I need some advise on a soft brake pedal problem (1997 FZJ80)

[edwards_rljr]

I've been having a problem where my brake pedal often feels soft and goes to the floor a lot, like there isn't good brake pressure. To be clear, the brakes work, and it stops, but it seems like a lot of the time I have to pump the pedal to feel good strong pressure. I will press the brake pedal, and sometimes it seems ok, but sometimes it will just feel like there's not a lot of pressure, and it will go down to the floor, and I will have to pump it to get good pressure, or I will be sitting at a red light, and the pedal will just start sinking to the floor. The vehicle doesn't start moving, but I have to pump the pedal to feel good pressure again.

Because of this, I recently decided to take my 80 to a shop to get the brakes checked out , plus several other issues that I had been putting off. The shop had good reviews online, so I felt like I might be able to trust them to do a good job. I told them if I needed new pads, calipers, rotors ,etc. to just do it, because I wanted to make sure the brakes were perfect. They ended up telling me that I needed new front pads, but all my rotors where fine, but one of my rear calipers was leaking, so I had them replace it with a OEM reman caliper, and they were supposed to flush out the brake system and everything in the process.

Even though they didn't take me for a ride, and tell me I needed all new everything, they told me that they didn't observe the soft brake pedal that I was talking about, so that made me question my trust in their work, because it's not something that was just happening every once in a while, it would happen at least once every time I drove it. So, after I went and picked it up, I immediately noticed the soft brake pedal again on my way home. I was frustrated, and wondered how they didn't notice the lack of good pressure, IF they actually took it out for a test drive after replacing the leaking caliper. I called them and told them about it, and they said there might be a issue with the master cylinder or the Load sensing brake proportioning valve, and that they might need to be replaced.

I searched on ih8mud, and read some posts about soft brake pedal issues and some posts talked about master cylinders, LSBPV, brake booster... some talk about brake systems not being properly bled after brake service. So, I guess it could be any of those things, but I'm wary of getting into a situation with someone just throwing parts at it and charging me more money. The fact that they said they didn't even notice the soft brake pedal going to the floor makes me think they didn't even drive it after they replaced the caliper. I hate that it's so hard to find mechanics that you feel like you can trust.

So, my question is, what do you think the most likely culprit is, given that the brakes are working, but it just feels like there is lack of pressure and I have to pump the pedal , probably half the time, when I'm braking. I've never felt like I had no brakes at all, but the pedal sinking to the floor like that makes me worry that they might fail and cause me to get into an accident.

The master cylinder and LSBPV don't really seem to be that expensive, around $150 each for OEM , from what I've seen online. I don't know if either one has ever been replaced on this vehicle. (I've owned it for 11 years). Would you just go ahead and replace them? Or, do you think that a professional shop didn't bleed the brakes properly after doing this work?

Also, how likely is the brake booster to fail? I read one post on here where someone was saying their booster was making a weird noise and they had to replace it. I'm not hearing any weird noises when I brake. I found what is supposed to be new OEM brake boosters on ebay for around $400. I don't really want to spend that I don't have to, but if I need to I will. I don't know if it has ever been replaced either, but we are talking about a 28 year old vehicle.

 

[NeverFinis]

OEM M/C, under the brand Advics, is sold at RockAuto for $72.

More Information for ADVICS BMT046

Also, OEM parts can be much cheaper overseas.

Brake Boosters can fail, but go through the FSM diagnosis check for it but it is more than likely a M/C issue..

 

[ChaseTruck]

…I will be sitting at a red light, and the pedal will just start sinking to the floor. …
.

Barring any external leaks, this sounds like an internal leak in the brake master cylinder to me.

 

[edwards_rljr]

OEM M/C, under the brand Advics, is sold at RockAuto for $72.

More Information for ADVICS BMT046

Also, OEM parts can be much cheaper overseas.

Brake Boosters can fail, but go through the FSM diagnosis check for it but it is more than likely a M/C issue..

Thanks, that's definitely cheaper than what I've seen.

 

[edwards_rljr]

Barring any external leaks, this sounds like an internal leak in the brake master cylinder to me.

Thanks, I hope that is all it is. I really don't want to have to buy the booster right now.

