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MG Midget and Sprite Technical - Brakes, long pedal travel.

Right, so it seems like I still can't get my brakes to work properly..
Car is frogeye sprite with disc in the front and a sleeved dual master cylinder to 3/4", Everything is new brakelines, hoses, wheel cylinders, callipers, master cylinder rebuilt. No leaks and the pipes and air nipples are fitted correctly. Clutch works as it should.

The cars stops alright but the travel of the pedal is really long and stops just about 2-3 centimetres from the floor, if i pump the pedal again it travels just half that and is completely stiff and stays where it is until released. Air in the system you all probably assume? I've bleed the brakes with a pushing type bleeder with a pressure of 2kg, I've even bleed the brakes pushing fluid from the nipples into the master to make sure all the air is out. I've bleed the brakes the old fashioned way and bleed them with a airpressuerd suction bleeder. So my question it what did i do wrong?

I've loosened the callipers so I could bleed them in angels to avoid air pockets in them. Has this something to do with me changing to discs in the front and having regular drums in the back? The master cylinder is sleeved and fitted with 3/4 pistons. The rear cylinders appear to be fine no leaks on the inside of the drums but can they still be the culprit? I've read somewhere that it's preferable to use morris minor wheel cylinders when converting to disc so are my current ones of the wrong fluid area?

It's either a faulty master or rear cylinder, a incorrectly assembled calliper so something is blocking something, or it might still be a leak in the system where it draws air in but not letting fluid out..

Am thinking of disconnecting one wheel at a time and plug that line and bleed the system again, if I get correct movement on the pedal I can isolate where the problem is. One option is to switch the output on the master and if the brakes work correctly on the clutch port, then it's a faulty master..This is all very messy though.


I've spent a lot of time on the car and would really like it finished soon, but the motivations is at it's lowest having to redo and check every work twice or more.

So anyone?
Anything would be helpful.

Regards
Alex
Alexander Sorby Wigstrom

Alex,
On the first pedal stroke, even though it is long, is the pedal firm, or springy?

If its springy, then maybe there is still air in the system, If its firm, but close to the floor then I would suspect there is too much clearance on the rear brake shoes and they need better adjustment. Be sure to do this with the handbrake fully released - or even disconnected.

The other thing worth checking is that the pivot point for the pedal isn't worn oval so that although the pedal moves a long way, the pushrod to the M/C isn't moving as far as you think.
GuyW

Guy,

Thanks for the response, the pedal is firm on the first stroke. I disconnected the handbrake and adjusted the brake pads as far as they go so that the brakes was fully engaged before i bleed them and then adjusted them back could it be as simple as one of the brake adjusters not engaging properly and releasing the pads to far when you release the brake?

I'm not sure what you mean with the pivot point (language) but the pushrods are new and at they are of the correct length for the cylinder. But I need to check how far they travel when the pedal is pressed.
Alexander Sorby Wigstrom

I did this on our Frog but replaced the backplates and cylinders with 1275 midget type.

It is recommended that MM rear cylinders are fitted to retain the Front/Rear brake balance.

If the rear brakes are the culprit you can usually put your foot on the brake peddle and operate the handbrake. If you can feel it through your foot it's rear brake travel. Operating the footbrake with the handbrake fully on and it feeling different is another sign.

Have you swapped the front calipers? (It's obvious I know but I've done it)

Rob
Rob aka MG Moneypit

The callipers are fitted correctly.

Will check, the clearance on the back once again. Or might as well order different wheel cylinders and check the fitment of the springs and adjusters in the rear then as well.
Alexander Sorby Wigstrom

Alex,
So if the pedal is firm on the first press, but just goes down too far then it is unlikely to be air in the system.

Sounds like you have the brakes adjusted correctly.
It could perhaps be a worn pedal pivot / fulcrum / lagertapp ?
GuyW

Alright now i get what you mean, but if that were worn would it affect the travel that much considerd that the travel is less than half as long on the second stroke?
Alexander Sorby Wigstrom

I don't know the maths of it, but a fairly small displacement at the fulcrum, will loose quite a lot of movement in the leverage - the ratio between the length of the pedal side and the pushrod side of the fulcrum.
GuyW

You haven't mentioned how much free movement you've got at the pushrod when the m/cylinder is relaxed. I adjust it so there's only a couple of mm of lateral play before the hydraulics start to operate - you have to feel this with your fingers. Then the pedal should start to work after about an inch of travel. To an extent brakes do self bleed over time but you can help the process by leaving the brakes wedged on and pressurised over a weekend. If you also dust all joints and nipples with talcum powder (one for Prop no doubt) you'll also easily see if you have the slightest weep of fluid. Make sure the rear shoes are properly centered - thumping the drum with a rubber mallet as the brakes are applied can help, but again after a period of bedding in they will need adjusting again to dial out any slack and subsequent long pedal.
Fergus

