Steering, Suspension, & Brakes

Hi all. Well we have the engine up and running and thought we would be able to take a run around the block soon but in the midst of building up the engine the front calipers were off for some paint along with new flexi lines and now with the system bled we have no brakes at all on the front and just a tad on the rear. The fluid coming out on the rear while bleeding isn't up to snuff so we are going to change the short flexi line back near the rear diff. Trying to figure out where the failure is at, the rear lines did have fluid in them as they were not disconnected at any point, the front however was empty while the items mentioned where being replaced. I have had several suggestions as to the issue but thought I would toss it out here. We initially used the EZ Bleed system to do the brakes but we also did the old style pumping too when doing the rear. Would doing this cause the brake fail switch to be triggered, causing a similar issue? I see in the Haynes manual it mentions centralizing the switch after bleeding. The plan is to try this and see if it improves anything. There were no issues with the brakes prior to this so I am trying to figure out if the M/C failed? Any ideas? Thanks!

If you bled the brakes, you must have been building pressure... doesn't seem to make sense that you could build pressure but not have brakes? Did you bleed all four? Starting at the right rear, then left rear, then right front, then left front?

Hey Rob, we have now bled it at all four locations at least two times. I am not sure if we did the front in the right order or not. But since there are two separate lines for the front would it matter?

It's generally faster to bleed the wheel furthest from the master cylinder 1st & progressively work closer. If you have seperate lines for the front, shouldn't matter. I still don't get how you can bleed the brakes but not have brake pressure. When you bleed them, are you pumping the pedal till you get pressure, holding the pedal down & 2nd person opens the bleeder valve to release fluid... person in the car keeps pressure as the pedal goes to the floor... person under the car tightens the bleeder valve before the person in the car releases the brake pedal? If you're doing that & getting clean, bubble free brake fluid at all 4 wheels, I don't understand how you'd not have brake pressure??

If that's not what you're doing, describe how you bled the brakes.

Rob, the first time we bled the brakes we used the EZ Bleed pressurized system and after that we did it manually as you mentioned above doing RR, LR, RF and LF. Still not happy we did it again with the EZ Bleed and next to nothing happens. If someone holds the pedal down I can't turn the rear wheels but the fronts keep on going. I am going to replace the short rear hose in case it failed and try centralizing the fail switch as I saw mentioned in the Haynes manual to see if that will help. If not I guess I will tear out the M/C and see about replacing it.

So the problem sounds like the rear is working & the problem is in the front circuit. If you bleed the front manually, do you get fluid coming out? I'm not familir with "centralizing the fail switch"; can't help w/that. Someone else will have to chime in.

I've only bled brakes the old-fashioned way... although I do use those inexpensive little ball bearing check-valves at the end of the clear hoses. Sometimes it just seems to take a long time and a lot of cycles to get all the bubbles out of a new brake system. Patience.


My '71 MGB did come with a fail switch, but I've disabled it by replacing the switch with a bolt. In other words, I'm still using the brass manifold that the switch used to mount in.

I've taken a moment to sketch the manifold - from memory and NOT TO SCALE - in case that will move the conversation along. As you can see, unless you disable it, there's a double-ended piston that WILL slide from side to side inside the manifold to equalize pressure between the front and rear brake circuits.



Michelle, did you install residual pressure valves? I don't think they're a solution to your current problem, but they do generally help with pedal feel and now (before the system is bled) is a good time to install them.

When bleeding the front we get fluid through and it seems like the calipers are fine, but the amount of fluid coming through is more like a trickle. I guess it is possible for the M/C to just fail but it would sure bite putty balls :). I have had company this week so I haven't been able to work on it much. So I just keep gathering the ideas. I personally think it should just start working if I were to try it today since it is my birthday but would hate to be disappointed.

Hate to say it, but the most likely time for a master cylinder to fail must surely be when you're bleeding the rest of the system because the seals have to travel further down the bore. I'd inspect the parts you already have (manifold and calipers) first though. Anyhow...

HAPPY BIRTHDAY MICHELLE

Curtis, is it possible the manifold has slid to the front blocking most of the front circuit? I know you said the pic isn't to scale, but it looks like Michelle could remove the front in or out line & see if the piston is blocking those ports.

I'll make a general brake related comment which might not be connected to Michelle's problem but which I've heard of being an issue nontheless - that's the issue of brake pedal "free play"
There has to be about a 1/8" free movement at the pedal before the pushrod starts to move the master cylinder pistons - if there is no freeplay the piston may not retract all the way and the brakes will stick on.
.......just a heads up......

Rob, I can't remember well enough what the piston looks like, so I'm not sure whether its possible for the piston to restrict fluid flow at the extreme limit of its travel. My instinct is that it's probably designed to recenter itself when a leak downstream is repaired and if that's the case then it doesn't block fluid flow. I should get in the habit of photographing everything I take apart...

Yeah, i was confident it was designed to self center -- was just thinking age/corrosion may be causing it to stick.

Good points all!
I have a thought that may alleviate the EQ valve.
Most new master cylinders come with plugs to bench bleed rather than the old plastic adapters and short rubber hoses.
If you could fab up a couple of plugs to thread into the master to "bench bleed on the car" it would build pressure if it is good and the problem is elsewhere. If it does not build pressure the weep holes at the back of the bore are plugged or the check valve at the back of the piston is wedged open by trash from sitting dry for a while.
I just went and looked at the M/C that came off my 77 donor car and you cant see the weep holes through the reservoir, but you could pull the snap ring and pull it apart to check it out!

We now have brakes, I won't tell you what happened because you would all sit and giggle. But from now on I will be sure to make more notes for myself. There is a chance it might get to drive around the block tomorrow if I get the seat bolted back in well enough. Now that is a birthday present :).

I feel like I've been robbed of a giggle manly chuckle.

Me too -- inquiring minds want to know!

And Happy Birthday!

Rob

Forgot to insert the cotter key?

JB

Key was in. Ok I give up, don't laugh too loud. We were in such a hurry to get the calipers back on they ended up on the wrong side and when the bleed screw is pointing the wrong way the air will not totally bleed out. Even though a couple folks on another site said they were not handed when putting them on but they are.

But I can now report the car has made her first trip around the block and is now officially off the lift and has taken over the husband's Porsche stall for a while. Time to take it to a muffler shop and get some proper pipes off so I can really tell what it sounds like. Right now it is a bit scary to listen to going down the block and my husband said that short shifter makes it really tight. I haven't driven her yet since he wanted to make sure everything was ok before I got in and tried it out.

Good work. Soon you'll be tearing up the neighborhood!

JB