power brakes helppppp

[truckdude239]

okay finally got around to installing my power brake unit well with the push rood adjusted all the way out it just isn't long enoughi mean i'm an half inch from the pedal returning which is keeping my brake lights on with it adjusted out all the way i have no brakes the moving parts behind the power brake unit are sitting on the firewall. what am i doing? i got it from another menber

http://67-72chevytrucks.com/vboard/s...d.php?t=202645


any ideas on what i'm doing wrong

the picture is of the one i got

[ChevyDude]

It is my understanding that with power brakes the brake pedal does not return all the way out to the return stop pad. Mine doesn't. You should be able to screw in or out to adjust the brake switch which is on top of the brake pedal assembly.

[truckdude239]

i can understand that but i have no brakes at all i know i can adjustr the stop switch for the lights to turn off but i need to figure out why i have no brakes

[ChevyDude]

Did you bench bleed the master cylinder? I just did this same install and the same thing happened to me. I was told I need to bench bleed the MC and then bleed the system at the wheels. You can do this with the MC on the booster by dis-connecting the brake lines and then fab up two lines the go from the MC directly dumping back into the resivoir. Fill MC and pump brakes slowly until all air is gone and fluid circulates. Re-connect brakes lines and bleed at the wheels.

[krue]

Have you adjusted the rod between the booster and m/c yet?

[truckdude239]

i shouldn't have to bleed the system i didn't unhook anylines no i didn't try that so i nned to adjust the rod behind the mc i'll try that in a little bit

[Steelawork'n]

If you pushed on the brake pedal without bench bleeding the mc, then you will need to bleed the system.

[John Fabris]

If i read your post correctly, you went from manual brakes to power brakes by just adding the booster. Is that correct? If so, did you resuse the rod that was on your brake pedel? The rod for a manual is shorter then a correct one for power brakes. If that is not it, check to make sure that the rod that goes from the booster into the mastercylinder is the correct lenth as well. I have seen two types of master cylinders where one has a recessed hole for the rod, the other one has shallow depression.

Good Luck!!

[rage'nrat638]

sounds to me the intermediate rod between the master and booster is not correct..
one push and the master does not return all the way..thus no brakes...

this happened to me..it took alittle fingering out before i got it right...
i am sure with a little work you can get the correct under dash pedal rod as well or modify the one you have to get full pedal travel..

need help just ask your pal mark

[truckdude239]

Originally Posted by John Fabris

If i read your post correctly, you went from manual brakes to power brakes by just adding the booster. Is that correct? If so, did you resuse the rod that was on your brake pedel? The rod for a manual is shorter then a correct one for power brakes. If that is not it, check to make sure that the rod that goes from the booster into the mastercylinder is the correct lenth as well. I have seen two types of master cylinders where one has a recessed hole for the rod, the other one has shallow depression.

Good Luck!!

the booster came with the rod this is the mc i have on the truck http://www.partsamerica.com/ProductD...pe=230&ptset=A
i tried to adjust the rod between the mc and booster and it doesn't adjust iots a metal smooth rod. i shouldn't need to bleed anything because i did not open any lines i just moved the mc back everything was already bled

[rage'nrat638]

ok this step is a little hard to get right..you have to measure how far the master cyl fits inside the booster,,,the length of the round flange on the back of the master cyl..from there measure the length the rod sticks out of the booster...now take this measurement and transfer it to a pencil..
now stick the marked end of the pencil into the hole on the rear of the master cyl...if the mark sticks out of the hole the rods to long...i think this is your problem? if its to short chould be a 1/16 shorter than the hole depth...wheres yours at? let us know...mark


i would bet from your picture of the way that little intermediate rod is sticking out you had to push hard on the master cyl to get it to seat while tighting it up..if so..you were pushing the master cyl piston in at the same time thus no brakes ..it can't return out

[jhow66]

With everything hooked up is your brake pedal close to the floor?

