soft pedal?

I'm having trouble getting m brakes working right. the pedal is very soft, it goes to the floor, but stiffens up if I pump it a few times.
It's a new master cylinder, disc front, drum rear. Brakes are from a 78 dodge motorhome. The master is a dual master from Speedway. I have residual valves on the front (2psi) and rear(10 psi) in line. I'm running a proportioning valve in the rear, and have no idea how to adjust it properly.

I've bled the lines, and bled them and bled them. Nothing seems to help.

any ideas? can I run without the proportioning valve? I'm reading that it's difficult to bleed lines with it?

Whoops

Replied on your build page. Adjust the portortioning valve so it's in the middle of its range to start. Let it sit over night hopefully the airr will work its way up. break each fitting loose to bleed at each one or use a pressure bleeder. [P

Let me know if you need a foot pumper.

Kurt

bleeding

Kurt
I'm not sure how I would bleed it at the residual valves. Wouldn't it pull air in between pedal pumps. Or would I need to use a vacuum pump? would it work to just cover the end of the line with my finger?? when the pedal was coming off ?

I have lots of helpers to pump the pedal, but just can't seem to get the air out.

I'll try closing the proportioning valve partway overnight and see if that helps.
thanks
Todd

By any chance, do you have bulkhead adapters going through the frame? Most times you see them on the front when used. If they are the large passageway style, they can give you fits, they need to be sleeved down to the same size as the ID of the brakeline feeding them. They can hold a big air bubble in them that is really difficult to bleed.

I built my brakes all from a '74 Nova and I had the same problem. Mine were power brakes with a booster and the pushrod in the master needed an adjustable one to work right.

Check the flex line between the hard line and brakes. They can get soft and cause problems.

soft pedal

First off make sure your rear brake shoes are adjusted right, if the shoes have to move too far, that could be taking the first pump to push the wheel cylinders and shoes out to make contact with the drums.
when bleeding at the fittings and valves, leave the pedal up, crack the fitting, push the pedal down and tighten the fitting before the pedal is allowed to come back up, repeat this step until you are satisfied the air is gone. I would start at the master cyl. bleed there, then move to the next fitting inline and bleed there, work your way all the way to the cylinders and calipers.
Bleed the furthest wheel from the master first, then the next longest one, ect.

I have not even had the wheels off the axles. So I'm assuming that the pads are adjusted ok. ? it seemed to work fine with the motorhome when I drove it home, so I didn't even think to pull the wheels and check the drums.

I got new hoses for the front. The frame passthrough fitting is straight from the brake line to the hose, so I don't think there's a problem with that.
The rear one is the original stock one from the motorhome.

I strongly suspect a problem with the master cylinder or the adjustable proportioning valve. I did bench bleed the master cylinder (I think correctly?) but I'm questioning that now.

I think my next step will be to eliminate the adj. prop. valve and bleed to see what I've got.

meteorman said:

I have not even had the wheels off the axles. So I'm assuming that the pads are adjusted ok. ?

Click to expand...

I wouldn't assume that at all. You need to take a look at the rear brakes anyhow, just to make sure everything is right back there.

To answer your earlier question: you can't run disc/drum without a proportioning valve.

Soft

How am I going to get an early look at your finished rat if you got all the help you need! [dr[dr[dr

To bleed at each fitting, start with the longest run but closest to the master. Pump up the brakes then brake the fitting loose, one at a time till you get to the slave or caliper. Make sure your bleeder screws are higher than we're the line comes into the caliper too.

You could pull the proportioning valve to get to the bottom of your soft pedal but will have to put it back in or will be more than a handful light to light!

You said soft pedal[S does it get better with multiple pumps? Does it ever pump up? Can you adjust the push rod tighter? With your adjustable valve you should be able to completely block off the rear brakes, if you do that does it solve the problem, get better, get worse?

This is most likely a simple problem that is compounded by. Being so close to the first road trip so step back and think through what you've checked and even list possible problems and take that apart and confirm all is good. Your local brake team or Midas could power bleed them for you if all else fails, maybe $50 but might be worth your sanity[S

I can't tell you how many times I've checked things 20 times but forgot the critical thing of actually checking it with a wrench or adding a gasket or checking for proper ground or ..... Good luck, keep us informed[P

Kurt

Kurt,
If I pump it 2 or 3x the pedal gets better and the brakes do work. it does maintain some pressure and stop. Just not good enough for me to hit the road
Although I do have a mechanic that's not too far.

Does pedal firming up some after several pumps indicate air in the lines? or something else?

I'll try bleeding it again, the adj. prop. valve is nearly closed down overnight, so maybe that will allow me to push more air out if that's where it is. (i think)

Then, I'll brake apart the joints and bleed sections.

If that doesn't work, then I may need to look at the master cyl. maybe bench bleed it again.

Air

If they pump up that Mae me believe that your master is working fine and its likely blead good. It might be the back pads really loose and taking many pumps to snug up to the shoes. I'd take a look at both of them before anything else then jack the back up as high as you can over night. Maybe it will help move the air up!

Kurt

Well.??????

Kurt

I pulled a drum off the rear axle and the brakes look good. almost new as a matter of fact. there is a full 1/4 inch of pad on the shoes, doesn't look like there is any wear. and the slave cylinder looks good.

So, I went ahead and re-bled the master cyl. it didn't seem to have any bubbles, so it didn't look like it was the master cylinder problem.

I'm thinking I'll check with a local garage and limp on down and have them see if they can suck the air out with a power bleeder. ? or vacuum bleeder or whatever they're called.

It isn't so much how the rear shoes look, it is whether or not they are adjusted properly so that it takes minimal stroke of the master cylinder to make the shoes engage the drum. If the slave cylindes have to move excessively it could take two strokes of the master to make the shoes move far enough to engage the drums.

If it were me, after all the messing around you have already done, I would pay to have the system pressure bled so that all the air is purged out.

Randy

That GM style master may be too small to operate the motorhome brakes. If you still have the master from the motorhome, compare the bore size with the one you have mounted. It may not be moving enough fluid per stroke. Always best to keep parts together from the same vehicle so everything is matched.

thank you to all who are helping.
I went back through the directions and realized that I had reversed the lines from the master cyl. oops. (embarrassing, but I'll post it on here for others to learn from my mistakes
I had seen diagrams that showed the front brakes coming off the back of the master, and vice versa. But since my master is under the floor and reversed direction from the firewall mounted ones, it's the other way.

Anyhow, I got the lines switched.
And I shortened the push rod, because according to the instructions, it was too long and too far out. I don't really get how it would matter, but I changed it and it's at least closer to the directions.

I started bleeding the brake lines again, but have no pedal at all, it just goes to the floor. I only had 3.5 inches of room for the pedal to go down, and the instructions call for 5.5, so I extended the pedal out 2 more inches and will try bleeding the lines again.

it's usually the basic things. It's a good reminder to go back through the fundamentals and recheck.

Cruzin

Funny these things sneak up on us. Hopefully this gets you cruzing soon. Summer is appon us and its time to get out and drive!

Kurt