I have recently restored a 1965 S-type. As part of the restoration, I rebuilt the original gearbox and overdrive, with all new bearings, synchro rings and seals throughout. There was very littleobvious wear on the Overdrive clutches, so I didn't change them.
Since then, I have done 500 miles, with the engine (Also completely rebuilt) now nicely run-in, with the gearbox and overdrive operating faultlessly.
However, the Overdrive has just started misbehaving - If I engage the overdrive, the overdrive engages OK, but if I try to accelerate at all whilst engage, the overdrive disengages, and then re-engages after releasing the throttle. (Much like the kick-down on my XK8, but not quite how it's supposed to work!)
To Investigate the problem, I've so far tried the following:
1. Gearbox oil level - which is fine!
2. Solenoid release arm adjustment - which is set perfectly
3. Solenoid electrical circuit - works perfectly, taking ~20Amps when actuating, and ~1A on hold, and a nice strong "pull" on the solenoid arm.
4. Cleaning the pump non-return valve (Spotless oil, and no sign of any dirt)
None of these have made any difference, so I'm worried that it may be something more serious. I don't think it can be the clutches worn out sine I've only done 500 miles since they looked fine. I'm currently suspecting one of the following problems:
1. Dodgy solenoid (Unlikely since It all seems to operate perfectly when watching it with the car up on my ramp)
2. Damaged seals in the oil pump or actuator pistons - I changed all the O-rings when rebuilding it, but could have damaged one whilst assembling it. This could cause a lack of oil pressure, so that there isn't sufficient pressure to hold the thrust plate against the clutch to hold it engaged under load.
3. Worn oil pump
I'm also a little surprised that this fault has developed suddenly after 500 miles of perfect operation.
So I'm hoping there's an expert on these Overdrives out there who can help or offer some advice!
Also, does anybody know if it's possible to measure the overdrive oil pressure? Or what the expected oil pressures should be?
Thanks!
Alan
Overdrive problems
Moderators:Aceman, ecosselynx
Hello Alan,
the oil pressure figure I quote is from my Triumph workshop manual, and is 330 to 350psi. You need to make up or buy an adapter to connect the pressure gauge which is fitted to the top of the casing. Above the operating spindle a cap is screwed into the casing, this is removed and the pressure gauge fitted. If the pressure is low, the non return valve may need re-seating. I would suggest a workshop manual to hand as it will give a better understanding of how the various components are fitted.
There is also a highlighted statement in the workshop manual about not using any anti friction additives with an overdrive.
Alec
the oil pressure figure I quote is from my Triumph workshop manual, and is 330 to 350psi. You need to make up or buy an adapter to connect the pressure gauge which is fitted to the top of the casing. Above the operating spindle a cap is screwed into the casing, this is removed and the pressure gauge fitted. If the pressure is low, the non return valve may need re-seating. I would suggest a workshop manual to hand as it will give a better understanding of how the various components are fitted.
There is also a highlighted statement in the workshop manual about not using any anti friction additives with an overdrive.
Alec
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AlanCoombs
- Posts:10
- Joined:Sun Jun 01, 2008 8:40 am
Hello Alan,
the oil pressure figure I quote is from my Triumph workshop manual, and is 330 to 350psi. You need to make up or buy an adapter to connect the pressure gauge which is fitted to the top of the casing. Above the operating spindle a cap is screwed into the casing, this is removed and the pressure gauge fitted. If the pressure is low, the non return valve may need re-seating. I would suggest a workshop manual to hand as it will give a better understanding of how the various components are fitted.
There is also a highlighted statement in the workshop manual about not using any anti friction additives with an overdrive.
Alec
Thanks! I've done a little more research on this too. My overdrive is the later type as fitted to the all-synchro gearboxes. The workshop manual I have doesn't give any details for the pressure measurement on this overdrive, but does state that the later ones should be treated exactly as the earlier ones, except for the details of dismantling and assembly.
For the earlier models, The figures quoted are 420-440psi for 3.4 and 540-560psi for 3.8 litre models.
This is a little confusing as I thought the overdrives were identical between 3.4 and 3.8 litre models - they must have a different pump assembly or pressure relief valve spring fitted! I guess one should bear this in mind if ever trying to source a replacement overdrive unit.
