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MG TD TF 1500 - Transmission Damaged???

After reading some threads on transmission oil selection I realized that I may have made a grave mistake. I got the drivetrain of my late 1952 TD all reassembled about a year ago and I filed the transmission carefully to the full mark on the dipstick, but I've now discovered it was a GL-5 type of 80W90 transmission oil. The car has not been started yet so the transmission gears have not revolved in this oil. I just now drained it out.

When I watched how little came out I wonder if any of the brass bits have actually been immersed in the oil all this time. I checked my workshop manual and it appears the oil is slung about by the layshaft gears and the oil level may not have actually reached the syncronizers, etc. However, I can not find any indication of just how high the oil level is in a properly filled transmission.

I'm hoping that one of you good fellows could tell me if I have a likely problem caused by using the wrong oil or if I escaped by virtue that the brass parts were above the oil level all this time.

Thanks,
Allyn
AC Davis

I don't see anything wrong with the 80W90 gear lube, and don't see a problem.
JRN JIM

I believe it's the GL5 as opposed to GL4 Jim that is the reason for the query. There is a fair bit on this archived, hence Allyn's concern. Barrie Jones would be the best person to answer this. Cheers
Peter TD 5801
P Hehir

Until recent times and the internet, no one around here had any idea about the GL-4 vs 5 and the hypothetical corrosion problem. Whatever 90wt that was laying around was used with no problem. Flush it, drive, and enjoy. George
George Butz

Allyn, Every MANUAL transmission in most every car has brass syncro rings of one type or another. I've only ever heard of damage to them from using certain gear oils, where the oil will EAT the brass, from a few individuals. I've been around car maintenance all my adult life, 60+ years, including race cars, farm equipment, construction equipment etc and the only syncros that I've replaced is because of two things. One due to dirt and crud in the oil and the other, most common, due to excessive wear from years of use. We rebuilt a road ranger transmission out of a Kenworth truck with over 500,000 miles on it once and the brass syncros weren't worn that much. I remember this because of the cost to replace a lot of the gears in it. No oil will eat the brass syncros! Some oils give a smoother operation giving less friction, but keep in mind that syncros need some friction to perform their job and stop the gears from turning briefly, that's why they eventually wear out. A test would be, put a piece of brass in a tub of the so called bad oil and look at it ten years later and see if it's gone! I think it'll still be there. Grin. JMHO. PJ
Paul S Jennings

I believe the issue is erosion, not corrosion.

The sulfur and phosphorus in EP oil makes a sacrificial layer on the gear surfaces. The alleged issue comes from the fact the layer that forms on the cone of the gear can be somewhat harder than the yellow metal of the syncro ring thus eroding a little off with every shift.

Way back the sulfur was actually corrosive but for the past couple of decades the sulfur is buffered thus not corrosive. The erosion potential, however is still there. I suspect it would take more shifts than any of use will ever do for it to be a problem but I don't know.

Like Paul, I have always mixed all sorts of gear oils and not had a problem.

The sulfur is why EP oil stinks so bad and also why the oil you drain out of an old rear end is so black. It's the culmination of all that sacrificial layer having been stripped off the gears and floating in the oil.

You didn't hurt anything. Have fun and drive.

Jim
JE Carroll

Since you are probably going drain off the GL5 standard oil anyway replace the oil with Redline MT 90 - super stuff :-)
Dave
D Moore

Allyn,

I heartily endorse Dave Moor's suggestion.

Redline MT90 seems to be an absolutely ideal gear lube. I've been running it in my gearbox which has not been touched in my 60 years of ownership of TF4592.

Gord Clark
Rockburn, Qué.
Gordon A Clark

Thanks for all the quick responses! I gather the thoughts are that no damage is likely to have occurred and I should fill-er-up with Redline MT90 and quit worrying about it.

I was curious though whether the oil level is up to the syncro rings when the transmission is filled to the dipstick full mark. Does anyone have a feel for that?

Thanks again!
Allyn
AC Davis

This thread was discussed on 31/07/2014

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