Overdrive disengaging on it’s own

[Efuentes]

Hello to everyone. I would like to pick your brains and your expertise on the possible causes of an issue I am experiencing with the overdrive.

I own a 1966 rigid axle TR4A, which I acquired in 2016 when I came back to Spain after living three years in Toronto. Since acquisition, the overdrive would engage and stay engaged with no problems. I had an issue with 2nd gear slipping out when shifting down to reduce speed, so I took the car to a garage where they sorted out the 2nd gear issue. Wwell, kind of sorted out, as it still does it, but way less often. They basically addressed part of the problem at the selector box, but I didn’t want to do a full gearbox out rebuild: it is tolerable, if not ideal now.

Anyway, as part of the service, and not knowing what oil was inside the box and OD and how long had it been there, they changed the oil and put fresh Castrol Classic EP90 mineral oil. Since that service, I am having the problem that, specially when the engine / gearbox is hot (ie: after 20-30 miles of driving) the OD engages without problem but, when I accelerate, it disengages on its own until I reduce throttle again. Solenoid and electrics seem to work fine as, as said, the OD does engage, light goes on and lever clicks. I have checked the oil level at the gearbox and it’s fine.

I am thinking that oil can be the suspect here, as there were no OD issues before the oil change. Having said that, and after going through a number of threads in this forum, I am a bit baffled that the issue happens when hot, as my first thought would have been that, maybe, the new oil is too viscous, but that would usually imply issues when cold, not when hot. As I said, I don’t know what type of oil was in the box before, so going back to whatever was there, which would be the obvious solution, is not possible.

Just in case it can be a tell tale symptom of whatever is the problem, another new issue I am having since oil change is a noisy 3rd gear, with vibration at the lever, as I go past 2.500 RPM.

So, what do you think?. Is oil the likely culprit?. Is Castrol EP90 inadequate, despite it being in line with the owners manual recommendation (and, yes, I have read the threads where some people say that the OD manufacturer specifically said no EP90)?. If so, should I go thinner or thicker?. I am generally cautious about putting engine oil in the gearbox, and more inclined to what Roger mentions in other posts: gear oil for the gearbox, engine oil for the engine

[Motorsport Mickey]

EP oil has additives for gears usage, normally in a diff. But will coat the “ cone clutch” ( a large tapered ( hence cone) 7 or 8” dia of clutch material ( it runs in oil) spinning inside the overdrive with their additives causing it to slip.... Wrong oil.

I would drop the oil ASAP and try a refill with 20-50 engine oil with a high detergent.  Although I agree with Roger regarding a straight oil ( I use a 40) you need to clean up the clutch material which I think the 20-50 will with it’s detergent action. Then drain it after maybe a couple of hundred miles of overdrive use where hopefully it will stop slipping, and then refill with the correct oil.

MickRichards

[ianc]

Disengagement of overdrive when power is applied is suggestive of movement causing the 2nd/3rd gear isolator switch to open, re-closing when on the over-run.

Check that the isolator switch has not come loose and, if necessary remove a copper washer to get the switch to seat further in.

Another possibility is that the thrust bearing(s) has worn to the extent that the gear cluster is moving back and forth, causing the isolator switch to open and close when it should be closed (i.e. making the circuit).

Ian Cornish

[Efuentes]

Many thanks for the replies. Where is the isolator switch?. Is it accessible, or would I have to remove the gearbox cover (and all the stuff that goes with that: console bracket, carpets...)?. If it’s accessible I can try. If not, I will try with the oil first. What makes me have the oil on top of the suspects list is that this didn’t happen before the oil change, suggesting that there was not a problem with the switch...

[Efuentes]

What Mick says gas reminded me of one of the ideas I had while browsing through the various threads: motorcycle oil. As you probably know, motorcycles have oil bathed clutches, using the same oil for the engine and for the gearbox, so motorcycle oils must have no anti friction additives. They also have synchronizers, so no large quantities of phosphor. The correct specification is JASO MA. My two concerns are that the torque that goes through a motorcycle gearbox is smaller, so I am unsure if it will withhold the shearing forces in the TR gearbox, and that it is difficult to find a 20w50 motorbike oil. It’s also true that the problems car oils not being compatible with motorbikes started with API SJ in the mid 90s, when they started to use friction reduction additives, so a good old 20w50 API SG or SH would also work. Maybe someone has tried this?

