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MG Midget and Sprite Technical - Starting empty, clutch 1275

Hello. I've got all new parts to try to solve my clutch problem. The new hydraulic line from Moss was great - all the right size, and fairly easy to form.

Is there a best way to fill the system with hydraulic fluid before bleeding? I'm planning to leave the slave unattached to the gearbox and bleeding while I'm holding it in the engine bay. Then I'll push in the clevis all the way, bleed it, and then attach the slave to the gearbox.

I do have a Mityvac. Is that the right tool to start? Should I have my granddaughter hold down the clutch pedal, while my wife keeps the reservoir full, and I use the Mityvac?

I should probably understand better how the master works, but I should have it all connected this morning and it would be great to get on the right path for bleeding.

Thank you.
Mark 1275

You could make up a remore bleed similar to the photo


Alan Anstead

And covert your slave to a slotted upper boss for a quick fit.
Alan Anstead

Picture of quick fit.
You can take it all a stage further and use an automatic bleed valve in the remote system


Alan Anstead

Interesting! Good ideas.

I'm installed now, and just need to test. Didn't use the Mityvac. Hope I've got a working clutch.

Thank you for the responses, Alan.
Mark 1275

Crushing disappointment. No clutch at all.

Starting to think my problem may be in the bellhousing, not the hydraulics. The clevis only moves about 3/8". So maybe the starting position is not with the clevis as far in the slave as it should be. Wonder what I could have done during reassembly that would cause that. Clutch seems to me to be pretty idiot-proof, but I'm not pushing the clevis very far into the slave to line up with the clutch lever.

Think I'll just drink beer for a while.
Mark 1275

I usually fill the clutch system from the bottom upwards using the Eezibleed kit. Gently pressure the fluid in the slave cylinder bleed valve and wait for it to appear in the master cylinder. The air bubbles are going upwards, the way they want to go. Has always worked for me.
Mike Howlett

Drinking beer - good idea while you wait for further inspiration to appear!

How hard is the pedal? It's a pita to bleed the clutch effectively. Alan's remote is a neat solution as it enables the air to gather at the top of the remote (as opposed to the dark reaches of the slave cylinder) and it is so much easier to get at.
I'd suggest ensuring your initial diagnosis of dodgy hydraulics is fully eradicated before moving onto the mechanical side.

Mike - like your idea, pushing the air upwards and outwards rather than trying to force it out at the bottom of the system. Neat.
Jeremy MkIII

Apparently some 1275 clutch kits have been received with 1098 carbon release bearings. They should still work but you start off with what is effectively a part worn 1275 carbon.

There is an inspection hatch into the bell housing opposite the yoke entry port. With someone operating the clutch you can, with a torch, see what is occurring.

Is what you have replaced the same: for instance have you unknowingly replaced the slave push rod with a shorter one.

Is your clutch yoke bent. A 1275 yoke should be straight but tend to bend at the narrowest point just before the clevis yoke. If it were out of the car its leading face should be flat upon the bench.

As a quick gauge place a dime (small coin equivalent to a UK 5p piece) into the slave cylinder piston recess effectively lengthening the pushrod and see if there is improvement suggesting either a bent yoke or short pushrod.
Alan Anstead

For that last suggestion of Alan's try substituting a 7/16 nut for the dime. The hole in the nut will locate onto the rounded end of the push rod better and the nut will neatly nestle into the concave face of the slave piston. Like this, it will effectively lengthen the push rod but won't readily drop out and the car can be driven like this for many miles of necessary.
GuyW

Sorry, I probably mean a 1/4" nut do I? I always think of nuts by the spanner size "across the flats". I can never remember what the convention is, or if it is the same over the oceans.
GuyW

Much appreciate the replies. I've just been leaving it alone, but at some point I need to acknowledge there is no right number of beers that will fix it.

I didn't realize there's a part that could bend. I really had to push to get the clutch lever to align with the pushrod the first time I put things together late winter. Is the yoke the same as the lever? If my thinking is right, then lengthening the pushrod will give me a clutch that works, even if it's not a long term fix.

