brake adjustment?

[wm69]

I just got a new Mc and booster put on my jeep and it feels like the pedal is getting a lot closer to the floor than it used to. It stops fine, but the pedal goes a little far for comfort and I am wondering if there's any way to adjust it? Thanks for any suggestions

[CJ-8_Jim]

Hi,
Here are some MC and brake line possiblities that come to mind:
1) Did you bench bleed the MC before installing?
2) The lines didn't bleed correctly.
3) Other failing brake system components.
4) You didn't hold-in the combination valve pin when bleeding.

Of course, there could be something going on with the booster... I can't speak to that component.


#1) MC BENCH BLEEDING:
A new MC is all air. If you simply install and fill without bench bleeding, then you have A LOT of air in your brake system that compresses rather than the brake pads/shoes compressing.

Bench bleeding involves sticking the MC in the "installed postion" in a bench vise, filling the MC with fresh brake fluid and then taking a wooden dowel to depress (pump) the MC piston until brake fluid flows freely without bubbles from the to two brake line fittings.

Make sure that while you are doing this that neither MC chamber empties of fluid, which means you need to start over and re-bench bleed.

#2) BRAKE BLEEDING:
Includes all possible problems normally associated with brake bleeding. Bleeding brakes requires two people (one to pump and hold the pedal while the other person loosens the bleed fitting and retightens before the pedal is released).

There are some gadgets (and speed bleeding values) sold at Auto parts stores that allow one man operation. Some work well, others not.

#3) OTHER BRAKE SYSTEM FAILURES
Inspect the entire system for leaks. You'll also see falling fluid levels in the MC.

#4) COMBINATION VALVE:
When you bleed the brakes, did you you hold open the combination valve when doing the rears first and then the fronts? If not, that could be part of the problem (either alone or inconjuction with another problem).

You have two choices, figure out what combination valve you have (one you push in the pin to hold open or one you pull out to hold open). This is a touchy subject since the FSM and Chilton's have conflicting advice. I'm guessing you have one where must hold it in (mostly 80s era CJs). I made a simple tool based on FSM drawings of the official tool out of a piece of 3/4" conduit. I took 6" piece, flattend one end and then cut a notch on side of the flattened end so that it slides over the valve and depress the valve pin.

The other option (without a proportioning tool) is to bleed the fronts first, then bleed the rears, then bleed the fronts again. Why? bleeding the fronts firsts sets the combination valve allowing you to bleed as normal (rears next and then finally the fronts again).

CJs have a combination valve which incorporates porportioning AND metering functionality. The "pin" on a combination valve is for the "metering" functionality.

Combination/Metering/Porportioning valves occur on just about all hydro-brake systems (the exception may be ABS systems... that's outside of my expertise).

Here's a good graphic: http://www.mpbrakes.com/combocutaway3.jpg

The "metering pin" issue when bleeding applies to dual brake systems using both disc and drum at the same time. The dash brake light will come on when there is unequal pressure between the front and rears (which can be caused by a number of different things including leaks in the front or rear brake subsystems, not "setting" the metering pin on combination valves, etc.).

In these JU posts you'll see the discussion on whether to push or pull the pin... FSM says that the later models you push; whereas Chilton says you pull... the CORRECT answer is PUSH). Bottom line, you need to depress the pin otherwise bleed in this sequence: Fronts, rears then fronts again.

Debates on push or pull... CJ-8 answer is PUSH.
http://jeepsunlimited.com/forums/sho...hreadid=385140
http://jeepsunlimited.com/forums/sho...hreadid=363308
http://jeepsunlimited.com/forums/sho...hreadid=279166

Hope this helps,
Jim

[wm69]

wow, so you know a little about brakes huh? I drove it for about 1 1/2 hours yesterday and I'm still not comfortable with the pedal where it is, so I'm gonna try bleeding it first. The shop that installed the MC/booster is a very reliable mechanic so I can't see him putting it mc on without bench bleeding it, but here again I can't see him not bleeding the brakes good before giving it back to me either. Maybe with the holiday weekend he got in a hurry, but I'll take some time today and try the things you suggest and see what happens. Thanks!

[tom keyes]

Your mechanic may not understand the need for the Proportioning/combination valve to be held open or depressed depending on what you have. My 1981 needs a special tool that depresses the proportioning valve neddle into it. Then bleed the breaks. To many younger mechanics think you can just bleed the breaks and your done. You could still have a small bubble in a line?

What about the rear pads being out of adjustment?

This is the Tool I use to do mine: http://www.cartools.com/Merchant2/me...de=sabrOTC7853

Good luck!
TK

[wm69]

Thanks for the link. Ran out of time last weekend so I'll get to it when I get a chance.... I'll let ya'll know how it works out.

[VinnyM]

WOW..... Jim

Thanks for all the work. I have been doing breakes for years, and could never pin point why my brakes .... well ..... suck. I am definatly going to try the front-rear-front bit over the week end.

Vinny

[CJ-8_Jim]

Vinny,
Give it shot, it's worth a try. Also, the $20 tool Tom listed a link for is a fool proof method. One effect of NOT using the tool is that the rears must do much more of braking then normal (hence the reason manufacturers many times substitute drums to save money in lieu of dics on the front). Normally, the fronts do most of the braking.

Just know that even after correcting depressing the pin when bleeding the rears, you may still have soft brakes.

From your CJ-8 photo, it looks like you are running near stock wheels/tires. Naturally, there are a number of factors that could contribute.

In my case, my brake booster is tired. Looks like I have a couple of options:
1) longer arm/rod that increases leverage from pedal to booster. I heard someplace out west like CA sells it... maybe $40-50 more than the cost to make one, but less time trying to make one by trial and error without a copy to work from.

2) GM Booster Upgrade to a dual-diaphram design: http://www.shortwheelbase.com/~dirtdog/booster.html

3) New replacement booster.

[tom keyes]

One other thing I thought I should mention. When I got my tool I had to do a slight modification for mine to work. The newer Proportioning valves installed in cars today (or maybe just my jeep?) have a larger gap to slide the tool onto. I had to take my belt sander and thin the bottom side down until I could fit it onto the gap or grove it slides onto. Here is a sight that has a fair image of the components from front to back:

http://www.allstate4wd.com/p8-7286.htm

Here is a little write up I found informitive:

Proportioning Unit Operation:
The proportioning valve section operates by transmitting full input pressure to the rear brakes up to a certain point, called the split point, and beyond that point it reduces the amount of pressure increase to the rear brakes according to a certain ratio.

Thus, on light pedal applications, approximately equal brake pressure will be transmitted to the front and rear brakes, while at higher pressures, the pressure transmitted to the rear brakes will be lower than to the front brakes to prevent premature rear wheel lock-up and skid.

If hydraulic pressure is lost in the front brake system, rear brake system hydraulic pressure moves the brake warning switch piston and opens a bypass in the proportioning unit allowing full rear brake hydraulic pressure.


Here is a image of the type of proportioning valve I have on my 81.

http://www.dippy.org/svcman/image/05d01.jpg

You can see the valve stem and the grove that the tool would fit over in this image.

Good luck and don't forget to by new Spring kits, new star wheel adjusters and even wheel cylinders if you have to. These are your brakes so don't skimp on the parts you need to replace.

TK