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MG Midget and Sprite Technical - More Bleeding Brakes


Hello Earthlings.

I have a midget Mk3 which I have owned since 2003. I have never been happy with the brakes despite replacing the master cylinder in 2003 bleeding & replacing the fluid every 18 months & adjusting the rear brakes plus re-newing the drums. In the past 2 weeks I have replaced the front callipers (new) & added Mintex 1144 pads.

I have read many of the archive entries on the subject but still think I have not removed all the air. I have tried the following bleed options:-

Easibleed - low pressure at the master.
Hand vacuum at the nipples.
Tilting the back & front end alernately.
An assistant to pump & closing the nipple on the down stroke.

Despite attaining fresh / clean / bubbless fluid at each nipple the breaks still need pumping to get a good response. I'm not saying I can't get the brakes to work well with 1 shove - only that my foot has to go 75% to the floor first. On the other hand if I give a light shove a couple of times & then a third I get full braking just 25% or so to the floor. This is really what I am hoping for on an initial shove.

Am I expecting too much? Would a servo help? Any other suggestions would be most welcome. Thanks
G Rowles

If after a period of use the lines are bubble free, and the level of fluid in the master cylinder is not moving it would point to the the hoses swelling as pressure builds. Without a servo the pedal should feel like you're standing on a brick, but with one you'll build in even more compliance.
F Pollock

a servo might mask the problem but certainly won't cure it. Could you remove the rear drums and post a pic of each side? I suspect you may have the shoes wrongly oriented.
David Smith

Just a thought - but you could try driving the car for a few hundred yards with the handbrake lever engaged by one or two (or three) clicks. If the foot pedal remains firm, it suggests that your problem lies in badly adjusted rear drums/shoes or that incorrect rear wheel cylinders have been fitted by a previous owner. The Midget has two versions of rear wheel cylinder, depending on year/model.
Andy Hock

If the bleeding has been done as you say, the problem must lie in the rear brakes or rubber pipes.

Either wrong/faulty cylinders, incorrect assembly of the shoes or very bad adjustment could be the reason for your problem, or perhaps ballooning rubber pipes.

You have fitted new drums so worn out drums can't be a reason.

I found fitting braided hoses all round made my brake pedal absolutely firm with hardly any free movement before actuation of the brakes.

Before fitting them the pedal moved noticeably before the brakes began to work.

A servo is not the answer.
JB Anderson


Thanks for these comments.

FP - fluid in equiled fluid out a far as I can remember. I certainly had to top up the easibleed or master dependent on method.

DS/AH/JB. I'm thinking maybe the rears are key as I have always had an issue over adjusting them. I'll try the handbrake engaged idea I have braided hoses all round. I'll also look into wrongly fitted shoes which I fitted & cylinders - which were fitted shortly after purchase by an MGCC/MGOC reputed garage. The new cylinders/pads had no affect on travel - I was thinking in particular the old cylinders were not moving freely.

The encouraging thing is knowing that I can expect better.

I'll try and do pics of the current set up at rear but the work will have to wait a while so expect a post in the future.

Thanks.




G Rowles

There is always the possibility that your replacement master cylinder is in some way not working correctly and is as bad as the one you replaced in 2003...not likely, but if all else fails...
JB Anderson

If everything is in good order as you seem to suggest and you're using braided hoses, there can only be a limited number of possibilities.

The symptoms you mention, first stroke of the peddle goes down a long way and subsequent applications go less far, would suggest that either the pads have moved back from the discs or the shoes aren't adjusted fully up. The first could be caused by excess runout in the discs, unlikely as I'm sure you'd have noticed it. I suspect your problem is adjustment of the shoes. My method for adjusting the shoes is firstly ensure the handbrake cable is slack, maybe even disconnect it, then turn adjusters until the wheel locks and then back off the adjusters until the wheel turns. A bit of drag is acceptable as long as you can turn it by hand. Press footbrake several times to centralize the shoes and check adjustment. Reconnect or adjust handbrake to take up slack in cable.

I use this method and also have braided hoses, my peddle only goes down a short way and is like standing on a brick. The difference between light and heavy braking is more about pressure applied than travel.

