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

[western]

OD let me down big time coming home today, just wouldn't grip disengaged, so drove home most of the way with it engaged, once home & after a brew, OD is now fully off the 110 & back on the garage bench, the new circular filter is covered in friction material from the cone brake as its been slipping like mad, & the fluid was a transparent black, its only done just under 1000 miles since it had new seals, springs, brake one, I don't think this unit is going to be refitted to my 110, I just do not trust it anymore, Not going to bother changing the springs & refitting it, I just don't have the time to be doing that & need my 110 fully on the road, its my only vehicle, 

 

[Anderzander]

Really sorry to hear that Ralph 😒

Is it worth considering a 1.2 transfer box?  Do you tow? 

[western]

I do tow occasionally off tarmac during car rallies, not overly bothered about swapping the transfer box, once Xmas& new year is over & my piggyback is a bit healthier then I might look at the Roamer drive unit instead, at least that can't slip when not engaged. 

[Bill pearson]

Evening Gents,

having studied the design and schematics of these and looked at many of the issues people face, I’ve come to the following conclusions:

- Mega piece of kit.

- do seem to cause a lot of issues, especially on the Land Rover installation. I’ve had some of these in other classics and not had any issues before.

So, first an apology for teaching grandma to suck eggs....

The first thing to rule out with any issue is electrics. Assuming that is ok then we have to move on to the oil system. Regarding the description of the issues above (disengaged skipping):

- is the unit making pressure when in the “off” position?

- this could be caused by incorrect solenoid operation, incorrect seal fitment to the solenoid.

- some part of the “bypass” path for the oil being incorrectly assembled (there look to be some channels that have to line up with holes, etc in the previous pages of this thread)

- I think there is a good reason overdrive repairs has a pressure gauge in its “j type” parts section. Clearly, testing the unit’s off pressure is a useful thing to do.

If it isn’t this, then, yes, it is probably the springs. As I understand it, when the unit is assembled, these springs should hold the cone off the brake ring making it hard to assemble. If not, where does the preload for the “off” position come from? 

I think the idea of some spacer shims is good, but these will also shorten the distance the springs can be compressed (overdrive engaged), so be careful. Longer, springs that don’t have significantly longer compressed lengths might be a better solution.

one idea to test the springs are working might be to try to see what torque the unit can take applied to the input shaft with the unit off the car and the body/output shaft prevented from moving. Not the easiest test, but fairly conclusive of what should be happening when the overdrive is disengaged.

Just my thoughts. Hope no one takes any offence.

BP

 

 

[Sigi_H]

It's a good aspect to have a look at the "off" pressure!

To my GKN: I am really surprised! Last action was to take gear oil instead of ATF, since I found out, that it can operate for a longer distance with higher viscosity. The result was it engaged perfectly, but didn't disengage any longer. That was last weekend. During this week I used it on short distance and was wondering ... it worked perfectly. Engaging and disengaging.

What I did too last weekend was to put the breather in a catch tank made from a PET bottle to see if oil is thrown out there, since I always had low oil levels. Everything was dry including the catch tank. Nothing in it and the OD still works.

What changed was, that I had the breather on a suction line. This line is linked to the airbox. This means that always slight vacuum is applied to all the gearboxes. I separated the OD breather into its own catch tank and since then it seems to work. Sorry, I can't see a logical connection, but it seems so.

Oil pressure equipment makes progress, but I don't have a banjo bolt for an eye fitting with an imperial thread. The screw at the bottom beside the plate is 16 G 3/8"

 

[western]

Yesterday my 110 wouldn't move along my drive in 1st or reverse gear, so no drive at all through the overdrive, once it was removed & normal transfer gear was refitted, 110 drove normally, the circular filter & the sump filter was/is covered in material from the friction material of the brake cone.

[Snagger]

That suggests insufficient spring pressure clamping the brake components together.

[western]

I might rebuild it & give it another chance, but it won't be this side of Xmas break,  the springs were new & side by side with the springs from my original unit look exactly the same in all respects, it worked OK engaged s that was the only way I could make the 110 move. 

[Snagger]

I admire your perseverance in how many goes you’ve has at this.  But the wearing of the brake cone says the springs aren’t pushing the brake parts together well enough, and that’s your slip.  Whether it’s the spring rate, spring length, or dimensional issues with the parts the springs press against is the question.

[western]

Its a bit weird seeing as the spec's noted by Sigi are what GKN/Devon4x4 supply , the new springs are exactly the same length & diameter as the originals from my 1st unit & the 2nd unit that V8Freak/Reb78 replaced.  I'll have another go at it after Xmas/new year & use the brake cone bearing part from my original unit, if it doesn't work after all that I'll probably scrap them so nobody else has the same/similar fault to deal with.

