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Triumph TR6 - Differential GL5 OK?

Well, we all know that GL5 gear oil is incompatible with the TR gearbox because of the high concentration of sulfur additives, right? Has anyone ever tried to buy GL3,4 other than through TRF? It's simply not available unless you special order it in mass quantity. How can a manufacturer claim that a gear oil meets GL3,4 and 5? The gear oil compatibility issue doesn't affect my gearbox since I run non-detergent 30W motor oil in it.

But my real question is for those differential experts: are there any brass/bronze materials in the differential that would make it incompatible with GL5?


Looks like a near-70 degree today in western PA! Vroom, vroom!

Rick O.
Rick Orthen


There are many differing opinions on GL5 in differentials, though most seem to agree it is not good for transmissions. Supposedly it can corrode the brass synchros above a certain temperature and, according to some, will do the same to bronze. However, bronze is, or at least was used in many diffs and I never read of any actual problems. My mechanic didn;t think there would be an issue in the diff., but agreed w/ GL4 in the trans. If anyone knows of any problems, please detail. I use a synthetic GL5 in the diff and a convential GL4 in the transmission. NAPA carries Sta-Lube GL4 80-90 in quart containers and they also carry the neat pump that screws on the bottle and makes filling the car much cleaner.

To all
I know what I am about to say (and show u) will become controversial. It is funny this subject should come up as I just did a WEB search on this subject...I wanted to confirm that what I was using in both tranny and dif was OK to the yellow metals (researched in 2000). This same subject is also past threads (2001) "oil for gear box j-type" and "transmission oil". The two letters EP are important ones. Check out the past threads and then go to
Check out the three letters behind Brads name...I even saw a sample exam on the WEB in order to get the letters. Date of writting..unknown
To put the ball in the GL-4 camp (which is the 1970s spec. for TRs)go to:
this is a 1992 writting.
I use Shell Spirax HD 80W-90 (GL-5)and will continue to do so.
I know one thing for sure...if I was to go away from GL-5 it would be to GL-4 not motor oil and that is my opinion. If u are comfortable with what ever u use...keep using it.
Rick O, do not totally discount GL-5. Sorry can not remember but one of the manufacturers of GL-5 specifically said "safe for all brass and bronze components"...if someone sees this let us know.
Then there is the subject of wether or not to use "lead substitute" ......
Rick C
Rick Crawford

Thanks Rick C. Now I know that there is "active" and "inactive" sulfur and will look for Brad's recommended manufacturers when I renew my differential oil. Regarding using motor oil in an O/D gearbox, I run it because my gearbox rebuilder requires it as a condition of the warranty and I also respect his knowledge base. I personally don't think it matters enough to lose sleep over. As I understand it, motor oil was originally specified by Standard Triumph waaaaay back when though.

Rick O.
Rick Orthen

Ha Rick
I think you took me personaly re my comments. It was not meant to be derogatory to you. Look back at the past threads and u will see that there are many people that use engine oil in there trannys and difs. This is where my comment re if you are comfortable...keep using it was aimed at. I do see your reason for using it and appreciate your reason. No offense given Rick. My purpose is to inform that the old feeling that GL-5 is bad for our cars is just that..old. As u saw that artical is directly aimed at our LBCs not GM or Ford. It appears that yes once upon a time GL-5 was bad for the yellow metals. Also there is a reason for EP additives in gear oils (not found in engine oils). Gears in both tranny and dif. are more akin to a sliding action and require an extra bit of protection as the gears slide past each other. There is very high pressure at this point and such require a lubricant that will with- stand this pressure and not break down. Thus the whole purpose of EP additives in gear oil and a reason why the API came up with this clasification of a lubricant....for gears. It is now (2002) a question of is GL-5 safe for our brass and bronze components in both parts. It appears so. You ask the question of API clasifications (American Petrolium Institute). WEB search "API" and at their WEB page do a local search of "1560.pdf" or the fast version at and go to application help..look for API gear oil service info.
Check out
So Penzoil is not a choice.
The one u want to read Rick:
This is the one that talkes about brass and bronze. Now if u can get it in quart form..ask ESSO.

OK enough. All I have done is a WEB search with "GL-5"
I have fully admitted, I am no expert and I am not trying to convince anyone that I am correct and anyone should not use engine oil in your tranny or dif. It is a matter of choice. This is entended for information only so one might be more informed.
Rick C
Rick Crawford

Rick C., as always you are quite a storehouse of knowledge. Kudos for supplying all the oil links. Just to clarify, I do not endorse using motor oil in a differential unit. About those EP additives, however: are the forces that much greater in a gearbox than they are on, lets say, a crankshaft journal or piston wrist pin on the combustion downstroke? Guess the crank journals present a much larger surface area than the mated gear surfaces, thus reducing forces. Just wondering (as usual). Obviously I'm not a lubricants engineer!

Rick O.
Rick Orthen

Rick O
Likewise..I am no engineer. Just going by what I read on the WEB from "experts" and manufacturers of oil products. Did a search this morning on pressures re engine/tranny and found nothing. Lots of talk about EP in difs and trannys though. Simply put, the gear boxes require that EP additive. Did you go to the Imperial Oil WEB page? Also is the consideration of using a synthetic gear oil in the dif. (NOT TRANNY). As u know it is not easy to change the fluid in it. Should have done drill/tap/plug thing while doing the restore...was a newbie then and sure wish there was a TIPS&TRICKS thing I could have gone to. Hint Hint guys.
20F in the garage and pretending vroom..vroom
Rick C
Rick Crawford

It is always embarassing to be proven wrong..especially if you do it to yourself. I asked Shell directly if Spirax HD 80W-90 was OK for trannies and Difs containing "yellow" metals the respose is:

Dear Mr. Crawford,

Thank you for taking the time to visit the Shell Canada web site.

