Oil pressure too low...

[Adrio]

Alan,

I am curious about your experience with oils and the A-type overdrive. years back I changed the oil in my TR3 gera box only to find the new oil made the overdrive not work. So I hunted high and low for a straight weight non detergent oil which solved the problem. It is time to change the oil again and I can't find the same stuff. Can you tell me what brand and type you used and how the O/D worked after.

Thanks

 

[Dave Russell]

Hi Adrio,
Engine oil viscosity is rated on a different system than gear oil. A 90 rated gear oil is fairly close in viscosity to a 20-50 rated engine oil.

The OD relies on clutches operating in oil to transmit power. Any oil which has friction reducers will cause the OD to slip. Any engine oil without friction reducing additives should work. Beware of "super slick" oils in the OD gear box.

If you use a gear oil, be sure that it is not GL5 rated. GL5 has sulfur compounds which may degrade the brass synchronizer rings in the box. GL4 rated oil will work.

Quite a few folks use Red Line MT90 gear oil in the OD boxes. It is formulated to have enhanced friction capabilities which improve the action of the synchronizer rings & OD clutches. I switched from 20-50 to MT90 & found better synchronizer & OD operation.

Attached is a chart to compare viscosities of various engine & gear oils.
D

 

[Alan_Myers]

[ QUOTE ]
Alan,

I am curious about your experience with oils and the A-type overdrive. years back I changed the oil in my TR3 gera box only to find the new oil made the overdrive not work. So I hunted high and low for a straight weight non detergent oil which solved the problem. It is time to change the oil again and I can't find the same stuff. Can you tell me what brand and type you used and how the O/D worked after.


[/ QUOTE ]

Hi,

I can't give you any performance info regarding the current A-type overdrive just installed in my car. It's not back on the street yet. Once the car is ready to run, I'll be using 20W50 Valvoline or Castrol "racing" oil in the gearbox and O/D.

20W50 and 90W gear oil are almost the same viscosity. 90W was the original specification for both non-O/D and O/D TR gearboxes. But over the years I've personally used and seen others use 20W50 "racing oil" in non-O/D and O/D TR gearboxes without any problems.

Perhaps the problem with your O/D was a detergent motor oil, not viscosity? It sounds like you already know, in the gearbox a non-detergent oil should be used, i.e. a "racing" oil. Detergent will lead to foaming and frothing, not good for the gearbox. Perhaps detergents would also effect an O/D.

When gear oil is used, it's most important to avoid GL5. Unfortunately this seems to be the most common type on the shelves now. It contains sulfates, which eventually damage brass components in the gearbox. GL4 is the correct stuff to use, although it's now harder to find.

Most gear oil on the shelves today seems to be multi-viscosity, too, such as 85W90. I don't know that this matters a great deal, so long as it's close to 90W.

As I already mentioned, I'm not sold on using synthetic oil in the TR engine. But I'd especially avoid it in the gearboxes! I've heard a number of reports of cars that started popping out of 2nd gear during deceleration after synthetic oils were introduced to the gearbox. Switching back to non-sythetic oils solved the problem completely.

Cheers!

Alan

 

[sparkydave]

[ QUOTE ]

If you use a gear oil, be sure that it is not GL5 rated. GL5 has sulfur compounds which may degrade the brass synchronizer rings in the box. GL4 rated oil will work.


[/ QUOTE ]

Is this true for a Midget 1500 gearbox too (non-overdrive)? I hadn't heard of this before. I'll have to check if what I replaced it with is GL5 or not, but I think it is. Will this hurt the rear end too? I put the same oil in both.
-Dave

 

[Dave Russell]

Now that you mention it, I'm not sure about the later gear boxes. They may have steel rings. If so, GL5 would be OK in the gear box.The earlier ones had brass rings. You should definitely use GL5 in the rear end.
D

 

[Alan_Myers]

Hi,

I can't say about MG gearboxes. If you ever have it out for a clutch or whatever, take a peek inside and see if there is any brass. Most commonly, it's used in the synchromesh assembly. If there is brass, don't use GL5. A manual might tell you what's specified. Likely GL4 or earlier, since GL5 has only become common recently.

GL5 used by mistake almost certainly won't cause a TR gearbox to immediately fail. It will accelerate wear and promote corrosion on brass parts giving the gearbox overall shorter life and will probably cause difficult shifting as a first symptom. If it's been used in error, just drain and replace a couple times as soon as possible to clean out the GL5 and stop the sulfer action on the brass.

Yes, later TR gearboxes have brass synchros, too. At least through the TR6. I don't know about TR7/8. GL4 is okay for the TR rear end, too, although GL5 is probably fine. I don't recall any brass inside the diff. If you happen to have a limited slip installed, something other than standard hypoid or EP gear oil might be needed. Not sure what's best, I'm looking into it since I'm installing a Quaife in my TR4. I know Redline makes some good products especially for use with LSD, either oils or modifying additives.

