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MG MGA - 'Bleedin' Brakes!'

Having imported my MGA 1500 (with standard drum brakes) to Holland, I have been totally restoring it with 2 aims: getting it road registered for the Netherlands where we live (appointment 12 July '05) and going to Silverstone (23-24 July' 05). I have struck a real problem with the brakes / clutch, with neither working yet. Despite bleeding them until no air is coming through, and no apparent leaks in the system, the pedals still go straight to the floor with no feel to them at all. Today I replaced the master cyclinder with a brand new one (I had rebuilt the old one with new parts) and although the brake pedal will now pump up to acceptably firm after a few pumps, after leaving for 5 seconds the brake pedal goes straight back to the floor. Several bleeding sessions, moving at least 2 pints of fluid, still seem to make no difference.

I would urgently appreciate all advice and ideas to getting this fixed, so that I can meet my 2 deadlines.
G.M. Adams

Are you using silicone brake fluid? With silicone fluid, it can be very hard to bleed the brakes properly. If bleeding by pumping the pedal, you need to do it very slowly to avoid creating bubbles in the fluid. Just letting it sit for a day or so can help. I prefer a pressure bleeder, but that of a vacuum bleeder will help greatly. Pressure or vacuum bleeding is almost a necessity for the clutch, since there is no check valve in the clutch side of the master cylinder.

Another thing to check is the adjustment on your brake shoes. If the clearance is too great, the brakes will pump up, but if you let up the pedal for several seconds, it will go back to the floor. I had a problem when I installed all new cylinders, brake shoes, and turned the drums. I had symptoms like you described. The brakes would pump up, but I could not get a firm brake pedal without pumping. I finally adjusted the brakes so they were dragging slightly, and drove the car a little. After that I was able to adjust them properly with a good firm brake pedal. If you have replaced the shoes, they may need to be bedded in to fit the radius of the drums.

Jeff Schultz

Sounds like the seals in the MC are leaking internally, then the system loses pressure without losing fluid.

There are seals around that are much too tight for an original MC. This may be what you need, order a set from Moss UK
dominic clancy

If your Master Cylinder is badly worn inside it may have a "ridge" at the end of the piston's travel that actually CUTS THE "LIPS" OFF YOUR NEW SEAL DUE TO PEDAL OVERTRAVEL, ALMOST INSTANTLY DESTROYING THE NEW SEAL! My old 1960s vintage "POPULAR MOTORING" magazine suggested placing a WOODEN BLOCK under the brake pedal to prevent the pedal travelling past the "NORMAL PEDAL TRAVEL RANGE". U.S. mechanics usually "HONE OUT" inside the Master Cylinder to eliminate the "ridge".
wh watts

This is very strange as you have replaced the master cylinder block?
I can give a tip for the clutch as it often does this and I now have a method. First thing to do is get down to the slave cylinder, remove the clevis pin and push the rod back into the slave as far as possible. Fix the rod in this position (I find wire around the clevis and slave body to work well). Now bleed the system. This removes air trapped in the slave as far as possible.

For the brakes I am not sure what the problem can be although I know that there can be a similar issue if the pads are quite worn (air sits in the slave cylinders). Maybe check that?

I hope you make it to Silverstone. I will be driving over on Friday morning from Brussels via the tunnel so will look out for you. If you see a white 1600 with boot rack and Belgian number that is most likely me!!

If you need any help then let me know. I don't have much time between now and Silverstone but could maybe help out if all else fails.

Neil

Neil Purves

I think Jeff's got this one spot on espacially as you have a new master fitted. The silicon fluid which I use too has to be bled carefully to avoid aeration and you should ensure that you haven't got too much shoe clearance. Are you turning them the correct way (been there !!)

Now, ensure that you use a clear plastic tightly fitting bleed tube and put the end into a jar containing a little brake fluid. Have a ring key on the nipple, open the nipple half a turn only and get the assistant to depress the pedal. Tighten the nipple and only then release the pedal. Slacken the nipple and depress the pedal again and so on. Top up the cyl after five or six pumps. The tightness of the bleed tube etc is vital to ensure that air cannot be drawn back in. Bleed the longest line first i.e. LH rear then RH rear, LH front and so on.

If as you say you have put a couple of pints through the system and still have a problem I really suspect shoe clearance. Do them all up tight and see what happens before you start bleeding again. You should get a pretty solid pedal. If not leave them like this and bleed the system.
Iain MacKintosh

Hi
Sounds a bit of a mystery, try clamping all the hoses on the brake system, this eliminates any problems at the wheel end of the system, if there is no air in the system, the pedal should be solid, if so unclamp one hose at a time to find the faulty brake. If your pedal is still soft when all hoses are clamped, the problem is at the cylinder. Do your pushrod's have sufficient free play? As mentioned, its better to pressure bleed than pump the pedal, this goes for the clutch aswell. Silicon or ordinary fluid makes no difference to bleeding etc, despite what people say. At least silicon doesn't take the paint off! Hope you sort it out

Terry
Terry Drinkwater

Thanks for your info,

I have today passed the RDW test, like a first MOT, and have the reg. number for the car. So I can proceed with all the finishing off prior to Silverstone, We are traveling this weekend by Ferry so our paths will not cross Neil.

The clutch problem was simple to solve, look in a book and realise that i have connected the inlet to the outlet and vice versa! then self administer No. 10 hammer.

The brakes were a combination of thorough check of all unions, correct adjustment of all shoes and some weeping of fluid arround the rear brum banjos cured by putting copper washer above and below banjos.

The pedal is now soft on the first push and then firms up well and the brakes work well enough for the MOT test brake machine, however after unloading the car form the trailer I see brake fluid by the right rear so hi ho off to work.

I have been working full time on the car since January 05 and in the last 6 months completly stripped chassis and body to bare metal, and re-painted then done a nut and bolt re build, I am proud to say that I have done so much work myself. The moment this morning when I drove the car for the first time from garage to trailer will stay with me for a while.

I have refered to this BBS link on a daily bassis and would like to thank all the regular contributors, keep on chipping in with your hints and tips it really makes a difference.

Thanks again Graeme Adams.
G. M. Adams

Graeme
Congratulations on a job well done. It is very satisfying to have that first drive? Even after just a small job it can be very satisfying. I spent last Monday replacing the cylinder head gasket as it had blown due to incorrect washers under the stud nuts and the first fire-up and drive was also an event!!

I wish you a safe trip over to the UK and maybe see you in Silverstone. I will look for a recently painted, Dutch registered car.

Neil
Neil Purves

Dear Graeme,

Just wondering where you're located.
We'll be driving to Silverstone as well, we'll leave on the 22nd.

Looking forward to hearing from you.

Regards,
Koen

struijk@ipl.co.uk / cstruijk@home.nl
Koen Struijk

This thread was discussed between 09/07/2005 and 16/07/2005

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