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MG MGA - gearbox findings

Hello,

I have been tearing down the gear box of my 1600 for rebuild. When I was first dismantling the car, I removed the drain plug and nothing drained! The dipstick showed plenty of clean oil in the box, so I felt up in the hole with my finger. I pushed a clog of crud aside and withdrew a finger freshly covered in oily glitter.

Thats been a couple of years ago. I am tearing down the box and discovered a few interesting things. At least 5 or 6 teeth are missing from the lay gear (this I already had discovered last year.) The whole bottom of the gearbox is covered with a thick film of old oil and debris that has an interesting silver metallic sheen to it. I bet if you rubbed that stuff on your hands you'd never make it past the TSA and their metal detectors at your local airport using airport transfers tunbridge wells.

The distance tube and rear needle bearings are not in the lay gear. Just not there.

I wonder if this box was rebuilt once previously and the parts not put back in. If the rear of the laygear could move that much, maybe that's why it thrashed the teeth off the gear.

Anybody seen anything like this?

Safety fast! -- and even faster with a strong precision remanufactured gearbox.

JM Greenlee

JM

When I did my box last year the laygear was a mess. Several teeth broken, although I did have all the bearings on the layshaft.

Fortunately I had all the internals from two other boxes in the garage.

Where did you get the new laygear from?

Chris.
Chris C

MGA layshaft will wear rapidly, especially with the single needle bearing at the rear. Reasonable life expectancy for the layshaft may be about 80,000 miles, after which the gears may whine in 2nd gear and possibly also in 3rd gear. This is a wonderful warning when it's time for a rebuild. A clicking noise on accelleration in lower gears is indication of brokjen gear teeth and should guide you to an immediate overhaul of the gearbox

If whining is ignored continued wear on the layshaft will eventually lead to more misalignmant and breaking of gear teeth. The layshaft can become dramatically worn down, but this is the first time I have ever heard of the needle bearings being missing. Something else usually breaks first while the needle rollers are still in pretty good condition.

Original layshaft needle bearings are full compliment with 20 rollers and separate end rings. "Modern" replacement bearings are most often cartridge bearings with as few as 11 rollers in a cage. YIKES! See here: http://mgaguru.com/mgtech/gearbox/gt204.htm

This is one of my greatest concers with replacement parts when mechanical integrity and reliability is compromized. When using the new needle bearings with fewer rollers a new layshaft will have even shorter service life, more like 60,000 miles (if not abused).

If/when original 20-roller needle bearings are still in place and still in good condition, I recommend retaining the original bearings and running them on a new layshaft. Any damaged needle bearings should of course be replaced if needed. I also recommend shortening the tube spacer and installing the fourth needle bearing next to the single rear bearing, especially when using the new cartridge bearings with fewer rollers.

Barney
Barney Gaylord

For what it's worth...

During my college years, I rebuilt many LBC transmissions from MGA/Bs, Spridgits, and others. The layshaft wear on MGAs and 3 syncro MGBs was always a problem. Even after 20K to 30K, the wear on the shafts was evident in virtually every tranny I worked on. Having a manual SAAB that I never had a problem with (transmission-wise), I started using and recommending SAAB manual transmission oil and never had a problem with wear again. It is a much heavier viscosity, 75W, than the 30W oil recommended by MOWOG, but it does make the layshaft and syncro rings last much longer than the recommended 30W. Also, using this oil I have never had a problem shifting. I have never understood why BMC/MOWOG recommended such a light weight transmission oil for a design that is prone to load wear as much as this transmission seems to be.
Steve Brandt

Barney,

I am using your instructions as a guide. MUCH easier to read than that dry shop manual written with the British accent.

I really didn't mean to imply that the bearings were ground away to nothing. They were simply not installed in this box, nor was the distance tube. I wonder if this is the cause of the missing teeth.

JMG
JM Greenlee

BTW,

Some DPO painted the gearbox. Some of the paint came off under the high pressure hose down at the car wash. What is a good method of stripping the rest of the paint? I thought of getting some of that citrus stripper down at Wally World.

JMG
JM Greenlee

Citris Stripper works well, but also have a spray bottle of alcohol, to keep the stripper wet while it is working. I have used it with great success in my home.
mike parker

Will the citrus stripper harm the aluminum or steel parts?

JMG
JM Greenlee

I don't know. If left on steel long enough, it will rust just like water would. I guess that you have to put on a piece of aluminum to check.
mike parker

The citrus stuff worked like a champ. Got 98% of the paint off with one try.

Found an interesting stamping on the rear case. 12/1/60. I want to read that December 1, 1960. However, it could be read January 12, 1960. My car's build date was 11 and 12 Feb, 1960. Any of you historians know about these marks?

Safety fast!

JMG
JM Greenlee

Most likely Jan 12. It's a US thing to do month first.
Art

This thread was discussed between 29/06/2005 and 01/07/2005

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