So I'll assume that the later type overdrives (The "A" Type compact unit") should have the same pressure. The workshop manual suggests that this should be measured by connecting a guage to the main operating valve plug - on top of the overdrive for early models, which involves stripping out the carpet and fiberglass cover over the transmission tunnel to get at from the top. However, on the later models, this plug is on the bottom (Much easier to get at, but there's no mention of measuring the pressure in the manual for later models).
I've now purchased a hydraulic pressure guage (up to 1000psi), and I'll have a go at measuring the pressure when it arrives. I'll make up an adapter from an old hydraulic brake hose and a bit of flared copper pipe.
My best theory is still that there's insufficient hydraulic pressure to hold the outer annulus clutch in place when under load (possibly due to a leaking internal seal) - as this is the only thing that I can think of that explains all the symptoms. It doesn't appear to "slip" when engaged, as I'd expect if the clutches themselves were worn, just disengages completely under load. Hopefully(!) the oil pressure measurement will confirm this.
I took the non-return valve seat, ball and spring out to examine - couldn't see anything wrong there, so cleaned and replaced, but made no difference.
I'm using standard EP90 gear oil in the box - which itself is a little confusing; the workshop manual reccomends 20/30 engine oil for the earlier units, and EP90 gear oil for the later ones! - Any Idea what's best to use?
Thanks again,
Alan
the oil pressure figure I quote is from my Triumph workshop manual, and is 330 to 350psi. You need to make up or buy an adapter to connect the pressure gauge which is fitted to the top of the casing. Above the operating spindle a cap is screwed into the casing, this is removed and the pressure gauge fitted. If the pressure is low, the non return valve may need re-seating. I would suggest a workshop manual to hand as it will give a better understanding of how the various components are fitted.
There is also a highlighted statement in the workshop manual about not using any anti friction additives with an overdrive.
Alec
Thanks! I've done a little more research on this too. My overdrive is the later type as fitted to the all-synchro gearboxes. The workshop manual I have doesn't give any details for the pressure measurement on this overdrive, but does state that the later ones should be treated exactly as the earlier ones, except for the details of dismantling and assembly.
For the earlier models, The figures quoted are 420-440psi for 3.4 and 540-560psi for 3.8 litre models.
This is a little confusing as I thought the overdrives were identical between 3.4 and 3.8 litre models - they must have a different pump assembly or pressure relief valve spring fitted! I guess one should bear this in mind if ever trying to source a replacement overdrive unit.
So I'll assume that the later type overdrives (The "A" Type compact unit") should have the same pressure. The workshop manual suggests that this should be measured by connecting a guage to the main operating valve plug - on top of the overdrive for early models, which involves stripping out the carpet and fiberglass cover over the transmission tunnel to get at from the top. However, on the later models, this plug is on the bottom (Much easier to get at, but there's no mention of measuring the pressure in the manual for later models).
I've now purchased a hydraulic pressure guage (up to 1000psi), and I'll have a go at measuring the pressure when it arrives. I'll make up an adapter from an old hydraulic brake hose and a bit of flared copper pipe.
My best theory is still that there's insufficient hydraulic pressure to hold the outer annulus clutch in place when under load (possibly due to a leaking internal seal) - as this is the only thing that I can think of that explains all the symptoms. It doesn't appear to "slip" when engaged, as I'd expect if the clutches themselves were worn, just disengages completely under load. Hopefully(!) the oil pressure measurement will confirm this.
I took the non-return valve seat, ball and spring out to examine - couldn't see anything wrong there, so cleaned and replaced, but made no difference.
I'm using standard EP90 gear oil in the box - which itself is a little confusing; the workshop manual reccomends 20/30 engine oil for the earlier units, and EP90 gear oil for the later ones! - Any Idea what's best to use?
Thanks again,
Alan
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AlanCoombs
- Posts:10
- Joined:Sun Jun 01, 2008 8:40 am
Well, my oil pressure guage has arrived, I've made up an adapter and measured the pressure. And the answer is..... 380psi.
