Car vibrates in high speed when let off throttle
 

My car basically vibrates when I let go the gas pedal or go in neutral at high speed. The vibration stops when I'm slowed down to about 25mph or so.

What is causing this vibration? I had a friend ride in the passenger seat today and he said he doesn't feel much vibration as I do when I'm in the driver's seat. I have a 5 speed tranny and custom exhaust. Previous owner said to replace the differential 'cos it's not locking, but is he correct?

For me that's always been the driveshaft's U-Joints.. Unfortunately to check that, you usually need to remove the cat/presilencer, Y-pipe, and a piece of the heat shielding, and then remove the drive shaft and feel if it's smooth tilting on each direction and twisting [check the front and back U-Joints].

it could possibly be something as simple as unbalanced wheels or alignment issues.

check u joints, or carrier bearing

Another thing I noticed today is that when the car vibrates in neutral, putting the gear into 4th or lower gear and taking it out right after would stop the vibrating. Any inputs?

have you checked anything that has been suggested?

I haven't yet and it's dumb of me to ask without checking first, but I thought I update with some findings. I plan to check those that were suggested when I get a stock exhaust and cat to smog. I figured I'll do it all when I'm under the car.

I got the same symptoms on my car right now, so I ordered a drveshaft from mazdatrix. Ill update if my problem fixes when I get it put on.

^alright cool, im looking forward to hearing from you. im still saving up money for parts right now.

Well I got my car back and replacing the driveshaft has fixed my problem. It cost me $266 for the aftermarket driveshaft from mazdatrix and it cost me $220 in labor. My car drives so smooth now. As far as you go I would not keep driving it since if it falls off you will have an even bigger problem. Also I noted some pinging noises along with the heavy vibration at 25 and at 40 mph. After a few weeks the pinging went away and the vibrations got worse. Well anyway gl with ur car I hope my info helps you.

Thanks! I get pay next wednesday so ill definitely replace it asap. Hopefully this will solve it

are the s4 and s5 N/A driveshaft interchangeable? I have a 1990 GXL and was wondering if I can use one off an s4.