PowerBrake booster

[RLCollins]

how do properly troubleshoot the booster, in a power brake system?. :headpop:

[freakjeep93]

whats wrong with the booster?

[RLCollins]

It Seem like there is no difference in the brake paddle with the engine running, or not running?

[freakjeep93]

how much pedal do yiou have

[cracker]

Can you stop? Is it a lot of work?

 

(stupid question). You sure you don't have any air in the lines?

[HellCreek]

I'm sure there is a more technical way to check it, but press your foot on the brake pedal and crank the engine. If the pedal goes down when the engine cranks, then the vacuum boost is working. If you have a single diaphragm booster, that would explain a lot. Believe me, the dual diaphragm upgrade is well worth it. :thumbsup:

 

-Tom

[RLCollins]

Cracker - I am sure there is no air in the lines. I have bleed them twice, thinking the same as you. :headpop: HellCreek - There is very little paddle after bleeding them twice. I have replace both proportioing valves and the master cyclinder, along with rebuilt calipers ,and rear wheel cyclinders, along with adjusting them till they had some "Dragging when turning to rear wheels. These brakes should have a firm brake paddle, and it does not - its like mush. This is why I am asking about the vacuum booster. How do you check it out? I tried the paddle test with the engine off, and than started the truck. The peddle did not sink any further to the floor. :headpop:

How can I check out this booster?

Which booster do I have in my 1989 MJ 4.0, I-6 4X4

How can you tell the difference between the single and double diaphram model?

If it is bad which one will fit in my truck. :help:

[HellCreek]

The only way I know to check to see if the booster is working is the one I told you. Do you have vacuum to the booster? If the engine runs, you should, but pull the plastic valve out of the grommet on the booster and crank the engine. You should have vacuum at the valve. If not, replace the valve. You can find these at most auto parts stores in the HELP section.

 

If the pedal goes all the way to the floor with the engine off, then you pretty much have to have air in the system somewhere, even though you have already bled it twice. If there is no air in the system, you should have a firm pedal, whether or not the booster is functional. If the booster is bad, you would simply have a hard pedal all the time, and you would really have to press hard on the pedal to stop your truck.

 

All this is assuming that by your saying, "there is very little paddle," that your brake pedal is almost at the floor and not that it moves very little when you press it. If the latter is true, then your booster is probably bad.

 

I replaced my single booster with a 1996 XJ Cherokee dual diaphragm booster. It's not a direct swap, but it is pretty close.

 

-Tom

[cracker]

The later model XJ boosters will totally work but it is a bit tricky to get the brake light set up to work.

 

Many folks have chosen to use the WJ booster/MC and it is an almost bolt in affair with minor modification to your firewall pinch seam and the brake light set up is slightly easier to get going. The WJ is supposed to have slightly more power as well. I am running the WJ set up currently on my MJ. :waving:

[RLCollins]

Thanks for the informatin. I will go back and bleed them one more time, and move the height sensing proportioning valve as well. I will also look at the booster more closely too see what the HEL is going on. i have done many brakes in my time, but never turn out like this :headpop:

[HellCreek]

You might want to read this thread on brake bleeding with the rear height sensing valve.

 

viewtopic.php?f=2&t=4917

 

- Tom

[JeepcoMJ]

The later model XJ boosters will totally work but it is a bit tricky to get the brake light set up to work.

 

Many folks have chosen to use the WJ booster/MC and it is an almost bolt in affair with minor modification to your firewall pinch seam and the brake light set up is slightly easier to get going. The WJ is supposed to have slightly more power as well. I am running the WJ set up currently on my MJ. :waving:

 

they really don't have all that much to do with making the brake lights still work.

 

...other than a full on cherokee conversion, the only thing that requires modifying/figuring out anything when it comes to brake lights is perhaps grinding a bit off the rod that goes to the booster from the pedal...and that's just to give it a flat side (if it's 97+) for the switch to rest on.

 

just did a '99 booster swap on my brother's '88. went in easy, I chose to space the booster off of the firewall a bit in order to make the pedal remain even.

 

 

 

 

anyways, if your brake pedal doesn't go down when you start the motor, you have a bad booster...or a complete lack of vacuum @ the booster. just pop the line that goes to the booster off and start the truck...if it doesn't have vacuum from the line going to the booster, the problem is the line rather than the booster. if it does have vacuum, replace the booster.

 

-Pat

[jmderyke]

If you have mushy brake pedal its in your hydraulic system Period! If your brake booster is not functioning, then its hard to apply the brake (if the hydraulic system is functioning properly).

 

get a friend to help bleed the brakes. If you are sure theres no air in the system and you still have mushy pedal, and theres no leaks, then your mastercylinder is shot. don't bother rebuilding it your self, even with a new valve in there you can still get a bad seal with damage to the cylinder its self.

[fiatslug87]

Back to the original question,here is the diagnostic check from the 1990 FSM. The last page has the booster check.

[RLCollins]

Now that it has stopped raining here in South Florida. We needed the rain so I not complaining. Now I can go back to working on my truck. I feel SORRY for all of you in the northeast, you probably are getting hammered about now with snow. So much for global warming. :rotfl2:

I want to thank Fiatslug87 for the Booster testing information - well; both the check valve and the booster pass the test. I lost about 10HG's in fifteen seconds. With the information you gave me it stated that a 33HG's loose was the cutoff line for being faulty. So thanks. :D

I believe I have tracked my brake problem down to two areas, either the new master cylinder is bad, or the height sensing proportioning valve arm which I installed, is 180 degrees out of proper position, which is allowing the brake fliud to flow freely in the loop, without any resistance. :doh:

Time to go back to go back to work, the sun is shinning and the temperture is probably about 70 degrees. I think that is good working weather, what do you think? :hmm:

[fiatslug87]

I lost about 10HG's in fifteen seconds. With the information you gave me it stated that a 33HG's loose was the cutoff line for being faulty.

I hope you mean you lost 10 milibars not HG, the "33" specification is in millibars which equals approximately 1 Hg (inches of mercury).

[RLCollins]

Yes 10 millibars. I Figured out my brake problem, I install the arm on the height sensing proportioning valve 180 degrees out of sink, changed it to the proper position and my brakes work fine now. After changing the blown-up transmission, timing chain, water pump, 195 degree thermostat, oil pump, rear main seal, hermonic balancer, oil pan gasket, change the cooling system from a closed one to an open one, complete brake job less the steel brake lines, clutch master cylinder and the slave cylinder and three months of labor, it is finally back on the road. I still have small items to take care of like the bad head light switch, AC fan motor is shot with bad bearing, speedometer does not work?, back-up light switch in the transfer case bad, drives side window regulator Bad, maybe the passanger too? Should I buy new ones or are pull yard ones ok? need to change all the window rubbers, fuse panel is eaten-up with brake fluid from the hydrallic clutch master cylinder - any suggestions? , innerfender doghouses, tires, some of the sensors need to be changed that control the ECU, any suggestion? and a paint job. After I finish the rest of this list, It will be looken fine:yes: