At low speeds, too little front brake. Driving normal, pedal a little low, but stops fine. You can feel the rear bias at low speeds. I replaced master, no help. Pumping does not help. No warning light. 4wheel ABS.
Anything to check before throwing expensive parts at it?
Could this be the ABS controller? Either the computer or the hydraulic unit? Prop. valve?

Thanks,
Jim.

you could possibly have a solenoid stuck closed or near closed, blocking fluid to the front. but that would still leave a hard pedal....maybe an internally leaking master cylinder?

Master was first thing I did. Any way to check solenoids? Isn't there a line to each front? Which would be two solenoids? Don't know have never been here.
Replace entire hydraulic controller?
Thanks, any more ideas?

Ron?

again

Front disc are not engaging you think... check this. Pop the hood and look down by the Master. You will see a valve that looks similar to the one pictured below... it should have a little rubber boot covering a pin on the front end.
That little pin should pop out just a little bit when someone steps on the brakes. If it doesn't, then your front brakes aren't seeing any meaningful force from the master. Very often these pins get stuck due to dirt and crap getting in and around the stem, that's why they have a rubber boot on them to protect them. If you think it's stuck, grab it with a pair of pliers and give it a tug, it's spring loaded so it should move back and forth. This is part of the Metering (Hold-Off)Valve assembly by the way. If you want to know what the pin is for, let me know and I'll tell you.

I'll check tomorrow. I think hold-off is to let drums take up clearance before disk apply, or may be backwards. Yes about pin purpose, jim.thorn@hds.com

J.

Well Fastback, good shot, but pins moves freely with application. Not as much as in your pic, but the rubber
cap would limit anyway. How much should it extend when applied?
Oh and I'm sure about lack of front brakes. We have steep drive, and if damp, rears lock-up real easy. Feels much like
oil seal leaking, but dry.
Thanks,

The pin is only going to move about 1/32" to 1/16", just enough to open the valve and allow fluid & pressure to enter the front lines.
You don't have any crimped lines up there do you?

Rears locking up on the first run on a damp day isn't really all that unusual, there's no weight back there.

Sounds like the shoes in your rear drums are not fully retracting. Assuming you've driven around for an hour or so... If you put the truck in gear, does it roll along okay at idle on a flat level surface, or does it feel like your dragging an anchor that wasn't there before... or does it perhaps have an intermitent drag, like someone is tugging on the rear every few feet? Are the rear brakes getting abnormally hot?

I'm pretty sure there is not a physical problem, I've had the truck since new, it has 230K mi. on it, and have done all maintenace. I had similar problem with rear seal a few years ago, replaced. Thought had same problem on other side, and everything dry. When had seal problem, ebrake was sticky, not now.
I think I have fluid flow problem, but what do I know, it's still AFU.
I have HCU coming (used), hopefully it'll have residual fluid in all the valves so I don't need DRB cycle bleeding
on it.
Thanks.
Jim.

OBTW, rear not dragging. Awhile back I backed off rear adjustment, better for a day or two. Reverse braking about
10' a day, parking. We've been in house for 13 yrs., familiar with driveway characteristics. Not being smart, just answering questions you had.
Anybody else?

Have you replaced ALL the rubber parts in 230000 miles? Hoses rot on the inside.

I would say that it feels more like normal bias after adjustment. Yes the rear is extra sensitive at low speeds.
No seals or hoses replaced, front hoses look good on outside, haven't looked at rear.
Is it possible hose restriction would block fluid pressure to front? Then both hoses would be bad the same amount, braking balance L/R is good, NO pull whatsoever.
As far as not letting pressure bleed from rear, I can pull either drum without backing off adjustment.
Driven on same steep drive for 13yrs. If I have one of the boats on the back, it'll push rear around.
If we don't come up with something, or the HCU doesn't fix it, I'll TEE the front lines and do away with AWALB.
But it'd be nice to fix it, my wife won't drive it.

Fastback don't know how often you check but you have email,,,,,,,

Jim

It still sounds to me like the rear shoes are not "fully retracting", especially with the high sensitivity at low speeds. They have to be sitting right there ready to grab to get that kind of high pedal sensitivity. That being the case however, it just seems kind of odd to me that you haven’t noticed any extra drag at idle or unusually high brake temperatures in the back, especially if you've been driving around starting and stopping for an hour or so. Perhaps the shoes are retracting just enough to clear the friction of the drum and that’s about it. If that were the case, I would suspect one or more of the following.

1. Bad wheel cylinder not fully retracting.

2. Brake drums and hardware so dirty that return springs can not fully retract the shoes without assistance.

3. Brake shoes have worn grooves into the mounting plate over the years, which are preventing the shoes from moving freely.

4. Partially clogged hose or tubing will pass fluid under pressure, but resists natural return flow.

Worth looking at anyway...

As far as the drum removal goes... My 67 had a problem with shoes not fully retracting once in a while. They would get pretty hot on a long drive, but I never had any trouble removing the drum. It was just a case of very light friction, but over time that friction would build as the shoes got hotter and started to expand a bit. Once you stopped however they would cool down pretty quick, so drum removal was never an issue.

You said you have a new/used conrol unit coming in... maybe you'll get lucky there. I guess we'll just have to waite and see.

I do a 200 mi round trip 2 or 3 times a mo., never sensed any obvious symptoms for drag. This is a mountainous drive.
Still getting high 14 low 15 avg through the mountains. About as usual. Never noticed any smell, or heat "popping, creaking", but also never checked wheel temp either.
Prob'ly not do anything with HCU until next weekend, maybe sooner. If that doesn't fix, or if I don't find a drag
problem, we'll do a major brake overhaul.
Thanks Mike,
J.

Update, did the mountain drive yesterday, ran 62mi., got off interstate and stopped without touching brakes. Drums cool to touch.
Then I got an IR temp. gun. 14mi. rural drive to work, LR drum 105*,RR 225*, front rotors within 10* OF EACH OTHER.
Other driving scenarios show RR drum allways hotter 30 - 100*, than LR. So might be something here for the close clearance/retracting.
Plan, hoses seem out of equation, or rear would be same temp. Cylinder(S), springs, yes on the plan.

Jim.

Sorry Jim, I've been away for a few days...

Well, it sure sounds like the retraction problem I spoke of earlier. It's time to pop that RR drum and perform an inspection. Try spreading the shoes apart using a screw driver between the shoe and the pin stop, and see if the springs will retract them all the way back to the pin or not. They should snap right back to the stop, but I'm betting they won't. Their probably hanging up on something, either that or one of your brake components is shot (Wheel Cylinder, Springs, etc)

Mike got it, sorry to not respond, as have been taking care of domestic recreation issues. I'm going to be armed with parts next weekend.
That's if I don't get sidelined with above problem again....

Let me know how you make out