View Full Version : TR2/3/3A TR3 OD troubleshooting help needed

08-23-2006, 11:21 PM
I've finally had a chance to drive the TR3 around since it got tranny and carb fixes...the Overdrive is also finally hooked up.

When I flip the switch, the OD takes about five seconds or so to engage. After the revs drop, if I push the accelerator, the tranny (I suppose) slips up to the non-od revs. In other words, no acceleration happens until the engine races back to the non-OD level of RPMS.

It also takes a while for the OD to disengage -- maybe 10 seconds or so.

So the question is: Is this a solenoid issue, a too much or too little (or wrong) tranny fluid issue, or something internal to the OD?

The OD appeared to work appropriately once or twice right when I got the car back (when the carbs were still set incorrectly about two months ago,) and then got slower to engage/disengage and then started slipping.

Any ideas?


08-24-2006, 04:43 AM
Hi Sam,

It could be a slow solenoid, but I think more likely that it's the pressure within OD is low and that will make it sluggish to respond.

It's an A-type, isn't it? Just from memory, I seem to recall the A-type runs somewhere close to 500 psi. When the car is driven, the OD quickly develops and maintains a pressurized supply of oil internally, ready for the moment the OD is engaged. If that pressure is low for some reason, the response will be slow.

J-type are inherently a bit slower to respond due to lower pressure operation, maybe 300 psi if I redall correctly, and the fact that it doesn't use any sort of pre-pressurizing/accumulation of the pressure, the way A-type do. However, even J-type are usually not as slow as you describe. Early/TR3-era A-type should pretty much "bang" into OD. Later A-type, perhaps from mid-TR4 production and on, have a very slight delay and not quite so harsh an engagement. They operate the same way, but have a smaller pressure accumulator.

The check valve that's actuated by the solenoid could also be dirty or partially clogged, causing delayed engagement. It's under a plug on the RH side, where solenoid adjustment can be most accurately checked with a dial micrometer measuring the lifting of the check ball, and where the OD is producing can also be measured with the right gauge and connector.

A third possibility is that the clutches in the OD are slipping. This might happen if they are severely worn, or if the wrong type of oil were used.

Personally I'd avoid slipperier synthetic oils in an OD gearbox, just because of the oil-bathed clutch. I don't know of any specific problems with the Laycock OD clutches and modern synthetic oils, but I have seen them ruin an oil-bathed motorcycle clutch set in a matter of minutes.

Also, I hope you didn't use standard motor oil in the geabox. All these oils have detergents in them (some have a lot!). This tends to foam up and can introduce air bubbles into the OD hydraulics that might cause similar symptoms to what you are seeing. IMHO, it's best to use non-detergent mineral based "racing" motor oil. (Foaming detergent oils can also effect lubrication in the gearbox, and cause early bearing failures or other lubrication related problems.)

If the OD has some miles on it, i.e. hasn't been rebuilt in recent history, it might help to increase oil viscosity (sorta depends upon what you already using). John Esposito at Quantum Mechanics recommends non-detergent 30w be used in a freshly rebuilt unit, but I suspect 40w might be needed in an OD that's got a lot of miles on it and has some wear inside. Triumph specified using 90w gear oil in the cars originally (which is similar viscosity to 50w motor oil), but that seems too heavy to me. It's best to accurately test the pressure being produced with whatever oil you choose, to see if it's too high or too low after the car is nicely warmed up on the road.

If you drain the oil, check it closely for any kind of swarf, filings or chunks of metal from either the gearbox or the OD. Brassiness might indicate rapid synchro wear. Steel grey swarf might mean other wear, such as on a main shaft. If any bushings or bearings are failing and shedding a lot of stuff into the oil, this will contaminate both units but is probably actually worse for the OD which has a pump and a couple pressure building pistons, as well as an accumulator to maintain pressure, which is fitted with a piston that's got compression rings in a bore, similar to those in the engine (just smaller).

I hope these ideas give you some leads to solving the problem. Let us know if you find anything.


08-24-2006, 04:22 PM
Alan is right on.

This link gets the O/D manual:


I used it to diagnose a plugged Operating Valve Restrictor Jet for my TR6.

08-24-2006, 09:29 PM
Let me ask a stupid (really stupid!) question:

Does the OD share a common oil supply with the main tranny?

I assume that I need to drain both the tranny and the OD seperately, but do I fill them seperately as well? If so, does pouring into the main tranny drain into the OD, or do I have to force oil in there somehow?

I'm guessing that I take out the drain and clean the filter in the OD (I hope I can find it.) I've never noticed a fill area in the OD, but I've never really paid much close attention to the unit.

I feel so dumb, because I know quite a bit about TRs, but this is the first OD TR I've owned, plus it's never been hooked up until recently.

Leebo, I'm printing out the OD manual -- thanks!

