I just bought a couple quarts of Mobile1 75W/90 gear oil for my LSD. Do I need a heavier oil, as the owner's manual suggested SAE90 or do I need an LSD oil additive? I would prefer Amsoil, but the Mobile1 is a lot easier to come accross, and I already bought it.
On an unrelated note, my car has begun to vibrate from 25mph upward. I've noticed that when I release the clutch too quickly, basically I feel a click in the shifter, like the engine or trans isn't the most secure. Could it be that a mount needs replacing, and that is causing the vibration? I just had my tires rotated and balanced. The vibration sounds like a low rumble, and is worst around 30-40 mph.
Thank you.
85 GSL-SE

 

Tranny mount and or drive shaft worn

 

I agree with Mr Slammed. On a side note, were having a meet in CR on the 27th of may, so be there. Check the midwest section for details...

Oh, and I have an extra driveshaft. PM me

 

driveshaft u joints are bad, replace asap!!
you also need a friction modifier for the lsd unit too

 

what about the lsd oil?
what does everyone recomend?
I am in the same situation.

 

I used lucas 75w90 in the LSD. I probably should've went a little heavier like 80w90. I just replaced the LSD oil like a month ago and forgot to put in the lsd additive, so, the car would shake on right and left turns from a complete stop. Added the additive and went away. All this has been covered in the search button though. God bless.

 

I don't believe that U-joints are available for my 85 Driveshaft/LSD. Either the trans mounts are worn, or I'll have to get a whole new driveshaft, more than likely? What about an LSD oil leak? I have a small leak in the diff. I don't know if that would explain anything, though.

 

My drive shaft had a single loose bolt. I thought my car was a gonner based on the crazy shaking. It was just a bolt lol.

I've never changed the fluids in there, don't even know how...

 

Those U-joints are still available, although sometimes shops will try to tell you that they are non-replaceable and try to sell you a rebuilt driveshaft. Check those first, because that's a serious safety issue, then check out the tranny mounts.

 

If you just changed your lsd then you might have a loose bolt, check the pumkin flange bolts and the drive shaft bolts.
Loctite is your friend with our cars.

 

What is LSD additive and where do i get it. ive been looking for Strait SAE 90 and it has ended up being a wild goose chase can i use 85 90 or 75 90 with out any problems cause the manual makes it real clear to use only SAE 90

 

People have used 75w90 and 80w90. You shold be fine. Im using 75w90, but could be using thicker. Ask fro LSD additive at any parts store and they should have it.

 

I had two quarts of Mobile1 synthetic 75W-90, but I just returned them as I have heard very little about it. It seems that most people prefer Redline, Amsoil, Royal Purple or Neo. All of the prices are about $9/quart, so I am guessing the quality can't be to different from one to the next. I have never seen the LSD Additive. Is there a certain type I should look for?

 

The later 83-85 cars DO NOT have replacable U joints. Thats why mazdatrix doesn't sell u-joints for the later cars, and only complete drive shafts. The 82 and older cars do have replacable u joints though.

As for the LSD additive, its just a friction modifier. You should be able to get it at any parts store. Just ask for gear oil friction modifier.

 

Just a note...most aftermarket driveshafts are being made with replaceable u-joints...I found that out when I went to buy some for my original 83 and they sold me some (auto zone). it was only after I damaged the driveshaft trying to remove them that I found out that they were non replaceable and the ones I bought were for the aftermarket shaft. Boy did I feel stupid...LOL

 

Thats exactly why I made the comment I did about the driveshaft. The stock u-joints are very reliable and rarely go out, but if they did at some point, most likely the driveshaft is either a stock replacement, no replacable u joints, or a new one with replacable u joints.