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Bleeding Brakes!

oxford

Jedi Hopeful
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Hi everyone
I am having the Devil of a problem bleeding the brakes on my BN4.
The fronts are drum.
I have a new master cylinder, new slaves on the front and rebuilt rears.
There are no leaks.
The shoes are adjusted so they can just be heard rubbing on the drums.
After endless bleeding the pedal just goes to the floor. Even after pumping there is no pedal and sometimes the brakes seem to work at the bottom of pedal travel, sometimes not.
I am using DOT 4 fluid.
I have been pressure bleeding using my compressor on a very low PSI. this seems to get the air out of the system, but if I do it the 'old fashioned way' with a faithful helper on the pedal, I seem to be continuously pumping air with the fluid. It's almost as if air is being drawn into the system.
I tested the MC by blocking off the outlet with a bolt and the pedal was rock solid. I also bled the MC by fitting a hose to the outlet and into the reservoir.
I'm thinking there is something wrong with the MC, but I'd like to know before I lash out and but a new one.
This is driving me (no pun intended) to distraction. No matter what I do I can't get any pedal.
Anyone got any brilliant ideas?
Cheers
Matthew
 

Lambdaman

Senior Member
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Ok, so master cylinder is rock solid when blocked, then go the next step. Clamp the two flexible front hoses and rear hose, if still rock solid unclamp the nearest wheel cylinder and bleed until working, then do the next front, if pressure holds remove the rear and bleed rears until successful . All books say start with furthest first but in your situation until you confirm issue is Master cylinder even block off 4 way Union and try to operate system on one cylinder
 
OP
oxford

oxford

Jedi Hopeful
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Thanks Lambdaman
I like the idea of blocking the union. I tried clamping the flexi hoses on the front but it made no difference.
Cheers
Matthew
 

Brinkerhoff

Jedi Knight
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I've had the best success bleeding the four drum brake cars by adjusting all of the shoes up tight so the drums can't rotate at all. That way you take any shoe movement out of play when the pedal is depressed. Bleed this way then see what your pedal feels like before you loosen the adjusters up.
 

steveg

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Air gets in past the bleed screws. Seal around the bleed screws with teflon tape or pack around the base of the screw with grease.

I've had good success using a brake syringe to pull the fluid out from each wheel. Order: LR, RR, LF, RF
 
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The old front drum wheel cylinders had a tiny ball under the bleed screw; I'd encountered cars where the bleeder was tightened down so much that the steel ball was locked into the aluminum casting (just putting that out there...).

I really like Brinkerhoff's suggestion; never needed to try that, but I can see the advantage for problematic circuits that don't act right!

The one thing that comes to mind, is did you bleed the m/cyl by itself__often referred to as bench-bleeding? Are these the original self-contained reservoir m/cyls, or the combined reservoir (the type used through the end of Healey production)? Even with the m/c mounted in the car, you can still bench-bleed it with a scrap of old tubing. Substitute the tube for the car's brake pipe, and make sure it reaches below the level in the reservoir. Several easy strokes will free the m/c of any air present.

When bleeding the front drum brakes, I don't rely on getting all the air out of the two (2) wheel cylinders through the one (1) bleed screw. Instead, I crack loose the fittings on the connecting pipe(s) in sequence. chasing the air out of the circuits. You can do this same practice at every union as well.

If there's air in there, cracking every union while maintaining a LOW (15 PSI is plenty adequate) column of pressure on the reservoir will expel it all eventually!

Picture of bench-bleeding in situ:

IMG_3228.jpg


scrap-tube coming off the brake m/c:

IMG_3229.jpg


opposite end of tube into the reservoir (remote on this MKIII):

IMG_3232.jpg


Good luck (I KNOW how frustrating this can be, but you'll get it__the car never wins...)!
 

steveg

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An elegant solution, Randy. Certainly beats doing it on the bench itself, then installing the wet MC in the car.

FWIW_1 -- A while ago Mike Salter told me the only way he could bleed some Healeys was to use a syringe to push brake fluid upstream from the wheel cylinders to the reservoir.

FWIW_2 -- My Fiat 124/131 dual MC is a notorious bench-bleeder and pulling the fluid out with the syringe (with sealed bleed screw threads) completely removed the need for bench bleeding on that MC.
 
OP
oxford

oxford

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Thanks for the replies and advice everyone. There is a lot there to go on. Randy, I did a 'bench bleed' in situ as you suggested earlier. (great pics) Not sure it helped much but it's a great idea. Just another question: I wondered if there was air being drawn into the MC through the union that goes to the reservoir. I seem to have a bit of fluid there. Is this possible? Does the MC draw the fluid from the reservoir or does it flow in by gravity?
Oh, one other thing: I have always thougt that faulty slave cylinders manifest themselves by leaking. Mine arn't so can I assume they are fine?
Thanks
Matthew
 

Bob_Spidell

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Thanks for the replies and advice everyone. There is a lot there to go on. Randy, I did a 'bench bleed' in situ as you suggested earlier. (great pics) Not sure it helped much but it's a great idea. Just another question: I wondered if there was air being drawn into the MC through the union that goes to the reservoir. I seem to have a bit of fluid there. Is this possible? Does the MC draw the fluid from the reservoir or does it flow in by gravity?
Oh, one other thing: I have always thougt that faulty slave cylinders manifest themselves by leaking. Mine arn't so can I assume they are fine?
Thanks
Matthew

Mostly gravity, I suspect, as I've never seen a reservoir mounted below a MC. However, when you let off the pedal the piston does retract, which would provide some suction, but if it had to pull against gravity it would likely cause problems.

