Brake question

[transalpian]

I'm learning more each day. Today's lession will be brakes!

When I picked up my truck, the brakes were pretty good. Occasionally, they would need "pumped" to stop easily however. It was as if the vacuum servo didn't "work" on the first try.

Yesterday, it seems to have stopped working completely. After I noticed this, I adjusted all four brakes so we're good there. Fluid level is good (and hasn't changed). Vacuum line to the servo looks good.

I could live with a firmer pedal, I just don't have the stopping power I had, even with a really hard push on the brake pedal. If I pump the pedal a lot (5-10 times), the braking power improves, but I really notice the stumble in the engine from all the vacuum being drawn off.

I've been reading about the brake failure valve, but don't think my '74 series 3 88" would have that. It's been dark, so I haven't looked (not really sure where to look, however).

The truck almost feels like the front brakes aren't working, but I've had no fluid loss. Is that possible?

Could it be the vacuum servo (diaphram)? Is the ProLine servo a decent unit?

Thanks for all the help!

Jeremy

[TeriAnn]

There is a master cylinder failure mode where the fluid does not leak out. Chances are good that the rubber seal on the piston inside is not sealing and is getting worse.

A vacuum tester like the Mity-Vac is always a good thing to have in your toolbox. Allows you to test the booster as well as your distributor's vacuum advance as well as do a vacuum bleed of brakes. Any shop should have a vacuum tester can can quickly check your booster in a couple minutes. Cheaper than replacing a good booster. It could be your booster, but the master cylinder is the more likely candidate.

It is anyone's guess as to what brand the Proline booster is, but I would trust Rovers North to try and stock high quality after market parts. They loose money on every return and they may loose you as a customer. They try to source parts fit for use that you as the customer will be happy with.

[transalpian]

Interesting, hadn't considered internal bleed through of the master cylinder.

I have a mitivac. How would I go about testing the booster?

If the booster tests good, and I have no fluid loss, does that point pretty strongly to the master cylinder? Is this a replace or rebuild type of thing?

[transalpian]

One more question (showing my ignorance).

Does the brake booster amplify the force, the stroke, or both?

Thanks!

[amcordo]

I had the same thing happen. It was the MC; but nothing looked awry on it. It just died on the inside. I replaced it.

[transalpian]

MC ordered from our hosts, will post update upon completion!

[cedryck]

share sympothies

I for one share your and others sympathies when it comes to reparing brakes on a series rover, the parts are garbage. One should NOT have to replace a new part, slave, master, or wheel cylinder after only 4 months. Poor, poor quality parts man.

[transalpian]

Update

New master cylinder (proline) received, bench bled, and installed.

Brakes (f and r) adjusted nice and tight

Bleed, starting in the rear, moving to the front. Initially, the pump and turn method, following up with vacuum bleeding.

Results?

Not fantastic.

I've got brakes, so thats an improvement, but the pedal doesn't have any lock-up. I've got brake effect, but the pedal slowly creeps to the floor. It takes less time than a stop light to go to the floor.

Next plan is to take to my mechanic to have them bleed again just to ensure no air in the system.

Any other suggestions?

(I have verified no brake failure valve on my truck, fyi)

Thanks!

[o2batsea]

you have to have both wheels up in the air, that is, both rear and then both front.
Rear first because that's where you bleed first, furthest away from the MC.
Once you get the air out of the lines, then you adjust the snail cams. Adjust them so that there is some appreciable amount of drag. You should be able to turn the wheel by hand, but with some difficulty. You can only do that with both wheels not touching the ground. Repeat for the front.
I guarantee you'll notice the pedal quite firm if you follow this advice.

[transalpian]

Understood about adjusting them firm. Thats where I am now. But why both wheels off the ground at the same time? What would be the difference between that and adjusting one wheel at a time?

[TeriAnn]

Update

I've got brakes, so thats an improvement, but the pedal doesn't have any lock-up. I've got brake effect, but the pedal slowly creeps to the floor. It takes less time than a stop light to go to the floor.

I'm confused from that statement. The pedal goes to the floor with you foot applying pressure or all by itself with no foot on it?

If it goes down all by itself: I can see that is you have air in the system and if the pedal spring(s) is/are missing. Depending upon the version there should be one or two springs on the pedal that keep the pedal up top.

If it goes down after reaching a firm brake and maintaining foot pressure on pedal:
This is a classic diagnostic of a bad master cylinder. Once you have pumped enough fluid into the cylinders to set the brakes they should hold solidly as long as your foot keeps pressure on the brakes.

Silly question. How are the rubber hoses on your brake system? Old hoses that balloon out under pressure can act like air in the system.

[SafeAirOne]

That's exactly what I was thinking--If you get solid pedal and you keep your foot there and it slowly sinks to the floor, there must be some leakage somewhere, either past the MC piston or back up into the reservoir or out to the world through the plumbing or wheel cylinders.

Even if you had air in the lines, you'd have a spongy pedal, but with constant foot pressure on the pedal, I doubt it would slowly sink to the floor because you're not increasing the compression of the air with a constant pressure on the pedal.

[o2batsea]

Understood about adjusting them firm. Thats where I am now. But why both wheels off the ground at the same time? What would be the difference between that and adjusting one wheel at a time?

Ill let you think about that for a second. OK still stumped? You can't spin the wheel if one is on the ground. If you can't turn the wheel you cannot tell if you have it adjusted tight enough.

[transalpian]

Ill let you think about that for a second. OK still stumped? You can't spin the wheel if one is on the ground. If you can't turn the wheel you cannot tell if you have it adjusted tight enough.

Oh. I've got freewheel front hubs. I can see how it might not work in the front without those.

The rear? I'd think one at a time would work
(did work, for me).

[bkreutz]

Ill let you think about that for a second. OK still stumped? You can't spin the wheel if one is on the ground. If you can't turn the wheel you cannot tell if you have it adjusted tight enough.

Only if you have a locked differential.