Time for another stupid question: how to change the diff fluid?

[Kalevera]

Guys -

I've searched the forums, read my bentley's, gone through my bookmarks of e34 sites, and nobody seems to note how to change the diff fluid.

I know that this is a very simple operation: 14mm hex key; drain it from the lower bolt, then refill to the bottom of the upper bolt's threading.

I found a distributor of Redline products, bought two containers of 75w90 fully synthetic gear oil for my 3.91 LSD. Now the problem:

How does one get the new stuff IN it?! Use a pump? Lower the diff? The fill bolt is conveniently located in an area that makes it impossible to fit the actual bottle in there. So what do I use?

Best, whit

[Rigmaster]

Many of the drain/fill plugs seem to be 10mm hex (allen) type- at least those that I've seen lately (and that's been quite a few!!).

To get the stuff in, I have had pretty good luck using a plastic pump with a ~2ft clear plastic tube attached to the end. I think I got mine from Autozone or Pep Boys. It's designed to screw into one of those short rectangular gear oil bottles, I've got an old one that I use- I just keep filling it with whatever oil I need to pump into the car (diff, tranny, etc).

I have not actually tried it this way, but you might be able to use a LONG piece of hose on the redline bottle (or a long hose + funnel), and hold the funnel up near the rear wheel well, then fish the hose down over the top of the rear tire, and into the diff fill hole. I've done something similar to this when filling manual tranny's in E30's as well as E21's and 2002's- basically run the hose up to the engine bay- near the firewall, and into the fill hole. It REALLY helps to have an assistant for this method.


Bret.

[Kalevera]

Bret - thanks for the info. I have helpers o'plenty, so I'll probably try the second method if I can find a length of tubing.

Once I get some money again, and my cooling problem sorted out, I'm going to email you about those lock actuators...hope you still have them :)

best, whit

[bahnstormer]

it is in the bentley manual...
make sure the car is level

take a clear tube, 3 feet long or so and hold it above the diff...
use that noggin =]

[632 Regal]

ummm Lowel? I believe the LSD differentials take the thicker 85w140 and not 80w90. Make sure you are able to remove the fill plug before you drain all the fluid...for obvious reasons :D

[bahnstormer]

Bentley's recommends Castrol SAF-X0 for non-LSD and BMW's "Synthetic Final Drive Oil" for LSD. The dealer currently recommends their own BMW brand (formulated by Castrol exclusively for BMW) SAF-XLS which has now been superseded by SAF-XJ. If you choose not to use the BMW fluid, get a premium quality full synthetic gear oil such as Amsoil or Redline. Most synthetics do not require the separate fricition conditioner additive for LSD. Click here for more info on BMW's fluid spec.



http://www.nmia.com/~dgnrg/page_16.htm

[Kalevera]

Thanks for the advice, guys.

I bought two bottles of Redline fully synthetic 75w90 w/LSD additive (for my 3.91s). In reading the board archives, I've noted that some people use it with no chattering, others use something a lot heavier (Jeff - I read something about you using 75w140?)

Bahnstormer - for the LIFE of me, I couldn't find the procedure in my bentleys, beyond the "drain the fluid" and "refill it"...nothing about the tubing in the final drive nor the maintenance sections.

It's a really simple procedure, but it looks like a pain in the ass, and I'm having visions of spilling diff fluid all over ME and the ground.

best, whit

[ryan roopnarine]

if the tag on your diff has a s before it, eg. S410 like mine (4.10 ls unit), it takes the saf-xj oil, which is a 75w140 oil. its what's in mine. others may have had success putting w90 into a lsd because of lubricant technology advances, but i probably ain't gonna "try" 0w20 oil in my crankcase. i change it so little that i would only put the w140 in there. if i were you, there's no way i'd try to change that oil without a pump to put it back in....you'll only do it once by hand before you buy a pump. i lost my pump before i changed mine, so i thought i could force it back in by hand....big mistake. took at least 20-30 minutes for me to squeeze the oil through the hose back into the unit. the pump takes a couple of minutes.


Thanks for the advice, guys.

