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MG Midget and Sprite Technical - Type9 woesery again guys Mk2

Sorry chaps this hasnt quite gone away.

I have the gearbox ready to go in the car but there is a drawback.

I have decided to fit a new concentric unit but I cannot locate one like my original Ford unit but have managed to find one with lower nose height so now I seriously need some GUYdance.

when it is inside the bellhousing does the nose of the cylinder have to be pushed in by the clutch fingers or does the nose of the slave bearing get pushed out further by hydraulickery to cause the clutch to loosen it's grip?

I have pictures explaining what I see but they are far to huge to show here, help how do I make them small enough to display?
Bill sdgpM

Phew got it in Paint resize 30%

The middle one is my original but I am reluctant to refit that after the gearbox issue is fixed.

The others are significantly lower inside the box, might I be better served fitting the new one, on the right but adding spacers behind the fitting points?

Bill sdgpM

This poor old box had a hammering before it ever came into my possession, but a Quik-Steel mix will soon fix that

Bill sdgpM

The clutch fingers have enough spring force behind them to overcome the coil spring/bellows in the slave, and push clutch fluid back up the line.

Only when you add the force of your foot, will the bearing press hard enough to disengage the clutch.

I like that type because there is no gap between the bearing and fingers to take up each time you press the clutch pedal.

On the other hand, the bearing is spinning all the time. But that too has an advantage, in that in my type without spring force, my bearing is like aircraft wheels touching down on the tarmac. Over time, it creates a bit of wear on my fingers.

But if your 'nose' is too low, you made need a spacer behind the slave, in case there isn't enough reach at full depression of your pedal.


anamnesis

Thanks Anam, adding spacers seems like the next thing to do before I stick in the new clutch plate and close it all up then.

So you think it best to pack out the new cylinder so its location depth is a bit like the one coming out, makes sense of course.
Bill sdgpM

I would think so. If the nose is too far away, too low, you could find the clutch won't disengage sufficiently for gear changes. Measure from the base of your original.



anamnesis

Hi Bill,
When I was looking to do the conversion SAAB and Ford were both used ISTR.
Burton Power seem to be the specialists for Ford clutch bits / conversions - maybe worth giving them a bell as they list a lot of different spacers / concentrics.

R.
richard b

Bill, When I did mine I machined a mounting block from a solid billet of aluminium. I later found that Burton Power made a series of packers that could be stacked to get the required amount. From memory (not good,!) I did a fair bit of puzzling over the thickness needed for the mount.

The critical thing seems to be the position of the central guide tube, relative to the clutch diaphragm fingers. On mine the external diameter of the guide tube wouldn't fit through between the fingers, so the slave unit needs to be far enough back towards the gearbox that they don't clash. With allowance for the fingers moving rearwards as the driven plate wears.

Against this, I was concerned about the possibility as it seemed to me, that the concentric slave part might move too far forward and if not actually drop off the guide, have insufficient support, twist sideways and jamb. So I opted for a minimum clearance with leeway for future clutch plate wear.

That theorising won't be much help on it's own. Somewhere I will have the dimensions I calculated to satisfy those two opposing risks. I may be able to find them but without knowing if our slave units are the same the packing measurement won't actually help.
GuyW

I do like the constant contact aspect of these concentric clutches. On the face of it, it seems to be a bit like riding the clutch. But the bellows spring is pretty light, just enough to take up unnecessary clearance and keep the bearing and clutch moving together. When considering the massive stop start rotation of a normal clutch release bearing at every clutch action, going from Zero to maybe 6000 rpm and back to Zero again in the split second time it takes you to press the pedal, the stresses on the bearing must be pretty severe.
GuyW

As I said Guy, like aircraft wheels touching down on the tarmac. Over time, it creates a bit of wear on my fingers. But interestingly, fortunately, the bearing shrugs it off.

