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TYpe A overdrive woes


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Hi.

 

I am trying to see if anyone has tips for a niggly O/D issue.

Mine is a type A from 1955 operating on top gear only.

The person that is working on my TR's overdrive has, after many attempts, basically completely overhauled the overdrive.

It was working well before but while driving fast, as I switched it just refused to engage and started slipping.

It seems I was correct in guessing that some oil seals had failed and this was repaired now with new seals etc. As far as we could see the clutch was still good and wasn't replaced.

 

The current issue is that the O/D engages immediately and well, but won't disengage promptly. It eventually does, but this time is unpredictable.

This issue is not temperature dependent. So we guess its a hydraulic problem, perhaps some oil channel or such is partially blocked.

The solenoid has been adjusted, so it is not that.

I am not familiar with the overdrive and my mechanic has double checked his work and everything looks fine.

 

So the question is, would anyone have an idea of where specifically to look for something that could cause this issue?

The only tip I found from an old manual is that there might be a blockage in the restrictor jet of the operating valve. Are there any other things that can get blocked?

 

 

Dirk

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If he has replaced the seal on the right hand side of the operating shaft I hope he has used the right one as the wrong one can mean the lever sticks or is slow releasing.

Stuart.

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Another possibility could be the sliding member release springs have weakened with age (providing that they haven't been replaced). I would certainly eliminate all of the other culprits first that don't require disassembling the OD.

Berry

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If he has replaced the seal on the right hand side of the operating shaft I hope he has used the right one as the wrong one can mean the lever sticks or is slow releasing.

Stuart.

+1

if it was working OK and engages OK then the 'O' ring on the rigging lever (assuming it was replaced) is the top suspect.

 

I used what was supposed to be the correct one (O shaped) and it was still sticky. I need to investigate a square section seal.

 

roger

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Thanks for the tips!

I will give that through to my mechanic. Hopefully it is resolved soon. I miss my TR. 8)

 

dirk

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  • 1 month later...

+1

if it was working OK and engages OK then the 'O' ring on the rigging lever (assuming it was replaced) is the top suspect.

 

I used what was supposed to be the correct one (O shaped) and it was still sticky. I need to investigate a square section seal.

 

roger

 

I still do not have a working OD so now I am going to continue to grasping at straws!

Roger, what is the "rigging lever"? My mechanic, given this info, tried the different seal sections as you suggested. I just don't know what his lever is and where it is.

 

Current situation after I watched while some work was being done on a bench. So any further ideas would be most welcome. I am going to try and oversee this personally. I wish there were more people that could work on this overdrive.

 

The overdrive seems to engage correctly. When we start up , the pressure rises to about 350psi very fast, which is right for a Type A (OD in top only with a pull button) as far as I know.

When we disengage the OD, the pressure drops to 300 psi immediately and then just stays there. Even operating the lever manually a few times does not really resolve this and we have to wait a VERY long time, or release it slowly by opening the operating valve nut.

 

1: We cleared the little hole in the operating valve (It was blocked).

2: We added a new ball as the old one wasn't sealing properly and made sure it sealed both the valve and the opening in the shaft.

3: we measured and double checked the valve's length and the ball size, both correct.

4: The valve's up and down movement looks correct operating the lever manually.

5: We double checked the setting of the lever shaft? (Where the solonoid piston goes up and down)and saw the shaft was a little worn, so that the lever did not "grab" it fully causing faulty adjustment. We filed a bit of metal away so that the "beak" could now grip the spindle properly when the screw was tightened. Now it looks correct when operating in that it clicks up and down with electricity promptly.

 

Any further ideas where something could be maladjusted or blocked?

The gearbox guy I asked said there is a welsh plug of source in the case that may also be blocked?

In any case. The problem seems clear that the pressure isn't dropping. Perhaps there is something that keeps blocking the operating valve again?

Are there some other small channels that I have to look at where a blockage may occur? A drain or filter of some sort?

 

A last question (For testing on a bench, disconnected from an engine or rotating device.).

If the OD is engaged and I put the gearbox into reverse, the drive shaft should not be able to rotate at all, right? I just want to be able to make sure that the OD is really engaged.

 

Dirk

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Dirk

Check out Elin Yakov s videos on you tube.

He did a whole series on the A type gearbox OD.

 

They helped me enormously.

This is the first one

https://youtu.be/rmEbgmwMLfY

 

But there are quite a few that takes you from start to finish.

 

Well worth the time in looking at them in order amoungst his other useful videos.

 

H

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Hi Dirk,

the 'rigging' lever is on the righthand side of the OD.

It is connected to the cross shaft.

On the lefthand side of the OD the cross shaft is connected t the arm that is operated by the solenoid.

