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MG MGA - Need more brake pedal

After I bought a '62 MGA MarkII, I discovered that the rear brakes were not working at all! The wheel cylinders were frozen, and had to be replaced. Front calipers in good shape, new pads, new rear brake shoes, and new cylinders. And the master cylinder has been rebuilt. But the brake pedal almost hits the floor!! When I squeeze off the rear brake line, there is good pedal. Looks to me like there is a problem in the rear cylinders. The bottom piston has to travel too great a distance before actually spreading the brake shoes, because of the parking brake lever.
Has anyone had this problem before? Is there a fix, might I have bought bad brake cylinders? Its no fun to have to pump the brake pedal everytime I want to stop. Help please??
ERB Brewster

Have you adjusted the the rear brake shoes using the adjuster (access through a hole in the brake drum)? - see section M2 in the MGA Workshop Manual.

Steve
Steve Gyles

Just guessing here, could you adjust the parking brake up to make it better? If so, would that be just a band-aid fix?
Tom

Dick, did you replace the rear brake hose?-- I have heard people say that a tired old hose can swell under pressure. FWIW
/gil
gil

Hi Erb. It sounds lile you may need to bleed the hydraulic braking system. If adjustment of the back wheels, and brake hose replacement fails, that is most likely the problem. Cheers. Glenn
Glenn

We had the same problem on our 1500. We adjusted the cylinders all the way out, and still too much pedal travel. Finally measured up the brake drums, they were way oversize. Bought 4 new ones (1500 has 4 wheel drums) and it fixed the problem. Fast fix, but expensive.

Russell
Russell

Thanks to all of you. Yep, no air in the brake hydraulics... bled and bled. New brake hoses and lines. Brakes adjusted, so that's not it. Am going to play with the parking brake adjustment, but I agree, this is a band-aid fix, if it works at all. Pulling the hand brake up a notch of two doesn;t seem to help. I will measure the drums, never thought of that. But, some of you R&D folks, do the new brake cylinders have too short a piston? Is there a way to make it a bit longer, with a washer? Or maybe a little stronger spring under it, so it doesn't go all the way back down? Like I say, and and all ideas are welcome.

Thanks again.
ERB Brewster

The comments about adjusting the e brake cable to make up for soft pedal is a Bad idea. If the e brake is too tight then all you do is stretch the cable causing soft pedal and keeping you from adjusting the brakes properly. To adjust the rear brakes the first step is to loosen the e brake cable then adjust the shoes untill the wheel won't move by hand then backoff 1 click. After adjusting push the pedal Hard to seat the brakes and then re check adjustment. If you cant get the brakes tight enough to keep you from moving by hand the the drums are likley to large inner diameter.
Only after getting a proper pedal do you adjust the e brake pedal.
When the shoes are installed you must put lube on the points where the shoes touch the backing plate. I use anti sieze. If the shoes are not lubed they tend to not "center" properly. Also if the cylinder is not installed correctly it won't "float" or slide back and forth to apply and release the "other" shoe.
I suspect that the spring clips that attach the rear cylinders are on wrong and causing it to bind.
Good luck
Randy
PS the cyl is supposed to fully return and seat, unlike a caliper that stays out.
R J Brown

RJ,

Thanks. A question. Should I be able to move the brake wheel cylinder by hand? Should it float that freely?

Dick
ERB Brewster

Yes, the rear cylinder must slide in the back plate, this allows the two shoes to balance on the presure (you will notice that there is only one piston)

The best recommendation I make with brakes are

1. to replace all flex hoses about every ten years,
2. use Si fluid
3. If a brake part is broken or worn out, replace it whatever the cost.
4. Use a pressure bleeder to get the system free of all air.
5. Flush through every few years to make sure any debris is removed (it's amazing how this accumulates, even with Si fluid).
6. Change Master cylinder seals when you change the flex hoses.
7. Use a little copper grease on the backplate where the rear cylinder mounts, also on the back of the brakepads if you have discs at the front
8. If you still have the original pipes, or a mix of pipes, change the whole lot to Automec or something similar.
9. Include brake fluid level control as part of the normal fluid control routine.
10 Use an eezibleed from gunson - very fast, very effective. Make sure you top up the tyre pressure after each cylinder, as the pressure drop in the tyre leads to a marked drop in effectiveness on the Gunson (I have never managed an airtight seal on this...)

This will lead to a hard pedal that stays hard.
dominic clancy

The fact that the rear brake cylinder also manages the parking brake is a red herring in this scenario. If, with the handbrake off, you have rotated the brake adjuster through the brake drum adjusting hole until the cylinder locked and then backed off one notch, the brake is adjusted both hydraulically and mechanically. Therefore, from all that has been decribed I put my vote with those who say air is in the system.
Steve Gyles

PS. I meant brake drum locked, not cylinder locked. Pity you can't edit your threads in this BBS.
Steve Gyles

Dick,
I had exactly the same problem when I rebuilt all brakes on a new to me 1500. I replaced all the cylinders, had the drums turned, and replaced the shoes. I tried bleading over and over again and the pedal would still go nearly to the floor unless I pumped it. The problem turned out to be that the curve on the new shoes did not match the radius of the drums. I adjusted the shoes so they were dragging quite a bit, then carefully drove it. After the shoes wore to match the radius of the drums, I re-adjusted the shoes, and had a firm pedal with very little travel.

