'85 SE, that exhibits severe vibration at 60 mph. Speed up or slow down even 1 mph, and it virtually disappears. Seems to have nothing to do rpm or gear. I'm suspecting either the exhaust or tranny mount. I'm going to start with R&R the mount.

Is it a big hassle to change the mount with engine / tranny installed?

 

nope its not bad. on a stock exhaust gsl-se it wants you to drop the exhaust, to get at one/2 of the bolts.

if you're lazy, you can do it without taking the exhaust off, its just a tighter squeeze.

interestingly on the SA, the exhaust is routed a little differently, and everything is right there.

btw its like 4 bolts...

 

That is usually contributed to tire balance not driveline.

 

Not what he is describing. True, vibration at highway speeds are balance issues, but he says that it goes away if he speeds up or slows down.

 

to me it sounds harmonic, how old are you stock bushings on your rear end/engine/tranny? this could all be a culprits

 

When you are traveling at that speed, take it out of gear and see what happens.

 

It does seem harmonic, which is why I considered a partially plugged exhaust, but since it only occurs when moving, I've focused on drivetrain. Could be the tires. They're definitely approaching the end of life.
Anyway, as far as I know, the bushing etc are all original.
114K on the odo.

 

taking it out of gear is a great idea. thx doc

 

Possibilties in order of likeliness:

1. Worn ujoints
2. Tire balance
3. Exhaust in contact with chassis
4. Tranny mount
5. Alignment

 

I agree. When radial tires first came on the market, before they were really perfected), they were notorious for setting up a vibration at a certain speed, but disapear just below or above that speed.

 

Actually I am having the same problem.. sorry to jack, but once I take it out of gear nothing happens, it still vibrates.. Not to sure its the tires we think it may be the tranny mount..

 

There are 2 other things that I know that cause vibration in cars really bad. Those are: water pump and U-joints.

Water pumps hardly ever go bad. U-joints are easy just see if you can shake the drive shaft, rotate 90 degrees and try it again. If so replace the U-joints/drive shaft.

I would run it by a tire store and have them check the balance of the tires. If you speed up and slow down it may go away because it is catching a "good skip" if there is such a thing. In other words it is not putting equal amounts of pressure on the road. Indexing your tires may also help out, most people call it a road force test.

at 60 mph, in 5th your tak, if i remember is around 3.5k. If you rev the motor up to this or around this sitting Idle does it vibrate? It is not under a load but if it is something in the motor it is going to do it not moving as well, I would think but I could be wrong.

In my personal opinion I would say tires though. They are the one of the easiest things to have checked out.

 

I first thought it would be your tires as well but if the vibration goes away if you speed up then maybe your U joints.

My car had some mad shaking issues above 65 MPH but since I got the tires balanced no problems.

Unless you've got some rust issues I wouldn't think the tranny mounts are bad but you never know.
Good luck.

 

I'll will pursue all suggestions, and post what I find to be the problem.
Thanks for all your help gentlemen.

 

FYI: rx7doc, I tried your suggestion. Taking it out of gear or pushing in on the clutch does not affect the vibration. The condition is worse when engine load is lite (level road or coasting downhill).

 

Can't interpet what you are saying?

Is the vibration still there when you take it out of gear?

Is the vibration felt in the steering or the chassis?

 

Tires! It's gotta be the tires.

 

I was having a vibration with my car at 3000rpms no matter what gear I was in,or if the car was even in motion.Clutch in or out it would vibrate. I thought maybe the water pump,but I just don't think the water pump has enough mass to vibrate the whole car. My car had a lightweight seel flywheel with the correct counterweight from Mazdatrix. I removed the lightweight flywheel a week or so ago,and went back to stock setup,and all is well now. I have no idea why this flywheel caused the vibration,but it did. I had this same flywheel with the corresponding correct counter weight in my 83 for years with no issue. I called Mazdatrix thinking maybe they sent me the wrong counterweight 2 years ago when I ordered it,but they showed my invoice said I ordered the right on,and they sent the right one. I am at a loss as to why this flywheel went bad from one car to another.

 

i still say u joints. under engine load youre holding it a bit more steady. when you are coasting or downhill it can flop around a bit more.

 

Sounds like you need to balance the tires.

 

I'm going to try a light steel flywheel again soon. It used to vibrate about as much as the stock flywheel in the white '83. So far a different stock flywheel hasn't vibrated as much in the S model. I might try a different counterweight since I'll be using the same flywheel. I compared this other counterweight to the known '83-'85, and it matched.

 

Sorry for the confusion rx7Doctor.

The vibration is still present (and just as bad) when I took the car out of gear.

I feel it in the wheel, in my feet, my butt, everything in the interior that can vibrate, does. It's all very loud.

 

I hate to sound like a broken record, but....

Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints. Its your U-Joints.

In other words, I'm pretty sure its your U-Joints....

 

Out of balance tire

Bent wheel

Bad wheel bearings

U joints loose

Loose lugnuts

Loose steering mechanism

Front ball joints

Old bushings

Fix and verify the easy ones first like balance, lugnuts, wheels true.

Its an old car, harmonics can happen at certain speeds for any of the above and not show up at other speeds.

Sometimes you get lucky and find the exact cause other times you start fixing things and suddenly one day its gone and your scratching your head trying to remember when you first noticed

 

i agree you will find it will get worse eventually and vibrate to hell under all load just replaced 3 u joint on my truck.
also my first rx7 i noticed vibration only at 75mph this was because i only had 3 bolts that were only on by 4 rotations check your driveshaft

altho everything else mentioned are factors that can cause such problem's