[Sigi_H]

1 hour ago, western said:

Its a bit weird seeing as the spec's noted by Sigi are what GKN/Devon4x4 supply , the new springs are exactly the same length & diameter as the originals from my 1st unit & the 2nd unit that V8Freak/Red78 replaced.  I'llhave another go at it after Xmas/new year & use the brake cone bearing part from my original unit, if it doesn't work after all that I'll probably scrap them so nobody else has the same/similar fault to deal with.

This is why I recommend one or two washers under the spring, because this will not increase the springrate, but the force applied to the cone clutch.

I had a look at the sketches

In the lower part of the sketches you can see, that the cone clutch bypasses the planetary gear, it is in direct drive mode. That means, that friction must be between cone clutch and annular carrier. If the friction surface of the annular carrier is worn, each of the procedures regarding the spring must fail. This could only get better, when the inner clutch coating is thicker or the annular carrier is new.

[Sigi_H]

another idea:

whats about the distance between the one way roller clutch and the pinion carrier?

If it is to big, you could have the effect, that the cone clutch can't reach the annular carrier so easy. If its only 1 mm thicker, the spring will lose force, but gears are still in mesh. Just an idea.

[western]

I have this thread in my watched content list, so can refer back to it later, 

[landroversforever]

Is there a way of stopping it building any hydraulic pressure at all? Sorry if you’ve done this and I’ve missed it!!  If you can stop it making oil pressure at all that would mean that it is then definitely down to something wrong in the cone/spring department. 

[western]

It doesn't build pressure in the disengaged position, I disconnected the solenoid in a previous post so I can't engage & it still slipped in the disengaged position, only way to totally stop any pressure is to leave out the internal fluid pump & relief valve, which would mean yet another strip down to remove it & then another strip to refit the pump & relief valve. 

[Sigi_H]

4 minutes ago, western said:

It doesn't build pressure in the disengaged position, I disconnected the solenoid in a previous post so I can't engage & it still slipped in the disengaged position, only way to totally stop any pressure is to leave out the internal fluid pump & relief valve, which would mean yet another strip down to remove it & then another strip to refit the pump & relief valve. 

Normally it should build around 30 bar. Pump is running always, but if the solenoid is not engaged, the oil will go through a bypass back into the sump. If this bypass is blocked a little bit, there will be more pressure than almost 0 bar (lets say 5) and make the clutch slipping in disengaged mode, because the springs can't press the clutch to the cone as much as it is possible.

[western]

No blockages as I made sure the rear casing & all the fluid ways were totally clean & clear, the solenoid, pump, relief valve all got new seals & both filters were spotless clean, the big circular filter was brand new. So I think it can only be down to weak springs even though they are new. 

[Snagger]

Metallurgy is critical to spring rate, not just the physical dimensions like wire diameter, pitch and overall size.  New pattern springs may share identical dimensions, but if the spring steel is too much mild steel, then they’ll be weak.  That’s why so many Series owners have problems with parabolics.

[Sigi_H]

I had another idea. I think, that geometry in the OD is given and good. Your problem points to worn clutch liner inside the clutch. It possibly slips, because the bars at the hydraulic cylinders  and the studs inside the springs restrict the way, the clutch can travel. Due to the missing liner it starts slipping.

That means in my eyes, if you put a washer between the bars and the studs (allowing the studs to travel more), the clutch will get contact again. The work can be done with mounted OD and shows definitely whether the clutch is gone, due to all that slipping.
This is a test, to get information, what's really wrong. If it still slips, its not the clutch.

[western]

The clutch friction material was brand new, so there wasn't any missing off the cone. 

I have removed the complet unit off the vehicle, & refitted the standard transfer box parts, my 110 is my only vehicle so I need to have it in use everyday. 

[Sigi_H]

if you got time, lets see pictures of the removed one

[western]

I can add some photos later, not much to see though as I've almost stripped it fully down, I won't be doing anything else to it this side of Xmas/new year. 

[Bill pearson]

The idea to check the disengaged pressure is a good one. Almost worth running it with the engagement pistons removed. 
anyway, completely understand you’ve had enough of it for now....

[smallfry]

A long time ago I had a Sunbeam Rapier series 4, which had a Laycock overdrive. That had the problem that the car would run in the low ratio (direct) after starting up, but after engaging O/D, would not disengage until the car had been stopped and left for a while, and then after restarting would repeat the process.

Turned out to be a tiny piece of friction material stuck in the dashpot/relief valve, not allowing the oil pressure to release.

Probably not your problem, but worth a look ?

I do remember when reassembling, winding down the case against the spring pressure

[western]

Quote

I do remember when reassembling, winding down the case against the spring pressure

Similar thing on these GKN units, once assembled then the outer body bolts are tightened the body compresses the springs at least tha's what it feels like