa, OK)

Post by seanof30306 » Mon Oct 03, 2016 9:40 am

Ok, so first, I'm not trying to freeload. I've been trying to find a shop with a PicoScope NVH in my area, but haven't been able to locate one.

OK, I actually did locate one, but it was at the biggest Chevy dealer in the area, and the service manager told me they'd had it for over two years, and not only did no one there know how to use it, they'd never even unboxed it.

I moved on.

I called Pico to see if they could refer me to a shop in my area that had one, but they said they couldn't give out customer information.

I'm in Tulsa, OK. If anyone has a PicoScope within a couple of hundred miles of me, I will GLADLY pay you for your services.

OK, 300 miles.

OK, 400 miles.

So I have a 1989 Pontiac Firebird Formula.

111,000 miles

305 V8

T5 manual transmission

I bought the car new, and have never (overly) abused it. It has always driven smoothly.

It is stock, with four exceptions.

It came with a 3.08 open differential. About 25,000 miles ago, I had a 3.42 gear and a Zexel-Torsen limited slip installed. There were no problems with the installation, and there were no vibration problems at all.

About 20,000 miles ago, the original, factory clutch began to slip. I replaced it with a Centerforce clutch kit. The flywheel was resurfaced. Everything was fine afterwards; no vibrations.

At around the same time, I installed a custom, mandrel-bent exhaust system. Again, no vibration(s).

At around the same time, I also installed Lakewood tubular control arms, KYB shocks and struts, and a complete Energy Suspension Polyurethane bushing kit, front and rear. No vibrations.

Around 10,000 miles ago, the car suddenly began vibrating at around 70mph. Beyond that, the faster you went, the worse the vibration got. I hadn't changed anything on the car for more than 10,000 miles.

I had the tires checked for true and balance; no change.

I took it to a driveline shop. He said the universal joints were bad, so I had him install new Spicer front and rear u-joints. No change.

Took it back. He said the driveshaft was twisted. I bought an aluminum driveshaft out of a 2001 LS1 Camaro (they interchange), took it to a local driveshaft shop, had it checked for true and balanced, and installed it. The vibration was unchanged.

Had the driveshaft balance checked by another driveshaft shop. It was dead on. The vibration was unchanged.

One day, I was sitting parked in the driveway with the transmission in neutral, and slowly revved the engine up. Starting at around 1,800 rpm, until about 2,400 rpm, it vibrated pretty significantly.

This was puzzling. In 5th gear, at 70 mph, the car is doing right at 2,200 rpm, so it makes sense that the engine vibration is causing it. What doesn't make sense is, the faster you go, the worse the vibration gets. When it vibrates while sitting still, with the transmission in neutral, the vibration tapers off after 2,500 rpm. What's more, when driving down the road at 70 mph, with the car vibrating, I can throw it up into neutral, and it still vibrates until the speed drops down to below 65, or so ... the engine is idling! I can run it up till it starts vibrating at 70 mph, throw it in neutral, and shut the engine completely off, and it still vibrates. The vibration actually gets worse at first, as soon as you put it in neutral, then it tapers off as you slow down.

I came to the conclusion that I had two separate vibrations. I decided to focus on the engine vibration.

I took the fan belt off of it . With them not turning, it would eliminate the alternator, power steering pump, water pump, air pump, etc as causal. The vibration was unchanged.

I put a new harmonic damper on it. The vibration was unchanged.

Every time I'd talk to someone new about the problem, they'd tell me I had to start back at square-one, so I'd have the tires re-balanced, and the driveshaft re-balanced. It was utterly demoralizing, and expensive.

I got disgusted, and decided to park the car; the vibration was getting progressively worse, and I'd already thrown over a grand at the problem, with no resolution in sight.

Well, that turned into seven years with the car parked in my garage.

Last fall, I put the car back on the road, and got back to lighting money on fire trying to find the vibration(s). The tires had dry rotted and separated, so I replaced them with new ones. I had the wheels checked for true when they were being balanced. They were fine. The vibrations were unchanged.