The new pushrod was almost identical to the (not so) old one. IIRC the new was 3 or 4 thousandths longer. This evening I'll take the old, cut a flat on the end, drill and tap for a bolt with a head that nestles nicely into the slave hollow.

The pedal is not hard at all, but it's like it's not being asked to do anything. I'm hoping with a longer pushrod, so the system actually has to disengage the clutch, I'll feel some resistance. The bleeding actually went fairly well. Had the slave in my hand in the engine compartment; bled until there were no bubbles for a while. Then pushed in the pushrod, held it with a tie wrap, and more bubbles came out. Then bled some more with no bubbles coming. Had the full crew of eldest granddaughter at the pedal and wife keeping the reservoir topped up.

I'll try to get the car up high enough so I can look into that inspection port. Would have been easy when I first restored it 18 years ago, but either the exhaust pipe's gotten lower or I've gotten thicker.
Mark 1275

Mark,
If as you say the clevis is only moving 3/8" (you mean the pushrod?, then this may be for a number of reasons:

1. There may still be air pockets in the hydraulics so not sufficient fluid is being moved in the hydraulics to displace the slave cylinder piston and therefore the pushrod.
2. There may be a problem "upstream" with the master cylinder operation, or with the foot pedal pivot and pushrod.
3. The slave piston may be starting too close to the end of the slave cylinder so that it comes up against the circlip in the end (if ftted, if there is no circlip the piston would pop out of the cylinder bore)
4. The pushrod itself could be too short - but you say its the same as the original
5. The clutch lever arm (AKA the yoke) is bent
6. The pivot for the clutch lever arm inside the bell housing is badly worn
7. There is a fault with, or faulty installation of, the clutch release bearing or the clutch itself
8. The clutch driven plate was put in back to front.


There may well be other possibilities, but that is sufficient for now!
The idea of adding something to the pushrod is best considered as a temporary test, which is what Alan and I were describing. You use this test to diagnose or eliminate problems. It is best not doing the more permanant adaptation that you are considering until you have done the temporary "fix" to see what effect it has. Overlengthening the pushrod if that isn't where the fault lies could damage or bend something else - like the release lever arm.
GuyW

Surely if the movement down at the slave cylinder is only 3/8" then only fault #1 or #2 on Guy's list are applicable. All the others on the list come into examination if you have full, normal pushrod movement but the clutch still doesn't disengage.
What is the correct pushrod movement for full clutch pedal depression, does anyone know? IIRC it's just over 1/2"
David Smith

Yes David, I measured it once when doing my conversion to a concentric slave system. It was 14mm in my case.

I listed all of those possible options as I wasn't absolutely clear about under what conditions Mark's repoted 3/8" of movement there was happening. For example, was this wih a full pedal stroke to the floor, or was the pedal stopping short of that? Or maybe he is meaning that the at rest position of the slave cylinder was only 3/8" in from the end of the cylinder to start with.

Having said all that, my money is on the most common problem, which is failure to bleed the system fully.
GuyW

This is extremely helpful. Narrows things down for me.

This might get wordy, sorry about that.

Worth mentioning that when I first put the car back together early spring, I backed it out of the garage, and drove to the walk to the house. So made it into reverse and into first. But, it wasn't happy. Slight grinding going into gear, so we cancelled the ride. Backed up, drove it into the garage. Figured I would bleed the clutch just to put it back to the state when I took it off the road last fall. Since then, I haven't had a working clutch at all, so maybe when bleeding, I let the reservoir get low and air came in.

Back to the present. I took a video in the inspection port, and things are barely moving. So I did add a bolt to lengthen the old pushrod. (I've been calling it the clevis, but it's definitely the pushrod.) The pushrod was 2.540" from the bottom of the hole (for the clevis) to the end of the pushrod. With the added bolt, I tried it at 2.715", and the darn thing's still barely moving.

