HELP! Replaced a rear disc caliper on my '69, and now no fluid to the front or rear.

[tbratz]

Time to ask for some guidance. I replaced a leaking rear disc caliper and rear brake hose, and adjusted both rear calipers (parking brake), and now I have no fluid going to the front or rear. It is a hydroboost brake system, and after changing rear brake parts, I got in, and the pedal goes right to the floor. I tried it with the engine running and off. I pumped the brakes and worked on them for hours, checking for fluid and nothing at both rear calipers. I even reset the shuttle valve in the proportioning valve, and still no fluid. I broke the line free at the proportioning valve, and no fluid came from the valve. I pulled both lines from the MC to the proportioning valve, and there is no fluid leaking from the MC lines either. Even when I pump the brakes, I don't get any fluid from the MC. I checked the pedal linkage to the hydroboost, just in case, and it seems to be functioning properly. Before putting on the new caliper and rear brake hose, the Bronco ran fine, and the brakes worked perfectly. What am I missing? Any ideas would be appreciated. I have messed with it for two days, and I am stumped.

 

[tbratz]

Since you’re getting zero fluid out of the master cylinder ports even when pumping the pedal, the problem is almost certainly at the master cylinder itself. Replacing the rear caliper + hose probably introduced a bunch of air, and on these hydroboost setups the MC can sometimes lose prime or the seals can get messed up once the system is opened.

I took the MC off and Bench bled it, and still no difference. But interesting to note. I bypassed the proportioning valve and ran a temporary brake line directly to the rear, but still no fluid. So, I could have done something to mess up the MC, which seems unusual but possible, I guess. I am about to go back to my old vacuum assist out of frustration, instead of buying a new MC and trying that.

 

[73azbronco]

I say the hardest brakes I have ever bled, are EB brakes...

 

[SLOWnEASY]

I have always had the best luck loosening the bleed screw and covering it with my finger tip to simulate a one way valve while someone slowly pumps the brakes. Have you tried disconnecting the line at the proportioning valve and have someone slowly pump the pedal while you cover the end of the line with your finger? It will tell you pretty quickly if you're getting fluid at the joint.

 

[tbratz]

I have always had the best luck loosening the bleed screw and covering it with my finger tip to simulate a one way valve while someone slowly pumps the brakes. Have you tried disconnecting the line at the proportioning valve and have someone slowly pump the pedal while you cover the end of the line with your finger? It will tell you pretty quickly if you're getting fluid at the joint.

No, I haven't done that, but I will give it a try. I did, however, completely bypass the proportioning valve with a temporary line and still get no fluid, so I am beginning to think that, for some reason, the issue is at the master cylinder.

 

[DirtDonk]

I'd say that there is no other conclusion anyone could make.
If fluid is not getting to any point in the system that you've checked (and it sounds like you've checked pretty much everything at this point), even the ports at the master itself. And if you're bench-bleeding and nothing comes out, then it's got nothing to do with ANYTHING before or after the master.
Why change out the hydroboost unit if the master is not functioning? Why not just change out the master?
Or better yet, pull it apart and see if you can fix it yourself. You've done practically everything else at this point. Why not just see what you can see by pulling it off and pulling the guts out?
If you need to get it back on the road quickly at this point, you should be able to get a new/rebuilt one pretty easily I would think.
Which master did you utilize for the hydro conversion?

 

[tbratz]

It is one of your kits that I bought a number of years ago, and I believe it has the Corvette-style MC. No complaints; it has been a great system, but it just has me stumped. I did remove the MC again this morning after letting it sit overnight and can get it to bench bleed. When hooked back up, it just doesn't produce enough pressure to move fluid through the system. I think the part that throws me the most is that it worked perfectly until I switched out the caliper and rear line. Stranger things have happened, so perhaps the MC did go out. I can source a new MC easily enough; I just wanted to fully troubleshoot everything first before I start throwing money at parts. Thanks for commenting.

 

[DirtDonk]

Gotcha. I claim to have coined the phrase "coincidental failure" on the forums, but can't say for a fact I'm the first to ever have used it. Or experienced it...
But it 'splains a lot of the weirdness that we live with, regarding our older vehicles.
You know, give the truck a good wax job and change the rear shocks, and the windshield wipers quit.
Change out a trackbar bushing and the parking brakes stop working.
Fix the long dormant horn, only to find the ignition switch as given up the ghost.
Stuff like that.
Unfortunately, yours is more intimately related than most. It's still part of the brake system. Does seem a little fishy, but in your case, you know for a fact that it worked before you changed the caliper, but not after. What's the common denominator? Hell, 'ya got me!

Paul

 

[EPB72]

It is one of your kits that I bought a number of years ago, and I believe it has the Corvette-style MC. No complaints; it has been a great system, but it just has me stumped. I did remove the MC again this morning after letting it sit overnight and can get it to bench bleed. When hooked back up, it just doesn't produce enough pressure to move fluid through the system. I think the part that throws me the most is that it worked perfectly until I switched out the caliper and rear line. Stranger things have happened, so perhaps the MC did go out. I can source a new MC easily enough; I just wanted to fully troubleshoot everything first before I start throwing money at parts. Thanks for commenting.

