Mopar Muscle Association UK

I have just fitted disc brakes to my charger and a fully rebuilt master cylinder.I bleed the brakes tonight and once i was done i was hoping my brakes would be transformed but sadly the are still not up to my expectations, no matter how hard i press the pedal the wheels wont lock. Having looked in the manual i saw that if the pedal goes rock hard that the brake boost is inoperative. So has anyone had experience with overhauling brake boosts and if so did it make any difference to your brakes. My brake pedal travel about 1 inch and then goes rock solid and no matter how hard i push the pedal i cant depress the pedal any further.

Can anyone offer some advice on how i can sort this.

Anton.

I have installed a proportioning valve to the rear drums. All my brake lines are new and so are all the pads and shoes.

I don't know if mopar master cylinder is like a GM one, but I had to first bleed my master cylinder in a vice - with little hoses poking out of the two outlets & back into the reservoir pot. Then, full of fluid, I had to install it in the car & carry on bleeding as normal.

PS: My mate just installed a new master cyl in his Trans am without Vice-bleeding & no matter how much he bleeds it on the car the pedal is always a little spongy - I take it thats because there is a tiny pocket of air behind the master cylinders piston ???

i did bench bleed the master cylinder before installing it on the car.

Pump the brakes with the engine off , start the car & take notice if the brake peddle falls , this will tell you if the servo is working.

Peddle rod should be around 1/8th" into servo when @ rest , any more & the rod could be bottoming out.

I had a problem whereby the wrong master was used , the bore was too large causing a hard peddle , i got over it by drilling the rod higher on the peddle , stopped on a sixpence.

Brutus
I have swapped from a drum master cylinder to a disc one.
I have adjusted the length of the servo rod to master cylinder so that when i install the master cylinder the rod doesn't depress the piston.
Can you explain what you mean by the pedal rod(is that on the brake pedal side).
I got the master cylinder off Clivey and when i order the rebuild kit from Hausers it was for a 67-70 b-Body(1 1/32 Bore rebuild kit).
When i still had drum brakes I had the same problem that the pedal went rock solid after about 1 inch. When i remove the master cylinder and press the brake pedal the pedal goes smoothly all the way to the floor no problem.
I don't know what else is wrong, I replaced or rebuilt everything except the brake boost.
Anton

Sounds like you have a leak on the servo and you can't get rebuild kits here for them they don't trust us to do it ,if you can take your servo apart you might find a hole in the diaphram had one in mine but managed to repair it with a bike puncture repair kit the patches are nice and thin could try that ,if your on tick over and press the brake pedal does the engine revs increase ?????? if it does quite a bit then you have a hole

My servo went back to the US for rebuilding.

Anton, you may wanrt to contact a rebuilder to see if they have one on the shelf you can have that you can exchange yours for as a core. Expensive but they do know what they are doing with them.

John R is right about whwere the problem may lie.

If i can diagnose that the problem is the servo i will buy a new one straight away regardless of cost.

I Have spoken to Baccaruda and he has a couple of brake boosters which he is going to lone me so i can swap them over and see if that resolves my problem.
I will let you know the results.
If there are any other ideas of what the problem could be please let me know
Anton

What manifold vacuum does the car make at idle?

Is the check valve 'gummed up'? , can you feel the servo hose sucking vaccume?

Brutus wrote:Is the check valve 'gummed up'? , can you feel the servo hose sucking vaccume?

I gave Anton a check valve tonight. he will check it at the weekend.

Pete the car makes 15 on a vacuum gage at idle.Derek and I set the vacuum level a couple of months ago.

It takes quite a bit to blow through the check valve so I'll try the one Derek gave me tomorrow.

If that doesn't work I'll try the ones Baccaruda is lending me to rule out my booster.

Brutus where is the peddle rod and how do I check it to make sure it's not bottoming out.

Have you anything else branching off the vac hose from manifold to servo? Can you feel the hose 'suck' when you put yer finger over the check valve?

Brutus
I got a new check valve off Derek as mine was a bit blocked.
With the new check valve things have improved. I also modified my pedal rod as you said and that also improved things.I am happy with the brakes now.