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Fun question - RP syncromax in rear diff: problem? :)

1K views 14 replies 8 participants last post by  JoeFromPA 
#1 ·
Title says it all - if there's some RP syncromax in my rear diff, should I be expecting some significant problems? I.e. chemistry of the lube messing with the metals in the diff?

Obviously there's a big viscosity difference, but the scenario I'm facing is maybe a 75% RP 75w140 / 25% RP Syncromax situation.

There may or may not have been a mix-up at the shop that did my diff swap and diff fluid change. I've been advised it's possible. I've put 1k miles on the car since then with no noted diff noise.
 
#2 ·
Now that's a tough question! Diff oils are loaded with extreme pressure additives which is why they sometimes smell sulphurous. I don't know if gearbox oils are. LSD oils also have friction modifying additives for the clutch plates. And who knows what the effect on viscosity is. Too many uncertainties.
I would just bite the bullet and change the oil for peace of mind.
 
#3 ·
Your differential won't immediately seize up (wich you already know), but that oil isn't even close to what should be in there.

Change it.
 
#4 ·
Your differential won't immediately seize up (wich you already know), but that oil isn't even close to what should be in there.

Change it.


ditto.


a clutch diff requires inter-plate friction to work. I would be changing it immediately, and then changing it again after 1000mi or so as a flush.
 
#6 ·
So what are the consequences of running synchromax for say 15,000 miles in the diff? I may have made a mistake.
 
#7 ·
Well first you have proven that your butt dyno needs serious calibration because your limited slip probably isn't working :rofl:

You may have more wear because of the viscosity of ATF, but your only real choice is to change the fluid to the right specification and try not to worry about it.
 
#9 · (Edited)
Damn, it appears to be confirmed now that the shop blended 1 quart syncromax into 3 quarts of 75w140 and used it for the diff swap.

Son of a gun....

Well, that might explain why my awesome 285 wide michelin ps2's would seem to not be engaging the limited slip as cleanly as I would wish. I'm guessing it's not damaging anything in everyday driving - most diffs can take alot lower viscosity in cool, normal driving that's not aggressive - but I'd be surprised if the LSD truly wasn't working right. AFAIK, this oil is spec'd for transmissions that can include LSDs in them (FWD/AWD cars), such as my 2006 honda civic SI. Maybe I'm wrong.

Sigh....I thought I had this thing mechanically sorted for the time being.

Rao: Didn't you use some off the shelf el cheapo oil that's working well for you?Supertech 75w140?
 
#10 · (Edited)
So the ride in the Phaeton was really cool, right hiha

It would be one thing if that had some reason to do that and informed you of their theory.

The Syncromax is the WRONG specification for the M5 differential. It doesn't matter that it is the most amazing oil ever, it is the wrong stuff to use.

I use SuperTech in my differential, others use all sorts of different brands, but the most important thing is to use 75w140 GEAR OIL, GL-5 rated and it will always be synthetic.
 
#11 ·
Drain,fill,drive.

drive 1000 miles,repeat.

Not many choices here.

:M5launch:
 
#12 ·
Rao - the shop did it by mistake. The guy who provided the oils put 6 quarts of royal purple in a box, 4 of 75w140 and 2 of syncromax.

The bottles look identical when grabbing them out of a box, so the shop grabbed enough for 2 diffs and emptied them all into a single pump. I can understand the mistake, even though it pisses me off, since they didn't supply the fluids. Hell, I saw the box and fluids myself and didn't notice there would be any confusion.

Why couldn't the rear diff be accessible with just a 1/2 drive....darnit, I'd drain the damn thing this weekend.
 
#13 ·
Anybody can make a mistake, at least you know about it and can fix it.
 
#14 ·
Joe,

I should have put tape around the three liters of Sychromax and again around the four liters of 75-140 before dropping my car off and heading to Vegas. It does suck that this happened but to what extent either diff is filled with RP sychromax who knows. I called the shop back when I got home and found 2 liters of Sychromax in the trunk when there should have been three (I was planning on changing the tranny later). They told me five liters went into their pump which I thought was excessive because the diff only takes 1.2 liters if I recall (I'm sure someone will jump right in and correct me if i'm wrong). So the question is did they put all the fluid in at once or did they add it as they went and at what point did the sychromax go in? I will research this further but will never know so it is best to change it for peace of mind. I have not noticed anything negative with the Dinan diff from your car that now is in mine as a matter of fact it is truly incredible. It is working fine LS and all so I will probably change the fluid in another 5K when I change the oil because i'm crazy and worry too much about this car. Don't get me wrong I do enjoy the M5 quite a bit but sometimes I think I go a bit overboard on things that probably will work out just fine. Anyway, I will talk too them again (they were upset by the news by the way) and see if I find out more. They said there was about two liters left in the pump they were saving for me. More later.

Curtis
 
#15 ·
Thanks man. The diff takes about ~1.8 liters each + the pump volume itself.

Makes sense they put 5 liters in there since they had it available. Sounds now like a 20% dilution of the 75w140 with syncromax.

Mine drives great too :)
 
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