TR6 Question about a TR6 J overdrive

[TR3TR6]

I picked up a J-Overdrive transmission out of a 75 TR6 parts car that I want to put in my 76 TR6. I thought I better run some tests on it before I installed it. I drained the oil and put in Brad Penn GL-4 SAE 80W-90. The solenoid works just fine. I hooked up a 600psi gauge to check the pressure using my 2800 RPM half inch drill. With the solenoid engaged, I could only get the pressure up to about 310 lbs in 3rd and 4th gear; so the overdrive won't engage. Could this be caused by any of the following items; the hydraulic pump, the high pressure filter or one of the two operating pistons sticking, or something else that I need to be checking? I read the article in the Buckeye Triumphs, but the didn't say what the problem would be if the pressure was low, only that it needs to be around 450psi for the overdrive to engage.

 

[TR3driver]

If you didn't see the OD engage at 310 psi with no load, then IMO there is some other problem. 450 is the correct operating pressure for a TR6, but that includes enough force on the OD clutch to handle the torque of the engine multiplied by 3rd gear. With no load, the OD should shift at under 200 psi. Check page 4 of the 4th article on the Buckeye site, where Nelson reported the pistons moving (meaning the OD clutch engaged since that is what stops them from moving) at only 170 psi with his unit.

The things you mention could be the cause of the low pressure (except for the stuck pistons); however the first place I would look is the relief valve and associated dashpot. After that, my next suspect would be the check valve in the pump (what the books call the non-return valve).

One additional test you might try is to run the OD at roughly half of the speed you used before (eg 1400 rpm instead of 2800). If the problem is low pump output or excessive leaks, then the pressure should be even lower at lower rpm. But, if the relief valve is still controlling the pressure (perhaps because the spring is weak or the dashpot didn't move all the way) then you should still see about the same pressure. The OD should still be able to build full pressure even below 1000 rpm (my drill only turns about 850).

 

[TR3TR6]

Thanks Randall, after posting the article I went back to the Buckeye Triumphs article and then started looking at old posts on the TR6 overdrive. It was kind of like overload. I found that there are a lot of overdrive issues. When I was spinning the transmission, I slowed the drill down and the pressure stayed at about 310psi. I need to study the operation of the overdrive some more for a better understanding of it. I will check the relief valve and dashpot next. Before I added the oil, I cleaned the magnet off. Since the transmission hadn't been used for a number of years, adding the new oil may have loosen some stuff up. I wasn't aware that it would engage at a lower pressure with no load.

 

[TR3TR6]

Update: I finally got around to working on the transmission. I cleaned the relief valve and the dashpot, there was dirt on the screen. After replacing the oil and getting everything hooked up I had the following results. Spinning the trany with my drill I was getting 20lbs pressure with the solenoid not engaged. When I engaged the solenoid, at 250lbs the overdrive appeared to kick in as it became very hard for the transmission to turn and then it locked up. I attempted this more than once with the same results each time. I could not turn it with my 1/2" drill. This was in 4th gear. Releasing the solenoid and the transmission turned fine. I assume I have an internal problem. Does anybody have any ideas as to what to check or try?

 

[TR3driver]

Are you certain you were turning it the right direction? It's normal for the OD to lock up in reverse (which is why those switches are there to prevent that).

 

[TR3TR6]

I had my drill attached to the shaft on the bell housing side and was turning it counter clockwise.

 

[TR3driver]

Should be clockwise.

 

[TR3TR6]

Randall, when you mentioned the switches, I hooked the battery up direct to the solenoid and by-passed the overdrive switch. Didn't think about that switch. Could that be my problem?

 

[TR3driver]

No, not the switch. You had the gearbox in 4th, so the switch would have been closed and the solenoid still energized.

But the engine runs clockwise (when looking back towards the input shaft), so you were turning the OD backwards even though the gearbox was in 4th.

You can actually encounter a similar situation while driving, if you come to a stop while still in 4th OD and let the car roll backwards down a hill. The car will stop as though you backed into something. Kind of surprised me until I realized what had happened.

 

[TR3TR6]

Randall, I can't believe I did that. It must be an age issue. Thanks, hopefully it will work now.

 

[tdskip]

Let us know Terry, hopefully it is as simple as that.

 

[TR3TR6]

That was part of the problem. The over drive engages now, but my pressure is only going up to 300lbs. I've drained the oil again. I'm going to check the non return valve spring and the relief valve assembly along with the O rings. I have another over drive unit and will compare the parts and may do some switching. Thanks for asking. You guys have been a big help.

 

[TR3TR6]

UPDATE: I finally got back to working on the overdrive. I can't tell you how many times I had the non return valve spring and relief valve assembly apart. I finally removed the overdrive unit and replaced the o-rings on the pumps. When I ran the transmission, the pressure went right up to 450 ibs and stayed there. Thanks again for all the help. Now to get it into the car!