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MG MGB Technical - Overdrive questions

I’m bench-testing a black-label LH overdrive unit before I install it. When turning with a large electric drill (800 no-load rpms), it won’t shift into OD as current is applied directly to the solenoid.

I’m using a 12 volt battery with the negative lead grounded to the OD case and I’m touching the solenoid wire with the positive lead. A test lamp shows continuity, but then I’m energizing the solenoid directly, without the lamp.

I’ve taken the solenoid out and tested it separately, and its piston clicks inward when current is applied.

The oil pump is not stuck, as I can see it moving up and down when I turn the drive shaft with the sump cover off.

The pressure relief valve parts don’t look exactly like those shown in my MG manuals. They are shown in the attached photo. Are they in the correct assembly order, and is everything turned the right way around?

Also, please confirm one more thing: the transmission drive shaft should turn clock-wise when looking into the bell housing and counter-clock-wise when facing the drive flange at the rear of the transmission. So a drill attached to the input shaft at the front of the transmission should be set to rotate forward, not reverse.

Many thanks in advance for your help! Mike


M.E. Whalen

Everything looks correct, but I would check out the 3 videos that Jonathin Twist, of University Motors, has posted on You-Tube. He goes into great detail in explaining the inner workings of the LH overdrive. Each video shows all of the components that make up the hydraulic operating system. 99% of all od problems can be repaired while the unit is still in the car. Your problem, most likely lies in the low pressure relief valve assembly. RAY
rjm RAY

Mike

Drop me an E-mail and I will send you the e-mail and phone number of our club member who rebuilds all types of british OD units as a side job. He is very good.
Bruce Cunha

What are you using to tell if it has shifted into OD or not? 800rpm is very low, you would barely see any difference on a rev counter at that speed. Also there may simply not be enough pump pressure at that speed to overcome the resistance of the piston return springs, OD doesn't engage until the engine has reached a certain speed. The parts look OK to me, about the same as mine which isn't the same as the manual, nor the same as each other (my roadster and V8 that is)!
PaulH Solihull

This thread was discussed between 02/01/2011 and 03/01/2011

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