• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR6 Overdrive does not engage

Share this page

Gerry M

Gerry M

Member
Offline
Up until yesterday the overdrive would engage as it should. Today it does not engage. The overdrive relay clicks but that is all that happens. Is my relay toast? How can I check this? Thanks, all suggestions appreciated.
 
Hook up a test light on the output of the relay (to ground); leaving the circuit to the solenoid complete. If light comes on full brightness, the relay and control circuitry are working and the problem is the solenoid or OD (or perhaps wire to the solenoid).

If light stays dim or doesn't light at all, you've got an electrical problem. Could be relay, or lockout, or operating switch, etc.
 
If it turns out not to be electrical, have you checked the oil level? Looks like you have a later 6 based on your avatar so it will be a j type overdrive. There are two filters to clean in the OD unit. Have these ever been done?

Cheers
Tush
 
If it is a later TR6 with J-type, it probably won't have a relay either.
 
Its a 74 TR6 fitted with an A type OD. Tranny with OD was completely rebuilt last fall and everything as been working fine until now.
 
The column sw is pretty fragile. For first and easiest test, take it for a drive and wiggle the sw up and down, if it engages in and out then you know its time to replace it.
Marv
 
Hooked up test light. Relay is working. Listened more closely and I do get a soft thud sound from the relay each time the OD is switched on and off and also solenoid clicks each time the OD is switched on so relay and electrical circuity seem to are working. BUT there is no sound from the solenoid when the OD is switched off.
 
Just a thought, have you double-checked that the OD is, in fact, not engaged? I ask only because I had a friend who had a short in the control switch (so it was engaging all the time) and he complained that it didn't work.

Otherwise, I agree, time to pull the cover and check out the solenoid operation. I've had trouble in the past with the adjustment slipping over time (and repeated operation). So it might be out of adjustment now even though it was working fine.

Another possibility is that the pull-in contacts (or coil) aren't working. That can sometimes lead to a solenoid that will move when there is no pressure against it (engine not running) but won't make it once the OD has built up it's 400 psi or so (which the solenoid has to overcome).

BTW, it is possible for wear to make the factory adjustment method be inaccurate. The Buckeye Triumphs article at https://www.buckeyetriumphs.org/technical/AOD/AOD4/AOD4.htm (about 2/3 down) gives an alternate method that is more complicated, but also more accurate (and compensates for any wear in the cam and plunger inside the unit). FWIW, I use 1/32" (.030" ) rather than the .016" the author mentions. I've checked several ODs with relatively low miles, and the factory adjustment results in more like .030" movement at the ball.

Also FWIW, I eventually got frustrated enough with the adjustment slipping that I modified the clamp a bit to make it more practical to adjust from under the car. A (hardened) socket head cap screw, plus a custom nut that engages with the clamp (so it doesn't have to be held with a wrench).
cgIpUNv.jpg
 
Not sure what happens at solenoid when car is running but I crawled under to look and the solenoid pulls up with a clear click when in 4th and OD is switched on but does not seem to come all the way down when OD is switched off and does not make any sound when switched off.
 
I wouldn't worry about falling down; if you've verified the OD isn't staying engaged. The plunger only drops under gravity and a bit of spring pressure from the valve. Many are supposed to have a rubber stop that makes disengagement pretty much silent anyway.
 
So I have double checked. OD does not engage when driving but the solenoid does pull up when the car is parked in 4th gear and the the engine is not running.
 
Another fairly simple check is to jack up the rear wheels, let the engine idle in 4th gear, and turn on the OD. Check that the solenoid plunger has moved all the way to the top; then try pushing forward on the adjustment lever over on the other side. If pushing on the lever makes it engage, the solenoid adjustment is wrong.

Here's a source of pressure gauge (and the special fitting to connect it with)
https://webspace.webring.com/people/tj/jholekamp/
 
Back
Top