In response to your inquiry, Spirax is not suitable for equipment with
yellow metals due to the extreme pressure additives in the oil.


Lilianne - Technical Department
Shell Canada Products

Soooo, the only one that actually mentions the words Brass and Bronze is Imperial Oil (WEB page above). I have asked LUCAS OIL products same question and answer is:
Thanks for asking. You can use the hub safely in your application

Dale Wilcox
Lucas Oil Products, Inc.
(800) 342-2512 ext. 115
SO I hope I have not got anyone out there running out and buying Shell Spirax HD. To say the least, it will not be going in my tranny and will now drain the diferential. The tranny will be filled with 50% heavy duty hub oil from Lucas and 50% Lucas 80W 90 gear oil. I will ask Esso the same question re their gear oil. Maybe I am making a big deal over nothing. Simply, Nothing but the best for my mistress...well I blew it for her first 600 miles but it is gone now(Shell).
Rick C
Rick Crawford

Rick C. Don't feel too bad, I still have my receipt for the Spirax. Why are you going to drain your differential unit of Spirax? As far as I can determine, there are no yellow metals in the unit that would be attacked by the super-duper EP additives. If you drain yours, I'll have to do the same with mine since it contains that "GL-3, 4, 5" rated oil. I still don't understand how a gear oil can be graded that way.

Guess your gearbox will be getting an early renewal however. Lesson learned is that if you can't find GL3 or 4, stick with motor oil until you find it.

Rick O.
Rick Orthen

Rick O - I used straight 30 non-detergent Castrol oil like it said in the S/T book from 1958 to 1972 in my TR3A and went through 3 full gearbox re-builds in 80,000 miles.

Since I completed my restoration in 1990, I have used nothing but Valvoline 20W50 (Racing - if I could find it) and changed the oil every 3,000 miles. I have an overdrive too. It never slipped.

I have driven over 60,000 miles in the last 11 years without more than the usual tiny flakes in the oil when I drained it. There was no problem with the O/Drive either.

I got this good advice from Ken Gillanders of "British Frame and Engine" in California. He also reported recently that racers have tried synthetic oil in their TR gearboxes. Don't do it!!! The synthetic is so slippery that the synchros slip and one TR racer acually totaled his TR when it slipped out of gear in a curve.

All the other racers who also experienced this drained out the synthetic oil, put in what they used to use and the problem was eliminated.

Don Elliott, Original Owner
1958 TR3A
Don Elliott

UMMM...sorry Rick..RETURN IT!! Had not bought the Spirax yet but have the Lucas stuff. I am under impression that yellow metals exist in the diff///no/yes?? If no yellow metals in the DIFF then will not change over till next winter idle time. (See new thread re drill/tap/plug the dif). Would someone please answer this question?? From what I can tell (and see) if it is rated GL-5 then it will meet the lower specs. (thus GL-3,4,5) BUT the GL-5 has 50% more EP additives than GL-4... 100% more than GL-3. It seems to be a issue of "DUTY USE" heavy vs light/ GL-5 vs GL-3. Rick, I do not think I did any damage to the tranny/od. Was only in it for 600 miles (with fingers crossed BOTH HANDS). The weird thing is when I went and bought the Spirax, I asked the question he made a phone call and came back with it is OK. Go figure! I guess lesson learned...go to the horse! Will be asking Esso..keep u posted.
Rick Crawford

Rick and Don
(composed my last reply off-line so did not see your posting Don)I can not argue with experience. Don, I know u have said the above before. Like I said lesson learned. What I went by is the shop manual says GL-4 and thought ok go 5 and find one that is safe to yellow metals. Have learned a lot about GL-X but now seems to be useless information. So I guess I am getting closer to being an "oldbe". Don would u please answer my question re yellow metals and the diff (before I drop the 6 off of the 4 jack stands).
Rick C
Rick Crawford

Don--Thanks for the real experience. I'll stick with the non-detergent 30W for my O/D warranty period, and then consider going with the 20W-50 after that. I guess the fact that the 20W-50 is available only WITH detergents hasn't been a problem for you either.

Rick C--My mechanic assured me that there are no yellow metals in the differential unit. Use anything BUT motor oil there. To me, a "GL3,-4,-5" rated lube is an oxymoron and I would never use it in a Triumph gearbox. I'm with Don.

Rick O.
Rick Orthen

OK heads hurting can stop slamin it into the wall:)...just kidin with ya. Why the heck does the manual say GL-4?!!! I just read my manual for the "Laycock-De-Normanville" A type OD and I quote Page 5... "under no circumstances should extreme pressure gear oil be used, because....". Now the killer, same page...."The oil in the overdrive is common with the gearbox. The oil to use is ordinary mineral oil in following grades..Summer climates...S.A.E. 30". I think I need another tylenol.. UMMM dumb mineral oil different from engine oil or is ALL oil mineral oil. Hay Don, do u think I did any damage with that 600 miles?
This is deffinitely one for the TIPS!
Rick Crawford

Rick C. Everything will be OK, relax. Manuals aren't always clear on what they mean anyway. I believe mineral oil is petroleum-based ("from the ground") as opposed to plant based oil (Castrol). Just use any conventional oil.

Rick O.
Rick Orthen

This thread was discussed between 15/03/2002 and 21/03/2002

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