Regarding the slave cylinders: did you pull the boots back to check for leaks?
 

rjc157

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To all forum members this fellows name is Matthew Randell you can see the progression of his car on Youtube a lot of great work and good watching check him out
 

blueskies

Jedi Warrior
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I also am frustrated trying to bleed the brakes on the BN4 - a Longbridge car with the reservoir as part of the master cylinder. All brake parts on this car are new, and it has no leaks. The first master cylinder (new from usual supplier) leaked back along the rod into the passenger compartment. After rebuilding the MC, it no longer leaks. But so far the system still has air in it. After working at it, with another person on the pedal and me under the car, it has brakes. But the pedal almost goes to the floor and only after a few pumps do the brakes feel good. Then, after a few seconds when one tries the brakes again, they again need to be pumped. We have made the circle from wheel to wheel a number of times without improvement.

I'm wondering whether one can bench bleed the MC (with the reservoir as part of the MC) in the car, just by hooking a hose from the outlet and then into a container placed at a lower level? How is that different from just leaving it hooked up to the brake system? The idea of cracking the fittings on both slave cylinders at the front wheels, while exerting pedal pressure, also might be worth a try.

I have been bleeding brakes since the age of 14 on all kinds of vehicles, but this BN4 is frustrating. The BJ7 also needed to have the brakes bled this winter. That took about five minutes, and they work fine.
 
OP
oxford

oxford

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Thanks again everyone.
rjc thanks for the endorsement! Bob, I have checked the slaves and they don't appear to be leaking. My bet is the MC. I tried bench bleeding off the car and it seemed to work ok but I really feel that air is getting in somewhere. I'll keep playing and let you know when I figure it out.
cheers
Matthew
 

steveg

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Thanks to Randy for his recirculating bleeding technique. I adapted it for an in-situ bleed of my recalcitrant Fiat dual MC.
Added the long clear tube to observe the bubbles.
After bleeding the MC, very little line bleeding was required to get a solid pedal (Dot 5 fluid).

RecircBleedSetup.jpg
 
Last edited:

Lin

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Hi Steve,
As you know I use your syringe method for bleeding brakes and clutch and like it. The only down side I experienced was that on initial bleeding when you don't have fluid in the pipes, you have to "empty" the syringe of "pulled" air several times, since the syringe is only 60 ml. I just came across this Sealey syringe made in England that holds 200 ml. I ordered it and found it to be very high quality. I like it a lot. It can also be used for "pushing" fluids such as filling a transmission or a rear differential. Check it out.
Lin
 

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steveg

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Hi Steve,
As you know I use your syringe method for bleeding brakes and clutch and like it. The only down side I experienced was that on initial bleeding when you don't have fluid in the pipes, you have to "empty" the syringe of "pulled" air several times, since the syringe is only 60 ml. I just came across this Sealey syringe made in England that holds 200 ml. I ordered it and found it to be very high quality. I like it a lot. It can also be used for "pushing" fluids such as filling a transmission or a rear differential. Check it out.
Lin

That looks super useful!
 

Michael Oritt

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Sometimes air bubbles will stick to the wall of a wheel cylinder even after it has been bled, resulting in a soft pedal. Tapping on the cylinder with a wrench, etc. will usually make them come up to the bleed nipple.
 

Rob Glasgow

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Lin, can you use this with your Dennis Welch slave cylinder bleed hose? My vacuum bleeder won't work with the end fitting that comes with that hose.
 

Lin

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Good question Rob. Unfortunately, I do not know as I have not tried that yet. However, the next time I have the car on the lift, I will check it out and report back.
Lin
 

RDKeysor

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While I didn't resort to bleeding my MC by running a line into the brake fluid reservoir, I did find that one of the soft brake lines I has replaced on my card threaded into a spare MC and could have performed that function. I had a really difficult time bleeding my replacement standard MC on my '60 BN7 several weeks back. My problem was a low brake pedal. Someone suggested that I go ahead and drive the car for a time, and then rebleed the brakes. As it happened I had the rear end on jack stands, so I took the opportunity bleed only the rear brakes with the conventional method. I got a surprising amount of air out of the rears given that I had previously bled them several times, but I also got a much higher pedal. As I recall Norman Nock's book recommends against using a pressure bleeder, and I have had not success with my pressure bleeder on this car. Just for what it is worth.
 
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