Overdrive Problem

[brdave]

Tried to get the OD working on 1973 B today which will not engage. Drained the gearbox and OD, replaced the large filter, installed new solenoid and refilled 20-50 Castrol. Overdrive still does not engage. With the key on in 3&4th gear there is power at the connector and with key on etc.we can hear the solenoid click when switching the OD switch on. Does anybody in this forum with more experience and expertise with overdrives have any suggestions or advice to offer?
thanks,
dave B.

 

[scott421]

Could be a pressure problem ? I dont know if you can drive the car with the box exposed ? On my TR6 the tunnel cover can be removed to do this . If possible drive and activate the solonoid , on the other side of the box from the solonoid is a lever , if you can , push the lever forward to see if that activates the o/d . This lever should be lined up with a small hole in the casing . This is conected by a rod through the box to the solonoid plunger . If the lever is not aligned correctly it will not engage the O/D. Try to get hold of a pressure guage to measure the pressure , on my A type a minimum of 380psi is required to activate . Check this and also the seat on the pump non return valve and accumulator valve . If a minute piece of dirt is there it can effect the presure too.

 

[AlanT]

With the internal solenoid , you should barely hear the click of the piston when the switch is turned on. From years at the dealer and beyond , the #1 problem with LH overdrives is a sticking oil pump. Following the manual carefully , you can unscrew the cover holding the check ball and see the bottom of the pump. Rotate the driveshaft and see if the pump piston moves. If not then push up on the piston. You will know if it was stuck by the sound it makes. If that is not the problem then check the non-return valves (balls). Note: Do not unscrew the cover that contains the pressure regulator valve.

Alan T

 

[BOXoROCKS]

Good questions, I am having a problem also on my 74. It works fine on cold days, but fades out after a few miles on warm days. I checked the oil, added some 80/90,(I am a TR guy also thats what the manual calls for)any way no change. I suppose I can give it a general cleaning,but I thought I would get some input first. It is obviously losing pressure, I think,..is it the cold oil that makes it work until it warms up and thins out? OR.. could it be that the selinoid is losing its charge.

 

[Keoke]

Seems like Scott gave you some good pointers Dave. I only want to add a small recommendation here. When you get the problem resolved, drain off the Castor 20-50 oil and refill the box with a single detergent free oil like Valvoline VR1 50 W oil.---Fwiw--Keoke

 

[brdave]

Scott, unfortunately it is an unassessable internal solenoid LH Type OD and cannot be tested as suggested.

Alan,
Is the cover holding the check ball the one with the two holes found under the large screen filter?
Secondly, Is the pressure regulator valve beneath the bolt type plug adjacent to the filter cover and solenoid cover?

Just as a note I have just had a consultation with a local british mechanic who is suggesting doing a pressure test which I believe would be using a pressure guage attached in place to that bolt type plug.
I am beginning to think that I should check whether the oil pump is sticking as Alan suggests first.

Regardless we have buttoned things up for now and will probably not be able to get back to it for a couple of weeks.

I will report my findings!

Thanks,
dave

 

[Steve_S]

A sticky pump will do it. Clogged oil passages are also a possibility. A pressure test is a good idea. Off the top of my head I think the LH should read around 400PSI but don't quote me on it.

 

[brdave]

Steve, thats exactly correct according to the manual!
dave