Alex you need to clamp off all the flexible brake pipes,(using brake pipe clamps)then try your pedal, if you now have a good pedal, you will know your problem is not the mater cylinder, or air between that and the flexible brake pipes, next get some one to sit in the car and feel the pedal, release the clamps one at a time checking the pedal movement after each removal, if the pedal drops after a removal then you will know which wheel your problem is in, and if you still have a problem with all the flexibles clamped off then your problem is between the flexibles and the master cylinder,this is the best way I know to prove where your fault is, as it eliminates each component in turn and cuts out the guess work and renewing parts that are not faulty, this method of testing cant be used if you have Goodridge type braided hoses, as you cannot clamp them to cut off fluid movement, A.T
Andy Tilney

Alex,
You need to determine which leg(s) of the brakes is giving the problem. Use a process of elimination. Method:

(i) With hose clamps (or modified mole grips), clamp off the two front hoses and the rear hose.

(ii) Operate the brake pedal. Do you still get the fault? If so, the problem lies with the BMC or pipework before the clamps.

(iii) Remove one hose clamp in sequence, each time operating the brake pedal afterwards. The process should identify which leg(s) is giving the problem.

(iv) If the problem lies somewhere with the rear brakes, you can remove each drum in turn and clamp the wheel cylinder so that it doesn't operate. Again, try the pedal.

Aside: you might have been supplied with wrong new parts. If you have a vernier measuring calliper, check the inside bore of the rear cylinders.
J Thomson

To centre the shoes I do as Fergus says and then also get the attractive assistant to gently footbrake as I am moving the rear wheel by hand while jacked up. I adjust up between thumps and rotations until no more adjustment is possible. Then I know they are as near as I can get to being properly adjusted without a road run like when I run the MoT out.

Before assembly I ensure the back plate and edges of the shoes are clean, flat and have a tiny smear of copper grease on the back plate rub area and the edge of the shoe to ensure free movement.

Hope this helps.

Dave Squire

If you do change the rear cylinders use later morris minor ones (up to 1971) with a 3/4" bore. The frogeye and early morris minor ones up to 1962 were 7/8" bore
Bob Beaumont

Remember too that it can take 200-300 pumps of the pedal to get new seals to bed in properly in M/C bores and this can give grief when trying to bleed. It is a relatively recent issue which must be due to synthetic rubber used in the seals.

It was pointed out in a previous issue of the MG club magazine, and it did happen to me a few years ago when fitting a new M/C. Went through my usual bleeding procedure which always works without fail, and was getting nowhere and I could feel the seals were just not bedding in, so I sat in the car for a few minutes and pumped the pedal many, many times, hundreds of strokes in fact.
Then tried the bleeding and it worked as expected.

May not be the problem in this case but it is something to remember, if bleeding with new seals is causing problems.

Mine has worked perfectly ever since
JB Anderson

A lot of good replies, My hoses are steel braided with a teflon tuben inside so i can't clamp those unfortunately. Clamping the rear cylinders though I can do. Small steps.

Thanks for all your input.
Alexander Sorby Wigstrom

A bit of a long shot...

Could it be something like the calliper seals causing the pistons to retract into the callipers? Can you see if there is any gap (or if the pads are loose) before the first press on the pedal (when you might expect to get your long pedal travel), and whether the gap has gone after you have pumped the pedal? If this is what is happening, maybe it might sort itself out once the brakes have bedded in and the pistons are 'resting' at a slightly different position.
Jonathan Severn

On that last point, it may also be worth checking the disc run out with a dial gauge. If they are warped, or have excessive run out then that will push the caliper pistons away from their proper close contact position against the disk. It then takes more fluid pumped, = longer pedal stroke - to bring the pads back into contact with the disc.
GuyW

I think this a good example for not using braided Teflon hoses, which I personally think are a complete waist of money on a road going car,
Andy Tilney

Can't clamp them, but the brakes feel loads better.
Rob Armstrong

Check simple things like wear in the clevis pin at the master cylinder, a small amount of wear in the moving parts is magnified to cm's at the pedal
Robin Cohen

Alex

Really good advice in this thread so far.

The Morris Minor 3/4 inch single rear brake cylinder that fits Frogeye Sprite rear brake back plates is for the 1098cc Morris Minor, part numbers: GWC1116 and Lockheed number LW11287.