Not sure if it's okay to link to YouTube, but here's a video of the movement. So my earlier theory about not having it in enough was wrong.
https://youtu.be/20m4yHxM3jg

As expected, the movement inside the bell housing is also clearly not enough.

Guy, your last is just what I needed. I think the short drives I took might rule out 4, 6, 7 and 8. I hope. FWIW, the old slave had the circlip in the end, but the new one doesn't. The master cylinder is brand new.

Got to run to dinner, but I really appreciate the advice.
Mark 1275

Lengthening the pushrod only really moves the portion of the slave cylinder that the slave piston operates over, NOT the total length of movement. It can be helpful in specific circumstances where for one reason or another the piston is operating very near to the open end of the cylinder. It can help in diagnosing problems.

It would seem that an insufficient volume of fluid moved is resulting in a short travel of the slave piston.
The fault is either air in the system that needs bleeding out, or what I refer to as an "upstream" fault.

If it previously worked OK and has since suddenly ceased to operate after you have done some work on it, then air in the system is most likely
If its a fault which has developed over a period of time, possibly resulting in a gradually deteriorating gear change, then it is more likely something is progressively wearing - pedal pivot perhaps? or progressively deteriorating - hydraulic seals in the master or slave clinders. (the latter would cause fluid to leak into the slave cylinder dust cover, but yours looks clean and dry)
GuyW

Which Eezibleed is the one best suited for the clutch? Options look like G4062, LSR40, BA4886, and others.

I'll check the pedal area to make sure I'm getting the travel I should, but I think it's time to try the Eezibleed.

Thank you.

Here's a video showing the limited movement at the lever: https://youtu.be/zPKrjk0ooEw
Mark 1275

Just a thought, have you done anything to the rod coming out of the master cylinder? If the pedal travel is OK, check to see when the rod actually starts moving. If you got a new MC the point where the rod makes contact with the piston may be different.
Martin

Two thoughts.
Did you install the new MC pushrod with the new master? Old ones wear in time to an oval shape and the petal hole can also elongate. I have one if that is the problem.
You mentioned a new line you formed. Did you also replace the flex line?
Don't extend the pushrod.
If you have bled the line repeatedly that is probably not the problem.
The slave is not moving enough.
Either a linkage problem or expanding flex line.
J Bubela

The rod coming out of the master cylinder is new, and the connections are tight. There's just a few mm of free play with the clutch pedal - I'm going to guess maybe 10 mm.

The travel of the MC pushrod is 20 mm, exactly what it was with the old master cylinder.

The flex line is also new. I can feel it stiffen when the pedal is depressed, but I don't think there's an unusual amount of expansion.

I'll swap back to the new, original length pushrod the next time I'm under the car.

I'd like to know more about the technique of pushing the fluid up to the master from the slave.

What could account for the slave moving so darn little? I really ran a lot of fluid through the system when bleeding, and haven't seen air bubbles for a while. I know bleeding the clutch can be frustrating, but I've always succeeded in the past.
Mark 1275

Mark,I don't know if this impacts on your system. The slave cylinder, as fitted in an MG is at an angle so that there is a portion of the inside of the cylinder bore which is above the outlet bleed hole. Consequently air can get trapped there and as the inlet and outlet points on the slave are close together air and fluid can remain safely stagnated in the cylinder whist the main stream you are bleeding through it goes in and out, bypassing the air pocket.

There are two solutions to this. One is to Jack one side of the car quite high off the ground (about 18" I think it is) which rotates the slave, bringing the bleed nipple right to the top.
The other is to start by pushing the slave piston as far back up the cylinder as it will go which reduces the volume of the stagnated part of fluid and air within it. Use a blunt dowl or similar and clamp it in position whilst you then bleed the clutch as normal. This usually worked well for me.
GuyW

Guy, yes, I did the bleeding with the slave piston in as far as I could get it. Bubbles definitely came out at this step.
Mark 1275

" I know bleeding the clutch can be frustrating, but I've always succeeded in the past."

It doesn't seem to be an exact science.

