Redid brake system but left with a problem

Kimuri · Oct 26, 2024

Hi all,

I finally started working on my jeep under supervision of a mechanic, I’ve done a few works on it but now my brakes are having a problem.

It is a 2003 Jeep Liberty 3.7 V6 automatic with ABS

Since the brake pads have been changed, the brake pedal won’t stiffen up. We’ve bled the system, changed the brake calipers, changed the brake discs, changed the master brake cilinder, still it won’t stiffen up when the car is on.

When the car is off, the brakes stiffen up and become loose as soon as the car is turned back on.

We hear a ‘sis’ sound around the ABS, so I’m starting to think that maybe changing the ABS pump will be our final resolution?

Does anyone have an idea?

Thank you in any case
Cheers

KJowner · Oct 26, 2024

If the brakes are soft then you still have air in the system, possibly trapped in the ABS unit if you have drawn air through there.
Did you open the bleed screws when you pushed the caliper pistons back? If not you risk blowing muck back into the ABS unit.
I would suggest bleeding the system more, if you can get it to work enough to drive, take it to somewhere with a loose gravel or similar surface and give the ABS system some work, bleed it and repeat. Hopefully it will clear.

DadOSix · Oct 26, 2024

Just to add -

A brake pedal will be extrememly firm with the engine OFF. With engine running - the pedal action is 'softer'
Your tell here is - Does the pedal continue to the floor with engine running. If yes, you have a leak somewhere. If just 'not what it was' before changing the brake pads, as KJowner above says - you have air trapped somewhere. Proper bleed procedure is to start with the bleeder furthest from the master cylinder. Do that one first and continue around the jeep. RR(right rear) , LR(left rear), RF(right front) , LF(left front). Until you get fresh, clear brake fluid.

and a side note to whatever guru in the auto world decided it would be neat to rearrange the letters when naming tire positions, torque specs, etc - I spit in your eye!

Kimuri · Oct 26, 2024

DadOSix said:
Just to add -

A brake pedal will be extrememly firm with the engine OFF. With engine running - the pedal action is 'softer'
Your tell here is - Does the pedal continue to the floor with engine running. If yes, you have a leak somewhere. If just 'not what it was' before changing the brake pads, as KJowner above says - you have air trapped somewhere. Proper bleed procedure is to start with the bleeder furthest from the master cylinder. Do that one first and continue around the jeep. RR(right rear) , LR(left rear), RF(right front) , LF(left front). Until you get fresh, clear brake fluid.

and a side note to whatever guru in the auto world decided it would be neat to rearrange the letters when naming tire positions, torque specs, etc - I spit in your eye!

The pedal continues to the floor when the engine is on, there is no ‘pressure’ at all but I have looked everywhere and can’t find a leak, we bled the brakes multiple times and I’m quite confident it was done well. What would you suggest could be the problem?

We hear a ‘hiss’ near the abs pump but no visible leaks at all. Tried soapy water, no leaks on the tubes either.

Thank you both for the feedback @KJowner

ltd02 · Oct 26, 2024

Is the booster toast?

Kimuri · Oct 26, 2024

ltd02 said:
Is the booster toast?

How could I confirm this?

I’ve changed quite a bunch of stuff on a hunch, but nothing is confirmed unfortunately.

If I buy the booster, I’ll be 300 EUR deep in brake repairs, trying to spare myself as much as possible from it.

DadOSix · Oct 26, 2024

Kimuri said:
The pedal continues to the floor when the engine is on, there is no ‘pressure’ at all but I have looked everywhere and can’t find a leak, we bled the brakes multiple times and I’m quite confident it was done well. What would you suggest could be the problem?

We hear a ‘hiss’ near the abs pump but no visible leaks at all. Tried soapy water, no leaks on the tubes either.

Thank you both for the feedback @KJowner

Are we losing brake fluid when the engine is running and the pedal goes to the floor?
- if yes - I suspect the master cylinder is leaking into the booster.
-- quick and dirty test - pull the vacuum hose at the manifold or the booster and see if it is wet inside.
--- yes - bad master / no - keep looking

- another possibility - you have a brake hose that has a weak hose wall. Sort of like an aneurysm in an blood vessel. The engine off might not generate enough pressure to baloon the hose. Running, definitely do-able. have to have a helper look while someone pushes the brake down with engine running.

Kimuri · Oct 26, 2024

DadOSix said:
Are we losing brake fluid when the engine is running and the pedal goes to the floor?
- if yes - I suspect the master cylinder is leaking into the booster.
-- quick and dirty test - pull the vacuum hose at the manifold or the booster and see if it is wet inside.
--- yes - bad master / no - keep looking

- another possibility - you have a brake hose that has a weak hose wall. Sort of like an aneurysm in an blood vessel. The engine off might not generate enough pressure to baloon the hose. Running, definitely do-able. have to have a helper look while someone pushes the brake down with engine running.

We're not losing any brake fluid when the engine is running and the pedal goes to the floor, is makes a hissing sound in the area of the ABS/master brake cilinder but there are no leaks. I haven't checked inside the booster yet, after spending a whole day today trying to figure it out, I'll check out the booster tomorrow by pulling the vacuum hose at the manifold as you suggest.