Bob
R.A Davis


Thanks Bob. Symptons as you say. I've just put new Pads in. The discs looked fine but I will check them again.

I'm pretty sure I've got the rears adjusted correctly as far as possible but am going to check I've put the shoes the right way round(!)or possibly that I have GAN 6 wheel cylinders.
Gavin Rowles

Gavin

Is your car fitted with a single circuit or a dual circuit system? If the car has been fitted with dual circuit master cylinder it can sometimes make brake bleeding a painful and long winded exercise.

A friend of mine gave up with a dual circuit set up he'd fitted to his racer, threw away the master cylinder and went back to single circuit brakes, because he simply couldn't get a decent brake pedal on the car...

JB
James B


James.

It is single. Thanks for the thought though.
Gavin Rowles

If your rear brakes are correctly adjusted and you are properly bled as you suggest then check the amount of rollback / drag on the front brakes. "New" caliper seals can sometimes allow the piston to retract further than you are used to, consequently a couple of pumps may be needed.
Alternativly try blanking off each brake in turn to isolate where the travel is occurring. not so easy with braided hoses though!
G Waite

One for my personal intrest
How mutch play is in your front wheel bearings?

Woble there due to play will also give a deeper pedal.
Onno K

Hello again.

Having checked further in the archive I have found as follows concerning correct assembly of the shoes:-

Looking at the nearside break, shoe on left (on side of forward diection of travel) the cut-away is at top.
Looking at the offside brake, shoe on right (again on side of forward direction of travel) the cut-away is at top.

I have assembled both correctly.

As far as the cylinders are concerned the nearside one has on it 'A3 12' but the offside says 'A3 5'. They look the same. Should they be the same reference & if so which is correct for GAN581957G?

How do I check out the rollback/drag & retracting pistons?

Not checked the disc yet. Mo play in the front bearings.

Any other idea's welcome. Thanks
G Rowles

As far as retracting pistons in the callipers is concerned, I would expect a little drag on the discs after the pedal is released, from the pads.

If the discs are completely free to rotate I would think the pads have retracted too far.
JB Anderson

If you jack the diff and have the rear wheels free to rotate, how many handbrake clicks does it take to lock the wheels?
F Pollock

Regarding Midget rear wheel cylinder types. AFAIK the pre-'74 Midget (1275cc) RW cylinder bore is 19mm. Post '74 (ie all 1500 Midgets) have a RW cyl bore of 17.5mm. Any casing markings on the wheel cylinders would, I think, correspond to the manufacturer's batch numbers. The only way to be 100% sure of the bore is to measure it.
Andy Hock

JB - there is a little drag on the discs suggesting this is not the issue. Thanks.

FP prior to recent work it was about 5 clicks. I know it should be less which is why I have purchased parts to renew the cable and levers.

AH - will check bores but:-

This AM with help of my better half I observed culinder/shoe action. Nearside is fine but offside trailing shoe does not move. I'm going to see if I can free up the piston on the rogue side. Does anyone think this could be the cause of my problem?

Gavin
G Rowles

Regarding the 'stuck' offside trailing shoe. With clean hands, holding both shoes of one wheel, one should be able to manually move them as a pair (as Brucie might say) fore and aft a few millimetres. If that is not possible, then one (or both) shoes/pistons have probably seized. It's not always possible to assess what's happening when viewing the shoes/pistons when an assistant carefully depresses the foot pedal - one piston might be a bit 'easier' than the other which can give the appearance of the non-moving piston being seized when it might not be.

Manually, carefully move the pair of shoes fore and aft - the pistons should follow.

Andy Hock

I suspect that in adjusting the rear brakes, you are backing off the adjusters too far. If you try and get them so that the rear drums are not dragging, then they are too loose. With the correct adjustment, you should be able to turn the wheel with one hand on the tyre, but it will still drag. This will then give around 3 clicks of the handbrake to lock them solid. This will feel like too much drag but after a few brake applications everything will self align and you get a correctly adjusted setting.

Probably too obvious to say, but when turning the adjusters do make sure that you stop dead centre on a flat setting, moving the adjusting spanner to and froe to find the sweet spot.
Guy Weller


AH - no movement at all on trailing shoe. I don't think the piston will come loose so it looks like the whole cylinder will need replacing. I've already looked in archive on this & the circlip looks like agro. Wish me luck.

