MGB: Newbie Brake Question

Great forum, I'm new to the LBC scene, but have spent a couple of weeks researching this issue, but so far nothing seems to quite fit my situation.

My recent intro to LBCs is via my (older, wiser) brother who flat out gave me a well sorted out '77 B. Runs great, looks great, nice chrome wires under red with a nice black cockpit, new top - a couple of DPO issues (but it was a gift after all!) I'll get an avatar up soon.

My issue is while it has plenty of go, it's got fairly serious stop problems. When received, pedal would intermittantly go to the floor and was quite spongy. I suspected bad slaves in the rear so I replaced slaves, adjusters, shoes, bled (or so I thought) and recovered some pedal travel, but still had the occasional pedal "to the floor". After about a week, I noticed the MC level dropping. The MC looked original, and I then noticed telltale paint issues underneath the MC so I went ahead and replaced it.

Borrowed a good friend's pressure bleeder and a Mityvac for good measure. Bench bled the MC, installed it, put the rear up on jack stands, filled up/attached the pressure bleeder and proceeded to the rear passegner bleeder, opened it up into a hose/jar and out came nasty, black fluid. This ran for a bit, then became clear with black specks/bubbles, then clear w/o specks or bubbles so I shut off the bleeder and went to the driver's rear. Here's where things started to get interesting. Opened up the bleeder- nothing. Attached Mityvac to assist and out came the black stuff again, then it went to clear, bubbles disappeared so I shut off the bleeder, lowered the car and proceeded to the front.

At the front, pretty much the same as the rear drivers side. Had to assist the pressure bleeder with the Mityvac, got black stuff, then clear, then bubbleless. Un-jacked the car, got in started her up,had pretty firm pedal, took it for a ride, then started to feel some spongy-ness in the pedal. Figured either 1) didn't quite get all the air out or 2) I had a brake hose problem. Ordered new brake hoses-yet to be installed. Last nite pulled out of the garage and had no brake - all the way to the floor, but the car was able to stop in the driveway. Got out and looked at the kraft paper I had on the foor (great idea, by the way!) and there was a 12-15" circle of brake fluid under the passenger side rear axle, inboard of the rear tire but not under the diff case. I inspected the rear hardlines and don't see the dreaded towing hook crush.

Would these symptoms correspond with a leaky rear hose? Also, since the pedal basically went to the floor, have I "blown" the new MC? That seems rather extreme....

Thank you for reading this - hope you can help.

YOu should start your bleeding at the d/s rear; furthest from the master, then work around to the closest corner. A leaky rear hose could cause this but only if you lost enough fluid to drain the master to the point that you would be sucking air. A leak will dispel fluid but not suck in air until you step on the brake and then release. Oh, well, I guess that could happen!

Since the MC is on driver's side, isn't the rear passenger side further - or am I missing something? (mine's a LHD car).

Thats where the rear hose is. You have them so I'd surely put them on. Should be no harm to the master. It gets cycled to the floor when bleeding the old fashion way.

I've said this before. When it comes to hydraulics on 30+ yo cars, you may as well bite the bullet and go through the whole system. Sounds like you are well on the way to that goal. Don't forget, the clutch system is the same age and unless it's been serviced will have the same black stuff in it. Can make shifting very dicey when it fails.

Oh, forgot my manners, Welcome. Congrats on the gift. At least you aren't starting out in the hole.

Yes, proceed on with replacing all the flexible line hoses.

What you might have done, and I've done this myself, is over-extended the passenger side rear brake cylinder.

B drum brakes are not self-adjusting. If not set up correctly, and occasionally readjusted, the cylinders will over-extended, and then piddle the fluid out on the group. Typically if you do this, you need to rebuild the brake cylinder as well. The cylinder rebuild kit is inexpensive, but before you start on it, check the condition of the cylinder walls. If pitted, don't bother, just get a new/rebuild cylinder. If in OK condition, and you have a honing tool, you can rebuild yourself.

Good luck.

