Midget gearbox oil

[Wampahoofus]

Hi all,

I'm pulling the gearbox for my 74 Midget to redo all the leaky seals and whatever light reconditioning it might need. It got me thinking about oil choice.

MG recommend a regular PCMO 20W-50. I have PYB 20W-50 in there now and it seems to do well, but I'm sure it's far from ideal. Problem is, a conventional 20W-50 at 40C seems to have a viscosity around 150 cSt. This is way beyond my go-to Pennzoil Synchromesh, or even a 75W-90 MTF. I'm sure HTHS is far too low in a Synchromesh-esque fluid as well. What to choose? I'm not interested in getting into 'boutique' oils for this car. If we start talking $20/quart I'll just stick with what works.

Thanks in advance.

 

[jacky]

they dont like to be called midgets call them little people

 

[Greasymechtech]

Use a 75w90 GL4 MT fluid. Redline, Amsoil, Ford... have one.

Or, use a full synthetic 20w50 motorcyle oil. Mobil1, Castrol, Valvoline... are common to autopart/dept stores.

Napa and Mobil1 have a 15w50.

 

[Kamele0N]

Any motocycle oil with GL4 spec......or UTTO oil (universal tractor transmission oil) will be ok as substitute.

 

[Doog]

Use a dino conventional 20w50. Do not use synthetic. It will penetrate the gaskets in a 1974 vehicle.

 

[Greasymechtech]

Synthetic doesn't penetrate gaskets. If a seal or gasket leaks, fix it. The OP is pulling the trans for resealing. This is the perfect time to start and stick with a synthetic.

 

[Whitewolf]

Originally Posted By: Wampahoofus
Hi all,

I'm pulling the gearbox for my 74 Midget to redo all the leaky seals and whatever light reconditioning it might need. It got me thinking about oil choice.

MG recommend a regular PCMO 20W-50. I have PYB 20W-50 in there now and it seems to do well, but I'm sure it's far from ideal. Problem is, a conventional 20W-50 at 40C seems to have a viscosity around 150 cSt. This is way beyond my go-to Pennzoil Synchromesh, or even a 75W-90 MTF. I'm sure HTHS is far too low in a Synchromesh-esque fluid as well. What to choose? I'm not interested in getting into 'boutique' oils for this car. If we start talking $20/quart I'll just stick with what works.

Thanks in advance.


This takes me back. I have built a number of these for friends that used to race them. As you say, the recommended fluid is engine oil, 20W-50 which is what we used but for low temperatures (below 5C) 10W/30, not that we ever got there. I'm not sure about materials compatibility with other types of fluid so be careful with that.

 

[dwgwater]

I had a similar question that was addressed at length here:
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3097400/1

 

[Wampahoofus]

Originally Posted By: dwgwater
I had a similar question that was addressed at length here:
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3097400/1


Looks like we're in the same boat on this one. I see Mola recommended a Synchromesh type fluid for you (~ 10 cSt @ 100C). What throws up a red flag for me is that a manual trans is going to be running closer to 40C when hot. At that temp there is a huge viscosity gap between the spec 20W-50 and other fluids. I.E:

All at 40C (in cSt)
PYB 20W-50: 145
PYB HD 30: 98
Amsoil 75W-90 (MTGQT): 88
Pennzoil Synchromesh: 42

I'm not sure how much viscosity is really needed in this trans. Seems like all the guys just run 20W-50 or SAE30 and call it a day.

Just curious dwgwater, what did you go with in the end?

 

[Doug Hillary]

Hi,
Wampahoofus - When these vehicles were new BMC (MG) recommended a SAE30 engine oil. In my case we always used a Castrol product of the era but never 20W-50 - IIRC we used Castrol's XL 20W-30

It seems that around 90/11.5 would be the viscosities you need and seeing that you are rebuilding/resealing I would use a GL4 75W-90 synthetic. Delvac/Mobil or Castrol have such products at reasonable prices

 

[dwgwater]

Still haven't changed out the SAE30. It works well, doesn't shear and it's Frank's (Spritenut) recommendation. Pay it forward.