A couple of times, I have either replaced or rebuilt the slave cylinder and it has bled really easily.

On my brother's midget, I replaced master, slave, pipe and hose and had a hell of a job to get all the air out and get a good pedal.

Dave O'Neill 2

Dave, I'm curious how you got it done on your brother's car. Did you bleed with the slave in place, a person operating the pedal, and a person keeping the reservoir topped up?

Did the bleed person crack the bleeder, hose attached and submerged in a jar of fluid, and say "down". Pedal person pushes down, says "down", bleeder person closes bleeder, says "up", pedal person says "up". Then bleeder person cracks bleeder, repeat? Or was there pumping of the clutch by the pedal person?

I have a Mityvac, but it hasn't solved the problem. It's interesting that replacing everything in the hydraulic system left me with the exact same situation I had before. I don't think the pedal or the pedal pivot is the issue, as it all seems tight, it worked last fall, and it kind of worked when I took the car out of the garage. I don't think the clutch is the problem, but only because the actuating system isn't moving the lever enough for the clutch to be doing anything.

Actually had a sunny day today (after more than 8" of rain in April) and the Midget just sat. Went for a bicycle ride, and it's not the same.

Thank you.
Mark 1275

Mark, I am lost as to which parts you have replaced, but is it possible that you have been supplied with mis-matched master and slave cylinders? Early slave cylinders were larger diameter internally and if you had one of these with a later style master, then you would get only a short movement at the slave pushrod.
GuyW

Hi Guy,

The 1275 slave is different from all the others as it has a flexible connection to the hydraulic pipe. You can't mix them up. The early slaves had a smaller diameter not larger. It really just sounds like there is air trapped in the system somewhere.
Bob Beaumont

Bob,
I may have got the smaller / larger age the wrong way round, but they are interchangeable. At one stage I accidentally fitted a small bore slave on my 1275 Sprite. As far as I can recall there was an adapter piece on the input connection on the slave.
The result was the clutch overthrew and eventually damaged the cover plate spring fingers. I believe that Bill Mohan had the same problem on his car, using mismatched parts.

Afterthought: maybe the slaves wrongly supplied were mini ones???
GuyW

Guy

Yes it is possible to fit the later 1275 slave with an adapter but the adapter is not standard and is not supplied with a new slave. Its the same set up I have with my 1275 Frogeye. Your right the earlier type slave with the smaller bore can cause clutch overthrow as well as a heavier pedal( I have the scars!) Mark does not appear to be suffering from any of this though!!
Bob Beaumont

I think part of the clutch bleeding problems are that the fluid flow is too slow and makes it more difficult to eject the air.

I have used the 'Colin' way from our Ausi cousins very successfully in the past :-

http://www.spriteparts.com.au/tech/bleeding.html

Difficult bit for R/H drives is getting into the footwell/under steering wheel !!!
Not so difficult for L/H drives but needs an assistant to push the pedal down.
richard b

No, I agree. Mark's problem is under throw, not overthrow
But that could be caused by mismatched parts if the supplier had issued the wrong items.
However, like you,I think that air in the system is still the more probable cause. Just trying to eliminate other possibilities.

I think one reason some have difficulty bleeding the clutch is because of the clutch springs. When bleeding brakes one gets to the stage when the wheel cylinders and calipers are locked on and then there is nowhere else for the bleeding air and fluid to go, but out of the bleed nipple. But with a clutch that doesn't happen as the clutch itself will absorb all the pressure of a single pedal stroke. Locking the slave piston up in the bore should help, as does holding the pedal down with the the nipple open for a while,pausing between each stroke. Slow and patient works best.
GuyW

I will definitely try slow and patient. And persistent.

It sounds like my method described above is the way it's done.

Colin's page is excellent to see, and I'll approach the process based on what I learned from his method about the timing. I do have really long arms, but will likely have a third person at the pedal.

