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J Type Overdrive engage problem


Senior Member
I just finished a TR6 restore that came with all running gear rebuilt but sat for 10+ years with no fluids. I inspected what I could and all appeared to have plenty of assembly lube so I added fluids and started it up. Everything is working good except the overdrive. Sometimes it shifts fine and sometimes it doesn't want to lock up. It tries but doesn't fully engage. Speed/RPM don't seem to matter. Possibly does it more when warmed up. How should I proceed with trouble shooting or fix?

Thanks in advance as I know I'll get some good advice.



Great Pumpkin - R.I.P
IMO, first step is to get a pressure gauge & adapter, so you can see what is happening. The cure may be as simple as removing and cleaning the "dashpot" and pressure relief valve, but it could be something more serious.

I made my own adapter, but it probably makes more sense to just buy the whole setup from:


Senior Member
I read a little on the pressures of the overdrive unit. Wasn't that thorough a piece and all I got out of it was that if the pressures aren't right, you have a problem. Is the pressure adjustable or does it just mean you have a problem?

If that is the case then I already know I have a problem. I would think I just need to pull the valves and filters to see if they are in need of attention.



Great Pumpkin - R.I.P
Knowing what the pressure is doing is the first step towards troubleshooting the problem. For example, if you are getting full pressure and it is still slipping, then there is no point in doing anything further, it has to come out to see what is mechanically wrong inside the unit.

Here are some fairly detailed instructions on troubleshooting:

Here's another good manual. Although written for Volvos (so some of the pressure values won't be accurate), the OD unit is the same other than the pressure and possibly some minor variations around the dashpot.

PS, if you want to take the "shotgun" approach, go right ahead. You asked for opinions, mine is that the systematic approach is always better.
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