• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

GL4 Gear Oil

Share this page

KVH

KVH

Obi Wan
Silver
Country flag
Offline
Please refresh my memory.

Only Redline, GL4 or similar gear lube should be used in transmissions? Or the Differential? Or both?

And no GL5, and reason being that the latter adversely reacts with brass or yellow metals?
 
Also -- some use non-detergent motor oil, typically 30W.

GL4 can be hard to find, Merles usually has some (Sta-Lube brand) -- but I only use it in the diff.

I use Redline MT90 in the OD/gearbox -- can be obtained locally at Ernie's.
 
It's really not a matter of GL4 vs GL5; but rather the additive package used. I've been running GL5 in all my Triumph diffs for many years now, and it works great. But, I chose a full synthetic GL5 (Valvoline Synpower) that doesn't use the nasty "active sulfur" additive that can erode "yellow metal" over time.

I can't prove it, but I believe that any oil rated both GL5 and MT1 should do fine for the diff. MT1 includes a long term, high temperature stability test that the "bad" additive can not meet.

Before I switched to MT-90 (which IMO is worth the price, I bought a case on eBay to get the per-quart price down); I ran Valvoline VR1 (racing) 20W50 motor oil. It worked well enough (the ZDDP helps protect the thrust washers, which are a known weak spot in these gearboxes), but the MT-90 works better in terms of easier, crisper shifts.
 
Back
Top