We changed the master cilinder today so I really hope that's not it.

Would a defect brake hose with a weak hose wall have a leak? What would I have to look for in this case, a hose that is a bit inflated?

When we looked around we couldn't find any errors judging on sight, we checked all 4 and honestly I have no answer to it at all, unless I take it to a master mechanic and have him diagnose it but that's going to cost me serious money, considering the amount I've already spent I'm not that keen on doing that

DadOSix · Oct 26, 2024

Kimuri said:
We're not losing any brake fluid when the engine is running and the pedal goes to the floor, is makes a hissing sound in the area of the ABS/master brake cilinder but there are no leaks. I haven't checked inside the booster yet, after spending a whole day today trying to figure it out, I'll check out the booster tomorrow by pulling the vacuum hose at the manifold as you suggest.

We changed the master cilinder today so I really hope that's not it.

Would a defect brake hose with a weak hose wall have a leak? What would I have to look for in this case, a hose that is a bit inflated?

When we looked around we couldn't find any errors judging on sight, we checked all 4 and honestly I have no answer to it at all, unless I take it to a master mechanic and have him diagnose it but that's going to cost me serious money, considering the amount I've already spent I'm not that keen on doing that

The defective hose will balloon out like an aneurysm - Pressure makes the weak place bulge. There may or may not be a leak, but if the hose is bulging, it needs replaced. There may be 5 hoses in total, one for each wheel and one from the rear brake line from the abs that hits a metering block at the differential and sends a line right and left to serve the rear brakes.

It will eventually leak, either by a seeping or totally blow out when you need it most - like in a hard stop.

Just for the fun of it, and since I saw it on YT last week, the calipers are on the correct sides, no? Hose connection lower on the caliper unit with bleeder at the top? If you are certain that they are correct, then logic says, the only place to look next is the place you have not. The abs unit. And I have little knowledge of that system, except to say that I have read that you can pull the fuse to disable it for diagnostics and have normal brakes with no ABS support.

On my big diesel truck, there is an ABS bleed procedure that must be followed on order to purge the air.

KJowner · Oct 26, 2024

How to Bleed ABS Brakes without a Scan Tool

Hi Folks, according to the Service Manual, you must bleed the brake system the first time using conventional bleeding methods. Once the brake system is bled, you need a DRB Scan Tool to cycle the solenoids in the ABS Hydraulic Control Unit to get rid of any air entrapment and then, bleed the...

www.jeepkj.com

Looks like this problem has been discussed before

Kimuri · Oct 31, 2024

DadOSix said:
The defective hose will balloon out like an aneurysm - Pressure makes the weak place bulge. There may or may not be a leak, but if the hose is bulging, it needs replaced. There may be 5 hoses in total, one for each wheel and one from the rear brake line from the abs that hits a metering block at the differential and sends a line right and left to serve the rear brakes.

It will eventually leak, either by a seeping or totally blow out when you need it most - like in a hard stop.

Just for the fun of it, and since I saw it on YT last week, the calipers are on the correct sides, no? Hose connection lower on the caliper unit with bleeder at the top? If you are certain that they are correct, then logic says, the only place to look next is the place you have not. The abs unit. And I have little knowledge of that system, except to say that I have read that you can pull the fuse to disable it for diagnostics and have normal brakes with no ABS support.

On my big diesel truck, there is an ABS bleed procedure that must be followed on order to purge the air.

Just for the fun of it, you were right.

I restarted from 0 and noticed the rear calipers were upside down.

Can you believe it, all that work

Thanks so much man

DadOSix · Oct 31, 2024

Kimuri said:
Just for the fun of it, you were right.

I restarted from 0 and noticed the rear calipers were upside down.

Can you believe it, all that work

Thanks so much man

Great to hear you got it sorted!

mike · Nov 2, 2024

Kimuri said:
the rear calipers were upside down.

Please explain

KJowner · Nov 2, 2024

mike said:
Please explain

They are handed, left and right, they will fit in the wrong side but the bleed point would be at the bottom of the cylinder instead of the top, making it impossible to bleed the brakes.

Kimuri · Nov 4, 2024

KJowner said:
They are handed, left and right, they will fit in the wrong side but the bleed point would be at the bottom of the cylinder instead of the top, making it impossible to bleed the brakes.

When I said this could be the culprit in the shop, the guys looked at me as if I was insulting them lol
Had to do switch them myself, only to sigh in excitement after realizing that they're finally stiffening up

Ohio-white-kj · Nov 4, 2024

KJowner said:
They are handed, left and right, they will fit in the wrong side but the bleed point would be at the bottom of the cylinder instead of the top, making it impossible to bleed the brakes.

A million years ago I worked at an import shop. A car going cross country had destroyed a caliper and rotor and was towed in. We had the rotor, but only had a caliper for the other side. Bleed it off the wheel inverted. Advised the customer that he should get it replaced when he had the chance.

DadOSix · Nov 4, 2024

Kimuri said:
When I said this could be the culprit in the shop, the guys looked at me as if I was insulting them lol
Had to do switch them myself, only to sigh in excitement after realizing that they're finally stiffening up

Exactly why I do my own stuff when i can. Congrats on getting it sorted out!

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