I should mention that all the parts came from Moss in a package; except the metal hydraulic line that came a few days later. Although it does seem the master isn't displacing enough fluid to move the slave the right distance, the advice here convinces me I've still got air in the line.

Thank you for the continuing ideas.
Mark 1275

Mark

I can’t remember the exact method used, but I’ve been using an eezibleed for many years. I’ve always bled with the slave in-situ, but with the arm wired to stop it moving.

When I put my MGB back together last year, it had a new master, slave and flexi - not the metal pipe, but that had been off the car for several years and probably blown through with air - and had no issues at all.
Dave O'Neill 2

Mark,

Jacking up the right front can help sometimes, see photo.

Flip


Flip Brühl

For anyone struggling with clutch hydraulics, you can in fact take the M/C, slave and pipe off the car, bleed them in comfort on your bench* and then fit the complete working assembly back on the car without undoing any of the pipes.

Adrian

* Clamp M/C in vice, you can push the piston by hand when it's not working a clutch.
AdrianR

Adrian, not quite true as you can't do that if you have the dual master cylinder.

Trev
T Mason

And then there is the flex hose attachment to consider on later cars.
Martin

Has anyone considered making a custom billet slave cylinder with a repositioned bleed to scavenge the air pocket. Perhaps alloy with or without a stainless bore liner?
Alan Anstead

Eureka!

I have found whilst making roller release bearings that different manufacturers castings vary considerably. Even when using castings that appear to the eye as identical when it comes to measurement and machining everything can be miles apart.

The 1275 clutch slave cylinder that I have used today is of unknown manufacture. It is of one inch bore fitted with a tandem piston that is to say that the rubber seal sits in the piston not behind it. The spring compresses to 10mm. There is no retention clip / washer to stop the piston ejecting.

The casting carries serial 3233-237C Q6.

This method can only be applicable to slave cylinders fitted with a flexible hose to a remote bleed that is sealed with a copper washer.

The slave cylinder abuts the bellhousing at an angle of 40 degrees.

All I did was drill through the bleed hole with an 8.5mm drill. On the slave casting that I have it appears by eye to have removed the cavity that captivates air. It also removes the hardline seating which is why this can only be done if using a flexible hose to a remote bleed.

See subsequent post.



Alan Anstead

In the picture attached you can see the import hole and then the bleed hole enlarged. The drill has cut slightly into the rear face. You should be able to see the extent of the drilled hole.
Any burring around the drilled hole is well away from the piston and rubber being within the area occupied by a fully compressed spring.


Alan Anstead

This was the last check. O.K. It is only 'by eye' but it looked good.
Only testing 'on the road' will tell


Alan Anstead

Lastly a picture of a flexible remote bleed.


Alan Anstead

Interesting experimentation Alan.
I presume you mean that flexible extension hose now seals onto the flat machined face of the boss with a copper washer, rather than onto the coned surface inside the tapping.
GuyW

Guy
That is it. It won't work with a bleed nipple nor hard line remote bleed as you remove all bar the thread.
Alan Anstead

Yes, I got that Alan. The question is whether the end of the boss is good enough to seal with a copper washer as is, or does that need dressing or machining ?
GuyW

Both of my cars are copper washered onto the bosses. Both of my cars have remote bleeds.
Alan Anstead

'...flexible extension hose now seals onto the flat machined face of the boss with a copper washer'

This is probably a very naive question but how does that work?
Jeremy MkIII

Jeremy
That particular end of the flexible is designed to seal upon a copper washer. It is one method of sealing used throughout hydraulic systems.
Alan Anstead

Thanks Alan,

learn something new here everyday!
I'll have to You Tube this as I have no conception how it fastens without a thread.
Jeremy MkIII

the thread's still there! It's the conical base sealing surface that is removed by drilling .
David Smith

Jeremy, the copper washer is sandwiched between a flat shoulder on the end of the copper pipe, and the end face of the boss on the slave cylinder where the pipe screws into the threaded hole. This requires that the casting of the end of boss has a smooth surface that is at an accurate right angle to the threaded hole, which is why I was asking if this needed any furher attention.
GuyW

I did say it was probably a naive question! I'd assumed that Alan had, by drilling with an 8.5mm bit, removed the thread as well as the conical base (and the narrow passage as shown in Flip's photo) so couldn't for the life of me imagine how anything could attach.

