Not impressed looking for advise

[IMPALAMAN1]

1968 impala.... heavy car.... oe was power drum brakes.... not the best but atleast they stopped the car....

fast forward to the 4 wheel disc conversion.
corvette disc/ disc master, dual 9" diaphram booster
disc/ disc prop valve
new 3/16 line the entire car.
hurst roll control (maine reason for the disc swap.... drum didnt work like i wanted the line lock to.)
front rotors... slotted and drilled 11.75"
front calipers, factory 1969 impala
rear rotors 1979 trans-am slotted and drilled i believe they are 11"
rear calipers are the cadi seville with parking brake

i have bench bled the master till my arms fell off
next tried mighty vac.... no go
next tried traditional 2 man... you kick the pedal nad ill crack the line. no go after 3 hours of roamin under the car.

next took it to a shop and had it pressure bled.... said he got a little air bit nothing to write home about.

so the symptoms are... no and i mean no panic stop possible.
you can feel it grabing and it will get stiffer as it goes to the floor.
then the last half inch or so..... it grabs and starts to slow.... it will eventually come to a stop..... there is no noticable nose dive like modern vehicles..... i would like more pedal and it stop on a silver dollar.... shoot ill even go for for a manhole at this point.... the dime seems so far out of reach it isnt funny.

[GetMore]

Have you tried applying the parking brake and then seeing how the pedal feels?
The parking brake mechanism has a ratchet in it and you must first step on the brake pedal before applying the parking brake for the mechanism to adjust. If it does not take up the slack then you will have excessive pedal travel before the pads will touch.

[MuscleRodz]

unhook the booster and see if it changes, you may have a bad booster

[Tom Welch]

brake pedal pushrod might be too short to fully engage the brakes.

[IMPALAMAN1]

FELLAS THANKS FOR THE RESPONSES!

GetMore.... i do not have the parking brake set up yet. working on a new rachet setup as the foot lever is long gone. but i have been racheting it with the wrench.... just havent done it with the pedal pushed.... ill try that one.

MuscleRodz.... i put in a new booster because i thought the old one was bad. it is holding vac if that is your question.

Tom Welch..... i have been thinking this may be a problem.... but i set it per the factory set... and wouldnt i have play at the pedal if it wasnt extended far enough? how can i check this?

[silver69camaro]

Time to install a pressure gauge.

[Charley Lillard]

My vote is also the pushrod between the booster and master cylinder is too short. Is it adjustable ? If it is, lengthen it so you can feel it plunging the master cylinder as you are pushing the cylinder onto the studs, take it back off and shorten the rod etc until you know you are almost plunging the cylinder when bolted down tight. Hard to explain but when it is too long you will know when you are trying to bolt it on. Or measure the depth of the hole in the master and measure the pushrod.

[MonzaRacer]

If you dont have pedal you will probably need the 2 psi check valves front and rear ,they leave just enough pressure so the master doesnt have to take up lots of space. Most brake companies sell them. Try these http://www.wilwood.com/Products/006-MasterCylinders/010-RPV/index.asp.
I have seen several systems used and newer brake part companies are using more angle/back cut seal to help the pistons move away from rotor so as to eliminate brake drag.
Sold many of these 2 psi units for car that were converted.
Good Luck

[oestek]

Had the exact problem on my '62 Galaxie, went through the same steps, tried 4 boosters, 2 masters, prop valves, push rods, pads, bleed techniques... couldn't lock 'em up at all.. only rolling stops possible. The fix? Hydroboost. Now it stops as smooth and as hard as you want.

[IMPALAMAN1]

i can see how the 2lb valves would work.... and i love the idea of a hydroboost.


i have a question relating to my situation and the hydroboost.

if the hydroboost is in essence a more consistant booster..... how is this going to build more pedal? if the pedal goes to the floor before it engauges the system..... now how is more assist going to help my problem?

[novaderrik]

what is the bore size of your "Corvette" master cylinder? it might be too small.

[oestek]

You obviously want to make sure the geometry of the pedal, pushrod, and booster is correct, and that your master is up for the task. The hydroboost unit just develops large amounts of assist pressure. You should check your system with a gauge now to see how much pressure your system is making. If it won's stop the car, it's probably not much. In my case, we got a booster / master combo spec'd by Hydratech.. they did the homework for me... and bolted it on and the car stopped wonderfully. We also added a new Saginaw P-style pump (found the factory Ford EFI Serp. belt bracket for that one... not easy... but your Imp already has that pump on it I bet.)

[IMPALAMAN1]

Either a 1" or a 1 1/8" ill check when i get home

[Ishmael]

I was thinking the master might be too big. A lot of the vette boosters measure in at 1 1/8th but so many people have told me my pedal would be to the floor.

[IMPALAMAN1]

1 1/8" i have a general question.... the car came equipped with factory power drum brakes. the pedal only has one hole that i am aware of... i need to double check and make sure that the bracket for brake light switch isnt in the other. my question is .... does it need to be in the bottom or top hole.... my under standing was that all power was to be in the lower hole... but after reading some of the hydroboost info on this forum some say to put it in the upper hole?

[novaderrik]

the hole for the power brakes will be lower than the one for manual brakes. that's why power brake boosters are angled on the firewall.

[Charley Lillard]

Did you ever solve this ?

[IMPALAMAN1]

Car has been on hold.... Ill try to get out there tonight and see what i can find.

OH YEA... MY BOOSTER ISNT ANGLED... BOLTED TO FIRE WALL STRAIGHT LIKE FACTORY.