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Chicagoland MG Club: Driveline
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  Chicagoland MG Club:Driveline
Go Brit Baby! - Tech Sessions

Steve Merical Tick, Grind, Chatter

In July we rebuilt a MGA gearbox and also had a good look a two MGB overdrive transmissions and one Midget tranny.

In some respects, the transmission of a MG gives the car its personality. Itís a joy to rev the car and quickly shift through the gears. This is what sport car driving is all about and the MG tranny makes it an enjoyable experience.

However, after many years and miles this personality changes. It becomes more talkative, perhaps too much personality and chattering to a point to drive you mad. Itís time for a tranny vacation and a renewal of this MG spirit.

Whoa, back to the tech session. Many MG gearboxes have bronze syncro gears, which help you shift from gear to gear smoothly. With time, these bronze parts wear down making it difficult to shift quietly - grind. Also, the layshaft wears down so that the gears are not perfectly aligned. A non-syncro first on early models may eventually wear and chip first gear - tick, tick. The rubber gearbox mount deteriates, the shifter bobs around loosely and chatters. The seals and gaskets leak with time and need renewal.

We opened up the side cover on the MGA tranny to do an evaluation. The gear work was in great shape. So, we moved on to check the syncro gears. We found significant wear on the 2nd gear syncro. This is fairly typical and expected with a gearbox that has been in service for a while. With a couple of long screwdrivers we pressed back and forth on the layshaft. Any noticeable movement indicates wear on the layshaft and it needs to be replaced. We found this to be the case on this gearbox. So, we went about taking this tranny apart.

The gearbox was thoroughly cleaned on the outside. You donít want to contaminate the inside of the box with dirt and grime. We removed the shift tower and other cover plates to gain access to the inside. We also took out the gear selector and removed the front bell housing from the rear section of the transmission.

We took out the gear forks and slid the gear fork shafts up to the point of the shaft-locating block. The trick here is to not pull the shafts all the way out. If you do, you will be searching your garage for the little springs and balls that fly in every direction. Just slide the shaft back to the locating block and remove all the shafts out as a unit with the block.

There is a small pin and spring on the end of the mainshaft that has to be pressed back before you can take the gears off. This was a rascal to get pushed back. It was a bit frozen and took some time to release. Otherwise, the entire procedure was quite smooth.

The 3rd and 4th syncros are the same size. The 3rd syncro may have a little more wear on it from usage. So we swapped the 3rd and 4th syncros to even up the wearing.

We replaced the layshaft. Itís easy to see the wear on the old part when it is removed. The bearings tend to wear a groove in the back portion of the layshaft. We also replaced the laygear bearings as the old ones had small dots of rust on them.

After replacing the worn parts, we re-assembled the entire unit with new seals and gaskets. There are many oil passages in the gearbox so itís critical that the unit is assembled properly or you risk blocking some of these oil passages.

The cost for this rebuild was about $100 in parts. This is very reasonable given that most parts suppliers want $1,000 or more for a rebuilt gearbox and probably a $200 core charge. The added bonus here is that you get to learn something in the process.

Barney Gaylord was the master mechanic on this job and he can usually rebuilt an entire unit in about 2 hours. We took a little longer on this project giving everyone an opportunity to take a look, handle parts, and understand the inner workings of a MG gearbox. Thatís what our club tech sessions are all about.

In August we will be having a couple of tech sessions. One, we will be installing an overdrive transmission in a rubber bumper MGB. At the time of this writing we donít have a confirmed date but please check back to the website for more information or contact me directly. Second, on August 24th we are planning a tech session on distributors. If anyone has test equipment for distributors - I would be interested in hearing from you. Hope to see you at our next tech session and the club gathering in Abingdon, IL.

Steve Merical   630-443-4985

Crowd around table with gearbox Open gearbox

Crowd on floor with OD gearbox Open Overdrive unit

See lots more pictures and notes on line at:

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