Tr6 Overdrive Fault

[Johnstrickland]

I recently made the mistake of stopping my TR6 while still in overdrive and didn't realise until after I had restarted that it was still switched in.

I had switched the engine off before restarting and when I realised, after restarting, that it was still engaged I switched out the overdrive.

It seemed to switch out OK as I felt the rise in revs, but it now will not engage overdrive.

I wondered if anyone else has experienced anything like this and might be able to help.

[RogerH]

Hi John,

turning the ignition on/off with the gearbox in neutral should not affect the OD as the inhibit switches override such things.

 

If you were in neutral and you could sense the OD coming out then there must have been previous fault.

 

Have you done the following -

In neutral.

Ignition ON

Engine not running

Select OD

 

Did the OD make the audible clonk during engagement - it should not have.

 

Do the above with the gearbox in 4th - you should now get the clonk - did it.

 

Have you got the wiring diagram http://www.advanceautowire.com/tr2506.pdf

 

With the Column switch selecting OD and in 4th check for volts at the relay (ignition on)

Check also that there are no loom earth shorts.

 

Roger

[Johnstrickland]

Thank you for your reply.

I have done all the checks you suggest and the electrics are all OK, there is a clonk from the solenoid when in 4th gear with ignition on and o/d selected.

So I guess I'll have to think again.

Maybe something is sticking in the o/d itself.

Anyway many thanks for your help.

[AlanT]

Try these excellent OD articles:

 

http://www.buckeyetriumphs.org/technical/AOD/AOD5/AOD5.htm

[Johnstrickland]

Thanks to you both for your help.

I am now very pleased to say that the overdrive is now working again.

Having taken it out for a drive this afternoon it just started to operate again so I suspect there is either an intermittent electrical fault or the solenoid is intermittently sticking. I will investigate further.

Whatever, at least it's not something serious!

Once again many thanks.

John

[RogerH]

Hi John,

it could become serious IF the solenoid sticks in and you try to reverse - although this is the opposite to what you experienced.

Try and locate the fault sooner rather than later.

 

 

Roger

[Johnstrickland]

Hi Roger

Thanks for this advice.

I had heard that reversing with overdrive in was catastrophic so will sort this out quickly.

 

John

[AlanT]

So many owners DONT KNOW that the overdrive WILL break if you reverse when its engaged.

 

The stuff on the Buckeye site will explain all about this.

 

Reverse into parking bays until you are sure the OD is fault-free!!

[BrianC]

So many owners DONT KNOW that the overdrive WILL break if you reverse when its engaged.

...

Reverse into parking bays until you are sure the OD is fault-free!!

What? How does that work then?

[stillp]

Alan, did you mean "Don't reverse into parking bays"? Don't reverse at all unless you're sure the O/D is disengaged might be better advice!

[AlanT]

These overdrives get stuck sometimes when you stop.

So if you drive fowards into a parking bay you cant get out.

 

If you go to reverse in. and your OD is stuck then you wont get in and can go home fowards.

[stillp]

Strange, I replied to this a few days ago! Where's my post gone?

It was along the lines of "Thanks Alan, now I know what you meant".

[AlanT]

We had a case on here a month or so back where someone felt forced to reverse against the clutch because we was in a multi-story bay and could not get out.

 

He broke it of course.

 

Should have called recovery and got lifted up.

[stillp]

What actually breaks, and why?

[AlanT]

Well the failure is almost designed in.

 

There is a thing a bit like a roller bearing but the rollers are on tiny ramps so it rolls one way but jams if turned the other way. Called a unidirectional clutch.

 

This is so that power is transmitted before the OD engages fully but after the direct drive is released, I think I got that right its a while since I studied this.

 

Its a bit on the weedy side anyway and if you drive against it, well if you are lucky the rollers slip.

 

http://www.buckeyetriumphs.org/technical/AOD/AOD3/AOD3.htm

for pictures.

[stillp]

Thanks Alan. I understand the unidirectional clutch, but still don't understand why damage is caused (and to what) by reversing in o/d. Why doesn't the clutch just slip?

 

Intersting link, although it does nothing to encourage me to delve into the innards of an overdrive! At least I'm not the only one to make a dummy shaft from wood.

[stillp]

Having read Alan's buckeye link, I'm beginning to see the light!

 

Pete

[AlanT]

Actually an OD comes to bits quite easily, all except for the bearings in the tail.

 

In pulling these out I used a piece of 1/8in thick stainless plate to push on the big castle nut.

After it separated there was a clear impression of the nut left in the stainless plate.

[stillp]

I'm sure it comes to bits easily Alan, it's the reassembly that would worry me. I detached mine from the gearbox to change the gaskets on the adaptor plate.

[Motorsport Mickey]

Pete,

 

The unidirectional clutch should only transmit torque in one direction, as per the description the unit is cog like and made up of a number of ramps (5 or 6 as i remember).

In it's correct use the rollers are propelled up the ramp and protruding through the clutch cage against the housing dia (making all these names up) and transmits the drive, when the overdrive sticks in reverse the rollers motion is screwed backwards down the ramp into the cage until they come to the inner dia shoulder which...stops them abruptly and in a paraphrase " the immoveable force meeting the irresistible object" .

The clutch sprocket is made of material harder than the hobs of hell (to avoid excessive wear over many overdrive applications) and doesn't like compressive forces one little bit, objecting so much as to either have many spider like cracks formed in the ramps cores (got one of them) or if unlucky splintering into many pieces within the cage.

 

If in doubt with an overdrive operation NEVER select reverse, and if you do and the car appears reluctant to move don't bully it, try another way around the problem and check out the overdrive operation.

 

Mick Richards