Dave on another thread - Pedal Box Adjustment - offered this advice on adjusting the brake pushrods on the master cylinder, which goes rather well with Fergus's advice above:


1. Slacken the adjuster nut on the m/c push-rod.

2. Set the length of the push-rod to give a free movement of the pedal pad of approx. 5/32" (4mm) before the m/c piston begins to move. the push-rod must have a minimum of 1/32" (.8mm) free movement before the piston begins to move.


Best wishes
Mike

PS Do not give up - I have been having similar problems!
M Wood

Alex, just a thought have you checked the internal dimensions of the rear brake drums? If they are older and either worn or been skimmed too far then there will be a long pedal travel before the shoes fully engage with the drums sometimes even when fully adjusted. Drums can also wear so as to be tapered making accurate adjustment difficult.
Chris Hale

Jonathon's long shot definitely does happen, I have found it more than once. It only takes 20 though of spring-back and you need almost the full stroke of the pedal to get the pads back to the mark.
Solution is to dismantle the caliper, clean everything and lubricate the seals & pistons.
Paul Walbran

(sigh) I see fat fingers goofed again, make that 20 thou in case anyone can't work it out.
Paul Walbran

Hi all, I've been having brake problems for a while and my Frogeye hasn't been on the road for a year or more now due to this. I'm at the last hurdle now and need some advice.
The car is a Frogeye, front discs, new M/C 3/4" bore, new front calipers (pattern ones are all you can get these days it seems) new flexi hoses front and back, new rear cylinders, Moris Minor ones (3/4" bore I think?)
Mostly new copper pipes apart from the long front to back one and across the front of the car. Absolutely no leaks and bled with a lot of brand new Dot 4 with a new Easi bleed, no air in the fluid at all!

The pedal travels too far and goes rock hard v.close to the floor. I clamped all 3 hoses and it's rock solid. With pressing very very hard on the brake pedal I did manage to get it to sink to the floor a few times but it then seemed to stop. I double checked I had no leaks thinking I'd burst something but no problems.
I unclamped the front 2 pipes and the pedal felt good, about as much movement as I would think acceptable. A few quick pumps in succession and the pedal was a little higher but not spongy at all.
When I unclamped the rear flexi it went back to being terrible, close to the floor before it goes hard, a few pumps and it feels OK, not spongy and the travel is less.
I adjusted the rear adjuster to lock up the brakes and it made no difference at all. Clamped up the rear flexi just to check and it was good again.
So, I know it's the rear brakes, I know the shoes are in the correct orientation so how do I fix this?
There was some less than even wear on the shoes so what should I be looking for?

Thanks
MArk
Mark M

Are you adjusting the rear brakes with the handbrake slackened right off, or better still, disconnected?
Adjustment does need to be very closely set, almost dragging.
GuyW

No, handbrake is off but not disconnected.
I understand about the dragging comment but even if I lock up the drum via the adjuster I have the problem.
I will remove the drum and take some measurements across the shoes and check the cylinder can move freely.
Mark M

Puzzling! Narrowing this down then.
If the pedal travel is too long, but ok when the rear hose is clamped, then the extra fluid displaced on the longer stroke must be going to the rear cylinders. Assuming they are not leaking, then this must also result in movement of the rear cylinder pistons.
If this movement is taking an excessive amount of fluid, then either the rear cylinders are the wrong size to match your disc brake (m/c) conversion, or the shoes are wrongly adjusted.
Or, you still have air in the rear cylinders!
GuyW

agree - I'd go for 17mm rear cyls not 19mm
David Smith

Mark.
Your conversion should not be a problem. I have done it as a demo at the NEC before now. Some (most?) parts did need some fettling.

Ensure that you have the 3/4" bore Morris Minor cylinders at the rear and that the cylinder can slide up and down.

Undo the cross rods for the handbrake when you adjust and ensure that they are not impacting on your fitting nor adjustments.
They may need their lengths altered.

Have you replaced the original foot pedal to master cylinder pushrods to suit the master cylinder pistons. There is about 1/2" difference between the pushrods used for 7/8" & 3/4" master cylinders. I think suppliers just supply one length and you are expected to trim as required.

There have been numerous faults associated with TRW brand Master Cylinders see www.mgaguru.
This site is a haven for information on many issues.

