Here's Royal Purple's description: "Synchromax is a synthetic manual transmission fluid designed to increase performance and expand the life of your manual transmission. Using Synchromax improves shifting, reduces gear noise and increases power transfer to the wheels. As a performance transmission fluid, it also lowers operating temperatures and provides outstanding wear protection. Synchromax is recommended for manual transmissions that specify an automatic transmission fluid. It’s also ideal for 4×4 transfer cases and motorcycle gear boxes. Fully compatible with all types of friction materials, Synchromax provides excellent corrosion and oxidation protection without affecting the soft metals commonly found in manual transmission synchronizers."

So if you've been using it in both the gearbox AND diff of your beemers, I'd say your diffs are living on borrowed time, unless BMW has come up a way to use GL-4 specs in a GL-5 application.

I use Motul GL-5 75W-140 fluid in my clutch-type NISMO LSD.

 

GL-5

Lost 3rd, 4th, 5th, and 6th gear synchros. Was able to get it to the dealership with just 1st and 2nd.

 

By the way, I currently use the following fluids:

Transmission - Redline MT-85

Diff (Quaife) - Motul 75w140

0 complaints about either. I used Redline diff fluid in my VLSD before I made the swap to Quaife and I thought it was great also.

 

Cool, thanks! I have my hands on a stock VLSD that I plan to put in this weekend. I will take your recommendation on fluid.

 

Did you get a chance to crack it open to see what's wrong with it?

 

Hope that you aren't thinking of taking the VLSD to the track. It's OK for street use, but will quickly overheat on the track (no matter what fluid you use).

 

Agreed. The VLSD was a big upgrade from my base open diff but it is a very unpredictable LSD, especially for the track. I learned that during AutoX and decided to bite the bullet and get the Quaife. Couldn't be happier with my decision.

 

After dropping the diff and removing the cover i found no fluid and two silicone plugs the filler nipple and drain nipple both plugged with silicone. in the short time of driving the car all the fluids drained causing it to lock up. there’s a little bit of metal shavings, it doesn’t look like it overheated to much, my opinion it can be brought back to life .

 

So it was never filled?

 

Yea that'll do it lol

 

When we filled it, we removed the whole plug and not just the silicon in the plug. The wholes in the fill and drain plug were plugged with silicone that must have became brittle over time. The silicon in the drain plug came out as soon as I started driving, causing the fluid to leak out and diff to lock up.

In hindsight, I would have replaced the silicon or changed the plug type. But I had never encountered a fill/drain plug like this before so didn't really know to check that.

 

Sorry to hear this, but any drain plug on the tranny, engine or diff with silicone sealing it should be cause for alarm. Did you torque the drain plug to OEM specs after installation? If the unit is totally locked up, I suggest you have it checked by a diff specialist before you reinstall it. Damage to the internal clutches and/or the ring and pinion lash may only be another way to shoot yourself in the foot again.

 

The drain plug is not what backed out, it was the silicon inside the fill whole inside the plug (if that makes sense)

After inspecting the diff, everything looks okay with the exception of the pinion bearing which is ruined. That being said, I will be taking it to a differential specialist to press the bearing and give the diff a once over.

Full disclosure, before this incident, a differential was just a magic box that made the wheels turn. I have learned more about differentials in the last 2 days than I have in the last year I have been "a car guy." Just trying to find the silver lining here.

Plus I am happy it puked oil out at 20mph and not 120mph like I had planned for it at Big Willow this Saturday.

 

If you can swing it, do all new bearings and races throughout. No use in doing it twice.

 

I realize this is a learning experience, but ANY hollow fill plug (with silicone filling the HOLE) on the engine, tranny or diff should be cause for alarm. Fill plugs are usually solid lumps of metal! This thread may help another new Z owner (or rookie car enthusiast) to understand that.

Good call on having a diff specialist check over the unit, but whatever he says needs replacing, I'd replace it! These LSD units were never, ever designed to be run dry and can be badly damaged in seconds even at low speeds.

 

That's not a fill plug. It's an AN adapter fitting that someone filled with silicone. Bite the bullet and pay the dealer for the correct drain and fill plugs.

I'm guessing the previous owner had a diff cooler with AN lines and when they sold the car, they just removed the cooler and filled the fittings with silicone.

As previously stated, use 75W-140W gear oil. Synchromax is close to 30W.

 

This. I was so confused. Definitely not the stock fill and drain plugs. Mine are solid, no silicone.

 

all this talk off silicone is making me want to visit The Chive to see it used in other manners

 

Yes, there was a diff cooler originally there. Not sure why that wasn't mentioned to me when I bought the car, but also it was an over site on my part.

 

I mean... I don't think it is really fault on either side. How were you to notice that? And maybe the previous owner should have mentioned it, but maybe they thought that it would be fine.

Just chalk it up as one of those unfortunate events and fix it so you can enjoy the car.