Misc. Help.. Soft Brake pedal after converting from front manual drum brakes to front disc brakes. :/

[76cj7chick]

Hey, may I get some ideas why I have a soft brake pedal?

I converted my manual drum brakes to (YJ jeep) power disc brakes in my 1976 CJ7 jeep.

When installing the booster, I did notice the piston rod was slightly longer on the disc brakes than the drums. So I lowered/loosened my pedal to allow the extra length. (bad idea?)

Then, after converting to disc, I now I have soft brakes. I have to pump the pedal before the brakes engage which is scary.

I bled the system 4 plus times (probably more.) I Don't think there is any air. ~But I didn't bench bleed the mc.
And the pedal hardens up after I pump the brakes. (air? Or too long of a piston rod, or wrong pedal?)

I read I may be able adjust (lengthen) the piston rod in the booster slightly to firm up the pedal.

Any Idea On how to fix it?

Hope you're all having a blessed summer! Thanks for the help!

 

[NP435]

Bleed and bleed some more, yes it can be stroke related. If you don't get all the air gone you may chase this a while. I am unable to say if the stroke is long or short now or how its fixed. I assume you used a new master cylinder?

 

[76cj7chick]

Thanks for the response. I bought the booster used off eBay for $30 shipped. It came with the bracket, booster with master cylinder and proportion valve. The guy said it worked fine before pulling.
I may try to bleed a few more times.
But I remember the brake rod was slightly shorter on my manual drum brake system. One guy n YT suggested to drill a hole 1" below the original hole on the brake pedal.

 

[76cj7chick]

Well, I can't get the brakes to firm up.. I'm starting to think that the booster or mc is bad so... Can anyone give me a part number for a good CJ7 brake booster with master cylinder and proportion valve?

Much thanks!

 

[76cj7chick]

I just realized I posted in the wrong section.
Please delete this thread as I started a new one in the correct section.
THANX!

 

[elwood blues]

I can't speak to your swap because my '78 came w/ front disks and power brakes. But, a soft peddle can be from air in the lines, or a loss of vacuum in the power booster.

You said you've bleed the brakes repeatedly, how are you bleeding the brakes? I've found these things to work a lot better than the old school way of cracking open the bleeder when someone steps on the peddle.

Amazon brake bleeder

The other thing I remember from when I changed my master cylinder was that there was a rubber insulator between the MC and the booster. It wasn't listed in any Hanes, Chiltons or the Factory Service Manual I have at the house, but it was there, and when I didn't put it back in, the brakes were real soft. Put it back in, and they worked perfect.

The last thing I can think of is have you checked the vacuum lines and connection to the booster?

When get home from work I'll see look at my FSM for part numbers for you.

 

[76cj7chick]

Thanks for your thoughts Elwood blues. I bought the YJ brake booster, mc, proportion valve and bracket from someone on eBay. It was pre-assembled when I got it. Someone else was complaining about soft pedal when swapping out to a YJ booster assembly. Maybe it's not me.
I had a helper to pump to brakes while I cracked open and closed the bleeder screw.

Only thing,
I didn't bench bleed the mc... But did have to lower my brake pedal to get the LONGER YJ booster brake pedal rod to reach my CJ7 brake pedal ...
So, not sure if it has something to do with that?


I am considering buying a complete aftermarket kit that is specific for my CJ7 with disc/drum conversation. It will cost close to $300 but if it fixes my brakes it would be worth it... Just fear, they'll need something else like an adjustable proportioning valve...

One last thing... I noticed that I have both front brake lines going to one port on the proportion valve... But pictures for YJ wrangler PV show each front brake line has it's own port... Could that cause my issue of soft slow to act pedal?

Thanks again for your suggestions...

 

[elwood blues]

Sorry I'm a couple days behind on this, my family and I ran away to a state park in the mountains of western VA this long weekend, hiking, fresh air, no tv, no cell service.

I do not believe that the proportioning valve set-up or your pedal location are your issue. Unless you're leaking pressure from the proportioning valve, it shouldn't matter how many lines go to the front brakes. You've said that you didn't bench blead the MC, but if you've bled the brake lines until there are no more air bubbles, then you should have gotten all of the air out of the system.

When I changed my MC I went through a lot of brake fluid before I got rid of all of the line, I want to say I used an entire quart bottle of brake fluid pulling fluid through the system before all of the air was gone. I remember thinking to myself that I should have been done by now more than once, but I just kept pulling bubbles out of the system.

I really believe that you've either got a vacuum leak, or air in the system somewhere. Those are the only 2 things I can think of that would cause a soft pedal. The proportioning valve being incorrect "should" cause the pedal to be real stiff, like its fighting you to provide fluid to the brakes.

