I'm planning to change the (manual) transmission oil on my 1970 MG Midget. The original specification was to use 20W-50 engine oil in the Spridget. The consensus back in the day was that the usual GL4/GL5 gear lube then used in most manual trannys was incompatable with the yellow metals in the synchros, so regular motor oil was specified. When Mobil 1 and the other synthetics first came out, people tried them, but found they didn't work very well. My recollection was that the synthetics were too "slippery" for the synchros to work properly, causing shifting problems, so people stayed with regular oil. So here we are in the modern world, with reduced ZDDP in motor oil, enhanced friction modifiers, special MT fluids and who knows what else and I'm wondering whether there's a better choice than sticking with the old reliable Castrol 20W-50. My initial thought is that modern oil isn't a good choice for the low temperature, high shear conditions in the trans, or is at least not optimized for those conditions. Would a synthetic motorcycle oil having friction modifiers for wet clutches be a better choice? One of the new special MT fluids? Is modern gear oil now compatable with the yellow metals and a better choice? It's an unusual application, and I'd appreciate any input.
MG Midget trans oil
- Thread starter dwgwater
- Start date
- Status
- Joined
- Dec 30, 2006
- Messages
- 29,558
I`ve read where people have used Mobil 1 15W50 in 3000GT manual trannies with good results. If your tranny is shifting flawlessly with the 20W50,I`d just stick with it. Manual tranny/gear oil experimentation can be a huge pita.
Last edited:
I'm pretty sure the 1275 gearboxes had brass synchros, so GL-5 isn't recommended. I have a 1500 which doesn't seem to have that problem. Could stay with 20W-50, but there are alternatives. You could use Redline manual transmission fluid, or you could even try Honda manual transmission fluid. Honda's oil is more like 10W-30, at least, my '04 CR-V with a manual said to use Honda MTF or 10W-30 engine oil.
I can't speak for how well well modern 20W-50 engine oil does in gearboxes since my Midget calls for 90 weight oil, but I use Valvoline VR-1 20W-50 in the engine for the ZDDP. Maybe somebody can chime in on their thoughts about motorcycle oil; I would think if it also lubes the gearbox in motorcycles it should work.
I can't speak for how well well modern 20W-50 engine oil does in gearboxes since my Midget calls for 90 weight oil, but I use Valvoline VR-1 20W-50 in the engine for the ZDDP. Maybe somebody can chime in on their thoughts about motorcycle oil; I would think if it also lubes the gearbox in motorcycles it should work.
Dave,
Take a look at Chevron Delo ESI 80W-90 conventional gear oil. It is rated both GL-4 and GL-5, as well as MT-1. It contains no sulfur or phosphorus to degrade yellow metals, substituting an "inorganic borate compound", to quote the blurb.
Take a look at Chevron Delo ESI 80W-90 conventional gear oil. It is rated both GL-4 and GL-5, as well as MT-1. It contains no sulfur or phosphorus to degrade yellow metals, substituting an "inorganic borate compound", to quote the blurb.
I'm with Marco. It's been many years since my Sprite and Midgets but 20W50 is what we used in the day with good results. As Aquisarium said, experimentation can involve some PITA actions like immediately draining the oil back out if it doesn't work well. Today I'd be tempted try a high end 85W90 GL4/5 mineral oil. I'd also be tempted to try some of the MT "Synchro" oils out there. Though they might be a little lighter in viscosity than the 20W50 (which is about a thickish gear grade 90), the MT oils are in the 75-80 grades and friction modified to be compatible with synchronizers. Anyway, the nice thing about experimenting with a Spridget gearbox is that they don't hold much so the cost of experimentation is low.
I use Redline MT-90 in my Austin Healey box...GL-4 and works perfectly. Tried the Castorl 20w50 and other dual rated lubes and they were horrible...notchy and almost impossible to hit a gear without grinding...switch to RL MT-90...end of problems.
I run two cars much older than yours (see below) and follow the long standing advice to use only straight 30w oil in the gearbox (transmission).
If the original spec was for 20W-50 dino, probably Duckhams back in the day in UK, then stick with it!
Most 20W-50 oils still have >1000 ppm Zinc, so don't worry about the 'modern oil' aspect.
If the original spec was for 20W-50 dino, probably Duckhams back in the day in UK, then stick with it!
Most 20W-50 oils still have >1000 ppm Zinc, so don't worry about the 'modern oil' aspect.
Thanks for all the comments. After a little more research, I'm leaning toward experimenting with the the Redline MT-90. I may also look into the other specialized MT fluids, but the blurb on the Redline site suggests they aimed the performance characteristics at trannys that specified engine oil, with some interesting observations on why engine oil is a lousy lubricant for transmissions. Of course that lousy lubricant has worked OK for 40 years, so far.....
If you are worried about using something other than 20w50, Motorcycle specific 20w50 might make sense, because motorcycles often share the sump with the gearbox.
i researched this 6 or so years ago and, after trading emails with Dave at Redline, settled on their MT-90 for my TR6. prior to that i was using NAPA GL4 gear lube in my 6 as well as in a Midget 1500. The shift quality is good on my low miles car, but i can't say it is significantly better than other oils...the '6 has a pretty nice shift feel, as does your Midget.
I'd use the Redline, though any high end 20w-50 would probably be adequate.
I'd use the Redline, though any high end 20w-50 would probably be adequate.
Last edited:
Originally Posted By: aquariuscsm
I`ve read where people have used Mobil 1 15W50 in 3000GT manual trannies with good results. If your tranny is shifting flawlessly with the 20W50,I`d just stick with it. Manual tranny/gear oil experimentation can be a huge pita.
This is a very good point ^^ - [but not the usual recommendation].
I'd persionally favor a modern dedicated full synthetic manual trans lube. Amsoil or Redline in the heavier normal viscosity. Remember, a 90 W gear oil is comparable to a 50 motor oil because they are tested at different temperatures.
I`ve read where people have used Mobil 1 15W50 in 3000GT manual trannies with good results. If your tranny is shifting flawlessly with the 20W50,I`d just stick with it. Manual tranny/gear oil experimentation can be a huge pita.
This is a very good point ^^ - [but not the usual recommendation].
I'd persionally favor a modern dedicated full synthetic manual trans lube. Amsoil or Redline in the heavier normal viscosity. Remember, a 90 W gear oil is comparable to a 50 motor oil because they are tested at different temperatures.
- Status
