TR6 Late TR6 OD Query

[Halkett]

This may sound a bit anecdotal but here goes..

When embarking on a drive, once at speed (60mph/ 3000rpm), I can engage the OD as normal the revs drop to 2750rpm. I can run in this steady state (4th gear with OD) for as long as I need, however if I slow, or downshift the OD disappears and can’t be reactivated.

I am new to this having just 1000 miles on my restored car. – I did have the gearbox off the engine during frame-off restoration but as the car only has 40,000 miles, only to externally clean the oily grime off it..

Comments welcome/thanks.
Stephen.

 

[tdskip]

Have you checked the oil level?

 

[angelfj1]

I agree with Skip. Check the oil level. Most Lacock O/D problems are electrical. However, since you are able to engage the unit this means that you are completing the circuit to the O/D solenoid and the operating valve is working. You might consider now a good time to drain and re-fill the unit. I did this last night. I used Valvoline VR-1 20W-50 Racing Oil. The TR250 has an "A" type unit. I believe you would have a "J" type. In a transmission equipped with the "A" type unit you have to open two drains, one for the transmission and one for the O/D. Although the tranny and O/D both use the same oil, you cant completely drain both by opening one plug. You need to open both. If you have ever done an oil change you can do this. Just for reference, after draining the box and O/D last night I used approx. 1.5 qts of oil to re-fill.

Good luck

 

[RonMacPherson]

There is an overdrive repair shop in the Northeast section of the mainland. Called Quantum mechanics. The owner is very affable, and quite knowledgeable and willing(at least was) to share that knowledge about overdrives.

If I were you, first thing I would do is change the trans oil, per his recommendations. If that doesn't solve the problem, then further investigation/diagnosis needed.

Oh, did you make sure that the trans/overdrive is grounded well. There should be a ground wire running from one of the bellhousing bolts to the frame....

 

[TR3driver]

In a transmission equipped with the "A" type unit you have to open two drains, one for the transmission and one for the O/D. Although the tranny and O/D both use the same oil, you cant completely drain both by opening one plug. You need to open both.

Same thing applies to the J-type, except that the OD drain is a rectangular plate, rather than a plug. I would suggest removing the plate (you'll probably want to have a new gasket and lockwashers on hand) and cleaning the magnets and screen found inside. If you can find or make the tool required, it wouldn't hurt to remove the plug and clean the "high pressure" screen as well. Don't get carried away when tightening those 6 bolts; overtightening can distort the plate and cause hard-to-solve leaks.

But I doubt your problem is dirty/low oil. I would be looking instead at the quality of electrical connections to the solenoid, IOW how much voltage the solenoid gets in operation. It's resistance goes up when it gets hot, which reduces the current; and it takes more current to move it into the engaged position than to hold it there. So a bad connection or switch contact might reduce the current enough to cause the problem you describe.

The solenoid could also be hanging up when it's hot, so disassembling it for cleaning (and O-ring replacement) might help.

 

[Halkett]

Thanks’ fellows,

..excellent pointers - I will run these down and get back to you.

Cheers / Stephen.