Any of the used parts you bought could be bad, without knowing they were good before they were removed, it's hard to tell. I don't want to recommend dropping more $$$ on your project, I think this is something you can figure out, I hope someone that's done this can chime in, because brakes aren't really my specialty.

 

[76cj7chick]

Hey Elwood blues,
Sounds like you and your family had a peaceful and relaxing adventure... Welcome back..
Thanks for the ideas on what the issue could be.

I didn't want to do it but...... I figured good brakes are important.. And so, I ordered a new brake booster assembly kit with an adjustable proportion valve...

I should receive it on the 9th of this month.

Once I get a chance to install it, I'll give you all an update.
I sure hope it works out..

 

[76cj7chick]

I received the brake booster assembly yesterday. And even though it was OK boxed ad some cushioning the box was broke and I could see the mc.

I got it installed yesterday in the Jeep. I couldn't hold the booster and tighten the bolts under the dash by myself so my brother helped me on that part. Which is very nice, as I couldn't have gotten it in without his help. Thanks David!

Mods I had to do so far:
*I had to cut off approximately a quarter of an inch off the threaded pushrod as it was too long.
*Need a smaller diameter vacuum line
*The Master Cylinder pushes against my radiator support rod somewhat. (may need to move the rod slightly). ?
I didn't like the PV just hanging under the MC as the air cleaner didn't have enough room. So I tried to straighten out the MC lines and bring them to the side.
*I found a nice piece of metal on the side of the road. So, I'm using it to make a bracket to hold/secure the PV to the booster.

I busted one of the old front brake lines while trying to bend it to the new PV so now waiting on some new brake lines. (But since the left front brake line is quite long, I did however, manage to cut off the damaged part and re-flare it. But I don't want to take a chance so, I ordered new lines.

Other than that, the booster assembly fits.

I bench bled the MC in the vice yesterday and hooked up on side. Dumb me didn't tighten the bottom line so the brake fluid emptied out on to the garage floor.
Looks like, I'll have to bleed the mc again.
But, at least it's not that difficult and the kit came with a brake bleeding kit.

That's it for now. I will post more info and more pics when I get the chance.
Thanks again for all of your suggestion and support.

PS. Looks like the seller sent me the 1 1/8" mc instead? Well, that's what the paperwork says anyway. Maybe better than just the 1"?

He also included instructions.

I included one pic but it's not finished yet. It's not a great pic because I used my ZTE. I'll use the Samsung next time it has a better camera.

 

[76cj7chick]

I record the Master Cylinder. Then my brother helped me bleed the brakes..
But....
I didn't get any fluid from the left rear drum bleeder screw.
I took off the bleeder screw and replaced it with another new self bleed screw (as one of my speed bleeders disappeared after I brought my jeep to A local "auto repair shop")..
But still nothing.
A small amount of fluid did Run out when I took the bleeder screw completely off.

But another strange thing is,
The fluid in the reservoir didn't go down either..

Anyone have any idea to what might be wrong with it now?

And, I only replaced the front left brake line with a new DIY copper/nickel made line. But it looks like I will more than likely be replacing the rear lines too...

Thanks again for all of the help and ideas..

 

[76cj7chick]

Oops. I meant I re-bench bled my mc

 

[RiverandSand]

If you are getting good flow from the right rear, it's probably a plugged up bleeder hole, pull the wheel cylinder, take it apart and clean it out. Grit and gunk is usually the culprit. There is one hard line running to the rear then a rubber line attached to the rearend. I have seen the rubber lines deteriorate internally and send pieces to the wheel cylinders and cause havoc. If it's old or hard I would replace it.

 

[76cj7chick]

If you are getting good flow from the right rear, it's probably a plugged up bleeder hole, pull the wheel cylinder, take it apart and clean it out. Grit and gunk is usually the culprit. There is one hard line running to the rear then a rubber line attached to the rearend. I have seen the rubber lines deteriorate internally and send pieces to the wheel cylinders and cause havoc. If it's old or hard I would replace it.

Thanks for the suggestion. I will take a look at how to remove the wheel cylinder... Think I have to remove the front part of the drum brakes.

 

[RiverandSand]

It's fairly easy, remove the drum, you don't need to completely remove the shoes, just unhook the top springs and maybe the spreader bar. Then the brake line and the 2 bolts holding it to the backing plate.

 

[76cj7chick]

Hey Guys! It's been awhile since I posted anything. I wanted to let you know that I figured out the soft brakes jist Inc are anyone else runs into the same predicament... Evidently the spacer/bullet in the master cylinder fell out. Once I installed the bullet, I had my brother help me bleed the brakes again and now the brakes are nice and firm....


Happpppppy JeeepN

 

[elwood blues]

Glad to hear you figured it out!

 

[Patrick]

Good news!

 

[76cj7chick]

Thanks Guys! Here is a picture of the new brake PV hooked up to the new brake booster assembly...