Rick is correct, in most circumctance soft means air, and a boosters easy to test, get a small vac gauge and pull vac on it and see if it holds. My brakes are stock but they will throw you through the wind shield.

 

Check to see the pushrod is adjusted for the new master cylinder. I have had to turn the adjuster out as much as 2 full turns to get it back to par.

Test master cylinder by plugging off the outlets with the plugs contained in the box for bench bleeding, then push the pedal. If it falls, is spongy, or moves more than 1/4" it is either the pushrod adjustment, or MC. Was it new or a reman? I, along with many others, have had horrible luck with reman MCs. I've even had to return one new one.

Adjust rear brakes til they wont go out anymore. Back off 15-20 clicks (evenly) per side. They are now adjusted. You should have a substantial drag on the wheels as they turn by hand. The "turn til you feel light drag" is for using the self adjuster, which I have rarely seen work, even if new.

I would only replace the booster if the pedal is hard. Otherwise you are wasting time and money. Booster has nothing to do with hydraulic performance.

Daniel

 

As mentioned the self adjusters don't work very well, so to really adjust them right you need to do them by hand.

This is what I do and it has worked well for me, jack the rear of the truck up then get a screw driver and turn the adjuster wheel until there is a slight drag. make each side as even as possible.

I do this when I start needing more peddle to stop, after adjustment the peddle is back up to the top.

 

Colesdad,
If the rear brakes are adjusted properly, and especially since the change happened all at once, it is most likely the ABS dump valve on the frame rail at the rear of the truck. The shop replaced it, but they may not be aware that the valve needs to be bleed at the valve itself. There is a bleeder on the body of the valve, and I can't remember for sure, someone with the FSM should chime in, but I think the wiring harness needs to be dis-connected when the valve is bleed. If bleeding the valve doesn't correct the issue, I'd look for an electrical problem. Is the ABS light on in the dash? Something may be causing the ABS computer (behind the glove box) to hold the valve open. On my rig there was an accumilation of shavings on the ABS sensor in the rear diff that had confused the computer into thinking the rear wheels were in lock, so it was trying to dump rear pressure all the time. I read another post (Ace maybe?) where someone found a bad wire in the harness between the ABS valve and the computer in the truck that was causing the same issue.

 

Good point and if it is the abs is always trying to dump pressure, just unplug the computer which is behind the glove box, and try your brakes. Unless something mechanical inside the valve broke then it won't help.

 

i am going to vote for either the adjustment or the rod in the booster not lining up or rubber lines from the truck to the axle. i've replaced the entire system, booster, master, wheel cylinders, rotors, drums, pads, self adjusters, and the hard brake lines from the master to the rubber lines at the axles. i removed the entire abs system and the stock proportioning valve. i ran a hard line from the master through an adjustable pro. valve then straight back to the rubber line over the axle. i know EXACTLY the feeling you are talking about. i adjusted the rears but don't think i did a great job and i am planning on trying the "adj till it doesn't spin then back it off this many clicks" i didn't replace the rubber lines over the axle cause i was planning on lifting it. and i have been suspicious of how the master and the booster matched up. so i will be trying to figure this out same as you... if you figure it out let me know. i don't believe the abs is your problem though!

 

Ahhh the spongey brakes, one thing I haven't heard mentioned specifically, but I have seen, is the "dump valve", "accumulator", "little valvey thingy on the left rear frame rail" whatever the name is to you, bypassing internally. I have replaced them before just to find out the new one was bad. I wonder how long that thing has been sitting on the shelf? But a cheap and easy way to find out is to get a couple of brass double flare adapters and some fittings and bypass it. temporarily if you want, I don't like modules telling my truck what to do, so mine are both permanent. other than that, I agree, check your rubber very closely, check your pushrod to master cylinder adjustment...should be right up against the piston with the foot off the pedal, and then suspect the master cylinder. Good luck!

 

WOW! Thanks for all the awesome replies, some GREAT info. I am taking the truck back into the shop and will log in so the tech can read all the posts.

I'll post when we find the culprit.

Thanks again to all.

David

 

You can do a quick check of rear brake adjustment by applying the parking brake part way, if the pedal comes up on the second application, the brakes are out of adjustment. (while driving)

 

Just got back from the shop and here is what we found. I tried the parking brake 1/2 way down ....no change. We by-passed the booster and no change. The tech clamped off something at the rear and no change, he then clamped off both front brake hoses...BINGO! Brake pedal right up at the top and solid as a rock. We were thinking hoses but both of em look great so it's lookin like the problem is in the calipers.......???

David

 

Only if the calipers are leaking. I'd replace the hoses.

 

The tech was saying that if the pistons weren't doing something correctly they could produce the soft pedal senario....... (shrugs shoulders) anyways this problem is something the previous owner is having repaired (part of the sale agreement) so it's up to him what we do next. Good thing is that he is a man of honor and is very interested in getting this problem fixed right.

I think replacing the hoses first makes the most sense also.

 

Hey colesdad,
The problem you describe is identical to the problems I have been having...

Did new front Brake hoses solve the problem?

Or was it something else?

Maybe the proportioning valve?

Thanks,

 

I had an 87 dodge van and did a complete brake job except for hoses. I also had a soft pedal and also killed a set of pads in short order.I changed the hoses and brakeing improved greatly.