 

Roger

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It is currently still not operational. I was hoping the operating valve clean would have solved it, but perhaps there is something in the unit that keeps blocking the hole.

I have had a look at those videos and they have really been useful in helping me understand how the overdrive works!

 

I am going to take the gearbox to a general gearbox specialist where I told them I'll keep an eye.

They have the tools and the time to go through everything and check it as my current mechanic does not seem able to spend the solid time required to re-strip the overdrive unit, clean it out and reassemble with care.

I do not have the tools or space to do so myself or I would have.

 

If the timing wasn't so bad I would have stripped the car for restoration while this is going on, but I have already lost 6 months of use of my TR for nothing and I need to restore my Porsche first.

 

Dirk

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At least I know that my gearbox is also matching my car, so it is a complete matching numbers car.

TS 5379-O with TS 5822E and TS 5827 gearbox.

 

Out of curiosity though, I am not sure if the Overdrive unit is the opriginal TR2 one, or a replacement from a Vanguard? This question is based on something I read about a cover plate on the solenoid side.

Anyone know more about this?

 

Dirk

post-14709-0-77029600-1531259465_thumb.jpg

post-14709-0-80223700-1531259468_thumb.jpg

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Check the cover on the left (the one with the solenoid) for misalignment : the accumulator spring(s) usually cause this cover to not be positionned correctly when bolted, thus the operating shaft do not move as it should.

 

Easy to check : remove the solenoid, you should be able to move the little lever very (very !) easily with 2 fingers.

 

The OD engage with the power of the solenoid, but desengage very slowly when the cover (and its o'ring) are not aligned.

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You should study the Greasy Hands guides on overdrives.

 

https://vintagetriumphregister.org/maintain/TransRebuild/TranIntro.pdf

 

My bet is on the operating valve. The setting of these is critical. The method with a drill-bit though the operating lever worked when new maybe but is flaky when wear is present.

 

Do it with a dial-indicator or a depth-micrometer.

Edited by AlanT
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  • 4 weeks later...

Hi again.

After some further checking (and I realise this might be stupid, but I don't know better), I was wondering about the oil the guy is using.

In any case I am taking my car back and will drive it without an O/D for the time being, but it is bothering me greatly.

I have checked the very significant amount of older posts about the oil, but none answers my specific query.

 

Everything I check says the TR2 gearbox should use SAE40 oil (warmer here in SA, so not SAE30 as in the UK), but the guy is using EP90 (which surely is a heavy diff oil?).

The existing posts indicate that EP90 should be ok when warm, but a little sluggish when cold.

I am really struggling to understand the viscosity tables to be able to compare how big the difference is between these oils in terms of flow rate at temperature.

 

So in a nutshell. Is EP90 so much thicker thatn SAE40 that it would cause a significantly slower release of the overdrive due to the oil struggling to drain through the operating valve hole?

The other posts seem to indicate this could be so when cold and I know the OD gets very hot indeed after some time.

 

I see oil viscosity charts have a mm(squared) / second rate, but this seems to be higher for higher values, where I would expect higher for lower values, assuming this means flow rate?

Can anyone explain?

 

Dirk

Edited by irrational
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Dirk

I use EP 80/90 GL4 in my od ( a type) and gearbox and diff as did the previous owner of over 40 years.

So dont worry.

H

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Thanks for all the info.

I will archive it for now.

I am tired not enjoying my TR, so I will drive it without OD for a few months before I start on a body restoration.

At that time I will spend effort on the OD again and try to find someone where I can assist or even do it myself.

I already missed several great summer runs due to this and I am not planning on missing out more. It has made me quite upset for too long.

 

Dirk

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Thanks for all the info.

I will archive it for now.

I am tired not enjoying my TR, so I will drive it without OD for a few months before I start on a body restoration.

At that time I will spend effort on the OD again and try to find someone where I can assist or even do it myself.

I already missed several great summer runs due to this and I am not planning on missing out more. It has made me quite upset for too long.

 

Dirk

 

Good plan, Dirk. DRIVE IT!!!

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There is a simple answer which worked for me. I had a number of "specialists" work on my overdrive including one in Warwickshire who told me that I had dropped the gearbox/overdrive unit and that was why it did not work.

 

My answer is to send the whole unit, gearbox & overdrive to Overdrive Repair Services, Sheffield, and ask for a full overhaul. When they have completed the work it is run on a test rig and properly adjusted. Mine has been working faultlessly for over 6 years after years of problems. ORS have years of experience, use the right quality seals and have a test bed.

 

In your situation I would ask them to overhaul the gearbox as well while it is out of the car. They do not take long to do it and removing the whole gearbox/overdrive in winter is a long time in the cold garage.

 

This was my answer to a very long standing problem. :)

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