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MG MGB Technical - Gearbox - Effects of overfilling?

I know the problems associated with overfilling engine oil. What are the problems with overfilling a gearbox? Does overdrive make a difference in the effects?
Steve Simmons

What year is your car? On the newer models you can't as the excess comes out of the filler hole. Don't know about the earlier models
Bob
R Etches

I would suspect that the result of overfilling would be oil being pushed out of the breather on the trans. You may experiance excess drag in the trans from the friction of throwing more oil around but I doubt you could tell the difference.
John H

Steve It depends on how much you overfill but I have seen over the years a couple of gearboxs split the case from the extreme pressure created between the gearsets and the last one was an early MG. Denis
DENIS H

Hi Steve:

Should take approximately 3qts of oil. My 72 has the fill on the top of the tranny, which is accessible from behind the radio console and my 76 has it in the side, which is much more convienant. I use 20/50 weight and replace it every 2 years.

Shawn
Shawn Herndon

The transmission is a '72 LH-Type OD unit. The dipstick has high and low marks so I assume overfilling is bad but I can't think of why.

I just did a fluid change and accidently overfilled it. The manual states the transmission will accept 7 US quarts. I drained the transmission, including removing the OD filter plate to let the oil out of the rear. I refilled with 5.5 quarts of oil, drove around for a couple miles and then checked the level. It looks like at least a quart overfilled if not two! The fluid is nearly to the top of the dipstick. I can't imagine that 3-4 quarts remains in the transmission after draining the front and rear!!!



As a side note, due to the lack of ZDDP and other protective elements in modern motor oil, I also added half a bottle (about 1/5 quart?) of STP oil treatment. This is less than half what STP recommends adding.

I don't know if it's from overfilling, from the STP, or both but the transmission feels great and the overdrive is smoother than it has ever been.
Steve Simmons

Denis, would the pressure not simply pop the dipstick off before cracking the casing?

Shawn, this is an OD transmission so it takes a bit more than standard. I believe 2 or 3 quarts IIRC.
Steve Simmons

Hi Steve,
Not wishing to be a party pooper, but in "my opinion" the addition of "friction modifiers" stp inc is not really a good thing when it comes to the MG tran/overdrive. The overdrive relies on a double cone clutch for both o/d and non-o/d operation and any increased chance of slippage here will result in premature failure. Also the syncro rings rely on friction to work.
Now I fully agree with STP, Wynnes etc use in the engine.
As said, just my opinion
cheers Ric
R.A Willis

First, pardon my brain malfuntion, I mixed up quarts and pints in my last post.

Ric, I agree about friction modifiers in the Laycock OD unit. However I feel that the new motor oil formulas which have recently removed zinc and other critical protectants from the formula are not lubricating the gearbox as they should be. So a small amount of STP seemed like a good idea just for the protection. I don't think STP is as much a friction modifier as a protectant. And since the oil is not as slippery as it was just a few years ago, the STP is probably returning the oil to the way it was!
Steve Simmons

This thread was discussed between 24/10/2006 and 25/10/2006

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