Alan
Alan Anstead

Thanks all for your comments.
I have painted the backing plates so the cylinders may not be sliding as they need to, I will check this for sure.
I should also add I had this problem before I changed the rear cylinders when I first replaced the M/C last year. When I was able to start working on the car again this year the whole back axle was such a mess I decided to remove it, clean it up and refit and used this opportunity to add the Morris Minor Cylinders. So although the cylinders have changed, the drums and shoes have not.
I will disconnect the handbrake to eliminate this.
The pushrods are cut down ones as you say, I have adjusted the pedal travel and there is minimal play before the MC actuates, in fact when I clamped all 3 flexi's and touched the brake pedal I was surprised how little the pedal moved, as soon as it touched the piston it went solid which was encouraging.
I thought the M/C was a Lockheed one, when I had it removed last weekend I'm sure it has Lockheed cast on the side, I could be mistaken..
I've ordered a set of new shoes as they are cheap, if I get time one evening this week I will pull the drums off and have a look at the basics, the more prep I can get done before the weekend the better the chance I have of being able to take her for a drive this weekend which I sorely miss.
Mark M

Long overdue the follow up to this. The Frog is now roadworthy and I have taken it for a couple of hours of driving including some aggressive brake applications when safe to do so.
I checked the rear cylinders were free to move and they were but I disconnected the handbrake and replaced the rear shoes as the wear wasn't even on the old ones. Putting the retaining spring/clips back on took a ridiculous amount of time but I finally found a technique that worked so the final one was faster than the first.
I'm still not 100% happy but at a bit of a loss now, the brakes work well and I can lock the front wheels but the pedal travels further than I would like.
Even if I take all the slack out of the push rod so I know the pedal is actuating the master as soon as I touch it the pedal moved further than I would like.
After a run and using the brakes many times I re-adjusted the rear shoes but it remains the same.
If I clamp all 3 hoses the pedal is solid, no movement, as I release each clamp the travel increases slightly until all 3 are released and I am where I am now.
Everything is new other than the front brake pads and discs and 2 hard brake lines. Zero leaks which I have checked several times. Any suggestions?
Mark M

Mine is VERY sensitive to rear shoe adjustment. Just one turn back and they feel spongy. They aren't bedded in yet though so I'm hoping they will get better. I have to adjust them to the point they are binding then go for a drive and back off if they are still dragging.
John Payne

I always find the brakes on my car are much improved if if set them up, adjust and bled them and then use the car for maybe 100 miles or so. And then adjust and rebleed them again. The 100 mile 'shake down' literally does that. Vibration and repeated heating of the fluid dislodges air bubbles trapped at the various joints and bends in the system, causing microscopic bubbles to coalesce until large enough to bleed out properly.
Brakes are always noticeably firmer after this routine
GuyW

Thanks, that was what I was hoping, plenty of driving, re-adjust and maybe re-bleed (I've become quite adept at this now!)
Mark M

Mark, in my theory it is that the second bleed is the key part. Otherwise it probable that after 100 miles you have just got used to it!
GuyW

Mark M, I think you said that you replaced the rear shoes because they had worn unevenly but you had not replaced the drums. If that is the case, I wonder in what way the shoes had worn unevenly, and whether the drums are badly worn and in need of replacement? If the drums are worn then their curvature will not match that of the shoes, so you will have only a small portion of the friction material in contact with the drum surface when you first apply the brakes. I don't know whether continuing to push on the brake pedal provides sufficient force to deform the shoes so that more friction material comes into contact - and whether this shoe deformation therefore accounts for the longer travel.

Of course, this may all be a red herring, but no doubt someone else will tell me if this is so!
Jonathan Severn

Alex, I have only scanned this long thread so may have missed something. But you say the MC was sleeved. The smaller pistons are shorter than the 7/8" diameter ones. This means that the small hole in the cylinder bore needs to be in a slightly different place. Was this taken into account when the sleeving was done?

Les
L B Rose

Hi

When the combined dual cylinder was changed to 3/4inch diameter (or modified in the case of the first poster in this thread by sleeving from 7/8 inch diameter) to suit front disc brakes, was the residual valve changed to a restrictor valve?

See: https://www.gerardsgarage.com/Garage/Tech/DbrakeUg.htm which also has information on pushrod lengths that Alan refers to above. Useful info also in: https://www.gerardsgarage.com/Garage/Tech/DBrake/TandemMC_Part1e.htm

Not sure why I did not post this in 2016 including the links!

Thanks
Mike
M Wood

PS - Alex did you get your brakes fixed - if so what world?
M Wood

Jonathan, Good point, the drums appear to be fine. They were replaced in the past, quite some time ago but due to the very low mileage I have done over the past 10+ years they still look in good shape.
I believe the shoes weren't really fitted well which is down to my bad!
Mark M

This thread was discussed between 01/11/2016 and 16/06/2020

MG Midget and Sprite Technical index

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