[truckdude239]

mc slide right on no trouble the brake pedel sits an 1/2 from the stop(release postion) it only has about an 1 inch movement when presseing th brakes

[PICKMUP]

David,
That rebuilt system is off a running 71 and ready to go!. No adjustments are needed and may even damage the unit if you increased the pedal travel too much.
You should check the hole depth in the mc vs the rod out of the booster...but that rod is not adjustable.
Put the rod to the pedal back in the original position, so the pedal hangs much lower than the manual setup. Look at anyones 67-72 1/2T with PB and you will see the lower pedal. This will get you back to the correct angle and throw on the pedal/booster.
Frank

[jhow66]

Mine did not reach the stop either but had brakes but the pedal was close to floor when applied. I cut the rod into that hooks to the pedal and made it longer so that I could adjust it back to the stop. Unbelieveable how little pressure it takes to stop with it this way.Mine had been changed over from manual I presume so there must be different length rods for each. Did my son's Blazer (orangeuavol) this way also. Try this--remove MC from booster and have someone push pedal inside to see how far rod in booster moves. This seems to be where your problem is.

[truckdude239]

thanks frank i'll dheck the mc frist thing in the morning i already put the adjustment back to where it was but i am thinking it is the mc beacause there is another mc listed for power brakes at the parts store and mine is manual but i will check in the morning

[53burb]

More than likely it is your master cylinder bore depth. The master cylinder that should go with this unit, its bore is shallow, thus the rod can contact it when pushed. The master cylinder on your truck now is deep, so when you push on the pedal, it never comes in contact like it should. I had this same problem. I never installed the booster, because I plan on upgrading the frontend to discs & I haven't done it yet...Compare a power MC or a disc/drum MC & you will see the difference...at least that is the difference between a '69 3/4T Burb & a '71 3/4T...

[truckdude239]

okay i got my new mastercylider installed today the brakes pump up i bleed everything. heres the problem i have at most 1 inch pedel movement. 3/4 of that is free play and the last 1/4 of it is brakes truck is hard to get stoped at 15 mph. i was told this booster shouldn't need any adjusting just install and go. any ideas? i goign to go try and adjust it some tomorrow. is there a Proportioning Valve just for power brakes will that make a difference i am going crazy

[PICKMUP]

Where does the vacuum hose from the booster attach on the engine? Sounds like you don't have vacuum. Any chance?

[truckdude239]

it is atrtached to the vac port on the manifold and its getting good vacuum

[shelby987]

I did this same swap, is there any chance while moving around those old brake lines you tweaked on just a little? Does your MC fluid level always remain at the same height?
I cracked mine ever so slightly at the coupling just below the frame, thought it just needed a couple more turns, turned out it was a pin hole leak at the top of the line, didn't leak until I applied the pedal, every time I let up, I put more air into the system.

Also, it sounds like you still need to shorten the rod between the pedal and the booster (also, had the same problem)

Good luck.....we've all been there with the post that seemingly never ends in a search to find the right answer....you can get there!

[truckdude239]

the only lines i opened where the ones at the mc the fuild isnot leaking anywhere i just dont have a good pedel its adjusted as far as i feel safe trying to get a pedel. i think i am just messing something http://www.partsamerica.com/ProductD...pe=230&ptset=A
this is the mc i got in the store it was labeled as power brake mc the front res is larger then the back res on this one. and everythign is bled

[PICKMUP]

The MC looks correct. Did you bench bleed it real well until there were no bubbles coming out of the plastic bleeding tubes?
When in doubt...bleed the whole system and never let the MC get down to the bottom, it will let air in and you will have to start all over again.

[truckdude239]

yup everythings bleed i'm going to adjust the rear brakes in the moring and see if that makes a difference

[John Fabris]

Ah, in your ealier posts you say you did not open brake lines, and then now you say you did.

With mine, I did not have any pedel after I bled it, much like what you describe. After I replace my MC, I could not get any brakes until the last inch or so. I then used a vacumn bleeder on each wheel, and then I have full brakes.....