For the early 3.8 models, I was expecting around 550psi (or 430psi for a 3.4), but my manual doesn't say what to expect for the later ones - so I don't know if 380psi is good or bad. (Unless the overdrive should be the same as in Alec's aforementioned triumph manual, in which case 380 would be good!)
There seems to be no discernable drop in the measured oil pressure when the overdrive is actuated, and the pressure is held up for a good long while after stopping the engine (Due to the accumulator spring), so I don't think there can be any leaks in the pressure system serious enough to make the overdrive as bad as it currently is.
So I think I'm resigned to having to take it all apart again! Does anybody know if it's possible to separate the overdrive from the gearbox with the gearbox still in the car? It looks as though it ought to be possible if I drop the rear engine mount and rear stabilizer bush, but there's probably something subtle preventing it that I haven't thought of!
For the early 3.8 models, I was expecting around 550psi (or 430psi for a 3.4), but my manual doesn't say what to expect for the later ones - so I don't know if 380psi is good or bad. (Unless the overdrive should be the same as in Alec's aforementioned triumph manual, in which case 380 would be good!)
There seems to be no discernable drop in the measured oil pressure when the overdrive is actuated, and the pressure is held up for a good long while after stopping the engine (Due to the accumulator spring), so I don't think there can be any leaks in the pressure system serious enough to make the overdrive as bad as it currently is.
So I think I'm resigned to having to take it all apart again! Does anybody know if it's possible to separate the overdrive from the gearbox with the gearbox still in the car? It looks as though it ought to be possible if I drop the rear engine mount and rear stabilizer bush, but there's probably something subtle preventing it that I haven't thought of!
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AlanCoombs
- Posts:10
- Joined:Sun Jun 01, 2008 8:40 am
For those following along at home, here's the latest in the saga:
It turns out that it is possible to separate the overdrive from the gearbox whilst still in the car - the nuts at the top are a bit tricky to get at, but it still took less than an hour to get the overdrive out of the car and onto the bench! Getting it back on might be a bit more tricky since lining up the splines might be a bit awkward without easy access to the 1st motion shaft to help align them.
I've stripped down he overdrive, and found nothing serious wrong. There was quite a bit of sludge at the bottom of the unit which seems to consist mostly of old gasket paste. This must have come from the last time I put it together - I'll make sure I don't use any gasket sealant when I reassemble it! It is possible that some of this sludge has bunged up the oilways, but it didn't seem too bad - I've cleaned it all out thoroughly now.
There was also some fairly deep scratches on the sides of the accumulator piston - which I must have missed last time I assembled it, or it's happened within the last 500 miles! I'll get a new piston and rings, and a new seals set for it and put it all back together. I'm tempted to replace the clutch assembly too just to be sure, but I can't see anything wrong with the clutch linings. There are also a couple of scratches on the accumulator cylinder bore, but I'm not sure if it's possible to replace this without machining out the only lining and pressing in a new steel liner.
However, whilst It was all apart, I think I've got to the bottom of another gearbox issue I've been having - the gearbox has been making a rattling noise whilst idling in neutral - which sounds much like the layshaft bearings - dispite me having changed the layshaft and all the needle roller bearings. The reverse idler (Which is in constant mesh with the layshaft, so rotates continuously) had considerable (about 1/4") axial play - which turned out to be a worn setscrew in the actuating lever pivot - It didn't look worn, but replacing the setscrew has removed almost all of the axial movement (It's easy to change this setscrew and examine the reverse idler with the gearbox in the car, but the overdrive removed) - Hopefully it'll now also be quieter when I get it all back together.
I've got some interesting photos of all of this, but I can't work out how to attach them to this forum!
Alan
It turns out that it is possible to separate the overdrive from the gearbox whilst still in the car - the nuts at the top are a bit tricky to get at, but it still took less than an hour to get the overdrive out of the car and onto the bench! Getting it back on might be a bit more tricky since lining up the splines might be a bit awkward without easy access to the 1st motion shaft to help align them.
I've stripped down he overdrive, and found nothing serious wrong. There was quite a bit of sludge at the bottom of the unit which seems to consist mostly of old gasket paste. This must have come from the last time I put it together - I'll make sure I don't use any gasket sealant when I reassemble it! It is possible that some of this sludge has bunged up the oilways, but it didn't seem too bad - I've cleaned it all out thoroughly now.
