Wont Stop (brake troubles)

[k20]

Alright guys, fired up the new motor today, took it for a drive I have no brakes. You push down on the pedal, for the first....half inch or so it will move, then it is hard, and it doesnt want to stop, you can push for all you are worth and it wont stop any better.

I put a vacuum gauge on it, thinking that the new cam was a little large for the vacuum booster, and in park it was pulling 13, in drive it was pulling around 8. So I adjusted the carb, and bumped up the idle, and in gear it was pulling ~11 and in park it pulls 14.

Does this sound like the booster is bad? I dont want to throw a booster at it and not fix it, and I have been wanting hydroboost, but current funds dont really allow that. Anyone have any ideas?

 

[k20]

Ok, worked on it some more. Turned the idle up on it, it increased the vacuum a little but it stopped no better. Then I pull the master cylinder lid, the fluid is pretty dark, so me and my buddy decided to bleed it, if nothing else change out some dark fluid. We bled the rear, good flow from the rear bleeders, nothing out of the ordinary.

Then we moved to the front. The front bleeders were insanely tight. The calipers arent that old, and I dont recall wrenching em down that tight, but whatever, ended up snapping off the one on the drivers side tryin to loosen it, it was still fluid tight so we didnt bleed it, Ill replace the caliper later this week.

Bled the passenger side however, and it was weird, holding down the brake pedal and opening the bleeder, fluid would slowly dribble out as the pedal slowly fell to the point where the pedal always got hard, then it would feel like something popped and the pedal would fall really quick and shoot out a geyser of fluid.

What the heck is wrong? Does that sound like a booster or a proportioning valve?

 

[SRLRacing]

From my understanding I don't think your pulling enough vacuum. I hear 16" is the minimum to operate a power brake booster.

 

[k20]

See Ive heard its more 10-16 with 12-14 being optimal.

That could be it, but I am more inclined to think its either the booster or the prop valve b/c of what I was saying when we tried to bleed em, how the pedal slowly went down to where it normally got hard, then 'popped' and fell really quick.

 

[SRLRacing]

manifold vacuum on a normal properly operating motor I know is 18-22", I'm not sure about a hi performance one, plus I don't think stock braking systems have anything that I would identify as a proportioning valve

but maybe you have a block or a kink in your brake lines

 

[shaun89]

i have the same problem as you, i cant seem to figure it out either....brakes were fine, then the new motor with a cam, lost a lot of braking...

 

[k20]

It does have a prop valve just a....low tech one. Its on the front crossmember, conveniently located directly behind my steering box brace.

If I cant figure it out, Ill just stick hydroboost on it. *sigh* its just more time....and money.......I just wanna drive the friggin thing again.

 

[SRLRacing]

I just went out and disconnected my vacuum line to my power brake booster and my truck had the same exact symptoms you were describing as far as the peddle feel and not stopping no matter how hard you pushed it. So I think you either lack the vacuum needed or you have a vacuum leak.

 

[k20]

yeh those are the 3 things I am struggling with, less vacuum than needed, vacuum leak, or bad booster. All of the above could affect it. If I narrow it down to less than needed or bad booster, I have a line on a hydroboost setup, if that hydroboost setup is bad, Ill rob the one off my CUCV until I can find another one for it.

Now Im sittin here thinking. On my testdrives it seemed like it wanted to shift late, and the th400 has a vacuum regulator....I gotta find some info and see if low vacuum causes a late shift......Course it has been 3 months since Ive driven the damn thing, I might have just forgotten how it shifted....

Well I just read that low vacuum causes a late hard shift, these seemed a little late, but they were anything but hard, I didnt even feel them. The shifts in my mothers jeep liberty are harder....

Oh yeh SRLRacing, I like your user title right now, "Brakes only slow you down"

 

[SRLRacing]

haha yeah a term we use in vintage auto racing since many of the cars are running brakes so bad you need a fricken anchor to slow them down

Here's what I would do:
1. find out how much vacuum you actually need and figure out if you have enough

2. Look for vacuum leaks, a lot of people will say that you just need to unplug the vacuum line and if holds pressure you don't have a leak, but that isn't necessarily true I had a vacuum leak in my check valve rubber grommet causing the same basic problem that would come and go, still need to replace the damn thing take me $9 and 2 seconds to replace

3. if all else fails swap it with the one off your CUCV and if it works on your CUCV and the one that came from the CUCV doesn't work you obviously have other issues

 

[k20]

Well I cant swap it with the cucv, the cucv is a diesel so I cant run a vacuum booster, I was just sayin rob the hydroboost off it till I can find a setup for it.

 

[Smitty]

The hydroboost is the way to go. I'd be looking for one off another vehicle vs taking the one off your CUCV (just to save on the extra work of putting it back on the CUCV). I put the hydroboost on my '56 when I put the truck together because of the cam I decided to use in the engine and I doubt I'll use a GM system with a vacuum booster again.

Sounds like you have something else wrong in addition to the vacuum. There seems to be some type of restriction and I would be looking at the porportional valve.

Sucks about the broken bleeder. I put antiseize on the threads of the bleeders since the sealing surface is below them. It seems to help down the road when most threads are rusted tight.

 

[Rob 85K5]

Did you put the vacuum gauge on the same port/hose going to the booster? Is the hose to the booster on the right port on the carb, if you have one?

 

[k20]

yeh I put it on the booster line, Im sittin at the gf's house right now so I dont recall exactly where it is coming from, IIRC it is coming off the manifold behind the carb, either that or off the carb baseplate, its how I had it hooked up before the motor rebuild.

Yes it is an 87 with a carb, I got sick of the TBI