Master Cylinder/Brakes Question

this would be my first post here, I tried searching but I cant see that my question has really been asked let alone answered. So if this is a repeat thing, by all means point me in the right direction. Thanks.

Ok so I have a problem with spongy brakes. You have to pump the system up before you get a worthwhile pressure in the brakes. I've already bled the system with new fluid....same result. When the engine is off you can build up more pressure than you can when its running, but it still doesnt feel as solid as it should. I have no leaks or loss of fluid in the system. So I'm at a point where I start to look at the Master Cylinder.....but its not losing fluid and to me that would seem strange. Is it possible to have a faulty master and not lose fluid?

If it is then thats gotta be my problem, if its not then what else can I look for? Like I said there is no fluid loss in the system. Its just not holding the pressure you need in order to stop correctly. As it stands the truck really isnt safe right now.

Just for reference its a bare bones 2wd 2005 single cab w/manual transmission. No options, it doesnt have traction control or any of that....just abs. Any help is appreciated.

 

I thought the same thing about the brake booster line, because well its really the only other thing there that would seem to matter outside of the booster itself and the master. But it really doenst seem to be in bad shape. I kind of bent it around looking for cracks in the rubber and such....no dice.

 

wolfpack.....ya the brakes arent the greatest, but theres something up here. It takes a double pump in order to actually build up the brakes enough to come to a regular stop......never mind an emergency situation.....right now a hard braking situation would lead to me filling out police reports and filing and insurance claim....

 

I've lurked in this forum for over a year, but I might have something to contribute here....
RIAlltrac, it is possible for brake fluid to pass by seals in the master cylinder and return to the reservoir, causing a spongy pedal and no loss of fluid. The need to pump the brakes is a bit confusing; that used to be a symptom of brakes out of adjustment. The only brakes that could be out of adjustment are the rears; disk brakes are self-adjusting. Could it be that for some reason, your rear brakes aren't adjusting properly?
My best guess would be worn-out seals in the master cylinder.
HTH,
Hoodat

 

Ya I made a profile today....and specifically to ask this question/start this conversation. A lot of times you get people (like myself) that use forums for information and thats really all. So its nice to start a topic that you cant find an answer to just to add to the knowledge base of any forum. I havent had much need to do much on this truck and honestly its not my toy by any means. I do all my wrenching and playing with the celica. But I've used this username in other forums as well....goes back to when i first bought my alltrac and got involved in that community. I am one of very few or the only alltrac owner in RI....kinda lame but funny at the same time. Out of curiosity what are greenies?


Back on topic....

Hoodat....so your saying its possible? Everything in the braking system looks good, calipers move properly up front....I didnt actually remove the rear drums because I couldnt find a bolt to match up to the holes that you use to remove them...Ya I'm definitely losing pressure and the pedal will slowly go to the floor with little braking response. I may just have to bite the bullet and replace the master.......anyone got a good writeup on that procedure?

 

Have you checked & adjusted your drum rear brakes? It can sometimes cause a spongey pedal. Does the motor change in sound when stepping on the brakes like it has a vaccum leak? If so it could be your brake booster.

 

http://www.kondratyev.com/porsche/technical/body/vacuum_boost.htm

This may help.

 

I'll have to go give that a try and see if I notice anything. I'm used to dealing with random vac leaks in other cars so I know how they feel when they have one. The truck doesnt feel that way, but I'll give it another look. I would imagine that without the brake booster it would just be harder to engage the brakes, similar how its harder to turn without power steering.....its not like that, its like I just cant get the pressure up to stop properly. Correct me if I'm off base....I havent ever had to change out a brake booster and honestly dont know their in's and out's

 

based on that.....my brake booster is fine

 

Okay I would have to agree with you say that it is a faulty master cylinder. It is possible to have a faulty master cyl. and not lose fluid. Just remember to bench bleed the master cyl before installing it on the truck. To remove all the air out of the master cyl. Also have someone press the brake pedal while you observe the reservior for bubbles or swirling fluid if possible I know alot of times the insides of the reservoirs are stain due to old brake fluid making it hard to see. Do not do this with the cap off. If you see bubbles or swirling fluid your master cyl is bad.

 

your bleeding them with 2 people? and doing it correctly right?

rear brakes are self adjusting......VVVVV

Spot on. I just replaced my rear pads and one rear wheel cylinder 2-3 weeks ago.

 

yes brakes were bled with engine off and with two people, I've done my fair share of brakes in the past so this type of stuff is not foreign to me. The fluid in the resi was sort of amber in color.....seemed typical, although the replacement dot 3 fluid that I picked up was clear....When going around the truck I did get some contamination that came out of the driver rear wheel cylinder...but after a couple of rounds the fluid was coming out clean. Not really sure if the rears need any adjusting....they've never really been messed with since new from the factory. I do need to pop off the drums and take a look at them, but even if not adjusted properly....they shouldnt cause me to have to double pump the brake pedal just to get pressure in the system.

 

rears are only 20% of braking so even if they were totally gone you should still stop OK.

How many miles you got on it?

amber is typical. if you ran the fluid out the bleeders till it was clear (new) and it wasn't full of crap my guess is master cylinder, but thats just a guess.

so it gets good pressure when turned off but not while running?

 

Its got roughly 147k on it....commuter type of use. Lots of stop and go thru boston type of traffic (assuming you have any idea about boston traffic)

Ya I really doubt the rears have anything to do with it. I am able to build up more pressure in the system with the truck off, but it still takes like 3 full pumps of the brake pedal and even then there is a little dropoff. When the truck is running though....its like 3-4 full pumps and it doesnt stay strong....it drops off a lot faster.

 

If you lightly press the brake and it slowly sinks to the floor it's the master cylinder.

 

FUBAR master cylinder. At least they are under $100 and a easy fix.

LMAO....my rears were toasted after 74k of Philly traffic so I would taker a look at yours while fixing the master cylinder. if you need new rear pads grab new springs as well. They get sprung after many years

 

Yup. Thanks for the greenies (and the explanation).
I figured I lurked here long enough, so I should offer to help.

RIAlltrac: yessir, it's quite possible. I have many years experience with Girling hydraulics, and they fail with startling frequency in this way: fluid past the piston back into the reservoir.

Note: Girling hydraulics are found on old British sports cars.

Hoodat