The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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PostPosted:Thu Mar 25, 2021 4:23 pm 
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Joined:Thu Sep 28, 2006 9:06 pm
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Location:Bristol
I believe that my O/D has stuck in I know that I must not reverse the car as this will cause damage but how do I get it to release?

Will know that I will do damage if I reverse the car but can I push the car backwards with the gearbox in neutral?

Will it just be the solenoid valve that has stuck?

So far I have checked that the 12 volts is getting to the solenoid when the switch is operated.

I have checked the oil level, it was a bit down but I assume low oil level stops it going in.

The car is up on axle stands and when it is in third gear and with the engine running there is no indication that the O/D is switching in or out.


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PostPosted:Thu Mar 25, 2021 7:35 pm 
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Joined:Fri Apr 15, 2016 10:08 am
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Location:Ayrshire, Scotland
Shortly after I got my 1850HL back on the road I had this problem. The OD would come on but was reluctant to drop out. In my case changing down through the gears and doing some accelerating and slowing made it come out eventually. Changing the solenoid cured it completely. It is hard to get a spanner on the solenoid in situ, but I managed it with this tool https://www.jamespaddock.co.uk/overdriv ... spanner-2
I'm no expert on these units but it is hard to see how you could damage it by simply pushing the car backwards. Don't forget that removing the solenoid will cause the oil to drain from the gearbox, so do that first!

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Mike
(MGB GTV8, and Dolomite 1850HL. New: a 1971 MGB roadster in need of welding)


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PostPosted:Thu Mar 25, 2021 8:34 pm 
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Pushing the car backwards with overdrive engaged will have the same effect but maybe to a lesser extent on the cone clutch as driving it backwards, so try not to!

Reasons for J type overdrive not disengaging in order of severity are:

1. Fault in electrical control circuit - check for a closed circuit
2. Sticking solenoid valve - remove solenoid and check valve
3. Residual pressure too high - fit pressure gauge and check residual; if too high check for sticking relief valve
4. Control orifice blocked - check and blow through with compressed air, do NOT probe with wire
5. Cone clutch sticking - tap brake ring with hide mallet
6. Internal damage - remove, examine, overhaul


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PostPosted:Thu Mar 25, 2021 10:52 pm 
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Joined:Sun Sep 08, 2013 2:35 pm
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Location:St Annes on Sea, Lancs.
The overdrive on our Herald had no gearbox switch and was either on or off, and I kept leaving it on and reversing, maybe a dozen times or so.

I fixed the GB switch so it's only on in 3rd and 4th, but nothing other, and it's still working 4 or 5 years on and maybe 10000 miles

So I'm of the opinion that they don't necessarily die the first time you run one in reverse.

That being said, it may not be good idea if it's avoidable.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


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PostPosted:Fri Mar 26, 2021 9:41 pm 
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Location:Bristol
I have now had a look at my records and back in 2016 I noticed that this O/D was slow to drop out of O/D when it was hot and I had to ask a local classic friendly garage to change the solenoid valve over to one that I had taken off another O/D unit as I could not undo the one on the car. When this was done the problem went away.

I have also found that the workshop manual provides a list of faults that could cause the problem and the actions to be taken. Some are a bit more than I would wish to do with the car on axle stands so today I removed the solenoid and checked it out. As the workshop manual did not indicate that the gearbox needed to be drained, I decided to give it try without draining the gearbox. I just had a container in place to catch any oil that came out. When I removed the solenoid, a trickle of oil did come out but if I had a replacement to hand the loss would have been very little. When I applied 12volts to the solenoid the plunger seemed to be sticking in the engaged position so I soaked the piston section in white spirit but this did not cure the problem. I noticed that there was a very small circlip that kept the piston arrangement in so I struggled to take this circlip out. The next struggle was to get the plunger out but in the end I achieved this. The workshop manuals and the parts catalogue do not go down to this level so I have not been able to replace the O rings on the plunger. Having given all the bits a good clean I put it back together and retested it across the battery. It now seemed to be working fine so I refitted it and topped up the unit. It needed about 0.5 Ltr so it was a pity that I did not drain the lot before removing the solenoid.

See photo of stripped plunger arrangement.

As the car is on axle stands I ran it up in third and engaged O/D it seemed to engage and disengage normally. At 30 mph the revs reading was about 2200 and when O/D was engaged the revs dropped to about 1900. These figures are what I use when the car is out on a run and I wish to check if O/D is engaged or not.
As it was now about 16:00 hours I decided that I would leave the true road test until tomorrow. Lets hope that it does not stick again when it warms up.

Image


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PostPosted:Sat Mar 27, 2021 7:21 pm 
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Location:Bristol
I am able to report back that I took the car out for a 25mile run this afternoon and the O/D worked fine even when it had warmed up. I just hope that it will continue to work as I was unable to replace the O rings on the plunger.


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