Hey folks, I'm changing what is presumed to be original fluids on the T-case, manual tranny, and rear diff. I ordered a gallon of GL-5 and GL-4, intending to use GL-5 on the rear diff and T-case, and the GL-4 on the tranny. The FSM states that we can use either GL-4 or GL-5 for the T-case, but it ALSO says that for the m/t (which we all know we shouldn't use GL-5 on the R150F).

I should have enough either way, I just wanted to make sure.

 

Some people have had problems with t-case and tranny fluid mixing, but there's definitely a seal between them so it shouldn't happen.

I ran gl-5 in the t-case and redline in the tranny for awhile. When I drained both they had not mixed, so your call it's probably fine.

 

Thanks GSP. I think I should start a website with all the stuff yall've said

 

GL-4 is specified in the transmission to help the syncro's spin up faster so you can shift more easily. GL-5 is technically slipperier. Use that in the transfer case because there are no syncros. There is a seal between the transmission and transfer case. The seal will eventually get old and hard. When this happens, there won't be any external signs of leakage, but the transmission oil will slowly work its way into the transfer case. So when you pull the transfer case fill plug, oil will pour out due to being overfilled. Along with that, the transmission will be slightly underfilled. I'm currently working on a video showing how to remove the transfer case and replace that seal. It's fairly straightforward to do.

 

Thanks Lindsay!

 

A previous post (that was awesome) discussed gl5 vs gl4 in great detail. Gl4 is a no brainer for the manual trans. Gl5 is good to go for the diffs. If i misunderstood the previous 20 plus thread someone will let me know.

 

Yeah GL4 is *The* way to go for the tranny!
I was just making sure that fluids weren't shared between the tranny and t-case. In any case, my tranny doesn't appear to be leaking as it was full, and my t-case output seal was slinging gear oil out the back so it was low.
I put GL5 in the rear diff, plus the t-case, and GL4 in my M/t.

 

There actually are synchronizers in the VF1A chain-drive transfer case, which is what's behind the V6 with manual transmission and ADD. One synchro handles shifting from 4-low to 4-high, making it possible to shift from low range to high range without stopping (but not high range to low range). The other synchro handles shifting from 2wd to 4wd. It spools up the front drive shaft to allow on-the-fly shifting from 2wd to 4wd. That being said, those synchros are not nearly as critical to the daily driving experience as the ones in the transmission, so GL-5 is probably OK in the tcase.

The tcase is sealed from the transmission, as has been noted, so fluids are not supposed to mix. However, a seal failure where the input shaft of the tcase enters the tcase adaptor on the transmission can allow leakage between the two without any external evidence, so it's worth keeping track of the individual levels in the two gear boxes. After 215K miles and 23 years, I still have no evidence of internal leakage, so the seal can last a long time.