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Stiff overdrive actuating valve


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Hi guys and gals

My overdrive investigation continues.  The new solenoid has certainly helped with the blowing of fuses, but I can't help but feel that there is something with this 2nd hand o/d that is the root cause of the solenoid problems.  Even on today's test drive, on a couple of occasions the solenoid twitched as if it was trying to pull in, but did not actually lift the lever.  Fortunately I was being very careful to monitor this and turned off the overdrive within a second or so.  99% of the times I flicked the switch, though, the o/d engaged as it should.

What I have noticed is that the actuating mechanism on the overdrive is very much stiffer than the mechanism on the original overdrive that is now out of the car.  The original overdrive actuating mechanism is comparatively light to the touch, while still returning to the off position in a positive manner.  The o/d box that is now in the car is very much more stiff to operate, requiring much more pressure on the lever when engaging manually. 

I have removed the valve and spring / plunger / ball etc and notice that the spring is very, very stiff.  It is 11/16" in length.  I have been unable to remove the same items from the original box, because the top bolt is so tight I think I need to get an impact wrench on it (something I am yet to acquire).  However, I am almost certain that the spring in the original o/d must be significantly less stiff, otherwise the operation would not be so light.  I have compared the spring with the springs found in the synchro hubs: the synchro hub springs are shorter and thicker wire, but I would estimate the compressive effort is similar between the two.

Can anyone comment?  Below is a photo of the spring with other components.  It looks heavier than the spring shown in a o/d guide I downloaded from the interweb (also inserted below), but that could be a trick of the photo.

My spring etc:

image.png.b235f2ccb3c8d21d880b0ac583b36309.png

 

Spring shown on Green County Triumphs guide to overdrives:
image.png.62ec02b7884fa6e439cede3c6e1406df.png

 Thanks!

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Hi Malcy,

I don't like to say this but your ball looks dirty or dechromey. Might be worth replacing. 

Make sure about any options available regarding spring strength.

I seem to remember  that there are o ring seals on the  actuator shaft which can and do decay and bind up.

Here is a useful read attached note the different ball sizes.

A Type Overdrive.pdf

Edited by Rodbr
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There is often an oil leak from the actuating shaft which some owners try to fix with a larger O ring pushed onto the shaft and into the gearbox casing. If this is too tight it will interfere with the od operation.

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Hi guys - with the spring and plunger etc removed, the lever operation is similar in weight to my other overdrive unit, possibly even a little less heavy, so I don't think the seals are the root cause.  

Interestingly, when I purchased the overdrive and tested it with the seller, we discovered that the actuating piston thingo (with the tiny hole for oil pressure release) was bent... no idea how this would happen, but it also points to something being not quite right in this area.

Also - that o/d info sheet posted by Rod seems to confirm that the spring I have installed is a heavier wire than shown elsewhere... the pitch of my spring is approx. equal to the thickness of the wire, whereas the others use much thinner wire, see one example below.

I am going to have a crack at getting my other overdrive actuating valve removed so I can see what is in there... I might even swap the components over to see what happens.

image.png.b198b3c83bc56885ca963387019398fb.png 

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Good idea to swap the operating valve, ball, spring and cap from the old overdrive.  Take care when replacing the operating valve

Bent Operating Valve.

Years ago I was told something like this - When the operating valve is lifted  out the external side lever can be rotated so far that when the operating valve is replaced it does not sit on the internal actuating cam of the operating lever, but passes down the side of it.  The heavy handed will then try to move the external lever down but end up bending the bottom of the operating lever.

 

Buckeye Triumph Technical

https://www.buckeyetriumphs.org/gearbox

The pdf posted above is the A type overdrive section from the Buckeye web pages.

Cheers

Peter W

 

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Hi guys - so I've finally (I HOPE!) got to the bottom of my stiff overdrive actuating lever and the resultant issues with solenoids.

I compared the spring in the actuating valve from the recently acquired overdrive with the spring from the original overdrive and to my relief, there is a clear difference between the two.  

HOWEVER! As hinted at by Rod, I also discovered that I was not helping the situation by being too cute with the gasket I cut for the solenoid mounting plate: it was too tight around the actuating shaft, resulting in the action stiffening up to the point that the lighter spring would not return it to the "off" position, but only once the solenoid plate was bolted tight against the mating face.  Who knows, maybe in the past, this happened to the previous owner of this box and they decided to put in a heavier spring to overcome the friction.  

Either way, a quick trim of the gasket, and now I have a much lighter actuating mechanism, and everything is back together awaiting a test drive.  Fingers and toes crossed... getting a little tired of taking this thing apart and putting it back together, although it has been a good learning experience.

Thanks for the input! Photo below is of the heavy spring and what I presume is the correct spring... the heavier spring is also much shorter than the lighter spring.

 

 

 

 

image.png

Edited by bigmalcy
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Grrrrrrr

Getting really tired of this now.  Took the car for a road test just now and the overdrive operation STILL is not working properly.  