I bought a new bearing for when I last rebuilt my engine. I assumed after 15 years, a very good 20/30 thousand miles, the bearing would show signs of needing to be replaced. But the original bearing was still nye on perfect. So it's still in use and my new one sits in the box with the new clutch kit I bought, and also didn't need.



anamnesis

Just be aware that the free length you're measuring there doesn't completely determine the height of the unit, one could have more overall stroke than the other. To determine the thickness of packing plate needed the original cylinder needs to be measured in the fully compressed position, they squish up easy, then compare that height to the compressed height of the new shorter one and add spacers/plate to make up the difference -if needed
William Revit

Bill, there's another thing I did, which I think relates to Willy's comment.
I set up a bench test of my slave, connected to the clutch m/c, to see what movement I got at the slave for a single pedal strike. Matching of mis-matched systems I had no idea if the concentric would move far enough, or even overthrow the clutch. So it needed testing. Very much to my surprise it was almost exactly the same travel as the standard MOWOG external slave produced, through the ratio of the 1275 lever arm. That saved a lot of headaches!
GuyW

Burton spacers, concentric mount for the front of the box, and their slav. Set bearing 6mm away from the fingers, go.

Just done that with my k and T9, works perfectly.

Rob Armstrong

Rob
That'd be 6mm with the slave at compressed height
Just added to make sure the message was clear---

willy
William Revit

I may have done mine wrongly then, but its worked just fine for over 20 years.
I didn't set the bearing thrust face with that 6mm gap. The green bellows part has a good long travel, assisted by the light coil spring. What seemed critical to me was that the bearing support 'nose' didn't foul the clutch cover fingers. I did keep that clearance to a minimum (allowing a little margin for future driven plate wear). But maybe this positioning comes to the same thing.

The thrust bearing is in constant light contact with the clutch and spins with the engine speeds. (no tyres on tarmac, Anam)
GuyW

I can post pictures of what burton supply. It's the SAAB type concentic that the 6mm gap refers to.

The Saab type isn't sprung internally.

Guy's type is a sprung bellows, and the bearing face is held sitting against the thrust pad or fingers. Hence as I said, it doesn't have to make an aircraft landing (tyres on tarmac spinning up to speed) each time, as the Saab type does.

But in reality, in use, the Saab type is never pushed back to a 6mm gap. It extends under foot pressure, and retreats/receeds only as far as the clutch pushes it back. It ends up sitting close to, and scuffing the fingers. There is still a bit of a 'lag' and a 'landing', but it's not felt, and produces little wear of consequence.

The initial Saab type 6mm compressed setting gap, is to account for future clutch friction plate wear. As the friction wears, the fingers rise, and push closer to the release bearing.

As you said Guy, your calculations accounted for that on your internally sprung bellows type. Else you'd have had clutch slip by now. You must have done it right it seems to me. So Bill can follow that I reckon.




anamnesis

Back in the day when Guy was making his car concentric and providing me with info and inspiration I first ran with a Saab cylinder in Lara.

A catastrophe caused by loosening mounting bolts made me get the new Ford slave instead.

The green bellows piece is obviously sprung but I'm at a loss with it's operation. Does the hydraulic action push it out further or do I need to compress it against the clutch fingers so the fluid pushes it out towards the stop for it to release the clutch.

This will allow me to decide how much packing, if any, I need to use when I set the concentric in place.
Bill Mohan

Does the hydraulic action push it out further ?

Yes.

The internal spring is no different to the spring pushing the piston out in an external slave.

You were unlucky with the bolts/screws coming loose/out. 20 years so far with my saab type and no issues. Replaced the o- ring seals only a a precaution because they were cheap and because you have to take the engine out to do it. Kept the used as spares.

anamnesis

As with a standard external MOWOG type slave, the piston ( in this case the bearing surface) moves forwards by a distance controlled solely by the amount of fluid pumped by a single press on the clutch pedal. On my Ford type green bellows one the start position of the bearing is in light contact with the clutch fingers, held in that position by the thin coil spring inside the bellows. For some magical or fortunate reason this distance moved from that contact position was correct for my 1275 clutch to fully disengage, without going too far and overthrowing it.

So, the concentric slave thrust bearing movement is sorted by that design. That leaves the issue of the central 'nose' piece that the bearing slides along. This supports the bearing, keeping it concentric to the gearbox input shaft, but it mustn't foul the pressure plate fingers. That is where the Burton Power packing shims come in, stacking them to move the fixed body and nose of the slave forwards towards the clutch, without actually contacting it.
GuyW

Press the pedal and hydraulic action obviously moves the bearing surface forwards and the clutch plate is released.

