Overdrive problems

[Chris Attrill]

I recently purchased a 1974 Man-O/D Stag which has had both gearbox and overdrive stripped and rebuilt last year, before my ownership. I suspect that the longest single journey it has done for some time was when I collected it from near Oxford to bring it home to near Cambridge, around 95 miles.

There were issues with the overdrive on my journey home, in that after about 50 miles overdrive wouldn't disengage when requested and wouldn't do so until I'd stopped to have a look under the bonnet. From that point I wasn't able to engage overdrive as (I later found when I got home) the fuse had blown. I replaced the fuse and all was well, although it seems to work properly until a few miles have been covered when it's reluctant to disengage but does so after a minute or two (not ideal).

As yet I haven't done anything about it but would be grateful of advice as to what the cause might be.

Also, how does one identify which type of overdrive is fitted?

Grateful in advance for your assistance

Chris

[trunt]

The 74 OD should be a J type, with the alloy finned cover on the bottom, A type has a large brass plug.

Lots of things it could be, do a search - there s loads of info on the subject. Wiring, switches but staying engaged is likely a sticky solenoid valve.

Terry

[StagJonno]

Do ensure O/D disengaged before selecting reverse as I've learnt on here, you can knack the unidirectional clutch.

Jonno

[Guest]

You can't damage the unidirectional clutch, it's far too strong for that.
I'm not sure where you get that story from!

FYI, Laycock in their wisdom made a vast number of the later cars with defective unidirectional clutches made out of a forged material...
They generated a magnificent amount of work for us.

The symptom was like a norrmal clutch slip, but intermittent....they then proceeded to fit them in Ford based ambulances (!) YES you couldn't ,make it up could you???
We used to laugh!
Load the ambulance with 2T of material and an emergency patient on oxygen and hey presto it wouldn't even get out of a courtyard or up a hill to hospital.

I retrofitted lots of later J type OD units with early series Unidirectionals, and it made people in the know, a nice lot of money.

Also Layock made a large number of defective sliding member which ended up in loads of Volvos.
They just used to SMASH. I had one last about 18 months ago, usual thing, a smashed OD sliding member clutch as a pile of fragments

Moral:-
Don't repeat dubious info, as it just becomes urban rumours.

[redstag]

I don't know what you are likely to break but there are definitely warnings in manufacturer publications that you can cause damage if you reverse with the overdrive engaged.

Pete

[Chris Attrill]

Thank you all for your info and advice - much appreciated.

When I get the chance, I'll get her up in the air and see if I can make some headway.

Regards

Chris

[Jeff]

Extract from Buckeye:

Now consider what would happen if the OD were to be engaged in reverse; the annulus will try to rotate 25% faster counterclockwise than the mainshaft. However, as stated previously, the unidirectional clutch prevents the annulus from rotating faster than the mainshaft in the counterclockwise direction. Lets say that again, the epicyclic gear is forcing the output to turn faster than the input while the unidirectional clutch is preventing the output from turning faster than the input. What happens? If we're lucky, the sliding clutch slips and the problem is discovered quickly and fixed. If we're unlucky, something breaks. The message: THE OVERDRIVE MUST NOT BE ENGAGED IN REVERSE!

[barkerwilliams]

Chris,


I had the same issue on a car that had done little mileage for many years.

If you are under the car remove the switched live wire from the solenoid and fit a length of wire to that solenoid terminal.

Don't start the car, connect the wire to the battery live you will hear the solenoid pull in. break the circuit and reconnect you will hear the solenoid pull in. Repeat 50 times.

Now connect the wire more permanently and go and have a cup of tea for 15 minutes or so. Come back and break the circuit and reconnect I would like to bet you will not hear the click of the solenoid as it will now be hot and jammed in, disconnect and reconnect a few times and it will start to work. Leave on for another 10 minutes and it will jam again.

When you disconnect the power the solenoid should return to the off position but when hot only partly returns. Re-energising moves the solenoid slightly and after a few pulses it manages to return fully.

Tapping it this way is safer than fiddling whilst driving and working it this way may be enough to free it permanently.

The solenoid draws about two amps so will not deplete your battery too much and obviously remains powered by 12v when in use so can't damage the solenoid. I believe the solenoid has a pretty weak return spring though a stronger one would make it harder to engage and draw more current and heat the coil excessively. The solenoid assembly also contains a valve which sticks, whatever the cause working the solenoid cannot be a bad thing, costs nothing and is easy, and if you are able to make it stick on then that is a pretty good pointer to your problem being the solenoid.

Alan

[Guest]

Fact is,- the unidirectional BLOWS UP in the A type overdrive for much simpler reasons....it's got a coarse spline machined with sharp corners in the splines+ stepped gears.I have one here.
ODA_614.jpg

See? BOOM - has shredded annulus and destroyed most of the rest of the overdrive.

WHY? Here>-
ODA_615.jpg

Stepped gears with tiny bearings and a sunwheel shimmed up with a silly little sintered brass bush that ALWAYS breaks:-
ODA_619.jpg

Now the J type,- fine splines - smooth edges non stepped planet gears.
ODJ_616.jpg
Non stepped gears with huge internal bearings:-

ODJ_617.jpg

You won't manage to break one.

[redstag]

down the plug hole - are you saying it is safe to reverse with the overdrive engaged or are you just saying that the unidirectional clutch is not the part that will break?


Pete

[Chris Attrill]

Thanks again everyone for your valuable advice

Chris

[richardthestag]

Should be J-type like mine

mine was sticking in the engaged position. Which was fine in 3rd and 4th, but then when dropping to 1st and 2nd gears the inhibit switch would cut the supply to the solenoid. fine while it was sticking but then it would start to unstick and make the most horrendous vibration. did it twice on the journey. fearful of breaking something heavy and expensive I didnt use it until new solenoid arrived.

fitting it is a pain but nowhere near as bad as a-type. Managed it with crossmember and exhaust still in place. crows foot spanner helps with removal, as does fitting the wiring to the new solenoid before installing it. then rummaging about to find the other end of the loom to connect it to.

issue I have now is that o/d will not engage until gearbox is warmed up. maybe 10 miles then it works perfectly. suspecting o rings are too phat

[Guest]

down the plug hole - are you saying it is safe to reverse with the overdrive engaged or are you just saying that the unidirectional clutch is not the part that will break?

Just saying, quite often the solenoid may misbehave in the J type and it sticks IN overdrive.
It's a right proverbial pain.
Obviously when you stick it in reverse, the thing is forced to revert to a more normal mode, which it usually does with some weird noises and sometimes a bit of a bang.

Are you asking me if I did it deliberately?
NO, it was the fault of "some'at or other", but being as they are quite strong they usually survive!

[redstag]

Just saying, quite often the solenoid may misbehave in the J type and it sticks IN overdrive.
It's a right proverbial pain.
Obviously when you stick it in reverse, the thing is forced to revert to a more normal mode, which it usually does with some weird noises and sometimes a bit of a bang.

Are you asking me if I did it deliberately?
NO, it was the fault of "some'at or other", but being as they are quite strong they usually survive!

Thanks.
I think I will err on the side of caution if mine ever gets stuck in.

Pete

[Will]

Where would you suggest getting a solenoid from