94 Grand Voyager brake problem

[Orangetona]

My friends are having some trouble with a 94 voyager. Basically the rundown is when brake pressure is applied the brakes actually lock up. Doesnt matter which wheel. It gets worse as the brakes get hotter. Throw it on the lift, pop a bleeder, frees up the whole system and releases the brakes. They are in the process of changing the master right now. If thats not the problem, is there something else? I was wondering if the check valve on the booster or the booster itself could be a problem?

[RoadWarrior222]

Booster problems usually show as needing excessive brake pressure, and the check valve usually fails to seal, meaning needing more pedal pressure when the motor isn't in vacuum (Vacuum reservoir leakage)

If it isn't the master and it's only the rear brakes locking, then something could be up with the proportioning valve.

It sounds like it could be a master problem, but there is also a failure mode of flex hoses where they can swell on the inside, i.e. pass external visual, and act as one way valves. So if the flex hoses are original or more than two years old, those should definitely be suspect.

[turbovanman²]

If the master is OE, I would bet the flex hoses are breaking down or someone has messed with the pushrod length at the booster. Make sure the brake pedal is coming back all the way.

[RoadWarrior222]

Oh good point about the rod there, is there any parts that could have been frankensteined in wrong, like wrong year or motor application rod?

[turbovanman²]

Oh good point about the rod there, is there any parts that could have been frankensteined in wrong, like wrong year or motor application rod?

Nope, MC is the same from 88-95 and the other stuff is close enough, IE they changed the calipers 91+ to the modular type setup and bolt in wheel bearings. AWD stuff is different of course, drum only. ABS was a different master, durr, :p

[Orangetona]

The pedal DOES come all the way back as normal. It just seems to hold the pressure on all the time. I havent checked with them to see if the master was the fix or not. However with the brake hoses, it should only affect that wheel that the hose is swollen correct? This is random because the system seems like it over-pressures.

Oh just so its stated since I forgot, the pedal is really hard to push. Ive had a problem with this when a booster failed. However it didnt lock brakes up.

EDIT: After re-reading what I just posted, yes...I believe the hoses are swollen also. (Its not my vehicle so I dont know much about it) but It makes total sense for it to push so hard. Thanks guys, im positive the master isnt going to help them,

[turbovanman²]

If the pedal is hard to push, the booster could be failing, but I've never seen one fail where it held the brake on.

To check the booster, see if you have any reserve when you shut the car off or deplete the reserve and put your foot on the brake pedal and start it, it should sink a few inch's.

[Orangetona]

Gotcha, ill see them tomorrow and give them some info. Thanks!

[Orangetona]

Just to update this, dont ask me how (because I dont see it) but the master was bad...interesting.

[turbovanman²]

Very!!! :confused:

I am going to go with my theory of somehow the pushrod length got adjusted incorrectly at some point.

[Orangetona]

Very possible...when they bought the master cylinder from me, I told them they were wasting their time. They may have lied to cover up something simple they overlooked too. ;)

(I get that a lot working for napa because a lot of guys dont want to admit a parts store counter guy was right)