There was also some fairly deep scratches on the sides of the accumulator piston - which I must have missed last time I assembled it, or it's happened within the last 500 miles! I'll get a new piston and rings, and a new seals set for it and put it all back together. I'm tempted to replace the clutch assembly too just to be sure, but I can't see anything wrong with the clutch linings. There are also a couple of scratches on the accumulator cylinder bore, but I'm not sure if it's possible to replace this without machining out the only lining and pressing in a new steel liner.
However, whilst It was all apart, I think I've got to the bottom of another gearbox issue I've been having - the gearbox has been making a rattling noise whilst idling in neutral - which sounds much like the layshaft bearings - dispite me having changed the layshaft and all the needle roller bearings. The reverse idler (Which is in constant mesh with the layshaft, so rotates continuously) had considerable (about 1/4") axial play - which turned out to be a worn setscrew in the actuating lever pivot - It didn't look worn, but replacing the setscrew has removed almost all of the axial movement (It's easy to change this setscrew and examine the reverse idler with the gearbox in the car, but the overdrive removed) - Hopefully it'll now also be quieter when I get it all back together.
I've got some interesting photos of all of this, but I can't work out how to attach them to this forum!
Alan
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AlanCoombs
- Posts:10
- Joined:Sun Jun 01, 2008 8:40 am
It works!
It transpires that it is possible to refit the overdrive with the engine and gearbox still in the car!
I rebuilt the overdrive (Again!), this time with new seals, accumulator piston+rings, cluch assembly and non-return valve. I also honed the bore of the accumulator cylinder to clean off some of the scratches.
I spoke to David Twigger at O/D spares in Rugby - who gave me some excellent advice, and furnished me with some very reasonably priced spares - All parts needed came to only around £115 including VAT. Apparantly the hydraulic pressure should be around 480psi - which, fortuitously is exactly the pressure my overdrive now supplies.
The overdrive now engages/disengages almost immediately, making it a real pleasure to use.
Most of the parts I replaced could have been done with the unit in the car - only the cleaning (I stuck the whole front casing/valve assembly in the dishwasher - she hasn't forgiven me yet!
) and the clutch assembly replacement (Probably not actually necessary) actually required the overdrive to be out of the car. But I would recommend my method of separating the overdrive with the gearbox in the car; the combined effort probably took no longer than a day's work to remove, rebuild and refit, so long as you are able to get the car high enough off the ground to work underneath it.
Thanks for the help!
I rebuilt the overdrive (Again!), this time with new seals, accumulator piston+rings, cluch assembly and non-return valve. I also honed the bore of the accumulator cylinder to clean off some of the scratches.
I spoke to David Twigger at O/D spares in Rugby - who gave me some excellent advice, and furnished me with some very reasonably priced spares - All parts needed came to only around £115 including VAT. Apparantly the hydraulic pressure should be around 480psi - which, fortuitously is exactly the pressure my overdrive now supplies.
The overdrive now engages/disengages almost immediately, making it a real pleasure to use.
Most of the parts I replaced could have been done with the unit in the car - only the cleaning (I stuck the whole front casing/valve assembly in the dishwasher - she hasn't forgiven me yet!
) and the clutch assembly replacement (Probably not actually necessary) actually required the overdrive to be out of the car. But I would recommend my method of separating the overdrive with the gearbox in the car; the combined effort probably took no longer than a day's work to remove, rebuild and refit, so long as you are able to get the car high enough off the ground to work underneath it.Thanks for the help!
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DannyJagTremelo
- Posts:1
- Joined:Sat May 19, 2018 9:36 am
Re: Overdrive problems
Dear Mr Coombs
Reading your post on separating the overdrive unit from the gearbox in place, you mentioned that you had pictures of this process.
Do you still have them and would it be possible to take a look at them please?
Beste regards from Belgium
Danny Deraymaeker
XK150 FHC 1958
Reading your post on separating the overdrive unit from the gearbox in place, you mentioned that you had pictures of this process.
Do you still have them and would it be possible to take a look at them please?
Beste regards from Belgium
Danny Deraymaeker
XK150 FHC 1958
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