GW - yes I think this poor operation on the offside drum could well be the cause of my original problemas I have not been able to get the adjustment right.

Thanks
G Rowles

Hey, Growl(e)s (if I may call you that) - there is a lot in the archive about fitting the RWC E-clip/circlip/Devil's Own Clip.

A few weeks ago, I decided to remove the mills pin on the RWC's and tap an M5 thread in the hole and bolt the RWC to the backplate. I don't subscribe to the theory of (by using the circlip it creates) 'play' between the RWC and backplate allowing for brake self-centering. I say, bolt on and be damned!

Here's a recent thread link:
http://www.british-cars.org/mg-midget-sprite-technical-bbs/old-chestnut-securing-r-w-cylinders-1500-midget-2012032708511716904.htm

Andy Hock

Have now replaced the offside rear brake cylinder.

I purchased 2 from Premier Supplies, Headcorn, Kent. These are of French manufacture (the packaging suggests) and usefully include a 7mm nipple which is larger & easier to use that the standard quarter inch - thought this was worth flagging up. RGWC1102 is the part ref for GAN5 cost 8.00 odd each. This slightly larger nipple goes through the backplate without any clearance issues. I did not even attempt to use the W clip for fear of acquiring a hernia so used the drill and tap method which was a breeze once the engineering was over. I used a 5mm bolt which does require a 6mm hole in the backplate but this can be done easily with a hand held drill.

Having had further thoughts about this being the source of my problem, I came to the conclusion that it would not help the pumping issue as the seized cylinder provided maximum resistance. This has proved to be correct but at least I've got 4 shoes working rather than 3.

Both sides were re-assembled to ensure that the hook at top rear went over the top of the brake lever ear to prevent rattle not that one is likely to hear it in my Midgetat over 20mph! I replaced the levers and lever to rod bushes. Tip to get this hook over the ear it is a lot easier to do this on a bench. This means taking out the lever attaching it to the rear shoe/spring & feeding it all onto the back-plate/cylinders with a bit of tooing & a frooing. Once assembled I bled the nipple not much had been lost as I had used the cling film trick on the master cylinder. I then gave the footbrake a good few stampings to centralise the shoes.

Before reconnecting the levers to the cable I adjusted up the brakes both sides & turned back 3 clicks & onto 1 of the flat spots. This seemed fine on the nearside with a bit of drag. On the offside there was more drag so I dropped it a further click which seemed acceptable. However, now the brake rods would not reach the levers which I thought was probably slack taken up by the new levers and bushes. So I relaxed the cable adjustment to get this right (having tightened it up over several years).

Anyway, the test drive did not disappoint what I concluded was correct this has not influenced the pumping issue. The way I see it is to check the following:-

1. Disc run out is within spec. I will need to borrow/purchase a dial indicator.
2. The new calliper pistons are moving OK. Anyone got some hints on how to check this please? Would driving the car a bit help?
3. There is a fault with master cylinder. How do I check it or is it just a question of replace & see? Or, I have seen comment about air locks in these items could this be the issue?
4. Despite making Halfrauds rich in June can there still be air in the system in spite of all the bleeding Ive done. It occurs to me that apart from the MC the brake switch is the highest point in the system so has anyone else found this to be an issue?
5. The shoes are undersized. I dont believe this to be the case as it was a fairly snug fit to put back the drum. The drum/shoes have done less than 2K & look fine with no score marks.
6. I have still not got the rear brakes adjusted correctly.
7. Faulty bearings neither front wheel gives any play.

Any other ideas, comments, ridicule would be welcome.

Gavin Rowles

Regarding the shoes' 'spring hook' position relative to the brake lever - I believe that he correct fitment is to have the hook lie under the brake lever. Anyway, that is not the cause of your low pedal.

If you've eliminated ballooning brake hoses, your problem must lie in a BMC malfunction. I presume that your BMC is not a dual circuit type? (ie your BMC has only one port/connection?)

Andy Hock

If you reckon you've got all the air out via bleeding, try wedging your brake pedal down hard with a piece of timber between it and the seat frame and then leave it overnight fully pressurised. You could then try bleeding it again next day. It worked for me as my brakes used to be a bit squidgy on first application. Just don't ask me why!
Matt1275Bucks


AH - single & I'm sure its on top.

