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Hydroboost/ brake issue

Smokinthehippies

Smokinthehippies

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I need some diagnosis help.

98 2500 with hydroboost

When braking everything works fine until I get to about 10mph, then the brakes surge and the wheel jerks to the left.

What could cause that? I checked fluid in the pump and master cylinder but that's as far as I've gotten so far. You can feel the pedal get funky when it does it so I'm not leaning towards an issue with the pad/rotor. Plus it is super super consistent. Same speed. Same feel every time.
 
Have you tried reving the motor a little when it does it, or before if it's that predictable.

How does the pedal feel if you pump it up a few times with the motor off? The start it with your foot still on the brake. You should feel it drop a little from the assist.

My hydroboost problems were fixed by a new pump. I had issues with no assist to the steering and the brake pedal not coming back up. The assist for the brakes felt great though, just no pedal return.
 
Given the imbalance, I would be checking pads and rotors, maybe MC. Hydoboost should not be able to cause an imbalance issue. It just pushes. Rotor/brake problems are often felt in the pedal, so pedal wonkiness does not mean that the problem is up on the MC/hydroboost end of things.

As far as the surge, my hydroboosts all lose effectiveness at low engine speeds due to lower pump speeds. So I find myself pushing harder at lower speeds than I would ever have to on the highway. Low fluid levels/air bubbles in the hydraulic lines will cause surging like this, but I wouldn't think it would be speed related, aside from all the fluid running to the front of the reservoir when stopping quickly. Try taking the truck up to higher speed, then shifting to neutral and letting the engine/pump get down to its idle speed. See what happens then. Also try revving it like toomany suggested. You should have a gain in boost pressure when it speeds up.

Is this a new problem, or has it always been this way?
 
campfire said:
Given the imbalance, I would be checking pads and rotors, maybe MC. Hydoboost should not be able to cause an imbalance issue. It just pushes. Rotor/brake problems are often felt in the pedal, so pedal wonkiness does not mean that the problem is up on the MC/hydroboost end of things.

As far as the surge, my hydroboosts all lose effectiveness at low engine speeds due to lower pump speeds. So I find myself pushing harder at lower speeds than I would ever have to on the highway. Low fluid levels/air bubbles in the hydraulic lines will cause surging like this, but I wouldn't think it would be speed related, aside from all the fluid running to the front of the reservoir when stopping quickly. Try taking the truck up to higher speed, then shifting to neutral and letting the engine/pump get down to its idle speed. See what happens then. Also try revving it like toomany suggested. You should have a gain in boost pressure when it speeds up.

Is this a new problem, or has it always been this way?
Click to expand...


its been this way since I bought it (since then I've only put like 15 miles on it after getting it home).
I guess the reason I didn't suspect the pads/rotors is that its so consistant at the same speed and pulls the same everytime. but through out the rest of the drive speed/conditions it brakes fine...

i'll try revving it and playing with it next time I drive it.
 
Smokinthehippies said:
its been this way since I bought it (since then I've only put like 15 miles on it after getting it home).
I guess the reason I didn't suspect the pads/rotors is that its so consistant at the same speed and pulls the same everytime. but through out the rest of the drive speed/conditions it brakes fine...

i'll try revving it and playing with it next time I drive it.
Click to expand...

It being at the same vehicle speed is why I suspect the pads/rotors/rubber hoses. The hydroboost has no way of knowing what the vehicle speed is. It is impacted by the engine speed. So if your problem is truly relating to vehicle speed, and not engine speed, I would be looking at things out by the wheels.

A collapsed rubber hose. A stuck caliper. Imbalanced pad wear. Worn rotor on one side. Etc.
 
Check the front wheel bearings...if they are loose or worn,it can cause that funky feel in the brake pedal,when you slow down to the 10 mph range,the wheel & rotor may try to wobble,that'll push on the caliper piston,and transmit the feeling back to the pedal..usually if the bearings are that loose though,you'll have to pump up the pedal at least twice to get a high firm pedal..the caliper has to push against the rotor until the play in the bearings is taken up,then the pedal will firm up..
 
diesel4me said:
Check the front wheel bearings...if they are loose or worn,it can cause that funky feel in the brake pedal,when you slow down to the 10 mph range,the wheel & rotor may try to wobble,that'll push on the caliper piston,and transmit the feeling back to the pedal..usually if the bearings are that loose though,you'll have to pump up the pedal at least twice to get a high firm pedal..the caliper has to push against the rotor until the play in the bearings is taken up,then the pedal will firm up..
Click to expand...


Yup! And if the ABS light is on that is a sure sign the wheel bearings are toast.
 
Well I've got it narrowed down to definitely a pressure issue. Leaving it in low gear and doing the same speed stops shows no issues whatsoever. I'm kinda leaning towards a dinked caliper. But either way I'm doing new odd rotors hubs and calipers right now. We will see if that does it
 
Smokinthehippies said:
Well I've got it narrowed down to definitely a pressure issue. Leaving it in low gear and doing the same speed stops shows no issues whatsoever. I'm kinda leaning towards a dinked caliper. But either way I'm doing new odd rotors hubs and calipers right now. We will see if that does it
Click to expand...

Wait...you're saying that switching to low gear eliminates the problem? That would make it sound like a problem on the hydroboosting side of things.

Or did I misread what you wrote? :dunno:

If doing front stuff, front hoses are a good idea as well. They tend to collapse over time and that leads to funky imbalance in the pressures going to each side.
 
No. What I was saying was not using the brakes and just downshifting and coasting to a stop the issue wasn't present. And now I got time to get hoses as I didn't get the right hubs. Napa dude gave me 2wd units and I didn't notice til I had it dismantled. Of course they didn't have the correct parts so it's gonna wait for a bit.
 
Smokinthehippies said:
No. What I was saying was not using the brakes and just downshifting and coasting to a stop the issue wasn't present. And now I got time to get hoses as I didn't get the right hubs. Napa dude gave me 2wd units and I didn't notice til I had it dismantled. Of course they didn't have the correct parts so it's gonna wait for a bit.
Click to expand...

Been there, done that. :doah:
 
Finally got the big stinky back on the ground. New unit bearings. New calipers and rotors.

Fixed the problem. I don't know exactly what the problem was but it brakes and tracks and straight so I'm happy.
 
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