08-24-2006, 09:32 PM
Just grabbed page 5 of the OD manual off the printer, and it just answered my question -- drain both, fill one! /ubbthreads/images/graemlins/wink.gif

08-24-2006, 09:39 PM
The manual has sections describing slow engagement, slow disengagement and clutch slip. All point to: Insufficient oil, insufficient hydraulic pressure (foreign matter on the ball seat of the pump valve.)

Looks like I have a project for tomorrow!!!

08-25-2006, 06:57 AM

Before you go pulling the plug on the OD check out the solenoid's ability to lift and drop the arm attached to the engagement lever shaft. On my car the lever was slipping on the shaft. I had to take the lever off and cut 1/8th off the pinch point (end where bolt go's through) with a hacksaw to make it squeeze tighter on the shaft. Make sure the lever with the hole on the opposite side of the solenoid lines up with the hole in the casing when fully engaged by using the drill bit technique. I swore the OD plates were slipping or the clutch was going but was pleasantly suprised by this simple fix. Of course I found it right after I visually inspected the movement of the piston and then pulled the pressure operating valve spring and ball, but luckily that was not too painful.


08-25-2006, 09:47 AM
Did you simply drive the car with the gearbox cover off, or did you put the car on jackstands and put it in 2nd?

How could you tell the lever was slipping on the shaft? You'll have to excuse my ignorance, but I've never actually seen OD engage. (I understand how the solenoid works.)


08-25-2006, 11:06 AM

I forgot to mention in the last post that another simple reason why it may not be engaging or disengaging properly is that the dust rubber boot may have come off the solenoid and is jamming the solenoid from raising all the way or lowering enough to disengage. This boot you may be able to get at from underneath but it will still be easier to remove the transmission tunnel. Make sure you take out your lower seat pads and cover the seats with something while working on this. You have to remove the gear box cover to check the solenoid mechanical adjustments. Once the tunnel was removed I grabbed hold of the lever on the right side of the OD and the actuating lever that the solenoid is attached to on the left and gently rocked the lever on the right side back and forth. If it moves then the actuating lever is loose on the shaft. You may have to remove the rock cover protecting the actuating lever first to get a hold of the actuating lever under the solenoid. There are non-running procedures to check all lever adjustments prior to driving but yes I drove the car around with the tunnel off and after engagement/disengagement I would check with the drill bit to see if it moved (thats when the dim bulb went bright and discovered the actuating lever was slipping on the shaft). I had my tunnel on and off so many times I was considering installing a door. The neighbors were sure wondering what I was doing. If it's not either of these simple fixes then your best to follow the OD hydraulics troubleshooting procedures that is in the Moss catalog for a start. If there is no air in the system and the piston isn't going up or down and proves to be the problem you will need to get a OD manual (I saw a good one on the Buckeye site a couple years ago when I went through this)and start asking questions. Not sure how you engage the OD but when engaging the OD you shoild push the clutch in, engage OD, and then let the clutch out. When disengaging the OD you simply disengage without the the clutch. Saves a lot of u-joint replacement not to mention lower back pain.


08-25-2006, 12:22 PM
Harry brings up a good point and I'd check those things as well, but I'd still drain and replace the oil, clean the filter (which is on the O/D drain plug), and clean out the Restrictor jet. If you've got the tranny cover off, cleaning the Restrictor Jet will take less than 10 min to remove and blow out with compressed air - I couldn't believe the amount of gunk that came out of mine.

If you haven't yet, go to John Esposito's site and read everything he's written (John makes his living fixing these quirky things):


I bot from John a shift-lever mounted O/D switch and love it (it replaces the shift knob.)


08-25-2006, 12:54 PM
The lever doesn't appear to be loose.

I'm draining the oil right now, and it appears really dirty, but I haven't noticed anything totally unusual. Haven't checked the OD filter yet -- I just dropped it and went in to wash my hands.

Luckily I only keep my tranny tunnel in with a couple bolts and screws, so it's easy to get out (and slighty harder to get back on, mostly due to the od wires.

08-25-2006, 01:04 PM
Oh, and if you choose to do your testing with the car on stands/wheels in the air with the tranny cover off, make sure you haven't just greased the U-joints - that grease will fly all over your interior - not as big a deal if the interior is black, mine's tan (ugh).

08-25-2006, 04:43 PM

Sorry to hear it wasn't the easy mechanical fix. Looks like your well into the hydraulics. I don't understand the wire problem? You should have only two wires with quick disconnect spade connectors coming out from the driver side of the tunnel. When I wrote read the Moss trouble shoot (which I just happened to get today) please DO NOT use 90 wt gear oil in the OD as they recommend. Don Elliot recommended Valvoline racing motor oil 20w-50 years ago and I've been using it since with absolutely no problems. Thanks to Leebo I now know where Quantum Mechanics is (amazingly, about 20 minutes from the house, guess I'll be taking a ride over there some weekend) and Johns recommendation of nondetergent 30wt also fits right in with what I've been hearing.

Good luck and keep lots of rags and speedy dry nearby!