Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Testing Overdrive in situ


Tried to find something on this topic in the archives. No joy.

Is there a good/any way of testing the overdrive in situ in a static project car and what's the best way of testing an overdrive unit out of the car? Both units '73.

Thanks in advance for any input.
Iwan Jones

Tuff to do without it being in use in the car. You need to spin the trans fast enough that the oil pump for the overdrive can build enough pressure to operate. While this is possible and you could tell that it shifts into overdrive there is no way to apply enough torque and load to make sure the cone clutch or the one way clutch are working up to capacity.

If you have it out of the car, might as well open it up and replace the seals and springs and inspect the internals for wear. Than you won't have to wonder if it will work when re-installed.
John H

Iwan. The method I made up for testing the function of the overdrive was to make up a tool which slipped over the first motion shaft, and had a set screw to be tightened between two of the splines, allowing the tool to turn the first motion shaft. The tool I made up was made from aluminium round stock, 1.25" diameter, and the front end of the piece was left solid for 1.5" (i.e. the back end was drilled and bored to slip over the shaft with the forwards 1.5" left unbored). The front was turned down to 1/2" for a length of 3/4", allowing a large electric drill to be attached. The drill was turned on with the transmission in 4th gear, then, power was applied to the solenoid. A change in the rotational speed of the output flange, or a slowing of the drill with the same output flange speed, indicates that the overdrive has engaged. Remove power to the solenoid and see if the transmission comes out of overdrive properly.

Both the overdrive inhibiter switch and the reverse light switch can be checked by the use of an ohm meter. Attach the leads to the two spades, put the transmission in the proper gear and see if you are showing zero on the ohm meter. A test light and battery charger can also be used to test the switches. (One note about this. Both John Twist and I checked the OD switch on the transmission installed in my daughter's car before it was installed. When installed, the OD did not work. The tranny had to be lowered and one shim removed from the switch to make it work properly. Seems to have been caused by the gearshift lever boot not allowing quite as much movement as was present when testing without the boot on. But, I knew the switch was good and it had to be an adjustment problem.)

Turning the first motion shaft with the electric drill does not tell us a great deal about how well the main portion of the transmission will shift, nor how well the syncros work.

In the vehicle testing needs to have the engine run and the same tests are performed.

Yes, there are methods of bench testing in the archives, but they are hard to reseach. I do remember one fellow using duct tape and some form of attachment to allow him to turn the first motion shaft using either a drill or an electric motor.

Les Bengtson

What Les describes it when the OD is out of the car and not in-situ of course. In-situ there is virtually nothing you can check except electrical continuity, you can't even check for solenoid movement on the LH as used in the 73 unless you remove the solenoid from the OD and supply a wired ground.
Paul Hunt 2

This thread was discussed between 22/03/2006 and 23/03/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.