why does haynes recomend GL-4 for xfer?

[VanIsleDSM]

reading my haynes manual I see that GL-4 Hypoid is recomended for the transfer case and GL-5 for the rear end, yet on the fluid faq on vfaq it says that you can use GL-4 or 5 for the transfer case.. I've already got some BG synchroshift for the tranny, and I'm kinda stuck here as to what I should do for the rear end and the transfer case, do they need different fluid or not?

I already posted this question along with a couple others in the newb forum but I think it's better suited here, I like to stick to stock recomendations, so I'll probably get some mobil 1 GL-4 75W-90 hypoid for the transfer and some mobile 1 GL-5 80W-90, assuming they make both of those.. but I know there are many people on here running the same fluid in xfer and rear end..

You can't use GL-5 in the tranny because of brass, is there brass in the xfer too for some reason? I want to understand what's going on here so I can make the best decision.

thanks!

 

[Defiant]

There's no hypoid in the transfer case. Hypoid are an odd duck in the flock of gearsets, as you have not only the usual extreme pressures at the mesh point, but sliding of the faces as well.
Print out this page, put it in your hymnal, and pray over it regularly:
http://www.roadraceengineering.com/eclfluids.htm
I choose to use Pennzoil Synchromesh in my transmission, because it's been working perfectly. Some disagree, and good on them. They don't drive my car.

 

[VanIsleDSM]

when I searched I saw that someone who had spoken to redline said that the heavy shockproof was not recommended for the t-case..

I'm supposing that the t-case calls for GL-4 instead of 5 because of the brass yoke?

Upon further inspection here I think I understand what's going on.. vfaq says you can use a gl-4 hypoid or a synthetic gl-5, from what I've learned conventional gl-4 have sulphur added to them to make them basically a gl-5 and they become corrosive to brass, however many synthetic gear lubes attain their pressure protection from other additives unharmful to yellow metals, this is why you can find a synthetic rated for gl-4 and gl-5, it has the pressure protection of a gl-5 without the yellow metal corrosiveness, basically making it a gl-4 hypoid, which must be why you can't find a gl-4 hypoid gear lube any more..

reading the spec sheet for heavy shockproof I see that it boasts about not being corrosive to yellow metal not at 200F like "most" but up to 300F it's safe... well that sounds great and all, but what is the actual GL-4 spec? does it specifiy 200F is acceptable? 300F? more? because heavy shockproof doesn't list a GL-4 spec like many other synthetic gear lubes without sulphur, so maybe it doesn't meet GL-4 for yellow metal protection? or it's does and it's just saying it in a different way?

Could someone point me to a GL-4 spec sheet so I can make sure? I searched and couldn't find anything.

If there are no hypoid gears in the transfer then I don't know why it would call for hypoid, I imagine there must be some reason it needs the pressure protection.. I'm fairly ready to just buy the shockproof for the rear for sure, t-case too if I find that non-corrosive to yellow metals up to 300F is as good or better than GL-4 spec.



I'm really surprised there isn't some good solid information explaining all this out there.. hopefully this thread will be it..

 

[Defiant]

I'm supposing that the t-case calls for GL-4 instead of 5 because of the brass yoke?

No, that wouldn't be it. The brass is just the plug in the center, not anything that moves or meshes. The transfer case is only four bearings and a pair of bevel gears in a 90° gearset. I suspect the "reason" they call for GL-4 is that it's what the shop will have on hand.

 

[VanIsleDSM]

meshing or moving would increase corrosion, but just sitting there it would still corrode.. I've never taken out my t-case.. but if the yolk is in contact with the fluid, that would be why it calls for gl-4 hypoid istead of just gl-5 (which is always hypoid)

I don't think they'd do it for ease either, because the rear end calls for gl-5, so if gl-5 was fine for the t-case too, that'd be easier than having another type of fluid.

As far as there only being bevel gears in the t-case I dunno.. not sure why it could call for hypoid... are both shafts of the 90° gearset on an intersecting axis?

whatever I do I gotta figure it out soon... I don't want to be waiting to put the car on the road because I don't know which fluid to run in my t-case.. I suppose I'll call redline tomorrow to see what they have to say..

Times like this I wish I had access to nabr, post a question about bov venting and you'll still get 30 replies, but post up a real question that acutally hasn't been thoroughly covered and you're the only one interested! (thanks by the way)