I bought two bottles of Redline fully synthetic 75w90 w/LSD additive (for my 3.91s). In reading the board archives, I've noted that some people use it with no chattering, others use something a lot heavier (Jeff - I read something about you using 75w140?)

Bahnstormer - for the LIFE of me, I couldn't find the procedure in my bentleys, beyond the "drain the fluid" and "refill it"...nothing about the tubing in the final drive nor the maintenance sections.

It's a really simple procedure, but it looks like a pain in the ass, and I'm having visions of spilling diff fluid all over ME and the ground.

best, whit

[John B.]

The original owners manual only specified a GL-5 rated 90w gear oil & didn't differenciate between LSD or standard. I've been using the Mobil 1 75-90 gear oil which is LSD compatible in my 3.46LSD for 12,000 miles with no problems.

[Kalevera]

hey guys - thanks for all of the advice.

I changed out the speed sensor and fluid today. Sweet - now I have a speedo again :) But man, those bolts are SURE hard to get at...

In terms of the fluid: yes, I used a pump :). I got almost 2 quarts out of the diff. Looked like it was newer OEM fluid. The PO mentioned something about putting $800 into the car prior to parking it...As the diff has very little/no grease on it...just a bunch of dirt, I think he may have replaced it or had it rebuilt.

Driving forward seems fine, but I noticed some chatter when in reverse...haven't quite figured out where that's coming from yet. Could I get chatter from overfilling the unit?! Doesn't seem logical to me, but any info would be appreciated.


Best, whit

[ryan roopnarine]

does it chatter in low speed tight turns (<10 mph)? if so, i'd say that the fluid is too thin for the app, and you can either add lsd additive, or get a fatter fluid. in my research at bobistheoilguy, i found that redline 75w90 is one of the kinematically fattest 90wts there is, that's why everybody recommends it for shutting up bmw rear ends. mobil 1 is one of the skinniest. i had mobil 1 75w90 in my rear end for less than 1000 miles, and just wasn't satisfied at the groan that was still there, despite the fact that m1 supposedly doesn't require a additive. i dumped it, and added 2qts of royal purple syn 75w140 with a tube of additive for the sake of being thorough. no noise anymore, so i won't tell anybody to use the m1 unless their diff is freshly rebuilt, or their rebuilder specifically requires it.


hey guys - thanks for all of the advice.

I changed out the speed sensor and fluid today. Sweet - now I have a speedo again :) But man, those bolts are SURE hard to get at...

In terms of the fluid: yes, I used a pump :). I got almost 2 quarts out of the diff. Looked like it was newer OEM fluid. The PO mentioned something about putting $800 into the car prior to parking it...As the diff has very little/no grease on it...just a bunch of dirt, I think he may have replaced it or had it rebuilt.

Driving forward seems fine, but I noticed some chatter when in reverse...haven't quite figured out where that's coming from yet. Could I get chatter from overfilling the unit?! Doesn't seem logical to me, but any info would be appreciated.


Best, whit

[ryan roopnarine]

The original owners manual only specified a GL-5 rated 90w gear oil & didn't differenciate between LSD or standard. I've been using the Mobil 1 75-90 gear oil which is LSD compatible in my 3.46LSD for 12,000 miles with no problems.

gl-5 isn't a specification that designates between synthetic and non-synthetic hypoid oil, only one that designates between crownwheel and pinion and hypoid gear types. that doesn't mean it's ok to use mineral oil in the diff. castrol ran off a proprietary w90 and w140, and the bmw designation was included in the name......the weight definitions for each are available on castrol.co.uk's website. i'm certain im not the only one that got somewhat disappointing results from use of the m1 syn. in their rear ends. i put m1 in because i couldn't get any redline, and i had to dump it 1k miles later. the w140 has been in for at least 25k and it hasn't started groaning yet. i haven't been in it for (differential) purposes for a while, but i'd bet the tis has a datasheet specifying the castrol fluids for the rear ends. i'm merely trying to pass along the fact that one of these fluids has a weight of w140, which is a significantly heavier oil than the 90.