Alan, David and Guy, thanks for the enlightenment!
Jeremy MkIII

Jeremy
the 8.5mm drill is, according to the chart on my workshop wall, the correct size for tapping a 3/8 UNF thread so it clears away all the unwanted material
and passes through the thread leaving it intact.
Alan
Alan Anstead

Are the large and small bore cylinders based on the same sized casting? If so, then a smaller bore cylinder would have a much smaller crescent above the bleed nipple hole, if any at all. It could explain the varied experiences of bleeding a clutch with some saying it is very straightforward, whilst others struggle for days.
GuyW

Guy
Slightly different designs.
Alan
Alan Anstead

I have just fitted a Frontline pressure plate, driven plate and release bearing to my 1098 Sprite, using the 1098 slave cylinder.
I find the clutch very heavy. Coincidentally, a friend has just done the same on his 1275 Midget and his clutch is, compared to mine, light.

My clutch is 7.5 inches and I presume the 1275 is 6.5 inches. So is it the fact that mine is a larger pressure plate that's making it heavy or should I try a 1275 slave cylinder to, as Bob suggests above, lighten the clutch.

Thanks as always.
Bernie.
b higginson

Is the frontline pressure plate a diaphram? The 1275 slave has a larger bore so you may find its throw may not disengage the clutch.
Bob Beaumont

Bob. Yes it's a diaphragm. I wonder why my clutch feels heavy and my friend's 1275 is easier. At the moment the bite point is correct, but takes a good prod to get the pedal down and it can catch you out as the pedal is released.
The Master cylinder hydraulics are unchanged from my last set up, which was standard 1098 six spring clutch cover with an Avenger plate and a Burton Power concentric release bearing.
b higginson

Bernie,

Out of interest does that diaphragm spring cover fit a standard 1098 2 dowel pin flywheel? When looking into these things years ago I always found the coil spring covers had 2 dowel pins and the diaphragm spring covers had 3. When I fitted a slightly tuned 1098 to my Austin A40 Farina I found the clutch wouldn't cope and slipped so I fitted a IIRC Hillman Hunter clutch cover and that worked great, it has a face for a carbon release and is the same size, I just had to machine the flywheel to take 2 new dowel pins, as the dowel PCD was the same for coil and diaphragm covers one existing dowel was used.
David Billington

David. The Frontline 1098 clutch has three locating lugs, but they also supply a 1/2 inch thick laser cut steel pattern which you bolt into place on the bare flywheel, using the exising top dowel to locate it, then drill through two holes to make the three dowel positions. They also supply the dowels. All clever stuff.
I'm sure that the 7.5 inch clutch supplied would cope with much more power than any A series could put out. It's a real beast.
b higginson

The 1275 slave also differs from the 1098/948 one as it has a flexible pipe rather than the hydraulic pipe screwing straight in. If you decide to try it then you will need an adapter . They are easily available. As you are using a concentric release bearing, it may work OK. It will certainly give you a softer pedal. I used to have am early cylinder on my 1275 Frogeye but changed to the later one (dicovered overthrow marks when I renewed the clutch) and it was so much better and more comfortable to drive
Bob Beaumont

Bernie,

I would have preferred to have the drill jig plate located by the 2 original dowels for accuracy. What happens to the lost original dowel , is it removed, cut off,

When I did mine I made a steel plug to fill the old dowel hole and drilled the new ones to an accurate depth to match the original ones in order to try a preserve the balance.
David Billington

Sorry, my mistake. The jig/pattern is located by both the original dowels and when bolted up tight gives exact location for the dowel holes to be drilled. The redundant bottom 1098 dowel can then be removed.
b higginson

This thread was discussed between 04/05/2019 and 13/05/2019

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