Incidentally, both GL4 and GL5 are "hypoid" or "EP" (Extreme Pressure) oils. These are primarily used in differentials to handle the special neads of the crownwheel and pinion, which have high surface pressure on the meshing tooth surfaces, due to design and load. The additives to GL4 and GL5 are what give them "extreme pressure" lubricating capabilities. GL5 has about twice as much additives.

The gearbox doesn't need extreme pressure oils. It has no hypoid-design gears (gears with a long, curved tooth). The reason many manufacturers now specify GL5 in both their manual gearboxes and differentials is mostly convenience and simplicity. One oil for both g'box and diff makes for easier servicing. GL5 is "overkill" in a gearbox. So is GL4, for that matter. Plain old non-detergent 20W50 motor oil or 90W non-hypoid gear oil (might be marked GL1, GL2 or GL3) is generally fine in a manual gearbox. There are some special products to promote easier shifts and quieter operation. And, there are some exceptions: for example modern gearboxes requiring thinner oils.

Dave, I'd be interested to hear how MT90 works out in the gearbox. It's the only synthetic I'm aware of that seems to consistently work well in TR gearboxes.

Cheers!

Alan

 

[sparkydave]

Thanks for the info, I checked the bottle and it is GL5 I put in the gearbox. Something tells me I might be looking for something else to put in there soon unless I can tell if it has steel synchros in it. I haven't noticed any changes in how it shifts since I changed it about 2000 miles and 2 years ago. So, would I be correct in reading from this thread that 20W-50 is okay to put in, even though the service manual says SAE 90?

 

[Dave Russell]

Hi Alan,
MT90 is a 75W90 GL-4 gear oil. It has less friction modifiers than engine oil or other gear oils. I've been using it in an AH 4 speed with OD for a couple of years. Almost immediately noticeable were quicker more positive synchronizer operation & quicker engagement going in & out of OD as compared to previous the 20-50 motor oil. This is a snake oil that actually works better. There is also a Red Line MTL gear oil which is 70W80 GL-4, for use in colder climates.

The can says "not intended for rear wheel drive differentials which require a GL-5 lubricant". As you know, hypoid gears have quite high sliding contact pressures & the extra friction modifiers in GL-5 help. The initial cost of RL is quite a bit more but I would not go back to the motor oil.
D

 

[Alan_Myers]

Hi,

If the service manual says 90W gear oil, then 20W50 *racing* oil would probably be fine. Just be sure it's *non-detergent* racing oil, not typical 20W50.

On the other hand, the GL5 may be fine, maybe not. I really don't know, I have very little experience with MGs. So hopefully someone else here or on the MG forum can tell you if there is any concern using GL5 in that gearbox.

It's not likely to damage the gearbox immediately, in any case, if you leave the GL5 in there for a week or two while you investigate.

On the other hand, the safest thing would probably be to track down some 90W GL3. Multi-viscosity gear oil seems more common now, something like 85W90, also fine if it's GL3. The alternative of 20W50 racing motor oil is always possible. Or, Redline MT90 might be an option. (Incidentally, Redline is very responsive to questions via their website, or may already have info specific to your car posted in FAQs).

Best thing would be to ask other Midget owners what they have had good experiences with, or do a Google search and see if there is any info on websites.

These older British gearboxes can be quirky. What works great in a TR or AH box might cause glitches in an MG, vice versa, etc.

For example, I've already mentioned that some have reported problems with TRs popping out of 2nd gear during deceleration, with synthetic oil in the gearbox. That's a good example of "quirkiness", since other cars seem to use synthetic oils with no problems. In this particular case, no harm actually seems to be done and just switching back to mineral-based oils appears to solve the problem.

Cheers!

Alan Myers
San Jose, Calif.
'62 TR4 CT17602L

[ QUOTE ]
Thanks for the info, I checked the bottle and it is GL5 I put in the gearbox. Something tells me I might be looking for something else to put in there soon unless I can tell if it has steel synchros in it. I haven't noticed any changes in how it shifts since I changed it about 2000 miles and 2 years ago. So, would I be correct in reading from this thread that 20W-50 is okay to put in, even though the service manual says SAE 90?

[/ QUOTE ]

 

[Guest]

I've also been using the Redline MT90 gear oil in my TR6 gearbox, the stuff is fantastic. immediate difference in the smoothness and quality of the shifts. Cold weather driving is also a pleasure, and to date, after a few years of using it, I have not experienced any of the popping out of gear syndrome that I know alot of folks have had when using synthetic gear lubes. As I said in my thread of a few weeks back when I changed my clutch, the only downside is the MT90 is a much thinner lube (it looks and pours like auto tranny fluid), so if you have gearbox seals and gaskets that are deteriorated it will work it's way out of there through any means possible. I replaced as many seals on the gearbox body as I could, and the input and output shaft seals as well. So far, a few weeks now, everything seems tight.