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MGB MGB transmissions Durability

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Montero65

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Hi all. I have a question regarding the transmissions of MGB's. I have a 1979 MGB roadster I bought not long ago, and it came with a spare transmission. Both the trans in the car and the spare are overdrive transmissions. Now, I know already how rare it is to find even one of these and how tough it is to get your hands on one. My question is this - As I'm looking to set my B up for racing, should I be expecting any durability issues from this transmission? Honest answers only please (no lying to me to convince me to sell you one of my overdrives /ubbthreads/images/graemlins/wink.gif)
If there are issues in the stock form, can the trans be opened up and have the parts hardened by chemical or heat treatment processes to increase strength and durability?
Thanks for the help.
 
Check out www.quantumechanics.com These guys are really great and I have trusted them for quite some time. Also, they will give you a lot of "what do I do now" advice. FOR FREE!
 
If you are going to race it, I would recommend that you keep the spare tranny...or spare anything, as you will be hard on all parts of the car if you race it. It would be a lot easier to swap an entire tranny than to try to fix a one and only one the day before a race, which is when your tranny is sure to fail...esp if you don't have a spare.

You might want to consider selling it and getting a non-overdrive tranny as a spare...or find someone who wants to trade up a fresly rebuilt non-OD unit. You probably don't need OD for racing but only for highway driving.

Other wise, I would keep it...it isn't gonna depreciate!

Bruce /ubbthreads/images/graemlins/cheers.gif
 
A non-OD transmission is lighter and less complicated. If the car will be used primarily for racing I would consider converting it to that style. As far as durability goes, the transmission itself is pretty tough. My 3-sync non-OD unit in my '65 B has been driven hard for over 300,000 miles with only two rebuilds (one at 300K). The overdrive unit won't be used for racing so that isn't really relevant. If you were planning to push it hard in OD with a race engine, I'd say don't do it. A non-OD close ratio box would be better suited to such use.
 
When it comes to the weight of the trans, the spare OD that I have is actually pretty light. I want to keep the OD trans for racing if possible because I like having the extra gears. My dad had a '69 MGB when he was young, and said that no matter if the car were going up hill, down hill, or on flat ground, he couldn't get over 96 MPH. Granted I plan to build a motor with more power than his had, I don't want to run out of gears on the track. Not that it's likely to happen at the two Michigan tracks I know of (Waterford Hills and Gingerman), but I would like to get it out to Pennsylvania sometime to take it to Beaver Run, and they have some looonnnggg straights there where the extra gear(s?) would be nice. Plus, if I need to use it, I have the set up where the switch is on the shift knob, so no real extra reaching for anything.

Although I'm primarily building this as a race car, I am considering making it just barely streetable so I can take people for rides and show them just how awesome MGB's can be, so that would be another reason to keep the overdrive.

I would like to tear down and rebuild my spare just to make sure it is in good strong condition. Does anyone offer replacement internals of increased strengths for these? Otherwise, I might look at getting some regular replacements and having them hardened to hold up.
 
My stock '65 B, no overdrive, has been well over 100MPH many times, mostly on bald tires. It's a wonder I made it through my teen years. /ubbthreads/images/graemlins/wink.gif
 
I had a B to 112 once. They get a bit floaty at that speed, even with a spoiler.

Anyway, count me in with the voices saying for racing a non-OD tranny will be your best bet, but both are pretty stout.
 
Bax, what type of suspension setup were you running? Tires? Rubber or chrome bumpers? I only ask because it seems some people have high speed stability issues and others don't. I've noticed most problems come from later model cars but I'm not sure if it's from the ride height, aerodynamic properties of the rubber bumpers or the extra weight at the ends of the car. Tall touring tires also seem to contribute but not quite as much.
 
i know that past i think 1974 that MG increased the height of the body off the ground due to meet some new government law that required all bumpers to meet at the same point. That would definitley cause you to sway around on the road at 112 mph.
 
Yes, the change to rubber bumpers and higher ride height was to meet US safety regulations. That and the tough smog laws virtually killed the car. Add all that to the budget cuts handed down by BMC / British Leyland and MG never recovered. /ubbthreads/images/graemlins/frown.gif
 
Hope you don't mind an opinion from a Triumph guy with an overdrive!
I have used my car for Solo1, usually involves 30 laps per event, about 5 events per year average, for 7 years. I used the overdrive to avoid changing into 4th gear on the straights and occaisionally to cover the biggish gap between 2nd and 3rd in a non close ratio (stock) gearbox. Changed the fluid once a year, no problems.
Unless you have a very low (numerically high) rear axle ratio you will never run out of gears on the tracks you mention, Mid-Ohio maybe as the straight is downhill.
Having said all that, I am nervous about putting all that torque through in the lower gear, and its pretty busy on the winding sections trying to steer, shift and switch the overdrive in and out.
Bottom line is I agree with Steve and bruce, best setup would be close ratio box with hardened gears, lower back axle ratio (higher numerically), and no overdrive. Weight savings should be about 30lbs.
Final note, the gearbox and overdrive on a Triumph and perhaps an MG share lubricant but ideally require different types, so under higher stress failure may be accelerated.
Keep it simple, less to break, racing will always find the weak points!
Simon.
 
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