Matt - funny enough I came across this idea looking on the archive yesterday. was it you who posted?

I'll give this a try & also tapping the pipes when bleeding - another tip from the archives.

I'll eat my trousers if it's not trapped air.
Gavin Rowles

One thing that I think has not been mentioned so far is the pedal pivot. They do eventually go oval and then a part of the volume of fluid pumped is lost with normal operation of the foot.
Guy Weller

Caliper pistons: The amount of retraction to cause the sort of problem you are having is only about 20 thou per piston. When I first found it (after a frustrating session like yours) that's all there was, I did the maths and yes the amount of fluid displacement involved would swallow up a bit over half the stroke of the pedal on its own. Add in the back brake displacement and the pedal is feeling well close to the floor before it takes up.

I spotted it with the aid of a helper to pump the pedal while I watched the caliper pistons.

Fixed by dismantling, cleaning and using fresh lubricant (rubber grease) on the pistons. It appears the old lubricant had got too thick and sludgy with age (bit like me really) and that was causing the problem.
Paul Walbran

OK Folks

I am going to inspect the movement of pistons in the calipers & remove if I think they require rubber grease. I will check the run out of the discs. Then reassemble and bleed all round. Then wedge down the footbrake overnight. I will then bleed again & tap the brake lines. There will be a 2/3 week delay on this as I have other commitments. You never know I might be driving on the road before the summer ends!


Gavin Rowles

I hate to put a dampener on the 'sludgy grease/caliper retraction' theory causing a low brake pedal, but surely a sticky caliper will result in less piston retraction and a firmer pedal? Assuming Gavin has eliminated ballooning hoses and sloppy rear brake mechanisms/pistons, the problem must lie in the BMC (assuming all air is out of the system).

Before dismantling the calipers, I suggest that Gavin clamps off all three brake hoses (two front, one rear).
Use brake hose clamps (or modified mole grips). Be careful not to damage the hoses. See what the pedal is like when the three clamps are on. Remove one clamp at a time and test the pedal each time. This will pinpoint the offending 'leg' of the brake system.
Andy Hock

Andy can one use those hose clamps with braided s/steel hoses? - I thought you couldn't.
David Smith

>DS asks>>can one use those hose clamps with braided s/steel hoses?

>AH replies>>Honest answer, I don't know. Using a clamp on a braided hose would probably leave the outer mesh marked/compressed. But I really don't know. Maybe others have experience . . . . ?
Andy Hock

Andy
You miss the point. When this happens, the piston doesn't stick in the caliper body, it sticks to the rubber seal. Being rubber, it deforms when pedal pressure is applied as the piston cna't slide through it. Once pressure is released, the seal acts as a spring and retracts it. It's a real effect. Clean & lubricate the pistons and the problem goes away.

This happens to a minor extent all the time - good thing too or the pads would always drag on the disc - the problem occurs when the seals have far more grip on the pistons than usual. It may or may not be Gavin's problem at the moment, but it does give the symptoms he described so he is right in checking for this along with other possibilities.
Paul Walbran

Thank you, Paul, for your explanation. It makes perfect sense now. And, yes, it does sound a possible cause of Gavin's problem.

Any ideas if one can clamp off braided brake hoses? Doing so would pinpoint Gavin's problem.
Andy Hock

DO NOT clamp "braided hoses". They have a thin Teflon tube inside the braid, and you will crush it and initiate fracture of the tube wall. It is NOT rubber, but plastic. They do NOT like kinks or crushes!

This whole problem sounds to me like incorrect rear brake setup.
Disconnect handbrake linkage.
Lock rear brakes hard solid with adjusters.

Caliper sticking as Paul says is possible but quite rare.
More common is one piston stuck in the caliper and the opposing piston bends the disc over to meet the now stationary pad on the stuck side. This gets worse as pads wear and eventually breaks the disc. Or the stuck piston breaks loose and the brake drags until the pad wears as the cycle starts over.
Watch calipers and discs as somebody leans hard on the brakes. You should see no movement. The actual movement is a couple thou maybe, once pads are worn in.
Any doubt on calipers, push each piston back in turn and watch the movement as it is pushed back out by light pedal pressure - hand pressure should suffice.