 

[Kamele0N]

Are these 20w50....30 etc oils Api SG rated or they have newer Api ratings?

I am asking that becausw SG has higher ZZDP content...that's why all motocycle oils for engine + gearbox are SG rated...nowadays Jaso MA also...

 

[Lapham3]

My wife has had a '76 Midget since new and I don't recall using engine oil in the 4spd in that car. In fact I changed it a couple years ago when I saw some old GL-4 on closeout at O'Reilly's. My '86 V6 Fiero specs engine oil(10-30?), which I used for many years. Last year I tried synchromesh and shifting is smoother-and if you're pulling the trans, you're also pulling the engine on that car!

 

[fdcg27]

This is what I recall from my old MGB.
20W-50 was among the grades recommended for the engine in hot summer weather, but not for the gearbox.
You've written in the past that the 20W-50 grade was developed for a very specific application.
How can it be that this grade spread like kudzu and came to be recommended for warm weather use in huge numbers of European and UK engines where it wasn't really needed at all, including that of my old BMW?

 

[Spazdog]

I always used GL4 in my Spitfire.

It shifted really well.

 

[Whitewolf]

In the manual that I have, for the gearbox it states, "Oil viscosity:as for engine". For the engine 20W-50 is one of the recommended grades and that is what we always used. There are some alternatives for extreme cold climate but that never applied to our usage.

 

[Wampahoofus]

Originally Posted By: Lapham3
My wife has had a '76 Midget since new and I don't recall using engine oil in the 4spd in that car. In fact I changed it a couple years ago when I saw some old GL-4 on closeout at O'Reilly's. My '86 V6 Fiero specs engine oil(10-30?), which I used for many years. Last year I tried synchromesh and shifting is smoother-and if you're pulling the trans, you're also pulling the engine on that car!


The 75+ models with the 1500 Triumph engine used the Marina gearbox, which required a xxW-90 GL4 gear lube.

Yup, pulling the engine to seal it up too! Giving a quart of various oils back to nature every 500 miles is a bit excessive.

 

[Doug Hillary]

Hi,

Originally Posted By: fdcg27
This is what I recall from my old MGB.
20W-50 was among the grades recommended for the engine in hot summer weather, but not for the gearbox.
You've written in the past that the 20W-50 grade was developed for a very specific application.
How can it be that this grade spread like kudzu and came to be recommended for warm weather use in huge numbers of European and UK engines where it wasn't really needed at all, including that of my old BMW?


It was used as the "fix it" lubricant - even when nothing really needed to be "fixed". It probably cured some oil consumption issues in some vehicles and caused oil pump drive problems in others

Remember this was a new technology product and worked well in a wide variety of applications - some better than others. Mono grade lubricants and the "new" 10W-30 were the "norm" in that era. Many Workshops still use 20W-50 as an oil consumption or low OP issue at idle et. "fix it" product

At the time it was widely promoted by Duckhams and then Castrol. In late 1959 we used Castrolite (20W-20), Castrol XL (20W-30) in the initial export Minis (A Series engines) in NZ where 20W-50 wasn't available until late 1960-61 or so. They sheared and flowed out or was burnt at alarming rates IIRC Castrol's XXL (30-40) helped a bit. The early Minis were really a technical challenge and I could fill one Forum relating to the issues in the initial CKD Export cars

In the 1970s and early 1980s I used Castrol's API SE Formula R Synthetic 15W-50 (an excellent ester based lubricant) in a variety of petrol and diesel engines under test. This was a truly excellent lubricant that later evolved into TWS 10W-60. By the late 1970s Castrolite was rated 10W-40 and XL was 20W-50

The "standard" HDEO then was Castrol's RX Super 30-40. It had SE/CD ratings and MIL L 2104C, 46152, MACK EO-J, GM 6136M, DB OM616 and Volvo B20A and was also recommended for Detroit Diesels. Caltex, Mobil and Shellhad excellent monograde HDEOs of course