Spongy brake pedal tightens when braking in reverse before going bleeding back down

[Joey 7]

There is only one or 2 reserve pumps in the hydro boost after that, the pedal will go hard. Be careful rebuilding the HB they can be dangerous if not done properly. That is one part I sent to a local rebuilder or bought a new replacement.

Yeah I've rebuild a PTO pump once or twice and had some experience with hydrolics and I found a few good videos on it.

What do you mean by the pedal going hard after the 2 reserve pumps?

 

[fast 99]

There is am accumulator. It is the horizontal can looking thing usually anodized in various colors. It provides 1 or 2 assisted stops if the motor quits, a safety device.

 

[Joey 7]

There is am accumulator. It is the horizontal can looking thing usually anodized in various colors. It provides 1 or 2 assisted stops if the motor quits, a safety device.

Okay I've changed the pump, hydro boost, and all the lines. I've bled it just by turning the wheel lock to lock. New pump obviously doesn't scream or slip, Booster feels much better than the old one. Accumulator is functioning properly, but I still have a soft pedal. I'm sure whatever the remaining issue is, it's gonna be in the brake system somewhere. Though, Sometimes the pedal seems to stiffen up for a few seconds and then goes soft.

Weird thing was right after I started up the engine and before bleeding the steering, the pedal felt pretty much perfect. And after bleeding is when it got soft. I've read a couple methods on bleeding a hydro boost but then others that say you don't need to.

 

[fast 99]

No special procedure to bleed a hydroboost. Just start engine and pump brakes a few times. May be someone else here can come up with a suggestion. If everything was repaired properly it shouldn't be behaving the way you describe.

 

[Joey 7]

No special procedure to bleed a hydroboost. Just start engine and pump brakes a few times. May be someone else here can come up with a suggestion. If everything was repaired properly it shouldn't be behaving the way you describe.

For sure. I know it's bled properly. I'm pretty sure the problem is in the brake system now, it's just weird I had a hard pedal at first. I know my pump was bad and hydro boost was getting there so it is what it is. I did find my mc is seeping from the plunger just a bit. I doubt it would cause this but I guess that's next.

 

[fast 99]

If the cups in the master are swelled or leaking could easily be a problem, fix it. Remember to bench bleed and not bottom piston doing it.

 

[Joey 7]

If the cups in the master are swelled or leaking could easily be a problem, fix it. Remember to bench bleed and not bottom piston doing it.

Yeah this is that brand new mc for a k30. First time I bench bleed it, all seemed fine and didn't have any fluid. When I changed the pump and hydro boost, I rebled it and since then there's a small leak. I'm assuming I bottomed out the piston. I guess I'm not really sure when to stop pushing the piston in on these. I still don't think it would be causing all this but it's somewhere to start. If that isn't it the only thing I can think of is that the shoes are coming out of adjustment and not making full contact with the drum.

 

[fast 99]

Back in my days of inexperience, during bench bleeding I bottomed out 2 new JB8 master cylinders in a row. Of course, it ruined them. After some discussion with another more experienced tech, he told me what I was doing wrong. 3rd time was the charm so to speak. Now I push piston in 1" or less today on all master cylinders. Never had that issue again. These sorts of learning experience mistakes are lifetime.

 

[Joey 7]

Back in my days of inexperience, during bench bleeding I bottomed out 2 new JB8 master cylinders in a row. Of course, it ruined them. After some discussion with another more experienced tech, he told me what I was doing wrong. 3rd time was the charm so to speak. Now I push piston in 1" or less today on all master cylinders. Never had that issue again. These sorts of learning experience mistakes are lifetime.

Okay that's good to know. Most people I've talked to and what I've seen online said to bottom out the cylinder. My first one I did that blew the seal, then I was going as far as I could without bottoming out and got all the bubbles out and I thought it was working until I saw it leaking.

I've been using the method where you run hoses from where the lines thread in that go up into the reservoir. Is there a better method you'd recommend?

 

[SirRobyn0]

Not sure how helpful I can be but I will try first off though:

Why change the prop valve? That is another part commonly replaced that usually doesn't fail. Is there some u tube video everyone is watching?

I think people change them because they don't understand how they work. Basically they are just a metering block, so the most common thing is they plug up with little chunks of rust if the fluid isn't flush and kept fresh from time to time. Symptom is front or more commonly rear not working, with the pedal feeling normal or high.

With a proper pinch off tool clamp the rear brake hose. Is the pedal normal?

Do not use a vise grip or similar to tool.

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I would still advise purchasing and trying this. They can be used for pinching fuel lines and come in quite a bit handy. If you pinch off all the lines, front and rear and the pedal is high and hard you know that the master, and booster stuff is all working fine, then release one front and test again, then the other front, and finally the rear. Sometimes some diagnostic work is far better than replacing parts and seeing what happens. Grated I understand you had issues with the hydroboost, but all that did not fix the poor pedal.

If I was a betting man, I'd bet that there is either air in the lines some where or something is wrong with the rear brakes.

Have you jacked it up and re-checked the rear adjustment?
I say that because I've seen guys have the brake shoes not well centered on the backing plate, they put the drum on adjust the shoes until they touch take it for a drive and have a poor pedal, because the first time they hit the brakes the shoes center and now they are adjusted way to loose. A simple readjust fix it in all of those situations.

Hopefully something in there was helpful....

 

[fast 99]

Okay that's good to know. Most people I've talked to and what I've seen online said to bottom out the cylinder. My first one I did that blew the seal, then I was going as far as I could without bottoming out and got all the bubbles out and I thought it was working until I saw it leaking.

I've been using the method where you run hoses from where the lines thread in that go up into the reservoir. Is there a better method you'd recommend?

That will work but I don't use them. As a line tech time is money. Was faster blocking and unblocking the outlets with a finger. Can usually bench bleed one in a couple minutes. Do not bottom the master either way you chose. Use whatever method works for you.

 

[Joey 7]

That will work but I don't use them. As a line tech time is money. Was faster blocking and unblocking the outlets with a finger. Can usually bench bleed one in a couple minutes. Do not bottom the master either way you chose. Use whatever method works for you.

Okay thanks. I should be back home someday this week and I'll give it a shot and post the results here. Really hoping it is the master after this headache