my car has a bad vibration around 1800 - 2100 rpm in fifth gear on the freeway of course. anything above or below this rpm range and the vibration goes away. When this vibration occurs the car also makes a loud humming sound and the vibration can be felt in the floorboards. U-joints seem fine, trans was rebuilt, rear end was rebuilt.

now I should mention I used a V-6 700r4 driveshaft when I did my T-5 conversion and I'm wondering if there is a difference between any of these driveshafts.

V-6 700r4
V-6 T-5
V-8 700r4
V-8 T-5

anyone who knows the answer to this please post this vibration is driving me crazy

 

As far as I know they all use the same driveshaft. If you still have your stock driveshaft you can compare the two. If it is the same, put it back in the car without doing anything to it and see if the vibration changes. If the vibration changes you've found your problem. If not you need to do more investigating.

Does the vibration change when you put it into a lower gear at the same speed? Does it change with throttle input? Does it vibrate when stopped and in neutral at that RPM?

 

I got an easy one only because i had a similar prob. Make sure your tires are BALANCED! I was too lazy to take care of the problem and i ended up getting a new pair of treads and the problem was fixed. so dont go jumping to major conclusions, like the drive shaft, just throw $20 at a shop and get your tires balanced, couldnt hurt?????

 

Lets see I drove it today and in 4th at around same speed but of course a much different RPM it still did it.

No when stopped and at this RPM range the engine runs smoothly

at this RPM in nuetral or with clutch pedal depressed it still does it till it falls below a certain speed then the vibration and the noise goes away.

I don't have the original drive shaft. this was a turb200 automatic car that had a 5 speed conversion.

doubtfull it's tire or rim related since with wheels spinning in gear off the ground rims don't look bent and tires only have a few thousand miles on them. Balancing could be the problem but I have had unbalnced tires on the car before and it's never done this noise or vibration.

the noise is more of a roaring noise much like a fan clutch thats locked up and the fan is running at high rpm. ( car has a electric fan by the way)

 

Lets say the vibration occures at around 60 MPH.

1. Same vibration at 60 MPH but different gear and RPM. Probably not the transmission.

2. No vibration when not moving. Probably not the engine or clutch.

3. Same vibration at 60 MPH but at idle RPM until it slows below 60 MPH. Vibration is speed related.

Try jacking the rear up and support it with jack stands. Remove the tires and hold the brakes on with the lug nuts. Run the car up to where it normally would vibrate. If it goes away, it is the tires/wheels. If it doesn't you need to keep looking.

Did the car vibrate before the swap? Is the rear end from the car or did you build one and install it? You need to figure out what you changed that is causing the vibration if this is a new vibration. It is a process of elimination. Check the transmission and torque arm mounts, rear suspension mounts, shocks, etc. Look for any worn parts and replace as necessary.

I'm not positive this is it, but I would suspect the driveshaft. If it is I would NOT bother with the GM driveshaft. Have a new one made for the car, with a new yoke. Steel or aluminum is up to you.

Rob

 

Your most likely cause of the vibration is the driveshaft. I've read that thirdgen cars that didn't have the 1LE package with the aluminum driveshafts were notorious for having vibration at speed. some low around 60 others such as mine at 95 mph. Look in Jegs, they sell an aluminum driveshaft thats a direct replacement for the stock one for 324.99. i'm putting one in my 89 RS cuz my shaft has a very slight bend in it in the middle. what you can do is jack the car up and put it in 1st gear engine idling and look at the deiveshaft and see if it has a slight up and down motion in any spot on it. if it isn't perfectly straight it's gonna vibrate. hope this helps

 

when the car had a T200 and original no it DID NOT have this vibration. The rear end is from my 84 trans am and I never recalled that car having it either.

the vibration started after the 5 speed changeover, however I doubt it's the transmission since it was completely rebuilt about a week ago and still makes the same noise and vibration.

