Does anyone know if it is possible to check if an overdrive unit is working correctly with it off the car and off the gearbox.
I have just rebuilt a gearbox which came with an OD unit and want to get it all bolted together with the engine.
My existing OD in the car is OK (does suffer from the abrupt release in a previous thread though) so I will have to reuse that if I cant check out the other one.
Checking overdrive
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Brian Wyld
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David Wicks
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- Forename: David
- Surname: Wicks
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Re: Checking overdrive
I have never done this but you may be able to hear the solenoid click with a 12v feed applied. Nothing will move in the OD unit of course because there is no oil pressure.
The Inhibiter switches can also be checked for operation using 12V and slecting 3rd and 4th but other than motorising the gearbox I can't see a practical way of a full function test.
Odd that you have the same problem with the j***y deselection as me on the original OD - is yours an early type unit? Maybe the vacuum relay is faulty?
Good luck with it all
David
The Inhibiter switches can also be checked for operation using 12V and slecting 3rd and 4th but other than motorising the gearbox I can't see a practical way of a full function test.
Odd that you have the same problem with the j***y deselection as me on the original OD - is yours an early type unit? Maybe the vacuum relay is faulty?
Good luck with it all
David
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Brian Wyld
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- Joined: Tue Aug 11, 2015 10:27 pm
- Forename: Brian
- Surname: Wyld
- MGCC Member: Yes
Re: Checking overdrive
Thanks David.
My unit is a 1972 and is the LH model. The gearbox is noisy which is why I have rebuilt a spare box so perhaps at some time the OD unit has suffered a bit making it abrupt. When I got the car (from as so called well respected dealer) it had supposedly just been been serviced. Checked it over on getting home and indeed the gearbox oil level was low amongst quite a number of other blatant faults which should have been sorted out. I'll check the relay on the spare and probably try it in the car. If it works OK fine, if not I'll replace it with the old one.
My unit is a 1972 and is the LH model. The gearbox is noisy which is why I have rebuilt a spare box so perhaps at some time the OD unit has suffered a bit making it abrupt. When I got the car (from as so called well respected dealer) it had supposedly just been been serviced. Checked it over on getting home and indeed the gearbox oil level was low amongst quite a number of other blatant faults which should have been sorted out. I'll check the relay on the spare and probably try it in the car. If it works OK fine, if not I'll replace it with the old one.
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David Wicks
- Posts: 29
- Joined: Sat Sep 24, 2016 9:02 am
- Forename: David
- Surname: Wicks
- MGCC Member: Yes
Re: Checking overdrive
My car was similar to yours in that it was supposed to have been serviced - it had quite a few issues that would have been picked up by any half decent mechanic, like carbs out of sync and set too rich, a dry steering rack with split boots and overfilled engine oil.
Anyway, I digress, there is a very good you tube video of an MGB box with OD undergoing an improvised bench test. It shows the unit running at speed with an oil pressure hook up with several changes in different gears - very informative stuff and entertaining for us petrol heads. Google it and enjoy!
The Laycock units are sans vacuum relay so that could not have been the cause. I took my car out for a run yesterday, she is a 74 model, and found that the OD was very smooth going in and out when cold but after a few miles became snatchy again selecting out - holding the revs with the throttle improved things but it's not as slick as I expect. Anyway I am going to live with it. Good luck with your box fitting.
Best regards
David
Anyway, I digress, there is a very good you tube video of an MGB box with OD undergoing an improvised bench test. It shows the unit running at speed with an oil pressure hook up with several changes in different gears - very informative stuff and entertaining for us petrol heads. Google it and enjoy!
The Laycock units are sans vacuum relay so that could not have been the cause. I took my car out for a run yesterday, she is a 74 model, and found that the OD was very smooth going in and out when cold but after a few miles became snatchy again selecting out - holding the revs with the throttle improved things but it's not as slick as I expect. Anyway I am going to live with it. Good luck with your box fitting.
Best regards
David