looking for some help with recent brake dramas

[benno440]

some may not have any clue about wilwoods but the problem is likely more of a universal problem, here goes

in my 68 charger i have Wilwood:
* dual tandem master cylinder
* 4 port prop valve
* 12" drilled and slotted discs
* 4 piston calipers
* all brand new stainless brake lines and stainless flex lines.

Car has been driving perfectly for a few weeks, then yesterday driving down the highway the brakes locked on, the brake pedal was hard as a rock and would not budge
managed to unwedge them and get the car home.

pulled master cylinder and brake booster off tested both and they both working fine, put booster back on and checked pedal movement, all good
put master cylinder in vice and ran the return hoses and bench bled the MC, it worked fine.

put MC back onto booster and reconnected the brake lines up and brake pedal is still hard as a rock.

Any ideas?

 

[Hemi Rebel]

Remove the vacuum source to the booster and see if the brakes lock up

 

[benno440]

nope,
only goes hard the mement the MC is on and brake lines on.

 

[BeastlyBirdie]

Check the prop valve. Sounds like its not allowing the pressure to bleed back.

 

[5.7 hemi]

Pedal rod too long?

 

[benno440]

i will check the prop valve,

pedal was working perfect not it does not, in the booster the rod has an adjustable end, i have it screwed all the way in, i cannot find any info on how much length needs to go into the MC.

 

[kiwigtx]

Separate the booster and master cylinder to see the pedal comes free. Then measure the depth inside the M/C to accurately assess the length of the rod from the Booster. The rod should barely touch the piston when the pedal is fully at rest. If it is still stiff after that...you have fluid issues in the M/C like was said above.

 

[benno440]

fixed my problem, I accidently set the bias all the way to the front brakes, evened it out and they function again

 

[benno440]

didn't fix the problem, they locked up again today fark sake.

Kiwi, when putting the MC on I have to push it on hard and quickly get a bolt into it as the booster rod touches the master cylinder piston before the face of the MC even goes on. it has always been like this, is this wrong?

 

[kiwigtx]

The booster actuator rod should be sitting still at rest (engine off - no touching brake pedal) - the rod length should be measured from the 'mating' face that the M/C bolts to the tip of the rod (has a ball end) - this measurement is the depth from the outer 'mating' face of the M/C to the inside of the 'cup' of the M/C piston. When the two are bolted together the rod and cup of the M/C piston should only just touch each other. The booster actuator rod should not be falling out or flapping about.

I hope that is clear enough to understand.

Also, have you altered the brake pedal actuation ratio - ie/ have you put a different to stock pedal box assembly in the car. If so, the pedal MAY be pushing the piston (or trying to) way too far, and causing the 'lock-up'. This can be checked by operating the brake pedal with the M/C disconnected - measure the difference between the "at rest position" to the "pedal fully depressed position". Then make sure that is equal to or less than the piston travel requirements.

 

[benno440]

ill get photos might help my explanation a bit.
the pedal ratio is all spot on and not been altered.

 

[kiwigtx]

Hokey dokey

 

[benno440]

kiwi, just thought of something, tell me if this is wrong but the flat surface of the booster where the MC bolts onto, (I also have the adaptor plate from 4 hole booster to the 2 hole MC) but the rod in the booster sticks out about 1/2" out of the hole. is it not supposed to? the wildwood MC has the billet spacer in the piston bore for when using a booster as well, maybe the combination of rod, spacer etc. are not letting the piston to come back enough to let pressure escape the calipers maybe?

the whole kit was supplied as one unit by magnumforce racing so I don't know yeh.

but will get pics to explain better in a tick

 

[kiwigtx]

Pics of the items would help. If the booster has a rod sticking out of it, this needs to mate up exactly to the piston in the M/C.

 

[benno440]

see what I mean about the rod in the booster, do you reckon that's too long? the round tip of it is adjustable and it is all the way in, maybe the aluminium spacer rod in the MC bore needs to be taken out maybe

 

[kiwigtx]

OK, I see what you mean. However, if you have a quality set of digital verniers - for measuring depth, you can work out the length required on the adjustable rod. The 'acorn' nut can be adjusted easily to suit the depth required. Make sure to write down your measurements off known reference points - probably the outer face of the booster, and the face on the M/C it bolts to. It shouldn't be too difficult to check the dimensions. You can see in the pics where the acorn nut has contacted the piston, so all you need to do is get those two points to barely touch with the pedal at rest.

....

Had another look at the pics, and I would say that either a spacer is required, or the rod need to be wound back quite a bit.

 

[benno440]

if that's the case then the rod is too long, as that nut is about 3mm off from being screwed all the way in, and the face of the MC sits neally an inch off the surface of the booster when the rod is touching the piston

 

[kiwigtx]

Is it possible to get a double thickness spacer (as an example)? It might look a bit Mickey-Duck with two spacers. I can see now that the rod is going to depress the piston without even getting close. Are there different size spacers available? The bolts on the Booster are certainly long enough to accept a thicker spacer.

- - - Updated - - -

I have just checked both Magnumforce & Wilwood websites.....very user unfriendly, with absolutely no links to the spacer block you have installed.

 

[benno440]

yeh, lol, that might work, im a boilermaker by trade, might be able to fix something up, in the meantime I might pull that spacer rod out of the piston and see how it goes.

thanks for the help, definetly found my problem.
now I think of it, as the engine/car was cold the brakes semi worked but hard to press pedal then when everything got hot the pressure would of went up and not let the fluid release from the calipers as the piston was not returning to stop.

 

[kiwigtx]

Be careful with that rod in the booster - I can't remember exactly, but I suggest you don't yank it out

Since you're in 'the trade'....it might be easier to make your own spacer block once you know the exact thickness required...get it polished up nice, and it will look the part. You still have some adjustment on that rod - so don't stress too much.

- - - Updated - - -

What you could do to test the depth, is carefully/slowly bolt the M/C up to the booster until the rod just touches the piston. Then insert a couple of packers between them, tighten down, and go for a quick (sedate) drive to road test the brakes. Let us know how that goes.