changed the motor, differential and gearbox fluids at 3500 miles today. Used synchromesh in the gearbox and Mobile 1 synthetic in the differential. There seems to be an increase in the noise from the rear end. Is this to be expected from using the synthetic diff oil?

 

First, did you use the Friction Modified for the tranny? If you used the plain GM Syncromesh, it may not last very long.
As for the diff, I've been using the Mobil 1 since the first fluid change and I can't honestly say the diff is any louder. Are you sure you put enough in? Also, a slight overfill of about 100cc is not a bad idea either (though not necessary).

 

Yes, a slight overfill on the diff.

I used the Pennzoil Synchromesh which I understand is the same formula as the GM but I have not heard of the friction modified formula.

Changed the fluids in anticipation of an HPDE event in early December. Do I need to redo the gearbox?

Thanks. Kyle

 

No, I think you'll be just fine. Just keep in mind that the syncromesh has been reported to not last very long. You might want to consider changing it out after only a few thousand miles or sooner if you notice odd shifting characteristics as this might be the first sign that it's time. Try some "friction modified" next go round. You might like it better.

As for the diff, you did good. I think it may simply be that you are either more sensitive to it after having done something new to it (new and different fluid) or getting rid of the old fluid that may have thickened up with crud may have reduced some of the noise dampening affect. Since you are tracking the car, it would be a good idea to do these fluid changes more often. The next time you dump the diff fluid, have a real good look at it. It will give you some good indications on how your diff is doing. Of course, a fluid analysis is the better way, but a good visual will tell a nice story too.

 

xviper you are right on! The stuff that came out of the diff was sludge. That's it. Thanks man. FM next time.

 

just a long shot but you put Mobile1 GEAR oil in the diff right (Mobile1 engine oil is a no no in the diff)?

 

hi tubedriver: yes it was gear oil for the differential. thanks for checking! kyle

 

Not true. Pennzoil synchromesh is a special fluid GM had developed for very specific trannies, mostly Getrags. It is not the same as GMS, or GMSFM. Even the part no's are different - and that settles that.

Texaco also makes a version of it:
http://www.stealth316.com/misc/pennz...oilsummary.pdf
http://www.stealth316.com/misc/Tex_5600_fluid.pdf


The Pennzoil product is very close to Honda's MTF, which shears down alarmingly fast. I would not see it as worth the trouble of a drain and refill with it.

Go with the GMSFM - most counter guys haven't clue about this stuff. On the S2000 Forum, we saw cases of guys beinbg sold ZHonda VTM-4 fluid for the S2000's diff!! The VTM-4 is a specialty fluid used in some of their AWD/4WD - we had a complete failure of one diff, and in the other case, I caught it fast enough that the guys was able to drain it.

The part number of GMSF< is #12377916

 

Thanks guys, picked up a case of GMSFM this morning and its in the gearbox now. Your help is very appreciated. Kyle

 

im running mobil1 75w90 synthetic in my differential and there is no increase in noise (compared to a stock differential with oem fluid).