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General TR Type A Laycock Overdrive Questions


Luke Skywalker
Country flag
Last year I meticulously set my solenoid operating valve lift by using the 3/16 inch drill bit direction from the manual. My Overdrive was erratic, sometimes working, sometimes not. So, I pulled the interior and reset the gap wider, actually at a valve ball lift of about .027 inches. I used a dial gauge and brass tube as the Buckeye Triumph instructions suggest. It all worked great.

Now, after fixing a bad leak, I'm nervous about reinstalling the overdrive using the 3/16 drill bit fix. In fact, I'm also nervous about setting the ball lift to .027. Here's my concern.

The Workshop Manual says that the ball lift should be 1/32", and that's actually .03125 inches. So, my question is whether I can just safely set it at .03125 which is really only .004 more than I had in my prior adjustment.

Also note, however, that using the 3/16" drill bit gives a ball lift of .025, which is .006 less than I am now suggesting. Do the stainless steel balls sit differently in the valve pocket? Am I worrying about something that will never be an issue?

OK, I also have a related question. That question relates to the bottom gap between the solenoid plunger and the casting seat. The Workshop Manual suggests .015 inches with the "operated" solenoid. It takes quite an adjustment of that Allen screw to narrow up that bottom gap to .015 with the solenoid operated. I'm worried that I'm leaving it too tight or misinterpreting the instructions.

Any advice would be appreciated. Thanks all.


Country flag
I found that my operating arm, shaft, and cam were worn to the point that the Drill bit technique was useless. I simply began increasing the gap while operating the solenoid. I was spinning the unit with a 1/2” drill as I worked. When I reached a certain gap, the OD worked flawlessly both engaging and releasing. That is what I set. I later had to remove the arm to replace the rod 0-ring and had to re-set the gap with the box in the car. This time I raised the rear wheel and used the motor to run the OD as I found the best gap.

The TR2 does not have a screw to set the relaxed solenoid gap...maybe someone else can help you with that one.


Great Pumpkin - R.I.P
Like John said, wear is what makes the 3/16 pin inaccurate. 1/32" ball lift should work fine (that's what I use). But .025" should be fine too. There has been some debate over what it should be (see the Buckeye article link below for more discussion); but anything over .015" or so seems to be OK.

Did you mean 0.150" drop? The solenoid has a fair amount of leverage to the valve, so it has to move farther than the valve. The ball is moving by .031", and the stem under it has to move farther than that. (The clearance between ball and stem is what lets oil out of the operating pistons when the solenoid is released.)

The original A-type manual calls for 1/4". Other manuals call for other values. ISTR I used 0.150" from the Buckeye articles. My OD originally had a rubber bumper under the solenoid plunger (and hence no adjustment), but the rubber is long gone and NLA last time I checked (P/N 502570).

The distance isn't all that critical; but it has to be enough to let the valve operate fully while not so much that the solenoid can't pick up the plunger under all conditions (low system voltage, bad relay contacts, etc). So I put a small socket head bolt in place of the rubber bumper (sorry, don't recall offhand if it was 6-32 or 8-32), and cut the other side to take a nut.


Makes a little bit of noise, sometimes I can hear the click when shifting out of OD; but usually it's covered up by wind noise, exhaust noise (and likely my loss of hearing).

The wizard at Buckeye Triumphs (who must not be named) had another solution, perhaps better than mine:



Luke Skywalker
Country flag
Thanks all. That makes sense.

So, Randall, just generally speaking, how technical is that 1/32 lift? For instance, I just rechecked, and I'm actually at .032, not .03125. Any cause for concern would you think? I can't imagine. Also, yes, on that bottom gap I did mean .150".


Luke Skywalker
Country flag
John, I'll test mine on my bench. It's not easy for me--I fasten a cooler motor (from Harbor Freight) to my bench with a mounting board and Stanley vices, and then hold my transmission still with one hand while hitting a start switch with my other. Then, with my third hand I switch the solenoid on by making battery contact.

I wish I had a better means of holding the transmission still. I'm thinking as a safeguard that I'll tie a nylon line from the transmission to another vice on the opposite side of my bench. I did something like that a couple of years back and it worked OK.

I guess I better fill the transmission with gear oil first. I hate to add even three pounds more to the weight of that tranny as I try to horse it back into place through the vehicle interior, a task that when successful always seems miraculous. Like "how on earth did that thing just suddenly go back in"!


Great Pumpkin - R.I.P
I believe the ball lift is not critical at all. Anything from .015" on up to .060" should work fine, I believe.

Just a thought, you could use cheap oil for the bench test, drain it, then put the good stuff in after installing in the car. That's what Herman told me he did, many years ago.

I consider a bench test, with pressure gauge, mandatory before iinstallation. Just not worth taking a chance on having a problem that would require taking it back out!

I used a scrap piece of 2x4 to make a cradle of sorts for the back of the gearbox to sit on. If necessary, you could tie the gearbox to it, but I never have. Another piece of wood at the front, drilled for two bolts at the bottom of the bell housing, would stabilize it even more.

Not much of a photo, but you can see part of it here:


Obi Wan
Country flag
I did this recently. If you research it, you'll find all kinds of long treatises on what the lift should be, and then, after a lot of painfully detailed discussion, they all converge on about 30 mils.

I guess if you made it too great, you could get rough engagement, and too small, you definitely will get slow actuation. But there is a wide area between those extremes.

Oh, and for locking the transmission into position: get an 18-inch piece of angle iron and drill it to match the holes in the lower edge of the bellhousing. Then bolt the transmission to it and clamp or bolt it to your workbench.


Senior Member
I had my overdrive reconditioned but found that it didn't engage.
I have a leak at the back of my engine so the gearbox has to come out anyway, so after removing the gearbox cover I decided that the most probable reason for the problem was a badly adjusted solenoid lever position.
I used the 3/16th drill bit method, it took me three goes but now it works well.
I don't have the tools or gear to shove a dial gauge down the appropriate orifice to measure the travel or a pressure gauge to ensure that I'm getting at least 350lbs.
Long story short the 3/16th method worked for me.
I think that bench testing the overdrive prior to installing is very important.

Alfred E. Neuman

Jedi Trainee
For anyone interested in seeing how the things work and what a basic overhaul entails, Elin Yakov has an excellent youtube series on his overhaul of 2 A-Types.
He mostly follows the Buckeye Triumphs technical papers on the A-Type:
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