Brendan

The FSM calls for GL-4 75w90, but it seems that all 75w90 is synthetic. Is there a conventional 75w90 and/or can I use 80w90 instead?

scuba

Look for Sta-lube.
My dealer sells it. But, I believe napa has it a wee but cheaper.

Brendan

Can't find Sta-lube anywhere locally and the only place that has conventional 75w-90 is the dealer and they only get it by the drum for their service dept.

jbtvt

I used this as a temp measure to flush the trans in a few days since it was pretty cheap and fast shipping (with prime) but I wouldn't recommend it for permanent use. It is much thicker than 75w and I have been getting a bit more grinding of synchros unless I double clutch. Probably the most I would go is 1:3 mixed with mostly 75w.

Allegedly the anti corrosion additives in the newer GL5 will not eat brass, but I will probably water some 75w down with the above to be safe. Why not use the full synthetic, other than price? Should be fine to mix with conventional.

Brendan

Price is the main reason. I've never used a synthetic oil, but it may be my only option at this point. Also, I'm in Canada and I don't see that sta-lube on amazon.ca

RustBucket

iTrader: (1)

80w is a lot thicker when cold than 75w. Nothing at all wrong with synth. Also the W56 is spec'ed for GL4 and GL5. You could use anything really and be ok.

Best I have found is Amsoil MTG 75w-90 or redline MT-90 or MT-85

MudHippy

Sta-Lube GL-4 is 85W90. For the record.

It's basically a matter of personal preference. Like RustBucket says, you could use any kind of GL-4/5 and be ok. Some might help the tranny shift a little better than others. But it'll all work.

Brendan

pretty sure i remember putting castrol 80w90 GL5 in there last time it was changed and haven't had any issues other than it feeling like molasses on cold winter mornings. I have read lots of good stuff about the redline MT-90, but was hoping to come across a conventional 75w90 GL4

jbtvt

Something to consider here with GL4 vs GL5: http://www.widman.biz/uploads/Transaxle_oil.pdf

"In normal operation, the sulfur/phosphorous additive forms a black sacrificial coating on the gears and anything it touches with a little pressure and temperature. As the gears turn, instead of wearing, the sacrificial coating of additives is pealed off or worn off. This is normal and acceptable in all steel gears. But when one or more of the surfaces is brass or another soft metal, the sacrificial coating is stronger than the base metal, and instead of just peeling off, it takes with it a few microns of brass that it is bound to. A normal GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the GL-5 product, so the bond is not as strong, and therefore can be peeled off without peeling a layer of brass (or less brass). This means that the GL-4 product provides a little less extreme pressure protection, so in the differential of a high powered car, it would not be the ideal product in the differential."

"But in the transmission, we should consider two factors:
• Due to the fact that the differential applies the final torque, normally we do not need the full EP protection in the transmission where less torque (about 30%) is applied.
• We need to be able to break the EP protection to stop the spinning of the gears long enough to mesh them or synchronize them.
When we use a GL-5 product in a transmission that requires GL-4, we normally find 2 to 4 times as much copper in the used oil as we would with a GL-4 product. Eventually the synchronizers wear to
the point that they no longer make contact with the other half of the cone, bottoming out before stopping the opposing gear. "


If anyone knows of any sources for 75w GL4 please post up, otherwise I plan on mixing the 85w Sta Lube with 75w GL4/5 to hopefully get more life out of the synchros. (Edit - or *gaaahhh* paying $15/qt for this - , depending on how rich I feel that day)

RustBucket

iTrader: (1)

Both Amsoil's and Redline's products are specifically formulated for manual transmission. These are not general-purpose gear lubes. Shift quality is excellent from very cold to very hot temps. Fill it up with this stuff once and leave it alone for the next 50k.

For further technical reading see bobistheoilguy.com

Or, if you want a straight-weight GL-4, pick up some of this:
(P.S. - 40wt motor oil and 90wt gear oil are the same viscosity)

jbtvt

$20 for 5 gallons including 2 day shipping?! Whaaat? That's gotta be a misprint.

I will be draining and refilling the trans on my '85 again next week (had some shavings in there) and since I already have the Stalube will do 1:3 Stalube:75w, will report back on performance and any grinding at that time.

For the final flush in ~1000 miles will probably usethe GL4 Redline.

Brendan

I found the MT-90 at the local parts place for $1 less than amazon.com which is pretty impressive considering that almost everything in Canada is more expensive than in the US and even moreso when comapared to online pricing.

Brendan

The FSM calls for a 3.9 litre capacity in the G58 but the fill hole started spitting out at less than 3 litres. I drained the old stuff until there was no dripping at all. I know that you can never get ALL the old stuff out, but 1 litre is a fair bit. The old stuff is conventional 80w90 and the new stuff is synthetic redline 75w90. Should I be concerned having them mixed together?

Jacking up the front end with the drain hole open and then also the rear may have been a smart idea in hindsight...

jbtvt

Yeah, but it should be fine mixed. Don't know this trans but many have areas with small passages that feed them and take a while to fill up. Check level again after it sits for a bit and report back. I've found several trans came up low the second check around.

Brendan

Will do, thanks.

wyoming9

iTrader: (1)

I used for the past 15 years or so 85W140 in all the gear boxes.

Then we have a mild climate here in eastern Pa

Brendan

Tranny was still full when I checked a few days ago. Also, is Redline MT-90 OK to use in the transfer case as well?

jbtvt

Yep

Damn 5 character rule...