Jeff
Jeff Schultz

Dick
Yes it should float that freely. Because there is only one cylinder it has to be free enough to allow the springs to return the cyl to release the "other" shoe.
The fronts have two cylinders and the rears have only one. With 2 front and 1 rear the rear shoes recieve 1/2 the force that the fronts do. This is how MG avoided using a proportioning valve. It is also why rears last longer than fronts, they do less work.
Dominic's advise is right on the button. Brakes are not a place to save $$$. Do it right at first and then flush the fluid every 2 years.
Randy
R J Brown

Please don't think I'm being rude but braking systems are VERY important!! If you're not experienced let somebody with the skill and knowledge do them. 10 out of 10 for trying but you might hurt somebody/yourself or your 'A'

Terry Drinkwater

Terry

You are absolutely right in every word you say, especially where safety is concerned. But surely one of the great things about this hobby is the learning aspect - learning to sort things out for one's self. For example, it has been good on this site in the last few months seeing someone like Tysen come on the site every day with a new question. He is having a go at everything on his car and, give it a year or two, will be an accomplished MGA DIY engineer, keeping another historic vehicle safely roadworthy and passing on his new found skills to others.

I have certainly been down the early learning road and played about with the brakes, the steering, the suspension etc, all without any formal training. Mostly I have got it right, but occasionally wrong, and yes, fortunately without any major mishaps. But I would like to think that I have asseessed the risks and carried out post rectification tests with due care and attention. I think also that people who come on this BBS to ask questions are thinking about the problems and want to learn. You have to give people that opportunity. They are unlikely to get that learning experience from a professional workshop jobsheet.

Certainly, the overriding caveat must be that if, at the end of the day, you are unsure of your ability get an engineer to check your work over.

Yes, Safety First, but also give people the chance to ask questions and learn.

Steve
Steve Gyles

Steve is absolutely right.
My first car was a 58 MGA coupe. With very limited training and a well read sevice manual I was able to learn more about cars by working on that car than any other experiance in my life. It taught me how to work on cars. I rebuilt the engine,put fresh syncros in the trans, replaced the clutch, rebuilt all the hydrlolics,learned to rebuild and set up the carbs, pulled the wings off and had the rust fixed and the car repainted. Changed a fuel pump in the desert, broke the crank in the winter.
Later after Tech school and a stint working for others, I have owned a repair shop for 24+ years.
To own one of these cars you need to know it intimately. They are as simple and as easy to learn as a car can be. Doing your own work is what it is all about.
When someone asks me if they can pay me to fix their MG I tell them "No but I will show you how you can do it". Advice , encouragement and a will to learn are all it takes. If you understand all the whats and whys you will be much safer on the road than if you don't.
There are enough good people out there that any question can and will be answered. The only stupid question is the one left unasked. There is nothing you can't work your way through.
Keep em rollin
Randy
R J Brown

Dick,
Having seen posts about the poor fit of replacement parts, and having torn my hair out over the same problem myself, I would suggest that you remove the drums and shoes, and check that the shoes match the radius of the drums.

The center of the lining on the shoes should contact the drums, and and there should be a very slight clearance at each end. If there is is a gap at the center, the shoes will not give full breaking power and may squeal or chatter. If the gap at the ends is too great, the shoes will flex to make full contact, and the pedal travel will be excessive. http://www.winbrake.com/trainingmaterials/SpongyPedalDiagnosisGuide.html

I don't know what the gap should be, but think I saw one web site that said about .005". I don't know if there are any brake shops around that still have a radius grinder. In the old days when most cars had drum brakes, most brake shops had them. Like I said before, after rebuilding the brakes, my pedal was going 3/4 of the way to the floor. I adjusted the brakes so they were dragging, and drove around the block several times stopping occasionally to make sure the drums weren't to hot. I was then able to adjust them properly, and have very little pedal travel.

This may not be your problem, but it is easy to check, and if I had checked mine before starting assembly, it would have saved me days of pulling my hair out.

Jeff

PS I agree with Steve and Randy.

Jeff Schultz

Hi Guys

Sorry if I have ruffled a few feathers, but as I have been a mechanic for over 30 years ( Am I that old!! )
I've seen more than my fair share dangerous workmanship.

'A' rear brakes are very simple, if your cylinders are new, both of the pistons should move freely, the lower one is hydraulic, the upper one is moved by the handbrake lever/cable, the cylinder must slide in the backplate, the handbrake cable should be disconnected from the cylinder lever when the rear brake are adjusted ( you only need to do one side as the cable is linked to the other side ) never tighten the cable to try and improve the brake pedal travel, this doesn't work. Adjust the brakes and the pedal should be good, the hydralic piston doesn't return and seat as suggested as there is spring forcing it up, the shoes are returned by the springs and rest on the adjuster which governs how slack or tight the shoes are. If it works please send me a new head for my twin cam, if not cry (works for me). Don't adjust the handbrake cable to tight. If you can't lock the shoes with the adjusters your drums may be worn out.

Good Luck

Terry

Don't listen to Steve Gyles, he knows how good my brake are !!!!
Terry Drinkwater

Good one Terry. Sensible advice. At least my brakes (and the rest of the car) stopped you straying across red traffic lights!!!!
Steve Gyles

This thread was discussed between 24/09/2005 and 27/09/2005

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