[RobH]

The interlock switches are on the gearbox remote which is the bit your garage must have worked on when fixing the 2nd gear selection.  As Ian says it is quite likely the problem is adjustment of the switch and not the oil, but getting to that means taking the transmission tunnel off.  

To confirm the fault without dismantling anything you could temporarily wire a small 12v light bulb between the C2 terminal on the overdrive relay and earth ( yellow/purple wire to the solenoid) . The bulb will light with overdrive selected but it will go out if the interlock switch misbehaves. 

If the light stays on when the overdrive drops out,  then it may indeed be the oil at fault. 

 

[Efuentes]

Hi, Rob. Many thanks. My car actually has an overdrive engagement light fitted, that switches on when the relay is on. I will check the wiring, but I believe it’s similar to what you describe, as it only turns on if The OD relay is engaged, not when I turn on the switch with the engine in neutral or in 1st gear. The light does stay on when my overdrive “misbehaves”, which seems to point to the oil. I guess the correct process will then be to 1st try the oil (I drilled an access to the filling hole in the transmission tunnel, so this should be easy) and see if the issue is sorted.

[RogerH]

Have a look at the rubber gaiter at the bottom of the gearstick.

It may be pushing on the gearstick and just moving the selector rod off the switch.

 

Roger

[ntc]

1 hour ago, Efuentes said:

Hi, Rob. Many thanks. My car actually has an overdrive engagement light fitted, that switches on when the relay is on. I will check the wiring, but I believe it’s similar to what you describe, as it only turns on if The OD relay is engaged, not when I turn on the switch with the engine in neutral or in 1st gear. The light does stay on when my overdrive “misbehaves”, which seems to point to the oil. I guess the correct process will then be to 1st try the oil (I drilled an access to the filling hole in the transmission tunnel, so this should be easy) and see if the issue is sorted.

If you have a earth to the light that is piggy backed to the realy that will be your problem 

[jerrytr5]

17 hours ago, Motorsport Mickey said:

EP oil has additives for gears usage, normally in a diff. But will coat the “ cone clutch” ( a large tapered ( hence cone) 7 or 8” dia of clutch material ( it runs in oil) spinning inside the overdrive with their additives causing it to slip.... Wrong oil.

Hate to disagree with Mick, but Triumph specified EP80/90 in overdrive gearboxes and it's something I've used for 40+ years.

I think the overdrive will run with almost any fluid given the multiplicity of options given by vehicle manufacturers.

In my experience, 95% of overdrive issues are electrical, could be something like a bullet connector disturbed.

Jerry

[RogerH]

I agree with Jerry about the electrics- if there is any strain on a cable in the loom then it make Break/Make with tension

 

However, regarding the oil spec.   In the very early days (TR2,3,3A,4) the Overdrive manufacturers actually warned against NOT using any EP oils.

They explained that the heat from the OD clutch could burn out constituents in the oil (sulphurs etc) turning them into solid particles and blocking the small oil ways.

When the TR4A ame along ther oil spec changed to EP with no explanation - probably due to the thinnner oil leaking more than the thicker EP80/90.

 

Mechanically there is little change to warrant the change in oil spec. 

It may be that the more modern EP oil is more temperature tolerant and can hold onto its constituents better ,

Many folk use the EP80/90 oils with success, likewise many people use the 30 or 40 grade gear oils successfully.

 

Micks trick with the high detergent engine oil in interesting (not heard it before) and sounds logical (better than filling with paraffin )

 

Roger

[Motorsport Mickey]

1 hour ago, jerrytr5 said:

Hate to disagree with Mick, but Triumph specified EP80/90 in overdrive gearboxes and it's something I've used for 40+ years.

