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MG MGB Technical - 1980 MGB brake bleeding

Afriend and I replaced the rear brake hose on my 1980 MGB yesterday. Our attempts to bleed the brakes did not get any fluid to the rear brakes. Will someone tell me what I must have not done prpoerly?

The usual cause is that the tow truck morons anytime in the past have crushed the steel pipes on the axle, usually adjacent to the spring mounts. Caused by the big iron J hooks that they tie the car down with, and the crush area can be very small and hard to spot; best to run your fingers along the entire length of the pipe. I wind up replacing one or both on every single car that gets brought in on a tiltbed/rollback/trailer. They can be like that for years, since the rear brakes do so little (even if they work) and most drivers never notice their absence.

Second possibility, if the hose was disintegrating inside, is that bits of rubber are blocking the unions or pipes anyplace between the hose and the bleed nipples.

Loosen joints sequentially from the hose to find the location of the problem.

FR Millmore

I had a crushed brake line on the top of my axle on my 65. I wondered for sometime why I couldn't get the left rear to bleed properly. Then I found the dent. These were the old aluminum lines that easily crushed. I bought a new line from Moss and bent it to fit the old pattern. It was a little long but I worked it out. No more problem.

Funny, I didn't notice that brake wasn't working until I tried to bleed it.
Robert McCoy

"Funny, I didn't notice that brake wasn't working until I tried to bleed it."

Not surprising, it only accounts for about 10% of braking effort. Any more and they would lock as the weight transfers forwards.
Paul Hunt

Gentlemen, thank you for your responses. Today I racked my MGB and checked for crushed brake lines and found them all in good shape.
I then loosened the fittings at all ends of the "T" at the rear axle, as well as loosening the brake line fittings at the rear drums to check for flow.
In all cases I got fluid flow. I then removed and blew out the bleeding screws. I eventually got fluid to pass from the right rear bleeding screw.
a co-worker helped me to try and bleed the rear brakes, but we were unable to get any fluid from the left rear drum bleeding screw.
The brakes are still very soft.
I'll look for new wet spots undeer the car in the morning.

Fluid passed through to the brake cylinder, but not out of the bleed screw after attaching the line. Have you checked the brake cylinder itself or at least the orifice for the bleed screw?
Rick Penland

master cylinder this problem whenever i bleed the brakes on my B. the only way i get them back again is by using an Eezibleed kit which basically connects to your tyre and uses 30psi to push the fluid through (
Ian Jackson

Should be pretty obvious that if you have fluid "to" the cylinder, but not "from" the bleed screw, then one of the two holes in the cylinder is blocked, assuming the bleed screw is actually clear. That will generally result in air in cyl. = squishy.

Bleed screws get cleaned out by means of two drills in the intersecting holes - if you can't see the central drill through the side hole it isn't clear! Blowing through them can be misleading.

If you have to do all that, then something is blocked or severely restricted someplace. I normally bleed MGB by gravity only; open a bleeder and let it go til it drips regularly, then do the next one. If the system was entirely empty, it may take a few pumps to get some fluid down the pipes.

I just finished a 77 that had hoses dated 76 (back, blocked solid), 79 & 80 (front, noticeably restricted), and both rear axle pipes crushed.
There were many bits of rubber in the calipers when dismantled, and I did have some difficulty bleeding the fronts until I took the steel lines off and blew compressed air through them - likely more rubber bits.

FR Millmore

Very often when bleeding the brakes air is drawn back around the threads of the bleed screw as you lift the brake pedal up. It is a two man job and the procedure is. Open the bleed screw, depress the pedal, tighten the screw, lift the pedal, wait a second or two, open the screw, depress the pedal and so on. Hope this helps. Trev.
Trevor Harvey

It's possible to bleed with one person if you don't mind getting up and down several times. Find a 2x4 and cut it the length needed to hold the brake pedal down and wedge it against the seat. Depress the pedal, insert the 2x4, crawl under and close (or open) the bleed screw. Repeat as needed until brakes are firm or your back or knees wear out, whichever comes first.

30 years back there inside your brake drums has likely corroded most of your brake components. It's not that expensive to change a lot of it. On my 80LE, I replaced the rear brake hose as you have (Moss replacement), took the brake pipes (crushed in a couple of places) to a local brake shop and had new ones made with British ends, cut to length and bent to the original pipe's shape for $25 for both.

Rear brake cylinder kits are available, but I got totally new brake cylinders (very good and exact replacements made in Italy) from Pat's MGB and Triumph (found them on E-Bay) for $19.95 each plus shipping. They're very nice people to deal with and ship quickly.
Rick Penland

I made up non-return bleed tubes. Take correct size neoprene tubing, close off end with a tight fitting screw and cut a small axial slit in the tube wall near the end. Fit open end on bleed nipple in normal fashion and open. On pressing brake pedal, slit opens to release fluid and on removing pressure, slit closes to prevent air getting in. Works a treat. (I read this somewhere and do not claim ownership of the idea!).

Good luck,

BJ Quartermaine

Thanks to all for their input.
After attempting to free the lines of any foreign material by loosening bleed screws and line ends I was able to get fluid to bleed from all four corners.

Being out of time and patience I then drove my B to my trusted mechanics at MG,Ltd. who reported to me the next day that they had no trouble bleeding the brakes.
I now have dard pedal and sure brakes.

Fortune has once again smiled upon me...
The starter motor finally gave up the ghost 17 minutes and two start attempts after I drove away from the shop. A friendly Sheriff pushed me to a start, I got back to MG,Ltd, and drove off soon after with a new starter motor.

Luck be a lady tonight!

This thread was discussed between 12/07/2009 and 20/07/2009

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