British-Cars.org

Welcome to the DMR Site for British Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Hot Transmission

I'm just pulling apart a (TC) tranmission from a car that was towed behind a vehicle for some distance with the driveshaft still attached. I'm amazed to see that all the gears are blued from the extreme heat, including the needle bearings. The input and output bearings are shot, as are the laygear thrust washers.

I don't think I have any real choice but to go ahead and re-assemble things with all new bearings, thrust washers and spacers, and see how it goes. I'm just worried that the temper has been lost from the steel, and that there will be problems in the future.

Does anyone have any experience with such an overheating problem, and any advice in the rebuilding?

TIA. Tom
t lange

Hi Tom, I was just curious about the damage caused when towing a vehicle without the driveshaft disconnected. What causes the tranny to overheat? Is there not still fluid in the box to lubricate the moving parts or does it all settle at back of the rear extension, leaving the gear clusters dry? I assume the front of the car would have to be jacked up quite high while towing for this to happen. Am I missing something ?
Many years ago I owned a Triumph GT6, which I had serviced at a garage, that forgot to replentish the fluid in the tranny after draining, so when the car was returned to me with the dry tranny and after a few days of driving things got rather noisy, Bottom line, all the moving parts had turned blue and were totally trashed. The garage never admitted their error and I had to pay for new tranny. It was after that experience that I decided to never take my car to a garage again and instead invested in tools, and workshop manuals and have been repairing everything myself for the last 50 years. Cheers Phil
Phil Atrill

Phil, he's talking about a TC. It's a different setup than the TD/TF box. I'm sure we'll hear more from those in the know. I know that the design of the gearbox in a 77B will allow it to be towed while connected without damage. Bud
Bud Krueger

I'm just as confused as the rest of you! I thought it was fine to tow like that, since there is plenty of lubricant splashing around. But everything in this one is certainly blued now, unlike any other transmission I have seen. I can't think of any other reason

Tom Lange
Bar Harbor, Maine
t lange

I recently towed my TD on a tow dolly for 550 miles with the drive shaft connected and there was no ill effects noted. I would however make sure the oil level is correct before towing and obviously make ABSOLUTELY sure it is in neutral. I was a bit worried that the angle of the car with the front on the tow dolly could have caused all the oil to remain at the back of the gearbox. I strictly adhered to the 55 MPH towing speed limit. I also have flat towed a Morris Minor with no ill affects but not sure if a TC is different.

John Quilter (TD8986)

Tom,

Perhaps it was run while dry prior to your teardown and now you are suspecting the towing was the problem.

Mark
Mark Strang

I was told the bearings were bad because it was towed, and have no reason to disbelieve. It was certainly HOT! I've never seen blued steel rollers before.

Any thoughts on the state of temper?

Tom Lange
t lange

Tom-
Pics?
What colour blue makes a difference, but any blue is well beyond permissible temp for rollers/balls/races.
"Blue" covers about 540-670F, but is affected by time at temp, alloy, and oil.
These temps will soften most steels, maybe down to Rc50 at worst, but gear teeth may be passable still, especially if they didn't make it to "blue". If they have gone to "light blue" or grey, they will be toast (sorry!). "Straw" to "bronze" is about 400-500F, probably acceptable for gear teeth.

FRM
FR Millmore

Check out the diagram of the transmission (TC basically the same as Td/TF, but no rear extention). The first motion shaft is in constant mesh with the cluster. If the engine is off, neither it or the cluster move at all. If the cluster needles/thrusts and first motion shaft bearings are fried, it was not from towing, likely no/low oil long before the tow. In neutral while being towed with the engine off, the mainshaft spins, and second and third gears, meshed to the cluster, don't move either, rotating on the needles between the gears and the mainshaft. They could get fried with low oil. Without the first motion shaft/cluster spinning (engine turning), all of the oil would be in the bottom of the case, not moving or circulating at all, so the rear ball bearing and the 2/3 gears/mainshaft/rollers could get cooked. Pretty suspicions much of the damage was already done. George
George Butz

FRm - I hate to say it, but it's almost gun blue - a deep, rich color. I'll send you some pictures tonight, with thanks.

Tom
t lange

Time for a 5 speed.
Gene Gillam

This thread was discussed between 09/09/2011 and 10/09/2011

MG TD TF 1500 index

This thread is from the archives. Join this live forum now