At the insistence of my mechanic, I had the driveshaft balanced again; this time up to 150 mph, not 80. No change in the vibration(s)

My mechanic put the car up on the rack, and we disconnected the control arms, torque arm, panhard bar and rear shocks and checked the bushings. They were all good. We ran the car on the rack until it vibrated (I know, I know). We could hear a bearing in the transmission squealing intermittently. Loudly. You couldn't hear it in the car, but listening to it up on the rack, it was alarming. The transmission shifted perfectly, but a squealing bearing probably eventually turns into a seized bearing, and I wanted to get it fixed before that happened, and did real damage.

We asked around for the best transmission shop in the area. One guy's name kept coming up. I took the car to him and let him check it out. He said he had a piece of diagnostic equipment called "Chassis Ears" which would allow him to isolate the causes of the vibrations. He said he'd put the Chassis Ears on it, then pull the transmission, tear it down, and call me.

He called me the next day, telling me the transmission just needed a refresh; new bearings, seals and synchros, and the Chassis Ears had indicated the clutch was bad. He said he'd pulled it, and he could see where the balancing weights were out of whack. We agreed he'd replace the clutch, have the flywheel balanced and turned, and then have the clutch balanced on the flywheel.

I went to pick the car up, and the vibrations were exactly as before.

I'm not going to go into detail over all the problems with the shop. I'm still battling with them, lawyers are involved, and it'll probably be a couple of months before it's resolved. There are two key elements, though:

1) I sent my old clutch back to Centerforce. Their engineer said there was nothing wrong with it. More importantly, he said there were signs the release bearing had been coming into contact with the balancing weights, which suggested an out-of-balance condition. Since the balance on the clutch had checked out perfectly, he said I should look at the flywheel.

2) After much back-and-forth, the transmission guy finally admitted not only had he not had the flywheel balanced, he hadn't had it resurfaced, either. He'd never taken it off the car.

This definitely leads me to suspect the flywheel is the culprit in the case of the engine vibration. The transmission isn't right, and it's going to have to come back out. When it does, I'm going to have the flywheel trued and balanced, and have my original Centerforce clutch balanced to the flywheel, and put back on the car.

That won't address the chassis vibration, though. When he'd rebuilt the transmission, the transmission guy had put a new transmission mount on the car, and told me the engine mounts were bad, too. After I got it back, I inspected them. Even though the driveline angles were dead-on, they did look a little sketchy, so I had them replaced. At the same time, I had the rearend gone through; all new bearings and seals, and the ring and pinion setup checked.

Something changed. The car still vibrates, but before, where it would start at around 70, and get worse as you went faster, now it starts to taper off at around 80mph, and remains constant as you go faster and faster. It's vibrating at a much less severe level than before at high speed.

"A-HA!" You say. New motor mounts and rebuilding the rearend resolved the driveline vibration!"

Well, not exactly. As before, get up to 70, where it starts vibrating, throw it up in neutral and shut the engine off, and it vibrates until it gets down to about 60. That can't be an engine vibration.

Wait, there's more! Now, sometimes it starts vibrating at 60, instead of 70. Sometimes it doesn't. Sometimes it barely vibrates at all, even at 70. Sometimes it's almost as bad as before.

Maybe I have/had three vibrations.

I'm totally, completely, absolutely, utterly exhausted, and out of things to replace.

Can anyone help?


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Re: 1989 Pontiac Firebird Vibration Problems HELP!! (Tulsa,

Post by STC » Tue Oct 04, 2016 12:05 am


Wow !!! So, not quite, but best part of 10 years you have battled with that ??
I can't help but to feel your pain Soldier

If you don't get any luck here then post your request on "Autonerdz" or "IATN" forums. Easily found on Google.

Hope that helps and good luck.

Oh, please keep us posted. I for one am very keen to know how you get on.

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