Take your foot off the pedal and the clutch spring (diaphragm type in the case of a 1275 clutch) pushes the bearing back to its start position, pushing that same quantity of fluif back up tge pipe. The bearing then remains held lightly in contact by the light bellows spring. It doesn't go further clear than that with this Ford type.

I'm not familiar with the SAAB type. But from Willy's and other comments I interpret that the moving bearing also remains in contact. The 6mm relates to the clearance used to set it up by manually compressing the light bellows spring, moving the bearing to the full rearwards extent of its travel. This then giving the 6mm clearance. Once the bellows spring is released the bearing then moves forward to its start position, making light contact just as with the Ford type.

PS
Alan needs to add his wisdom. He is the clutch specialist!
GuyW

There are no bellows on the saab type concentric Guy.

There is no spring pressure at all pressing the saab type bearing to the fingers. So it doesn't stay in contact as 'firmly' as the bellows type. In fact, as the pedal is lifted, as well as pushed back by the clutch finger(or pressure pad) pressure, the fluid is drawn back slightly, leaving the bearing sitting close to 'scuffing' the fingers. As I said before below.

I posted loads of the saab type concentric stuff here, including diagrams/measurement specs back in 2013.





anamnesis

Not necessarily pertinent here but IIRC the diameter in the centre of the Ford pressure plate fingers will clear the guide tube of the Ford gearbox, it's when using the pressure plate from a spridget where that centre diameter is smaller that the guide tube can be an issue and needs to be shortened. I first came across this when playing with fitting a smaller Ford 4 speed to my Sprite in the 1980s and found the guide tube got slightly chewed up by the fingers, the pressure pad having been removed, and made adjustments and left the pressure pad in place.
David Billington

Guy-
I see what you say here is correct-

""I'm not familiar with the SAAB type. But from Willy's and other comments I interpret that the moving bearing also remains in contact. The 6mm relates to the clearance used to set it up by manually compressing the light bellows spring, moving the bearing to the full rearwards extent of its travel. This then giving the 6mm clearance. Once the bellows spring is released the bearing then moves forward to its start position, making light contact just as with the Ford type. ""

I got one from Retro Ford, which I'm guessing is the Burton Saab one, had it in with a lightweight flywheel which must have had a heap machined off the clutch face side- it went about 12mm clearance with the cylinder compressed--I thought that'll be ok as it'll decrease as the clutch plate wears---big mistake--12mm clearance is enough to allow the slave cylinder to travel far enough out to clear the "O" ring and lets fluid piss out into the bellhousing--so yeah 6mm is it really.
William Revit

Yep, that's right David.

"-- the diameter in the centre of the Ford pressure plate fingers will clear the guide tube of the Ford gearbox --".


Right. There are ***two types*** of SAAB concentric releases.

One has a bellows, like the Ford type.

The other, also *supplied* by Burton, but *made* by TITAN, the one I posted pictures of below, does not have bellows. It has no spring, and does not sit in constant contact with the fingers in the way that the sprung bellows type does.

Bill's first type was the saab bellows type.

The set up, spacing, for the non bellows TITAN APC5, Saab type, is as shown on the pictures I posted.

Again here.





anamnesis

I see that some Saab ones have bellows but they seem to be mostly for later devices, Zafira and the like.

My old one had no bellows though, just an incredibly poor technician fitting it.

I will ALWAYS use thread lock in future, whatever's left of that.

So have I got this right?

When I assemble the gear box to the engine the clutch fingers should be in contact with the bearing face but not pushing it back much AND when the clutch operates the bearing will push forward of its factory, rest position?

And then return to 'REST'?

Its great to still have you guys here helping even after all this time.

Thank you.
Bill sdgpM

Correct David. When using a type9 with a 1275 clutch the ford guide tube fouls the diaphragm spindles. If using the normal external slave, pushrod and lever arm one shortens the guide tube. It then causes one of the problems of that set up as if there iscwear in the pivot points the release bearing 'nods' and can chatter on the revolving input shsft. Another story!

Anam, I did say I wasn't familiar with the SAAB version! 😁. I didnt remember you doing yours though probably just skipped the thread at the time since mine was ford and finished! I note from that drawing that the set up clearing they specify is 8mm, not 6, leaving 7mm to allow for clutch plate wear, which seems a lot.

