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MG MGA - Brake bleeding tips for spongey brakes

Guys,

I spent the day yesterday getting my transmission in and completing my hydraulics rebuild. Wow, what a long day but its very rewarding to see things go back into the car instead of taking them out.

With all new brake lines and a M/C rebuild, it was a perfect time to switch to DOT5 silicon fluid. I was rather disappointed though when after bleeding the brakes twice, it still took 5 or 6 pumps to get any pressure. I consulted this board and got a lot of great tips, and think I came up with one or two myself. The good news is that although I'm not done yet (still have three wheels to go), the brakes now stop after 3" of pedal travel.

If you want to read my experience in detail, navigate over to http://mgablog.com/archives/2005/08/brake_and_clutc.html. Otherwise, here's the gist of what to do if you have spongey brakes that just won't bleed.

1. Adjust all of your brakes to drag just a bit, and bleed again. See if the problem is fixed.

2. Let the car sit overnight with the pedals depressed. This allows air to rise to the M/C reservoir tank. When I woke up this morning, the brakes had improved from 6 pumps to 1 1/2. Also, my M/C tank had nearly run dry... and this was after TWO thorough bleedings!

3. Clamp off every flex line and try the brake pedal. It should have 100% resistance - if not, you have a problem with the M/C seals or brake lines. Check for leaks by putting the car on a clean surface and pumping the brakes. If you don't have a leak, then you probably have leaking seals in the M/C.

4. Otherwise, remove the clamps one at a time and see if you can identify where the problem lies. This is what happened in my case. Turns out that ALL the wheels are soft.

5. At this point, the wheel cylinders or the banjo bolts screwed into them are highly suspect. Check if you have copper fittings around the bolts - if not, get them and install. They seal the banjo bolt nicely.

6. If the brakes still don't work, you most likely have air trapped in the wheel cylinders. Disassemble the drum and drip brake fluid into the inlet into the cylinder. Pump the cylinder back and forth. Keep dripping even after air bubbles stop - it doesn't hold a lot of fluid, but it takes awhile to get all of the way in there. I did this for 10 minutes on mine.

7. Plug the hole with something. The plastic seals that Moss ships with their cylinders work perfectly for this!

8. Reinstall. Pull the seal and quickly screw the banjo bolt back in place. This might be hard because you'll have brake fluid all over you at this point.

9. Now bleed the system. I used a vacuum pump. Three tips here that I haven't seen from anyone else.

9a. Don't go over 10 PSI. In my case, this was so much vacuum that it was causing air to suck in through the bleeder tube where it was attached to the bleeder.

9b. Pump the brake pedal slowly 2-3 times to get fluid into the tube.

9c. If the drum is assembled, make sure that the emergency brake isn't on while bleeding - this will allow air to remain in the cylinder. If disassembled, pull the brake lever in while compressing the cylinder. You'll see a lot of air bubbles come through the tube.

R Stokes

You seem to have had problems. The entire bleeding of my brakes and clutch from a completely renewed system took something like an hour in total. I used a pressurized bottle of fluid that screwed onto the master cylinder. I then loosened each bleed nipple in turn until it ran clear fluid. Never had to depress the clutch or brake pedal during the process. Worked great first time. Over here the pressurised bottle system is called Eezi Bleed.

Steve
Steve Gyles

Steve- We have access to Eezi Bleed system over here thru Moss. I have one and have had the same results as you, well worth the expense. Gary
gary starr

It has been my experience on both our TD and Magnette, that when starting with a system that is completely new (or cleaned), with no fluid in the lines or the wheel cylinders, that it was necessary to fill each wheel cylinder with fluid before assembling everything together. This is because the bleaders on the T series, MGAs and Magnettes really only blead the lines up to the wheel cylinders and not the cylinders themselves. The result is that air is trapped in the wheel cylinders that is very difficult to work out by any of the normal methods. Cheers - Dave
David DuBois

I am very confused??? If you left the system overnight with the pedal depressed how did air rise from the system into the MC reservoir? With the pedal depressed there is NO CONNECTION between the master cylinder reservoir and the system.

I must be extremely lucky for when bleeding brakes I have never had a problem with such an easy task. Simply by filling the master cylinder and opening a nipple if you wait a few minutes fluid under the force of gravity will find its way to that nipple.
Bob (robert)

I seem to be in tune with you at the moment Bob. I have never had any problem getting air out of the system. It has always been a quick easy job.

The only problem I once had with the Eezi Bleed (I laugh now when I think about it but it was not funny at the time) was when I disconnected the pressurised bottle from the MC without first disconnecting the bottle from the front tyre inflator valve. I had 27PSI of silicon fluid blasting everywhere!!

Steve
Steve Gyles

Hi everyone,
why do people have problems bleeding MGA brakes? As Steve has mentioned, eazi bleeds are brilliant, max pressure as I recall is 14-15 PSI. My brakes are very good, Steve's rear bumper will stop you quicker though!!

Map Reading Terry
Terry Drinkwater

My brakes have been good from the start. However, every couple of months, I have to bleed the clutch. I have replaced the rubber in the slave cylinder and replaced the main hose that goes to the clutch slave cylinder, but I still must be getting air in somewhere. Any tricks to locate the air leak to the clutch?
Thanks, Jack
Jack Weiss

This thread was discussed between 07/08/2005 and 18/08/2005

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