If there is more than 3/4" of pedal travel after the free play is taken up, there is still air in the system.
Or, the pedal/cylinder assembly is loose or broken on the scuttle.
Fix that.

Then back off the rear adjusters Just Enough to turn the drum by hand, even with effort. I beat on the drum with a plastic mallet to help centralize shoes as I adjust. For new fuzzy shoes it might take 4 flats, worn in ones should be two. Drive the car around the block to center shoes in operation. If this results in a drop in pedal, tighten the adjusters a notch. Brakes will be warm but not hot. If the brake is really hot, you have to back them off a notch or two. New shoes commonly take two readjusts, after a day and a week of normal use.
Correctly bedded and adjusted brakes should have not more than 1 1/2" pedal travel, usually less.

When all is well, back off the HB cable adjuster, and drop the clevis pins in the lever (and split pins!).
Pull HB up three notches and screw the adjuster on tight by hand only. The detent will give added clearance, and the lever may come up half way - not a problem. Operate the HB a few times and recheck the cable setting - commonly needs a bit more tightening. Except for rare adjustments for wear, the cable should NEVER need adjusting again, if you keep your paws off it. Any deterioration of handbrake will be because the rear brake main adjusters want love. I might adjust a cable once in ten years regular use on a car.

FRM
FR Millmore

FRM - hear hear about the cable adjustment! A bit like carburettors really - overhaul and set up properly, then they seldom need touching for years.
And also like the handbrake cable, carbs are often the first thing people attack rather than the last as they ought to be.
Paul Walbran

Gavin,
Is your master cylinder one of the ones with an adjustable pushrod? Maybe that needs re=setting? I don't pretend to know what effect that might have as my car is a little later, but I can imagine that if the pushrod is wrongly adjusted it could have n effect on the amount of fluid pushed. Also, did you check the pedal pivot for wear?
Guy Weller

Guy-
No. Not adjustable, at least not here. Pushrod has nothing to do with it, unless it is so short, or sloppy, that the pedal hits the floor before the MC piston moves. Don't think it can be that bad, not seen it, and I have seen some with the clevis pins nearly worn through (and out the pushrod end).

FRM
FR Millmore


Just to let you all know after checking all components - discs, rear cylinders, callipers, bearings,rear adjustment it left the Master Cylinder. I replaced this with a new one.

I bled the MC on a bench by filling the reservoir just under half full. I then pumped the MC rod keeping all at an angle of about 45 degrees to ensure the fluid exited at the highest point and slowly released & at the same time backfilled using a syringe. Not very high tech admittedly. I then used a suitable cap to prevent loss when moving to car. Following installation the whole system was bled again.

Bingo!

Thanks for all your comments & suggestions.

Gavin.
Gavin Rowles

Gavin - I'm so pleased that you got to the bottom of your problem. It's a lovely feeling remedying a fault, especially one that has been nagging away for many years! Here's my brief, flickering thought in the afterglow, so to speak . . .

Your original post states "I have never been happy with the brakes despite replacing the master cylinder in 2003 bleeding & replacing the fluid every 18 months". And your final post confirms that bench bleeding and fitting the new BMC has sorted the problem. This suggests a couple of possible scenarios: the 2003-fitted master cylinder might still be a good, working unit that simply needed bench bleeding (unlikely) - or it could have been faulty from new (or an incorrect version/bore), or it became defective very soon after fitment (more likely). Likewise, your 2012 new BMC didn't actually need to be bench bled, it might have worked ok 'straight out of the box' with Eazibleed/pressure/foot ('conventional') bleeding. In 34 years of 1500 Midget ownership (and a few BMC replacements/overhauls), I've never found it necessary to bench bleed the BMC.

Of course, in nine years, memories and perceptions can be deceptive and you may have had other problem areas (eg rear cylinder adjustements) which you have subsequently fixed.

I guess we'll never know for sure. Personally, I'd be inclined to throw away the 2003 BMC and enjoy the new brakes!

Andy Hock

This thread was discussed between 09/06/2012 and 08/08/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.