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MG MGB Technical - Early MGB Gearbox Rebuild

My winter project is going to be a gearbox rebuild, the car has the
early 3 main/3 synchro setup. I had contemplated an OD gearbox but I
just don't drive on the highway often enough to warrant the expense,
and I want to keep the early feel to the car. Right now there is
pretty much no 2nd gear synchro, I have to baby it on upshifts and
downshifts into 2nd are a grind-fest, and the clutch is grabbing
higher & higher.

What I'm looking for is advice on what else to do while the motor and
gearbox are out of the car. I plan on the obvious like a clutch set
and new gearbox mounts, the motor runs strong with excellent oil
pressure & I don't have the finances for a total rebuild ofthe motor.

I need to know what I should do (if anything) to the motor and box
since I don't hope to pull it again for several years. I'll probably
do a new oil pan gasket and maybe a new rear main seal? Are there any
other "trouble" items or things that are more easily accessed while
the motor is out of the car? Etc. I'm open to any ideas/comments!

Thanks in advance!
Steve Bartley
Portsmouth NH
1963 MGB
stephen bartley

Just for temptation Moss has a rebuilt 3-main OD gearbox in their overstock clearance sale list on their website.
That may be a cost-effective option to rebuilding your own gearbox.

Rich
Rich McKIe

Stephen

Recommend replacing the U joints. While you have the motor out, you may want to consider dropping the front end and replacing all the rubber. Pretty easy to do with the engine out. Easier to replace the rubber with the front end out of the car.
Bruce Cunha

Hi:

Rebuilt several 3 sychro o/d and standard gearboxes over the past 40 years. Essentially, the same internals as the MGA series. Most of the rebuilds that I have completed; all usually needed:

1. Laygear and associated layshaft & bearings. The laygear (22H0054) is usually trashed because of the 1st gear spur teeth wear down. Recommend that you use the later laygear (22H931 or 22H1301) You will need to ream the layshaft holes to accommodate the larger layshaft, or use a case from the late 1967 ugraded gearbox. Must provide less than 0.003" end float via hardened thrust washers. Getting extremely hard to find. Also should replace 1st gear hub and reverse gear since it is part of the 1st gear mesh

2. Replace 2nd gear with upgraded gear and steel synchro (22H0249 & 22H0230), and check condition of the bronze bushing,

3. 3rd gear is usually ok, but check condition of the bronze bushing,

4. Replace front ball bearing and rear main case ball bearing (someome on e-bay has the rear bearing up for auction, use MGB NOS filter).

5. Mainshaft clearences via the 3rd gear thrust washer must be in tolerence.

6. Front & rear oil seals and associated cover shims. Also speedo gear oil seal. Replace clutch rubber gaiter

7. Complete gasket set.

Lots of money!!!

Recommend you contact John Esposito at Quantumechanics for rebuild support. John does most of the New England gearbox and Laycock overdrive rebuilds.

Good luck: Rich Boris 67B roadster
Rich Boris

Hi All,

I also have a 3 syncro OD box that I am fitting soon. Although it all worked nicely in the donor car and had no crunching in any gear I want to check it over before fitting. One thing I have noticed is that if you grab the input shaft you can feel a little bit of play when you pull up and down. Is this noraml or wear?

Iain
67 BGT and box from 67 car.
I D Cameron

Normal - the play in even new bearings allows about 25 thou of play at the end of the shaft.

Rotate the shaft and feel for roughness in the bearing - if it rotates smoothly then it should be fine.

Make sure you check the crank spigot bush for wear and replace if necessary - play here will wear the input bearing.
Chris at Octarine Services


My box is becomming very noisy, and it's one reason I don't use the car that often, and so is on my todo list.

What sort of price range are we looking at to get a rebuild job done? I have never attempted something like this, so would probably take it to a outside source.

I have to say that the moss 5 speed confversion is looking very tempting at the moment.
Tim Boyle

Hi Iain
If I am doing any major motor work I take out the box as well. I wouldn't fit any gearbox with out checking it. Stand it on its rear end, remove the front cover, pull out the layshaft (Drop a piece of wire or long screw driver down the hole so the laygear can't move too far) and check the shaft for wear. Also take out the first motion shaft & check the mainshaft spigot bearing.
Garth.
Garth Bagnall

Rich has pretty well explained the reality of doing this job. For less money than a proper re-build, (The laygear in Canada is over 1K dollars!) and a tranny that will oulast the car, see the following link.

http://www.rivergate5speed.com/rivergate.html
Pete

Is the layshaft and the input shaft the same thing?

Iain
I D Cameron

Ian, NO. The input shaft, also called the first motion shaft, is where the the clutch disc slides on. The laygear is parralel with and drives the output or third motion shaft in first, second and third gears. In fourth, the input and output shafts are coupled together resulting in fourth gear or direct drive. The laygear is supported by needle bearings riding on the layshaft which is supported by the front and rear cases of the transmission. Ray

RAY

This thread was discussed between 29/10/2006 and 06/11/2006

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