Bad brake booster or something else?

[Joesmith]

So my 07 JK X, blew an engine. It sat for 2 years until I could get enough $ to get a remanufactured engine put in. I got it back Friday, with a note saying the brake vacuum booster is bad.

So while driving it, the first push of the brake pedal is normal and feels fine, but any subsequent pushing of the brake pedal immediately thereafter, and it’s super hard to push and the brakes do not seem to grab until you force the pedal all the way down.

I pulled the check valve on the booster and it works like it should.

I just want to know, can a brake booster go bad while sitting?
Or could this be another issue?

I don’t have the money to buy a booster if it’s going to end up being something else.

Thanks for any advice/answers

 

[JPNinPA]

First inspect all the lines and make sure they are not crushed.
Then do a full bleed at each wheel. Replacing all the fluid while bleeding. Inspect pads for even wear

It sounds like either a damaged line or the rubber lines gone bad.




Never look down on anyone unless you are helping them up - Jesse Jackson

 

[Joesmith]

First inspect all the lines and make sure they are not crushed.
Then do a full bleed at each wheel. Replacing all the fluid while bleeding. Inspect pads for even wear

It sounds like either a damaged line or the rubber lines gone bad.




Never look down on anyone unless you are helping them up - Jesse Jackson

Pads have normals wear, but the rotors have sitting for two years, levels of surface rust on them.
When you say “rubber lines” you mean the brake lines at the wheel where they go into the calipers?

Or did you mean vacuum lines from the booster?
The booster lines look good.
I’ll be getting under the check the rest in the evenings this week.

 

[JPNinPA]

Yes on rubber lines. Last section attached to caliper. I had one fail and acted like s check valve. Would not release pressure and wore out a set of pads.
Brake lines that run from the master cylinder to the rubber lines. Some go behind engine or over the trans. Places they could get squished when changing an engine.



Never look down on anyone unless you are helping them up - Jesse Jackson

 

[JPNinPA]

I would think if they replaced the engine some of this was moved or disassembled.

Also be sure the correct pulley sizes are used and you have the correct vac pressure when running.


What RPM do you idle at?

Never look down on anyone unless you are helping them up - Jesse Jackson

 

[Joesmith]

I would think if they replaced the engine some of this was moved or disassembled.

Also be sure the correct pulley sizes are used and you have the correct vac pressure when running.


What RPM do you idle at?

Never look down on anyone unless you are helping them up - Jesse Jackson

Oh man, the lines that go behind the engine and/or over the trans have me concerned. Those are metal lines, correct?

The mechanic that replaced the engine said he checked the vacuum from the engine with a gauge and he said it was good.
When I pulled the check valve off the booster it was definitely under vacuum, it made the sucking noise when I popped it out.

I’m not sure what RPM I idle at but it seemed to be idling normally. I won’t be able to get back to the Jeep until Thursday, and I’ll post my findings.

@JPNinPA thanks again, you’re always on here helping me out. I appreciate it a lot

 

[Joesmith]

Ok, so I had some free time after work today, I went and traced all the brake lines, none went across behind the engine, but the front passenger side goes across the front bottom rad support, and could easily be crushed during the engine swap…fortunately (unfortunately for my diagnostics) none of the brake lines look damaged even a little bit, in fact when I wipe away any crud on them, the coating on them still looks in new shape, the rubber lines in the rear look old but no cracks or damage that I could find.

I will give all four a good bleeding tomorrow some time before the festivities, and be back with updates.

Thanks again

 

[mark sr]

The flexible brake hose can appear decent on the exterior but can collapse on the inside. If they are original I'd go ahead and replace them.

 

[Joesmith]

I would think if they replaced the engine some of this was moved or disassembled.

Also be sure the correct pulley sizes are used and you have the correct vac pressure when running.


What RPM do you idle at?

Never look down on anyone unless you are helping them up - Jesse Jackson

Ok so I couldn’t get them all bled, the front driver side bleeder valve is garbage and would not crack loose, the front passenger side bled just fine with zero air, all fluid.
The passenger side rear bleeder was also crap, but the driver side rear bled normal with zero air…but not as much “squirting” force as the front but that seems normal to me.
The brake problem still persists, the first press of the brake pedal feels normal and stops appropriately but if I give it a second press of the pedal as if pumping them, they get super stiff and hard to push and the Jeep doesn’t wanna stop.

The idle seems normal at just over 1000 rpms.

I for-see a brake booster replacement in my future

 

[JPNinPA]

Idle should be 750 rpm. Does rpm drop when applying brakes? It shouldn’t. But dropping rpm when applying brakes is a sign of failing booster.
You may have a vac leak causing high rpm and robbing some boost from the brake booster.
You need to get them all bleed. It is not a bad idea to change all the fluid by bleeding out the old. Brake fluid is hydrophilic so it absorbs water. That ends up Causing soft brakes.
Any contamination in the reservoir clean out from above. Siphon with a big brake syringe.

When the mechanic said the vac was good what was the value of vacuum he measured?.

