Half spongy brake pedal.

[mason]

Hi everyone, I have 91 warrior with 45'000 miles , My brake all of a sudden felt half way spongy after I had it for emission test in Jeffy loop. .I bled the rear tires and it felt good and solid but after a few days it becomes half spongy again.  I plan to replace the master cylinder(85$) this weekend. I appreciate if anybody has a similar experience to share . Air gets into the rear brakes somehow..

[MaineJed]

You have a leak somewhere 

[mason]

15 hours ago, MaineJed said:

You have a leak somewhere 

I haven't been loosing any brake fluid. The container has been full all the time.

[MaineJed]

8 hours ago, mason said:

I haven't been loosing any brake fluid. The container has been full all the time.

Air in the line then

[Toycollector47]

Rear brake adjustment?

 

at least on the late 90s Chevy half tons if the  rear brakes were loose it would produce a spongy pedal.

 

past that, if no air in the lines then I’d look at a master cylinder.

[mason]

On 10/12/2023 at 4:52 AM, Toycollector47 said:

past that, if no air in the lines then I’d look at a master cylinder.

Yes, I changed the master cylinder and the problem is gone. Thank goodness.

[Elena]

Hi, All - where do you suggest acquiring a master cylinder? I've had the same exact experience as Mason. Got spongy heading home from Letchworth State Park but after bleeding the brakes all seemed well for a short time, then we got spongy again. We've replaced all the hardware but I want to get my hands on a master cylinder sooner than later, as I have a sneaking suspicion something still isn't right / there's air getting in. Thanks in advance for any advice! Our "Connie" is a 1989 Gulf Stream Conquest. 

[extech]

i got mine from rock auto and it's been fine

[Elena]

Thanks so much. I've had so much trouble with fitment on leaf springs, etc. - other stuff underneath. But that's good to know. I'll see what I can find over there. 

[Ctgriffi]

I put this on mine (‘90 chassis) four years ago and works fine. I did paint the body of it to prevent corrosion. I liked that it came with new reservoir and cap. (Whoops, might be out of stock at the moment.) 
 

https://a.co/d/iwGNOAB

[Elena]

Thanks so much, I found the perfect Master Cylinder and it's ready to go in. BUT - my Haynes says I will also need a repair kit. I think that's Toyota part - 04493-35260 Brake Master Cylinder Repair Kit, which I have found and ordered several times, only to have my order cancelled because the part is discontinued. It looks like pistons and hardware, to me. It also wouldn't surprise me if THIS is what needs to be replaced after all this time. 

Anybody know where I can find this? OR - can I get the individual pieces off the shelf by just using info like the bore diameter, thread size, etc? Is that how it's done? 

Thanks SO much. Pics of what's included in the original part number are attached. 

[Ctgriffi]

What MC did you buy exactly? A new master cylinder doesn't need any parts—you just unbolt the old one and swap in the new, very straightforward (although follow the instructions for bench-bleeding the new MC, and then obviously make sure all brakes are bled thoroughly after the install).

[Elena]

Thanks so much, that is helpful info. SO - all those things must already be inside? 

I got this one (though I purchased via Rockauto). 

 

https://www.centricparts.com/brake-master-cylinder-130-44707

 

Elena

[extech]

yes the new one you listed has all the parts needed in it.  one other thing to check is the interface with the pushrod in the booster.  the pushrod should not push the piston in when the master cylinder is installed.

[Elena]

I so appreciate this. I will make sure the pushrod gets checked. Can anyone confirm we do NOT have a "load sensing proportioning valve" on the rear? Our mechanic that is helping replaced all of the brake hardware and says he didn't see any valves, but yotatech mentions this in several places re: diagnosing brake issues. I just want to make sure we're covering everything at one time so we're ready to go when it warms up again around here. Thanks! 

[extech]

unless someone removed it there should be a lspv . it is mounted to the frame on the right side. there is a long rod from the valve to the rear axle. viewable from the back

[Elena]

Oof. . . okay, let me look. Thanks! 

[Ssunrader]

Do yourself a favor and ditch that Haynes manual. While they used to be an amazing source of information, I found incorrect torque values etc in the one I found for my 1991 Toyota.

 

The needed info can sometimes be hard to find for some things but at least it isn’t wrong.

If you go to the internet archive, search for www.ttora.com for the month of August 2009, they have a database of the pickup FSM throughout the years.

 

You can download it from there and have it to use.

 

Edited October 17, 2025 by Ssunrader

[Elena]

That is so funny, I was JUST trying to get to ttora.com for a manual someone linked to from yotatech. I really appreciate the tip re: the month / year to use on internet archive. I'm going to grab the manual. I have FOUND my Load Sensing Proportioning Valve and some research on what line goes where is needed. I'll put the Haynes aside. 😄Thanks!

[extech]

the lspv has 2 lines into the front of it . the lower comes from the master cylinder, the upper one connects to the right front brake at a tee on the frame

[extech]

search   brake upgrade    see some pix of what i did