 

[robnicko]

Barring any external leaks, this sounds like an internal leak in the brake master cylinder to me.

this

had the exactly the same thing happen on my daily driver Ford not too long ago and MC was the culprit

 

[ppc]

@edwards_rljr ,
To me this is most likely caused by loose front wheel bearings. When preload adjustment is not properly set the rotor will have runout of wobble that pushes the pads further away from the rotor. That requires more brake fluid to extend the pad to contract the rotor.

A leak or bad master cylinder when you first press the brake it will feel firm but then drop to the floor.

 

[lumbee1]

Remove the LSPV completely.
If that doesn't fix it, remove the ABS pump.

The LSPV does not work on a lifted vehicle unless the arm is modified. At that point, the LSPV is literally doing nothing but acting as a T-joint. The LSPV is designed to optimize braking performance by adjusting the hydraulic brake pressure sent to the rear wheels based on the actual load carried by the vehicle. I personally would rather have full pressure to the rear and adjust with a manual proportioning valve. The LSPV causes weak braking when the rear is light or the vehicle is pointed downhill.

The ABS pump can get air inside of it that is very difficult to bleed and cause a soft pedal. There are methods to bleeding the pump but I and many other just chose to simplify the braking system and remove it. The ABS is first generation and while it works, it adds complexity.

 

[OffRoadScott]

I scanned over this whole thread and everyone was spot on with their recommendations, but I would like to add check the check valve on the brake booster too.

 

[Godwin]

As others have said a bad MC, internally leaking. I've experienced this on two different Cruisers. A quick jab of the pedal and you have solid brake pressure, but a gentle pressing of the pedal and it sinks to the floor. Replace the MC and you should be good.

 

[vfrer]

When my master failed I would be stopped and gradually lose brake pressure and the truck would start moving unless I pressed harder.

Here is the FSM booster test...

 

[edwards_rljr]

Thanks for all the advice guys. I appreciate the input and suggestions. Hopefully it is just the master cylinder.

 

[yknot123]

The brakes will always feel soft in the 80 but that doesn't mean you shouldn't stop.
Many challenges for YKNOT over the decades.
Clean brake fluid in reservoir, then do a manual bleed with help, old fashion pump at pedal. You will see dirty versus clean fluid at bleeder valve. Put the rubber boot back on or new boot on bleeder valve
Replace brake booster if pedal still slowly goes to the floor. Can often hear a hissing sound under dash or by booster of air.
At 28 years a good chance this issue.
Have yet to replace master after 350K +/- lots of front pads and recent new oem front discs (rotors).

 

[smorkington]

vouch for lspv delete

 

[landtank]

sticky rear slide pins and loose rear wheel bearings will cause you to pump the brake petal to get brakes. The severity can depend on how rough the terrain is.

Once when climbing a particularly challenging hill and didn't make it up all the way, the rotors had beaten and spread the calipers so much that the first press of the pedal went straight to the floor and I was in free roll backwards down the hill. Second push got some grip.

The boxers took a hit that day.

 

[tech_dog]

I'd suggest:

1) With the engine running, push hard on the pedal for a few minutes, pumping if necessary, and then check four wheels and everywhere else for a brake leak. Even a very small leak can give you a saggy pedal, so rule it out.

2) A bad booster gives you a hard pedal, not a soft pedal. It's probably not that.

3) How much did you have to pump during the few minute test in #1? If you eventually got a firm pedal, it makes air in the lines more likely. If you never got a firm pedal then it makes a bad MC more likely.

4) If you find the right fix, you don't need to delete anything, and you'll have a firm pedal and good braking.

I just finished replacing my MC, booster, all the rubber lines, and all 4 calipers, and that's my 2 cents.

 

[WESBC]

Activate the ABS and bleed the system. I’ve lived with spongey brakes since the beginning and replaced everything over the years and the only thing that fixed it right away was activating the ABS and pressure bleeding. I wish I started with this first.

Is there a way to trigger ABS actuator to combat spongy breakes?

Truck info: 1994 LC with ABS So after some brake work (Caliper replacement with pads) I had spongy brakes. Wasted good amount of brake fluid trying to bleed them. I suspected that Air was trapped in ABS actuator but short of buying the SST tool or driving on Ice I did not see a way to trigger...

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