If bench bleeding not sure of your process but when you think when your done ,, you could block both ports if you have the plastic screw in plugs or I just cover them with finger tips and mc clamp in a vise use a screw driver and push in on the plunger it should lock up at 1/8 . 3/16 of an inch of movment ,, If there is more plunger movment and your able to keep fluid from coming out ports then there is either still air or MC bypassing internet ,,, did the reservoir every go empty when you were installing the caliper and hose,,

 

[tbratz]

If bench bleeding not sure of your process but when you think when your done ,, you could block both ports if you have the plastic screw in plugs or I just cover them with finger tips and mc clamp in a vise use a screw driver and push in on the plunger it should lock up at 1/8 . 3/16 of an inch of movment ,, If there is more plunger movment and your able to keep fluid from coming out ports then there is either still air or MC bypassing internet ,,, did the reservoir every go empty when you were installing the caliper and hose,,

No, the master was never drained of fluid.

 

[tbratz]

Gotcha. I claim to have coined the phrase "coincidental failure" on the forums, but can't say for a fact I'm the first to ever have used it. Or experienced it...
But it 'splains a lot of the weirdness that we live with, regarding our older vehicles.
You know, give the truck a good wax job and change the rear shocks, and the windshield wipers quit.
Change out a trackbar bushing and the parking brakes stop working.
Fix the long dormant horn, only to find the ignition switch as given up the ghost.
Stuff like that.
Unfortunately, yours is more intimately related than most. It's still part of the brake system. Does seem a little fishy, but in your case, you know for a fact that it worked before you changed the caliper, but not after. What's the common denominator? Hell, 'ya got me!

Paul

LOL, obviously, because of this situation, I know exactly what you mean.

 

[Oldtimer]

Spitballing here, if the master cylinder piston cannot return fully, aren't the ports in bottom reservoirs blocked?

 

[Bruners4]

What I've had happen is that a working brake system has no problems until a component is replaced and the system needs to be bleed. First instinct is to press the brake pedal down, and it goes to the end of the stroke. of the Master Cylinder (MC). Up until that last pedal stroke of the master cylinder, the rubber cups have only moved a short distance in the MC bore. At the end of this 'normal' stroke is a corrosion pit or a piece of debris. When the MC cup moves over this debris or pit, it cuts the lip on the MC cup. This will cause brake fluid to bypass the lip of the cup and it does one of two things, won't create pressure or won't move fluid. Removing the MC, disassembling and inspecting after this event will confirm the internal brake fluid leak past the cup(s). Repairing the MC bore and replacing the cups will return the MC to a working condition.

 

[tbratz]

What I've had happen is that a working brake system has no problems until a component is replaced and the system needs to be bleed. First instinct is to press the brake pedal down, and it goes to the end of the stroke. of the Master Cylinder (MC). Up until that last pedal stroke of the master cylinder, the rubber cups have only moved a short distance in the MC bore. At the end of this 'normal' stroke is a corrosion pit or a piece of debris. When the MC cup moves over this debris or pit, it cuts the lip on the MC cup. This will cause brake fluid to bypass the lip of the cup and it does one of two things, won't create pressure or won't move fluid. Removing the MC, disassembling and inspecting after this event will confirm the internal brake fluid leak past the cup(s). Repairing the MC bore and replacing the cups will return the MC to a working condition.

Thank you for your reply, and that is going to be my next step. I am confident that the problem is with the MC, as you say.

 

[DirtDonk]

I don’t think I ever bought a new master cylinder until I’d been working on cars for a close to 20 years.
Prior to that we always rebuilt everything we had.
You could get a kit with all the new inside stuff for five bucks or less, and we already had all the tools, including hones we needed for the different sizes. Still have them in the toolbox.
Same for all the wheel cylinders. Many of our cars had the original masters and slaves for most of their lives.
If it wasn’t rusty, too far gone, or flat out broken, it got reused.

 

[tbratz]

I remember those days. I even remember rebuilding the clutch slave cylinder on my old '58 F-250. I still have a box full of old seals, springs, cups, and wheel cylinders. I have a '74 High-boy and just honed and re-sealed a leaking rear wheel cylinder. Most of the modern MC's you can't even get rebuild kits for.

 

[DirtDonk]

I bet. 'Round here we even had several steering box specialists, brake booster specialists, carburetor rebuilders, motorcycle and car racing tuners/builders, friction companies that would re-line your clutch disc AND your brake shoes. Even had a big truck shop that would re-tread your tires, and bend your radius arms and I-beams for alignments. Heck, we even had a couple of custom camshaft manufacturers to choose from!
Ahh, the gooder days...

Paul

 

[chuckji]

Did you happen to unmount the master cylinder at any point prior to testing out the new caliper? Just wondering if you forgot to reinstall the little bullet spacer in the master cylinder (if your master cylinder/hydrodoost takes one).

 

[tbratz]

Thanks for the suggestion. No, I never unmounted it before testing the caliper; I actually never even ran the system out of fluid.