Intermittent clutch after replacement - O/D Rebuild (Combined Thread)

[Sigi_H]

News

I've connected the hydraulic pressure gauge now.

After installation of the pressure measuring device the following became apparent: All measured with gear oil 75W90!
The pressure pulsates strongly. If the OD is cold, the pressure rises to approx. 30 bar. From approx. At15 - 20 bar the OD shifts into OD mode. If the OD is turned off, the pressure is 0 bar, the pointer does not move at all.

Frequent switching on and off shows the change between 0 and 30 bar and the OD shifts as expected. As soon as the OD has run approx. 35 km, it can be switched off, but not switched on again. The pressure then only rises to approx. 10 bar even if it was 30 or 25 bar before, which is no longer sufficient for shifting. The pump still delivers a little, but cannot generate the necessary pressure.
The next step will be to drive a longer distance and switch back to ATF. If the OD is not switched off manually at all, it will remain in OD mode permanently.

As mentioned above, I put a catch tank on and still there is nothing in it. Oil is still enough to shift. In my eyes this means, that the breather was a problem. No problem with the NTN bearing in the connection plate to the LT230.

Edited December 10, 2019 by Sigi_H

[Bill pearson]

So, does this mean the oil is too thin when hot? Or (more likely) is there a clearance/leak that only becomes a problem when hot? Are all the pump seals in place, etc?

[Sigi_H]

It maybe to thin, but I am not sure, whether there is a possible bypass. Thats why I use the 75W90 instead of ATF. A reason can be a worn pump piston or the ball valve in the pump.

As far, as I remember, there are no (kind of) piston rings in the pump, even though the piston has groves. It is just a piston in a cylinder. See here

Edited December 15, 2019 by Sigi_H

[Sigi_H]

hmmm ... I get the notification email, but when I click the link I land here. But here is not the post, I got the notification from.

The post was: "Pistons have single O ring rubber seal on each.  " from western

Yes, the actuating pistons. But not the piston of the pump like in the picture shown

[western]

I deleted as it was about the wrong piston, 

[Sigi_H]

Ok, I thought it could have been a problem with splitting the threads.

[Troll Hunter]

One aspect of the springs that does not appear to have been examined, although Snagger mentioned it in his 18th November post, is the spring metallurgy.  One test that might be worth doing is to test that all springs in a given set have the same performance.

To do this get a length of ~1/4" rod, weld a large washer on one end, thread the springs on, each separated by a flat washer.  Adjust the rod length to accommodate as many springs as you want to test, add 1/2 inch, and thread the last two inches or so of the rod.  With a washer under a nut on the end of the rod gradually compress the springs by tightening the nut.  All springs in any given set should remain equal in length as they are compressed.  The washers between springs aid in accurate measurement.

If there is one spring in a set that is out of balance with the other springs it might be causing uneven pressure on the clutch cone in the at rest situation.  Also, with multiple sets of springs on the rod you will also see if nominally identical springs do, in fact, have identical properties.

OK, I'm clutching at straws, but it seems as if everything else has been tried.

Mike

[Sigi_H]

But the spring rate cannot be calculated. If they behave identically, they appear to be good, but can still be too weak.

[lo-fi]

The problem with the weak spring theory is it should give reasonably consistent slipping. This is absolutely not the case. 

Edited December 19, 2019 by lo-fi

[western]

Paid a visit to Vulcam Bomber of this parish, after a good look at my overdrive, the only 2 things we could come up with are the friction material on the cone is a different material to the original & maybe reacting with the ATF FLUID & we found some marks in the piston Chambers as one piston was much harder to extract than its mate. 

A couple of pictures. 

[reb78]

The piston cylinder doesnt look great, but it did it with both rear sections (your old and the new to you one?) so I think that would rule that out??

The OD that you have has slipped on three clutch cones - the original and two new ones now? So pretty sure that would rule that out too? 

What did David think about the springs? Can you test them somehow?

[vulcan bomber]

When we pulled the pistons out, 1 took significantly more effort to pull out. Bores are damaged, pistons are damaged. The also wouldn't go back together particularly easy. I concluded with Ralph's description of the failure that something had got stuck. And that the pistons or the carrier of the brake material were to blame being the only moving parts.

