Overdrive disengaging on it’s own

[Efuentes]

Just to be clear, it does not happen only in 2nd gear. Apologies if I didn’t explain it clearly. It happens in all gears, but I only normally use the OD in 4th gear. When I accelerate, it automatically disengages, even though the relay light is still on. If I accelerate less, it does engage. I can keep it engaged if I accelerate gently, typically in a flat o downhill. If I need to accelerate significantly to maintain speed in an uphill, or to pass a car, it disengages. I will first check the cables and, as Roger pointed out, the gear lever as far as I can without removing the cover. If no results, I will change the oil. If the problem remains, I will then remove the cover

[Efuentes]

I saw in a manual for the OD the procedure to align the lever, but I guess it is also a gear cover off work, is it?

[Charlie D]

13 hours ago, RobH said:

Why would anyone want a radio that only came on when you were in overdrive? 

Come on Rob, isn’t that obvious?

The engine is so loud when not in overdrive that you can’t hear the radio.

Go into overdrive… drop a few hundred revs… you can hear every word of Walter Gabrial quite clearly.

 

As far as dropping out when accelerating and/or going up hill could it not be due to too little oil in the box.

(I know you said you checked it, but this is just a theory.)

Fast acceleration or going uphill pushes what oil there is to the back of the box and so starves the OD pump.

 

I know it will be frowned upon, but I use the operation of the OD as an indication that I have not lost oil from my gearbox.

 

Charlie.

 

[Charlie D]

8 hours ago, Efuentes said:

I saw in a manual for the OD the procedure to align the lever, but I guess it is also a gear cover off work, is it?

I "Think" you can get to that lever by cutting holes in the right place on the cover. I'm sure I've read it somewhre recently. It just depends if you don't mind cutting the holes.

 

Charlie.

[Lebro]

If you are sure that the solenoid is receiving power all the time (worth checking by monitoring the wire going to it directly) then O/D cone clutch slipping is my guess.

Bob.

[ianc]

Lubrication of gearbox & overdrive separates owners into 2 groups:

- those who use 40 grade, as recommended by Pete Cox

- those who use Hypoy or similar.

For some 58 years, I have used Hypoy - Castrol in earlier days, now Penrite Hypoid 80/90.  

Two friends whose judgement I value greatly, Ian Gibson and Tony Sheach, also use 80/90 grade, so I shall continue to use Penrite Hypoid 80/90 as it works well and never causes problems for me. 

BTW, the more viscous oil doesn't escape so easily!

Ian Cornish

[stillp]

I used EP80 (not Hypoid) for many years. My OD works, but has been getting very sluggish to engage when it's hot. I changed to Penrite GB40 last year, and the OD is certainly a little 'snappier', although still a bit temperature-sensitive.

Pete

[Ralph Whitaker]

If it was incorrect oil causing the clutches to slip in the overdrive, would not all power be lost to the rear wheels, same as if the engine clutch was slipping .

Ralph

[Efuentes]

1 hour ago, Ralph Whitaker said:

If it was incorrect oil causing the clutches to slip in the overdrive, would not all power be lost to the rear wheels, same as if the engine clutch was slipping .

Ralph

I don’t think so, but I may be wrong. From what I have read in the OD manual found in the internet, the role of the cone clutch is to block the casing of the sun gear, so that the planetary gears turn their carrier ring which then moves the transmission shaft. If the clutch disengages, then all the assembly turns and the gear shaft and the driving shaft move together (ie: no OD). You can find the manual here. Interesting, if a bit convoluted... https://www.nicolamarras.it/tr4/varie/triumph_tr4_laycock_overdrive.pdf

[Efuentes]

6 hours ago, ianc said:

Lubrication of gearbox & overdrive separates owners into 2 groups:

- those who use 40 grade, as recommended by Pete Cox

- those who use Hypoy or similar.

For some 58 years, I have used Hypoy - Castrol in earlier days, now Penrite Hypoid 80/90.  

Two friends whose judgement I value greatly, Ian Gibson and Tony Sheach, also use 80/90 grade, so I shall continue to use Penrite Hypoid 80/90 as it works well and never causes problems for me. 

BTW, the more viscous oil doesn't escape so easily!

Ian Cornish

You forgot a third group: those who dunno what the hell was in there, but it worked...

[james christie]

I’ve been sitting back reading the various comments from those with far greater knowledge of oils, gearboxes and overdrives than I - though I have taken one or two apart and put them together again.

I have almost convinced myself that your problem is mechano-electric. Solenoïds do fail but rarely and when they do it is totally. As your problem occurs on all gears, I would have a look at the pump engagement lever. I have a feeling that with age and use, the shaft that crosses through the overdrive from one side to the other, gets slightly twisted and thus does not fully engage with the cam on the pump. 
In turn, this makes a nonsense of the wonderfully precise instructions in the Workshop Manual, about using a 1/8th drill etc to set up the lever position ……

I set mine by trial and error, with the rear axle safely jacked up, you can experiment in all the gears. You will need to set it a little bit passed the point described in the manuals. The finesse required is to make sure the solenoïd is being put in the right place by the pulling coil and then is held by the low current holding coil.

Unfortunately it is a gearbox cover off job, which is a pain in itself.

Oh and I have been using Hypoid 90 oil for 51 years……..

james

[Lebro]

2 hours ago, Ralph Whitaker said:

If it was incorrect oil causing the clutches to slip in the overdrive, would not all power be lost to the rear wheels, same as if the engine clutch was slipping .

Ralph

No, because there is a one way roller (Sprag) bearing at the rear of the box, that will transmit power to the axle even if all of the cone clutches are slipping.

[Tr4aJim]

Could there be a difference in the chemical makeup of 50-60s era EP oils vs modern EP oils? Perhaps modern EP oil is more resistant to separation of the additives, which the OD manual warns about.

Jim