Works fine in he garage, then not when out on the road.  What I realised during this test drive, though, is that when the car is in motion, the oil pressure pushing down on the ball bearing is creating a sticking point in the lever action: the lever is light when the car is not moving, but when the car is moving the lever is stiff and requires a solid nudge to get it moving at first.  

Flicking the switch to acuate the solenoid when the car is moving results in the solenoid twitching, but it is clearly unable to overcome the additional force of the oil pressure on top of the ball bearing.  Flicking the switch while the car is stopped results in the solenoid operating perfectly.

The oil pressure in the o/d is approx. 350psi, which I think is reasonable, although I did put a washer in front of the accumulator spring to increase it a little.  I don't think this would be causing the issues, though.

I'm reaching the stage where I think I might just re-fit the original box and overdrive which has now been repaired... unless someone can suggest what could be causing this sticky valve.

 

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Hi Malcy,

I would suggest that you are very careful switching parts from working unit to test out. Always list the changed part so it can be refitted.

The only thing I can suggest is that O rings may be too soft and compressing enough to bind up but work OK static but not under oil pressure. When I had my overdrive gearboxes rebuilt I was given the option of three oil pressure settings. The lowest standard giving a kind of soft change, mid approx 650psi giving a snappy change and competition which lasted two or three races before rebuild which would snap halfshafts if used wrongly. So I don't think the pressure is the issue.

I would be looking at binding shafts either bent or swelling oil rings if different locations. 

Where was the unit rebuilt, UK or Aus? O ring source, If possible talk to overdrive services.

Are you using a new solenoid? Weak or sluggish pull in?

Rod

Edited by Rodbr
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Hi Rod

It's actually a Vanguard box which I bought as a semi-temporary stand in for the original box that lost first gear.  It hasn't been rebuilt to my knowledge.

The vanguard box worked well for a short period of time (two or three drives) before starting to blow fuses on the power supply to the solenoid. 

I am now using a new solenoid.  Nice snappy pull in when car is not moving. Have swapped over all the actuating valve components except the top cap and the little plunger that bears on the top of the ball.  No difference to symptoms, other than the lighter feel on the lever when car is stopped - this was due to the installed spring being too heavy.

I have re-adjusted the clamp so that the solenoid plunger has more room to build up momentum before it starts lifting the mechanism... this might allow it to overcome the initial resistance and pull in properly.  Still doesn't sound quite right and may just be a way of getting around another problem.  Will test that tomorrow and see how it goes.

I have measured the ball and it is 5/16" dia which is correct, I believe.  Later models used 1/4" dia balls, which would reduce the force on the ball by a factor of 36% or so.  The only thing about that is that I am not sure if the smaller ball with less force would seal properly on the top of the plunger and on the casing when the o/d is turned off.

Edited by bigmalcy
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Hi Malcy,

methinks you may have found your own solution. If the box has not been rebuilt and not used for some considerable time I think that may be the problem. The old adage that things not used decay. I think the issue may be an age old built up and decayed seals. I know I am clutching at straws but you need a start point to analyse an issue and that does not seem to be the case.The first two or three "drives"stirred the **** up and caused it to start to act up. Did you change the fluid before use? or just top it up.

never having had a vanguard box I am unfamiliar with the differences if any from later boxes.

Not sure I agree about the ball differences as surely the seat is cut differently for each size ball.

Not sure if it is even possible to flush a gearbox and o/d unit but worth the search for information but a flush and complete fluid change might help. 

I would caution against going too much further if the serviced box is due soon. you could piss your self off and start looking for issues when the "new box is fitted"

Tr ing is supposed to be a pleasure not a painful experience. LMAH!

Best regards

Rod

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Hi Rod

All good - adjusting the lever position on the shaft to give the solenoid plunger a bit more slack at the 'off' position has done the trick. The o/d worked perfectly and actually engaged with just the right amount of urgency. Back to using a 10Amp fuse on the power supply, too, so the solenoid should be protected if it ever gets stuck in the 'pull in' phase.

The Vanguard box and overdrive that I picked up for 250 pounds is almost identical to TR2 / TR3 units: the gearbox part is identical other than the clutch lever and selector cover etc. The overdrive is externally identical except for the solenoid mounting plate. It was easy to just swap the TR units over to remedy these issues.

Internally, the overdrive is identical to early TR2 overdrives, except it is a 28% reduction rather than 22% used on the TRs.  Makes for slightly more relaxed cruising.

Anyway - will put the inside of the car back together and then see how she goes over the next few drives.

Thanks for your input!

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Hi malcy,

You should be wearing a mask and stripey top as you stole the box for that money.

Delighted you have found a solution. It is difficult to help at distance but sometimes a problem discussed is a problem sorted, makes you look at things from a different perspective .

Thanks for the update as too often people fail to give an update as to a result or otherwise.

best regards

Rod.

Drop me a PM as I have drawing that if you know ought about electronics will give you the piece of mind regarding overdrive solenoid destruction.

R

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