And believe it or not, sorted Bs have very good brakes. Almost world class for a early 60s design. By modern standards, adequate is a better term.

[quote=tkoerber]
Since the MC is on driver's side, isn't the rear passenger side further - or am I missing something? (mine's a LHD car).[/quote]

If you look at the plumbing, the run appears to be longer to the drivers side rear. I doubt it makes that much difference and certainly not your problem with fluid puddled on the floor.

Welcome!

I have to agree with the previous advice. Given the description of what you found bleeding, and the age of the car, I would replace all hoses, the MC, the front calipers, and the rear cylinders....
Sounds like you have already replace much of this...so just complete the job, and you will drive with much more confidence....

oh yeah...do the clutch system now also...

good luck!

You will never go wrong replacing all hoses, master, slaves and calipers. Age has compromised their reliability, and by replacing all parts you will be assured of good, safe stopping for years to come.

Al is on the money... you need to adjust the rear brakes first. When you put the new shoes in, you may have backed the adjuster off far enough that the pistons came out of the rear wheel cylinder. You will need to pull the rear drum off and clean up any and all the brake fluid that ran out of the wheel cylinder. Then make sure the pistons are back inside the wheel cylinder. Put everyting back together and adjust each rear brake. You can then bleed away.

As others have mentioned, you might want to go ahead and replace the 3 rubber brake lines.

My brother (the generous DPO) had the clutch serviced. When I inspected the fronts, calipers/pads, et. al. seemed great. new pads, clean calipers, easily opened bleeders, The perplexing thing was the condition of the brake fluid. I should have mentioned that the fluid in the old MC was a dark gray and that there was a significant leak in the rear of the MC that leads be to believe the seals were disintegrating. I replaced the rear slaves when I saw their condition (leaky, shoe lining softened by brake fluid). I think I'll go with the hoses for a start (brake fluid is cheap) before I rebuild the calipers.

I agree in replacing all the flexible hoses. I had a similar problem this summer with a soft pedal. Everythign was bled properly, yet the pedal would very slowly collapse. It turned out that one of my bleed screws was shot, and would let fluid out only under the strong pressure of the brake pedal.

Great post and timely too. I'm going to tackle the brakes on my new 77 B within the next couple of days.

Kevin

The calipers are the one item that you may be ok to leave be. They usually start sticking rather than leaking. My theory is they run hotter and hence get rid of moisture that corrodes everything else. Also the pistons seem to have some sort of plating (chrome?) or maybe stainless? In any case, they don't seem to rust as much.
I just rebuilt a set on a 71. Had to use the grease gun trick to get the pistons out but everything cleaned up and is working fine. They weren't leaking but had indicated sticking on occasion.

Castrol LMA is the only thing proper for these cars...IMHO. New hoses are cheap as are slaves for the rear. Kits for the masters if they are scored or pitted are much cheaper than replacement but involve a minor skill level, and great sanitation. New are also cheap enough. The by the book way of bleeding would be the furtherest unit from the BMC...normally rear passenger side, near side (driver rear) font right (passenger) and front left is last. Rears typically run out of pedal first...if you have a spongy not caused by siliocon of US DOT 3 fluid, and you can double pump and lock the rears....the rear shoes need adjusting.

BTW, welcome to the madness! Great group and a lot of good free advice....not a bad deal at all considering the price!
;)

As a conclusion, the rear brake hose burst. I guess the new MC generated the proper amount if line pressure and the weakest link failed. New hoses all around, a quick bleed and I have stoppage!! ;) As an aside, on a '77 the rear hose is easier to change from the top with the battery removed.

Learned this lesson the hard way.

I replaced my brakes like Johnny Cash "one piece at a time".

Painful year for me. I should have just replaced the master, rear cylinders, hoses and calipers and been done. I must have bled those brakes 5 times. My wife will not help anymore. She bought me a power bleeder. That is a good thing.

Indeed the fast way to damage a marriage or ruin a budding relationship appears to be having the "little lady" assist in bleeding brakes....
Older, some still married men will attest to this truth...