Myles Maycher

I have a 1989 964 c4 manual transmission. I started to notice a grinding noise while turning either direction at low speeds. The noise seems to be coming from the transmission. it makes it only when i have driven the car very hard for a while. I got the car up on a hoist and line locked one of the rear brakes and spun the other wheel by hand and it made the exact same grinding noise. It seems to sound like an issue with the rear differential in the transaxle. I checked the fluid and it is full and clean. I have recently put in redline gl5 75- 90 oil in the transaxle and front diff. I read one post that the redline oil does not lubricate very well at high temperatures.

Does anyone else have this experience or suggestions on what i should do. From the reading I have done it seems that the best trans fluid is mobile delvac gl5 75-90. Would changing the fluid to that possibly fix my problems or do you think my gearbox is ruined.

Is there a lsd in all c4's? Should i be adding a friction modifier? I read that it is not recommended.

Please help.

Steve Weiner-Rennsport Systems

Hi Myles,

You didn't say how many miles are on your car and if the clutch was replaced or not.

I'm no fan of Redline gear oils in these cars so we use Delvac, exclusively. I would NOT add a friction modifier to the oil.

John McM

Myles Maycher

Sorry about not putting down the mileage. It has 115 000km. I bought it 4 years ago with 107 000km. I am the third owner. The last owner had service records. None show the clutch being done. There are no records from the owner before that. I suspect my clutch is nearly worn out and I may be on borrowed time. The engagement point does not seem to high though and there is no slipping. I have heard a very slight bearing noise from my throwout bearing. My car is very loud and hard to pinpoint these noises, especially because they are inconsistent. I was planning on doing the clutch next winter because my engine has what seems to be a leaky valve as well and I was going to do that at the same time. I was hoping to enjoy the car for the summer and do a couple track days, but maybe not now. The grinding noise is only happening when I turn the vehicle so I didn't suspect a worn out clutch to make that noise. But maybe there is more to it. Also one other thing that i should note, under hard acceleration 1 to 2 shift can be very difficult. It has done that since I bought the car. I always thought i was getting over excited and getting caught on the reverse gate by pulling the shift leaver to far to the left during a 1 to 2 shift. Maybe its not that and there is something going on internally.