I think the overdrive will run with almost any fluid given the multiplicity of options given by vehicle manufacturers.

In my experience, 95% of overdrive issues are electrical, could be something like a bullet connector disturbed.

Jerry

As posted by TR Mitch back in 2014 I think

“I spoke to Pete Cox about this very topic. His thoughts were that 30 may be too thin for a road car but 40 just right. A read of Richard Michell's "What Oil" is quite enlightening or shoukd I say lubricating?

Don't forget that the thinner oil will find new places to leak from vs 90 grade.“

...I reckon Pete Cox has rebuilt more Laycock overdrive boxes for TRs than any other single individual who rebuilds overdrives in the TR Register, dozens and dozens, and he used one himself.

He rebuilt race overdrives for me and when I need another for road use Pete will be getting the call.

Pete thinks a straight 40 is the “Goldilocks grade”,...”just right” that’s what I’ll continue to use.

Mick Richards

[Hamish]

PO of my car used ep90 for years if not decades without issue.

i changed to Gear 40 when Pete Cox rebuilt my box/OD as that's what he uses.

he has since gone on to fit my new diff ratio and LSD

so he is a man whose opinion i trust on these spinny in oil parts

[Motorsport Mickey]

Penrith Gear 40

https://www.classic-oils.net/Penrite-Gearbox-40?VariantID=35387&gclid=CjwKCAjwqcKFBhAhEiwAfEr7zam2keWBQGCI0R9hiTxwizagwfpry4Zi4lepboKJsdyz0wpMp9NrfRoCM_4QAvD_BwE
 

Non EP gear oil replaces straight SAE40. Good price also, again from Classic Oils, they seem “go to” people on oils these days.

Mick Richards

 

Edited May 28, 2021 by Motorsport Mickey

[ntc]

Opinions may vary 

[Efuentes]

7 hours ago, ntc said:

If you have a earth to the light that is piggy backed to the realy that will be your problem 

Please correct me if I am wrong, but if that would be the issue, wouldn’t the light be on all the time?

[RobH]

8 hours ago, ntc said:

If you have a earth to the light that is piggy backed to the realy that will be your problem 

 

33 minutes ago, Efuentes said:

Please correct me if I am wrong, but if that would be the issue, wouldn’t the light be on all the time?

Since that circuit isn't fused, an accidental earth would surely be accompanied by smoke and the smell of burning insulation .......

[ntc]

You are both wrong the relay has to be a clean connection had a car here that the radio had used a piggyback and that made the overdrive not operate as it should 

[RobH]

Er- no Neil. Why would anyone want a radio that only came on when you were in overdrive? 

Are you describing a system with a poorly-designed logic circuit perhaps?

[ntc]

As I said it needs to be a clear connection on its own many have found this out using a overdrive logic device the demand on the relay is high but what do I know 

[RogerH]

Hi Neil,

not quite sure what you wiring around the relay is doing but I have installed many logic boxes and connecting to the C2 terminal on the relay.

This is the terminatl that is connected to the solenoid via the isolating switches.

The solenoid takes apprx 1amp under normal running and the logic box 100mA if that. The battery can supply 500amps if pushed The should be no probem with piggy backing on the relay.

 

Regarding the fault could the garage have badly adjusted the solenoid (eb=ven though they where doing other things)

So with the solenoid engaged could the rigging arm hole (on the right hand side) be out of alignment.  The relay engagement light stays ON but the OD drops out

But this does not account for it only happening in 2nd gear and accelerating.

 

I still think it is a wiring fault.

 

Roger

[ntc]

That’s what I am saying anything that draws current from the relay will affect its operation

[RogerH]

Hi Neil,

nothing is drawing current from the relay. All the current is coming from the battery/generator. The LED and the relay will work perfectly together.

However even if the relay was being starved by the LED why is it only happening in 2nd gear during acceleration.

It must be the wiring being put under stress.

Roger

 

[ntc]

So you saying that only positive current is being drawn? Sorry disagree 

[Lebro]

I'm keeping out of this one