TR4/4A Overdrive piston is sticking

Hi guys, hope everyone is doing well. So I started to pick the 4A again and have made progress on the transmission issues. The sticking point, literally, at this point is the piston that pulls up the lever to engage the overdrive. The lever moves freely so it is not a case of there being too much friction there, rather it appears that the solenoid itself is not lining up properly and binding when it goes to engage. The electrical system to the overdrive works, the solenoid works, it appears that it is down to the alignment of the solenoid housing in the ass. I am very lightly with dry lubricant greased the pen but that has not helped. What did fix it is that I temporarily loosen the screws that hold the solenoid in place and then you do just fine. It appears that that's late with the room is enough to freeze everything up so it engages properly.

So, anyone else experienced this? Ideas on fixing it? I did think about elongating the holes slightly to allow me more adjustments on how the solenoid unit fits onto the mounting plate, but wanted to check to see if there something else that I should be thinking about before I do that. Thanks!

It seems unlikely to me that alignment is really the problem. That solenoid has to really yank on the lever to get it to move when the accumulator is up to pressure, so it's not likely to be stymied by just a little bit of friction from the plunger not being perfectly aligned.

The things I would look at are:
1) The pull-in coil is not actuating (burned out or contacts inside the top of the solenoid aren't making good contact).
2) High resistance somewhere (eg bad relay contacts) is limiting current through the solenoid.
3) The stop below the plunger is missing, and allowing the plunger to fall down too far.

One perhaps easy test for (1) & (2) is to check how much current the solenoid draws when it doesn't pull the plunger up. It should be close to 20 amps. If it's only around 1 amp, then the pull-in coil is not in circuit. If it is between 1 and 20, then there is a bad connection somewhere. You can also check the voltage between the bullet connector and solenoid housing, with the solenoid energized, to see if the problem is outside the solenoid.

I forget the "drop" measurement for (3) offhand, but it's in the articles on the Buckeye Triumphs site.

TR3driver said:

It seems unlikely to me that alignment is really the problem. That solenoid has to really yank on the lever to get it to move when the accumulator is up to pressure, so it's not likely to be stymied by just a little bit of friction from the plunger not being perfectly aligned.

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Hi Randall, as always thanks for the help.

Here is what has me stymied with the above - when I left the two screws that mount the solenoid to the mounting plate slightly loose it worked fine. Snapped in and out of OD just fine like that. I have not measured the current but my dash amp gauge shows a big draw when the solenoid is engaged but doesn't pull the lever up. When loosened it reliable engages the overdrive which would not seem to be the case if I had problems in the circuit or with the stop. Yes/no?

Maybe it working when not fully tightened down is coincidental and throwing me off here...

tdskip said:

I have not measured the current but my dash amp gauge shows a big draw when the solenoid is engaged but doesn't pull the lever up.

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That's close enough for me. Maybe it is misaligned that bad, tho it still seems unlikely to me.

But I would bend the lever to be better aligned, rather than slotting the holes in the solenoid. That is, assuming you pushed the lever hard against the collar and O-ring when you tightened it. (You do have the collar and O-ring between the lever and the OD, right?)

TR3driver said:

(You do have the collar and O-ring between the lever and the OD, right?)

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Oh, you mean all those parts do something? Nope, not there. I bet that has the lever in the wrong place resulting in then location of the solenoid making a difference as it is "compensating" for the lever being in mislocated.

Sound plausible?

Thanks!

Yup. Presactly what I was thinking.

Is the piston and bore clean? No gum in it? Just repaired my 72 MGB with the same problem, gummy piston. PJ

PAUL161 said:

Is the piston and bore clean? No gum in it? Just repaired my 72 MGB with the same problem, gummy piston. PJ

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Good morning, thanks for the idea. I did make sure everything was nice and clean before assembly,good idea however.. Thanks.

Ramdall, I'll get those bits on the assembly and give that a go, once again you have saved me from me. Grin.

TR3driver said:

Yup. Presactly what I was thinking.

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Well, as it turns out the collar and o-ring where actually already installed (professional rebuild who, apparently, did a professional job). What was missing however was the Actuating Lever Stop. When I went to install the collar we discussed above and realized it was already there I noticed the missing stop. I installed one to the spec on the Buckeye Triumph rebuild site and it is working reliably now.

We'll see how she holds up over the next couple of weeks of use.

Thanks guys, and very belated Happy New Year to everyone.

TDSkip, Thanks for the follow up. It's always good to know what solved a problem.

Wayne