The cure for Spongy Brakes

[Azca]

Well it appears that it significantly improved mine anyway and would like some insight and comments from the experts.

After replacing the brake booster I was very unhappy with the feel of the brakes. They were poor before but worse now. I had recently replaced the master cylinder and replaced all brake fluid. So I now again replaced all the brake fluid after trying to bleed the brakes and the LPSV, two hours and no improvement. I was resigned to the fact that the beast was going to have crappy brakes forever.

After the test drive I found the brake pedal, after the install, was lower than I would like and trying to stop her pushed the pedal way past the plane of the gas pedal.

So back to the FSM and then it struck me , I probably had an issue with contact between the master cylinder and the brake booster push rod. See the FSM below.

Crawled back under the dash and adjusted the plunger inward about two to three complete turns (see bottom illustration in FSM). Also readjusted pedal height to my liking AND...

OMG! I have firm brakes !!!

Now here are my questions before I get too smug. It is hard to know if adjusting the push rod is now causing the brakes to engage early although I do have a bit of play in the pedal, as described in the FSM, and it appears to be correct. Is there a way to tell without taking this contraption apart again??? Does this sound to you folks like a reasonable solution?

 

[itbrokeagain]

Can't see what you have on the phone app but adjusting my rear drums fixed my issue

 

[blkprj80]

Crawled back under the dash and adjusted the plunger inward about two to three complete turns (see bottom illustration in FSM). Also readjusted pedal height to my liking AND...

You can adjust this without taking the MC off the vacuum booster? Thanks for the enlightenment! Not that I really like to work on anything up in that area. I usually remove the whole seat if I'm spending much time up there.

It sounds like you may be able to adjust it to where you have play, and then adjust it out, on-the-fly.

I always thought you had to have it all apart to adjust it.

 

[M32H32is]

OP,

Do you have an FJ or FZJ?

 

[Skrewball]

Usually if you adjust the rod too far the master cylinder won't return completely. At first all seems good, but after a little bit the brakes will begin to drag.

Keep an eye on it.

 

[Azca]

You can adjust this without taking the MC off the vacuum booster? Thanks for the enlightenment! Not that I really like to work on anything up in that area. I usually remove the whole seat if I'm spending much time up there.

It sounds like you may be able to adjust it to where you have play, and then adjust it out, on-the-fly.

I always thought you had to have it all apart to adjust it.

I had to take out the brake switch to get adjust pedal height. I removed the plastic dash under the steering column (4 screws) the metal plate under the plastic (5 - 10 MM bolts) and the duct for the A/C. Much easier access.

Yes you can adjust without taking out the booster. If you don't have to adjust pedal height this will be much easier. Just loosen the 14 mm nut on the push rod and use a pair of pliers to adjust. Super simple.

OP,

Do you have an FJ or FZJ?

FZJ

Usually if you adjust the rod too far the master cylinder won't return completely. At first all seems good, but after a little bit the brakes will begin to drag.

Keep an eye on it.

I will, how long would you consider to be a little bit? Thank you for the info!

 

[Skrewball]

Probably after about 20 min of stop and go driving. Not an exact time of course...

 

[mod5csi]

I just went through the same issue.

I was able to "measure" the hole in the master cylinder, on the truck, with a piece of wire. I cut the 18g wire with about 1mm visible. It helps if you have another pair of hands pull the MC away from the booster, not enough to bend the lines. Then I used the cut wire to measure the booster rod length. Be sure to measure from the mounting surface's plane. Have a helper lightly push on the brake pedal to get at the adjusting rod.

I have been measuring the temps of my brakes to see if they are dragging. Using an infrared thermometer over the last week or so. I would jump out when I stopped at a destination and measure the temps of the rotors and calipers. I did not take before data, so I really have nothing to compare it to. But after a 30 minute highway drive with a couple stop signs to get home. My front and rear brakes measured 20* or so above ambient.

 

[Pin_Head]

Spongy brakes come from air in the hydraulic lines. Adjusting the pedal to booster linkage won't do anything about air in the system, but it will change the pedal height at which engagement begins. There is a spec for this adjustment and you want to be in spec.

 

[Azca]

Spongy brakes come from air in the hydraulic lines. Adjusting the pedal to booster linkage won't do anything about air in the system, but it will change the pedal height at which engagement begins. There is a spec for this adjustment and you want to be in spec.

Thanks Pin Head! I know it the air in the system should be the culprit to the spongy feel. I bleed the brakes and test drove them and had not only significant pedal travel but even once they started to engage felt soft. That certainly may have been a product of the travel distance and not stopping ability as the brakes did seem to function well once they seemed to engage.

To those of us who are untrained it certainly is quite possible that we are mistaking the travel distance with the spongy feel of air in the system. Before engagement of the brakes there still is slight resistance until you actually begin to apply pressure to the system. Does that seem like a plausible idea to you?

 

[Pin_Head]

To those of us who are untrained it certainly is quite possible that we are mistaking the travel distance with the spongy feel of air in the system. Does that seem like a plausible idea to you?

Sure why not. Spongy brakes feel like you have a sponge on the pedal.