Never look down on anyone unless you are helping them up - Jesse Jackson

 

[Joesmith]

The RPMs do not drop when applying the brakes, it’s stays at a steady needle just above 1000.
He didn’t give me the measurement from the vacuum reading, but said it was appropriate for the vehicle specs.
The brake fluid looks in decent shape, clean, no crud or any obvious contaminants. I imagine that I can’t see the water in it if it’s there.

I’m going to have to get the bleeder valves off of the driver side front and passenger side rear, and replace them to get those two bled.
It is possible it is a bad booster correct?
Am I doing all this other stuff just to avoid replacing the booster and it’s really not that bad of a job?
Decisions decisions

 

[JPNinPA]

It is not about the fluid in the reservoir. It’s about what’s in the lines in the caliper. You cannot see water in the fluid because it mixes the fluid. Brake fluid should be swapped out completely every few years because it was moisture.
Yes, it’s still could be your break. But you should idle at 750 RPM. You probably have a vacuum leak if it’s above 750.
Some mechanics will lie just to get the job done.

Never look down on anyone unless you are helping them up - Jesse Jackson

 

[Joesmith]

It is not about the fluid in the reservoir. It’s about what’s in the lines in the caliper. You cannot see water in the fluid because it mixes the fluid. Brake fluid should be swapped out completely every few years because it was moisture.
Yes, it’s still could be your break. But you should idle at 750 RPM. You probably have a vacuum leak if it’s above 750.
Some mechanics will lie just to get the job done.

Never look down on anyone unless you are helping them up - Jesse Jackson

Well I did the booster because I had some free time. And it did not fix the issue. The old one made the sucking sound when I popped off the master cylinder.
It definitely idles above 750, but it has always idled around 1100-1200 (just above the 1)even with the old engine.
I’m at a loss for today, I’ll see about getting some new brake fluid and bleeding the system dry-ish and refilling it.
And tearing these stuck bleeders off.

 

[JPNinPA]

You dont need/want to empty the system just exchange the fluid. Siphon the old fluid out of the reservoir. Fill with new fluid. Then go to your driver side, closest tire, open the bleeder valve and push the piston flush to the caliper. This pushes out most of the old fluid. Shut the valve and bleed until no bubbles and fluid is clear. Then do the same on the passenger side. Driver rear then passenger rear.
Never let your resivoir run dry.

To find vac leak take a spray can of wd40, starter, carb cleaner… and with the engine running spray around the TB base, the intake at each cylinder at the engine, each injector, and each vacuum line. When the engine rpm changes you found a leak.


Never look down on anyone unless you are helping them up - Jesse Jackson

 

[Joesmith]

You dont need/want to empty the system just exchange the fluid. Siphon the old fluid out of the reservoir. Fill with new fluid. Then go to your driver side, closest tire, open the bleeder valve and push the piston flush to the caliper. This pushes out most of the old fluid. Shut the valve and bleed until no bubbles and fluid is clear. Then do the same on the passenger side. Driver rear then passenger rear.
Never let your resivoir run dry.

To find vac leak take a spray can of wd40, starter, carb cleaner… and with the engine running spray around the TB base, the intake at each cylinder at the engine, each injector, and each vacuum line. When the engine rpm changes you found a leak.


Never look down on anyone unless you are helping them up - Jesse Jackson

I ordered a vacuum bleeder kit, the kind with the pump handle on top. I figure that will help me do it by myself.
While I’m at it I’m going to pull each wheel and caliper to make sure they aren’t seized up of anything weird.
Chasing gremlins is frustrating, and I have to talk myself out of ripping everything off and replacing it all….the shotgun approach .

I’ll try the vacuum leak test this evening and report findings.

 

[JPNinPA]

I see it this way. You must be able to stop and steer before you could go. So redoing the brakes is a good investment. I’ve done it several times to get good touchy brakes.


Never look down on anyone unless you are helping them up - Jesse Jackson

 

[superj]

i remember when i was a kid, we always had go carts with 5-8hp briggs and stratton motors on them. they were a ton of fun....... until you had to stop. they had those old school brakes that pushed a piece of rubber against the tire to try and stop it and since we were kids, we couldn't push the brakes hard enough to apply enough friction to stop the go carts. we always ended up running into something to stop, which sucked.

imagine having to run into something to stop your jeep.

 

[Joesmith]

So I got the passenger side rear to bleed, and I took of the caliper and made sure it is functioning as normal. Then I ran out of daylight.
I’ll be doing the other rear tonight.
The motive vacuum bleeder I got is absolutely garbage, I’ll be returning that and just using my son to pump the brakes for the bleeding

 

[Joesmith]

i remember when i was a kid, we always had go carts with 5-8hp briggs and stratton motors on them. they were a ton of fun....... until you had to stop. they had those old school brakes that pushed a piece of rubber against the tire to try and stop it and since we were kids, we couldn't push the brakes hard enough to apply enough friction to stop the go carts. we always ended up running into something to stop, which sucked.

imagine having to run into something to stop your jeep.

Stopping is over rated

 

[JPNinPA]

Sorry i didn’t think of this earlier.
Vac bleeders often pull/draw/suck so hard it pulls air around the threads of the bleeder into the caliper that it looks like you have air in the lines.
I use the siphon bottle to catch the fluid that is pumped out.


Never look down on anyone unless you are helping them up - Jesse Jackson