With Bill's choice of ford slave I wonder if the travel ratio is the same as the shorter version. i.e. does a single pedal stroke of the standard master cylinder still move it forwards by tge same amount. That is critical to the set up. It would need testing or calculating if one could find the relative dimensions from which to calculate the effective cross sectional area of the concentric piston. (difference of the area of two circles)
GuyW

To me Bill, there are two distinct parts to these concentric slaves. The first is the non moving parts consisting of the body and the 'nose' or guide tube around the gearbox input shaft. You need to check by measurement that none of that contacts any part of the clutch or flywheel assembly. In particular the guide tube must not catch the diaphragm, but it must still extend far enough to support the release bearing. Something like 6 to 8mm clearance there seems to be the consensus. Use the Burton Power packing pieces to get that position correct.

The other is the moving bearing /piston element of the slave. Once you have the body positioned then the piston will be correct, determined by the design so no further adjustment needed. The hydraulics take care of that.

The only thing that would concern me is what I commented on in my last message. If using a different slave, does the design give the same travel for a single pedal stroke.
GuyW

Bill, you probably said somewhere, but what clutch system are you using?

And:
Whichever concentric is used I think the release bearing needs to be pushed rearwards to near the start of its available travel (allowing for that 6 to 8mm clutch wear) Its the equivalent of the 'at rest' position of the piston being well up inside the cylinder bore in the standard external slave. If its start position is only a little pushed back by the clutch fingers, there is a danger of it popping off the guide tube and losing all its fluid past the seals as Willy describes
GuyW

Thanks for all your help chaps, just what I needed.

Guy I will aim to set the cylinder with its bearing pushed back a bit so I dont have to worry whether it will disengage in use.

Then when it is working I will have to consider whether my journeys with Lara should come to an end.

Driving her is still a delight but the acts of entry or exit have become more than just a penance, more of a sentence.

My painful knees and back and general absence of core strength have me wondering what is next?
Bill sdgpM

Bill, many of 'us lot' wonder what next, even if still able to get in and out of our spridgetly things with the roof up! The years keep slipping by and however young one may feel inside, the maths of it says that event horizon is approaching with nothing that can be done about it. To me the biggest scam of it all is that there will be matters that concern or interest me that I will never know the outcome of. Ever. Or at least, one presumes not!
GuyW

Even in my 20s/30s while I could get into and out of my Sprite as a driver easily I found getting into it as a passenger more difficult as I wasn't used to bending that way. Hopefully I'll get it back on the road to enjoy before that becomes to much of a problem. I wonder if a plywood mock-up would be OK for physio practice beforehand.
David Billington

Now I'm really confused. 😅😅😅

Bill, in 2015, you posted --
"bill l, SDGPM uk, chef82@sky.com
My original Saab unit has the famous bellows and insidew iut there was a large spring that pushed the bearing against the clutch fingers."

And below in your 2nd post here you said, " The middle one is my original but I am reluctant to refit that after the gearbox issue is fixed.-" referring to the picture you posted, which I've posted again here..

Now, a couple of posts back, you say, " My old one had no bellows though, just an incredibly poor technician fitting it."

Help!! I need someone. 😉😉.

https://youtu.be/2Q_ZzBGPdqE?si=42GVYgMM3tMh87H0


anamnesis

There are 3 in Bill's photo. The left has no bellows, just a large spring.
GuyW

Terminology (and memory fail Anam) sorry.

I could hardly remember anything much about concentric #1 except that it failed on the French highway passing Lisieux going uphill and passing a truck, a long one, when I needed to get over to the right before it stopped moving at all.

Hairy moments there.

The green bellowsed individual in my recent picture is the one I have been happily tooling about with since those days.

The one one the left I picked up speculatively for any unwanted rainy day a few years ago but the damned thing only has a 'IN' pipe and no access to bleed it in operation, just a hole with what looks like a ball bearing pressed into it.

If I felt I could trust getting air out of it I might have used it here and now.

But I dont know how.
Bill sdgpM

Ah ok. 🙂

Anyway. Speaking of memory fail.

I've only just realised/remembered, there are two BILLS. ðŸĪŠ.

I've been going round in less than concentric circles. ðŸĪĢðŸĪĢ.


anamnesis

This thread was discussed between 13/10/2025 and 16/10/2025

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