I am leaning towards the driveshaft since this was on the ground at pickapart when I got it. I'm fairly certain it is a f-body one though but that was a mistake grabbing it I think. the noise seems more pronounced in the rear seat area as well. another thing my torque arm was cut down to short and a piece of metal added to make up for it where the front torque arm mount is. so not sure if this is the cause of anything. My front torque arm mount is pretty bad too now that I think about it.

as for other suspension parts everything is good or replaced. this is a rust free car so we can eliminate suspension movement from that as the cause.

is it possible to put a 2 piece rear main flywheel on a 1 piece rear main engine ? ..... probably not my problem but thought I would throw it up in the air.

you are correct in saying this is a speed related vibration since when the clutch is depressed the motor drops to near idle but the car still vibrates and makes the noise. I used the RPM range since my speedometer wasn't working is all and to give you a rough estimate of the speed it happen.

A mechanic was telling me this vibrations could be causing a Harmonic noise in the driveshaft and thats what I am hearing any truth to this ?

 

Probably the bushing in the transmission that supports the drive shaft.

People don't replace those alot of the time when doing a "rebuild".

It can be done with the trans in the car. Call around to the transmission and drive train shops in your area, and ask them if they have the puller and installer to change out the extension housing bushing without disassembling the trans. It should cost around $30 labor and $5-10 parts, and take no more than 15 minutes. If they say it costs more or takes longer, then they don't have the right tool; keep looking. It'll be obvious when you come across one that does.

 

It sounds like the parts you do not have any history on are the transmission and driveshaft, correct?

The vibration started after the swap, and since then you have had the transmission rebuilt. Was the rear end rebuilt after the swap or before?

Change the torque arm mount and get another uncut torque arm, unless you feel 100% the arm is not changing your pinion angle.

While your changing the mount, check how much play you have at the transmission yoke. You should have some but not a lot. I would say anything more than 1/16" is too much, but check with your transmission shop to verify that number. You can also ask them if they did change the bushing in the tailshaft, which they should have when they rebuilt it.

The two piece engines have a different bolt pattern diameter than the one piece engines so you cannot swap the flywheels.

If you have, or have access to, a dial indicator you can check the runout of the driveshaft while your under the car. Check it at both ends, in the middle, and at about 1/4 length on both ends. It should have very little runout with zero prefered. You can also try unbolting the driveshaft and turning it 180* at the rear yoke. Sometimes that will eliminate the vibration.

Yes the mechanic is correct.

It still sounds like it is the driveshaft but keep working on the things you know need to be fixed, like the torque arm mount.

Rob

 

Harmonic? You bet. I use poly in my secondary cross member. At 4 or 50000 rpm, I'd experience a helva noise/vibration under the car. I loosened and torqued the pieces to spec--no more noise/vibration.

JamesC

 

the rear end was completely gone through about 30,000 miles ago and was in my 84 trans am. I am very certain this shouldn't be the cause. parts replaced in it were ring and pinion gears, new carrier, all bearings and it was around 700.00 for that alone to be done. the work was done by a factory trained general motors technician.

I would also have thought if it was bearing or tire related it wouldn't be a noise/vibration at a specific speed. this unlike parts that are ready to fail never changes noise and is always at the same speed.

I will be changing the driveshaft this weekend and let you all know if it cured the problem

 

Are you getting a new one or having yours balanced? From my searches on here and in my own experience it seems that the stock ones are prone to vibrate even after you get them balanced. I'd go for a 3" steel or aluminum with a new yoke.

Rob

 

I just wanted to update this .... last weekend I got a driveshaft & torque arm from a true 5 speed V-8 90'ish firebird. I took it and had new U-joints installed installed it all and the vibration and noise is gone from the car completely.

I compared the two driveshafts and the weights were in a different place aside from that they were visually the same. I didn't feel any play whatsoever in the driveshaft that was the cause of this noise & vibration. Perhaps I had a V-6 driveshaft who knows, I would like to get a aluminum driveshaft in the near future.

Another problem I failed to mention as well was fixed by these parts. The annoying clutch chatter is for the most part gone now to not sure why that could have been related.

Anyways thanks for your help on this and hope this thread helps someone else with the same problem.