 

Springs imho are fine, and I dont think shimming them is wise, it will take more effort to shift with the hydraulics to engage the overdrive, or if you like the grip will be significantly less.

 

Moving forwards, I'm going to show this case to my friend Shaun who does hydraulics for a living (also got him a lathe turret to rebuild) and see if I can come up with a repair for Ralph. The OD case doesn't have space for me to open up the bores and sleeve them, changing the size of the pistons will affect the working pressure that they operate under.

 

Richard, if I can bodge something up, would you be willing to monitor the pressure your OD works at. As far as we are aware, your the only person around with a reliable OD at the minute. 

 

 

[reb78]

It is odd though as it slipped with Ralphs back end and the 'new' ones back end, so they may be faulty, but its hard to imagine both back ends are faulty with the same fault? One of my spare ODs was also reported to be slipping - might be worth a look at that to see any commonalities.

I can try - the bottom bolt (that looks like it should be a sump plug) is for monitoring pressures. Whatever we do mine needs to be useable for long journeys though! If the bulkhead gets through the MOT this year it will have another 24k miles ahead of it in 2020! (maybe a week of rest for a chassis and bulkhead swap....)

[reb78]

Can the damage in the bores be filled with a TIG and then bored out to the same size?

[vulcan bomber]

4 minutes ago, reb78 said:

Can the damage in the bores be filled with a TIG and then bored out to the same size?

Personally I doubt you'd get it clean enough after this long soaked in oil. It will also provide almost impossible for me to find the middle of the bore after welding it up. 

 

I had.noticed the bolt for monitoring pressures. I will certainly use that, but whether I can get something cheap rigged up for you to comfortably do a Cornwall and return trip with is a challenge. I'll see what I can come up with. 

[FridgeFreezer]

Can the thing be bored out & sleeved somehow?

Surprised Ralph hasn't set fire to the thing out of frustration yet!

[Gazzar]

Kind of like a caliper rebore? Stainless steel sleeve.

[western]

49 minutes ago, FridgeFreezer said:

Can the thing be bored out & sleeved somehow?

Surprised Ralph hasn't set fire to the thing out of frustration yet!

It's getting close to becoming a work bench ornament. But it would be great if we can get it working properly. 

 

As to boring the cylinders out on the inner faces the existing material is quite thin, so would probably break through. 

[vulcan bomber]

1 hour ago, Gazzar said:

Kind of like a caliper rebore? Stainless steel sleeve.

Cast Iron or Bronze for a sleeve, stainless steel will Gall and make a hash of the seals. 

[soutie]

I work for a company that makes and repairs and overhauls aircraft propellers. For our aluminum hubs bores that are worn we have them bronze sprayed and then machined. Apparently the repair is better wearing than the original aluminum. I am not sure if this is economical for the OD unit, but it might be an idea.  

[western]

been a long time but bit of a update on my GKN Ovedrive, it's with Vulcan Bomber, & he has managed to clean up the 2 piston bores

still got a untouched area the darker part in this picture but the bores did clean up well.

& next step is a light hone & manufacture some new piston & sort more robust piston seals.

really missing using this unit, we are hoping it becomes much more reliable. if the work on this one [my original] is successful then the 2nd unit will be reworked & ready to use.

Edited December 5, 2021 by western
dead photo links removed

[robperrie]

ive been also running a gkn for the last over 8 years, so I'm hitting about 100k so far, had a few little issues, but totally stripped down rebuilt, found a broken thrush bearing,. and now its not working, got stuck on , then stripped again, changed the spring position and now wont engage, would the speed sensor cause that ..??

[vulcan bomber]

You can rule all the electronics out by wiring the solenoid to a normal switch.

[western]

Speed sensor only operates at 30mph to tell the control box to disengage the Overdrive if the vehicle is below 30 or above 30, just connect a on/off switch direct to solenoid as noted above

[reb78]

And you can test the solenoid easily off the vehicle by putting 12v across the terminals from a battery. You should see the plunger move.