hi everyone,
been awhile since I posted, many issues with car and working too much, lol. newest issue is my brakes. car had 4 wheel power drums with single res. converted to dual res. 7 inch brake booster from speedway. everything in system was replaced including all the lines. still have drums all around. problem is I barely can stop car, I cant even take it out for a ride. called their tech dept. and they stated brake pedal ratio or booster might be to small?? I have 19 in. vacuum at manifold?? any ideas?? calculated brake pedal ratio and it comes out to 2.6 to 1, they said this is no good, any help would be appreciated. (62 starfire, 394)

 

Why do people even buy 7" boosters? There must be one thread a month on this very topic.

Is this a single or dual diaphragm booster? A single diaphragm 7" booster is worthless. Manual brakes would be a better choice.

 

You might want to read this thread (though you can ignore the part about the British cars and hydrovac boosters).

 

hi joe, it's a single diaphgram, I wish I would of known this before I started this project, sending it back for a dual 8 inch unit.

 

Put your old booster back on with the new master cylinder.

 

The car is a 62 Starfire. The new M/C will have a shallow piston to match the new booster. The old booster needs an M/C with a deep piston. The only readily available dual circuit M/C that would work with the old booster is the 62-66 Caddy unit.

 

Didn't see that...

 

old master and booster were junk

 

And now I remember, that's the booster that has the M/C piston integral with the booster, so only the original M/C can be used.

 

yup, you got it, first time I saw that setup!!!

 

Oh, yeah I remember. I misapplied the initial suggestion. Can you find a dual diaphragm booster?

 

yes, speedway motors has one, sending the 7 incher back

 

hi everyone, here's the latest, got speedways 8 inch dual diaphgram booster today. hooked it up, step on brakes, pedal goes down and that's it. booster is no good

 

There may be a mismatch between the booster actuator and the master cylinder where the booster pin goes inside the master instead of pushing it down. Don't ask me how I know.

 

eric, do you mean the pin at the end of the booster that matches with the master??

 

Yes, is it slipping inside the spool on the master cylinder and not pushing it in? I slipped a piece of 3/8 aluminum round stock into the hole on the master cylinder cut to length so as the pedal had a small amount of free play.

 

i don't understand what you mean when you say it's slipping on the master and not pushing it in??

 

Is the pedal just going to the floor? If yes, then separate the MC from the booster and look at how the booster plunger mates to the MC.

 

ok, no this last booster it would go down about 2 inches from the floor and not come back up

 

Does it do the same thing with the engine running or not?

 

with the engine off pedal feels almost normal , when its running is when pedal stays down after u step on it. Comes up very slow, that's why I sent it back. This is starting to drive me nuts.

 

Ok, different problem than I thought. You may have gotten a bad booster.

 

hello again,
here's the latest, got the new booster, installed it, does exactly the same thing. Do you guys think the brake pedal ratio ( 2.6 to 1) has anything to do with it??? I doubt it's a bad booster, even though it acts like one.press pedal down, it stays down, again I have good vacuum. help please, i'm at the end of my rope here!!!!

 

Is there any resistance as you push it down with engine running? How far down does the pedal go until the brakes engage?

 

Eric, yea there's resistance, pedal goes down about 2 inches from floor, it returns very slowly, and the brakes suck, very hard to stop. I wouldn't drive it like it is.

 

Perhaps you should have your original one rebuilt. Theres a place in Oregon called Booster DeweyPowerBooster, I havnt used him but i did talk to him on the phone. I probably will send him my original booster after i get moved. His prices are very reasonable. Just google BoosterDewey.

 

If the system is bled, I'm going back to my original assumption on the mismatch between the boost and mc. Separate the 2 and see. You don't have to disconnect the lines, just remove the 2 nuts and pull the master forward a bit.

 

I haven't had a chance to bleed the system again. I hope that's the problem. As for getting the old system rebuilt, it was junk, got rid of it, although I wish I hadn't. What gets me confused is this was already a power brake setup. All I did was install a 2 compartment m/c. and run another line basically. I might be looking for an original setup soon if I can't figure this out.

 

just found out that rockauto has a remanufactured booster- m/c combo for a 66 Cadillac. I thought I read somewhere that would be a direct fit for my car???

 

hi again, just thought I'd post if anyone's still following this. Got the master/ booster from rock auto for 66 caddy. Bolted up , bled and seems to be working fine!! Only issue is pedal a little low, i'll just deal with that, thanks for all your help.

 

You should be able to adjust the pushrod between the booster and pedal. If there isn't enough travel, they make extensions that screw on.

 

tried that Joe, screwed it out, didn't seem to make a difference.

 

Time for a little logic.

If you think about the brake pedal geometry, the length of that pushrod is the ONLY thing that governs height of the brake pedal (since you haven't changed anything else). Obviously, you didn't lengthen it enough. If you run out of adjustment, get an extension.

http://leedbrakes.com/i-19296658-pus...-coupling.html

 

that's what I figured, maybe the rod coming out of the booster is all the way out???? I will try an extension , thank you

 

I'm sorry, hit the enter key before I got done typing. Joe, wouldn't the rod fall out of the booster if it's screwed all the way out?? Like I said I will try an extension, thanks Joe for your help!!