ABS Problems...

[icanfixall]

Ok abs gods... I need some help... I seem to loose my brakes in any kind of a panic stop. The brakes grab but then the peddle goes lower and the braking seems to deminish. I have in the past felt the pulsation in the peddle but not so much any more. I have adjusted up the rears so thats working. As so recall I have the hydroboost and the large 1 5/16 bore master cylinder. This issue seems to be getting worse each time I need a quick stop usually because some ***** cuts me off or stops short in front of me. I'm kinda lost here so any thoughts will be watched... Thanks all....

 

[93cc7.3]

i almost said vac pump but u said hydroboost ,,,, i guess maybe the hydroboost could be failing

 

[pybyr]

Mine was acting similarly to yours

-- and then changed suddenly after one very fast stop over a heaved up culvert-

and then suddenly the braking was more powerful but the ABS ceased to work

in my case I am about 98 percent sure that the solenoid hydraulic valve on the ABS had some crud or water in it that had been partially blocking the flow to the rear brakes

I wonder if you might have the same thing going on-- try doing a total bleed on the brakes that keeps pushing all the old fluid through until the new fluid comes out at all corners-- and then see how it acts.

I'll bet you'll see some crud come out that'll be old enough to vote.

 

[bikepilot]

Does it do the same thing if you press on the pedal hard when you are stopped? If so, you could have a bad internal master cylinder seal (assuming brake fluid isn't leaking out).

The valve mentioned above is a known trouble spot as well.

 

[icanfixall]

When I apply the brakes in a panic stop the rears will start to skid for just less than a second... Then the peddle gose farther towards the floor and the braking seems to be much less. The fronts never lock up and I know we don't have abs up front... Or does the abs valve work there too by reducing the braking pressure so nothing locks up and skids... I'm kinda lost here. I really don't want to start throwing parts at it when I don't know what the problem is. I am leaning towards the abs hydraulic section like has been posted above. The wifey was driving the rig Friday and tore me a new you know what for having faulty brakes. She tried to panic stop for a lite and ended up in the middle of the intersection... She said if a car was in front of her she would have hit it...

 

[icanfixall]

Just another thought... The rear tone ring senser in the differancial might be dirty and not sending a good signal... I may try to clean it later... It may have gone bad too... Lots of possibilitys. Ebay has several abs valves for everything but my truck. Most are new oem from Spokane Wa. and cost about 85.00.... One seller has cleaned used and calibrated inuts really cheap.... I don't think so.... Scooter.... Brakes are the last place to go on the cheap.... I might end up in a worse position than where I am now... Hopefully the wifey will only be driving the rig tomorrow... Then again its a new workweek... Maybe she will call in sick.... She hasn't worked a 5 day work week in probably a year... Thats really a sad thing... I worked sick or in pain and proud of the work I did. I always felt someone would end up doing the work that was planned for me and didn't want to burden co-workers...

 

[pybyr]

Just another thought... The rear tone ring senser in the differancial might be dirty and not sending a good signal... I may try to clean it later... It may have gone bad too... Lots of possibilitys. Ebay has several abs valves for everything but my truck. Most are new oem from Spokane Wa. and cost about 85.00.... One seller has cleaned used and calibrated inuts really cheap.... I don't think so.... Scooter.... Brakes are the last place to go on the cheap.... I might end up in a worse position than where I am now... Hopefully the wifey will only be driving the rig tomorrow... Then again its a new workweek... Maybe she will call in sick.... She hasn't worked a 5 day work week in probably a year... Thats really a sad thing... I worked sick or in pain and proud of the work I did. I always felt someone would end up doing the work that was planned for me and didn't want to burden co-workers...

I think the tone ring is really unlikely-- if it is that dirty, your differential itself is probably close to R.I.P., as the whole tone ring is protected right in there with the ring gear.

Try the total flush of the brake system with 100% new fluid. It won't be very expensive and you can get wifey to help push the pedal to bleed it through. I wouldn't even think of buying any parts at all until you've pushed new fluid through all of the lines and etc. stem to stern. the fluid may solve things, and even if it does not, then at least you know that any new parts will be starting out with fresh fluid, not some ancient stuff that's inherently full of contaminants (since brake fluid is intentionally formulated to absorb and suspend water and other crud).

 

[GOOSE]

If you are gonna bleed your system, take out the rear abs valve and clean it first. I am not well versed in how to clean it but have heard it being done. Your symptoms are identical to what mine were and replacing the rear abs valve solved my woes. I heard about cleaning them after I bought my new one so sorry on the lack of info on how to do so.

If you are already gonna bleed the system, this could be a free fix if the cleaning works.

 

[towcat]

gary-
you need a new ABS valve. it's dumping off the rear pressure. the one ton versions are all iron whereas the 3/4t version has a alu body.

 

[OLDBULL8]

On the ABS valve, there is a large nut (plug) remove it and take out the spring. There shouldn't be any fluid come out there. Replace the plug without the spring and operate the the brakes several times, then replace the spring. If you bleed the system (replace all the old fluid) do that before replacing the spring.

 

[Agnem]

Dump the ABS! It's for people who don't know how to drive.

 

[icanfixall]

And that would be my wifey... Mel... She drives them till they stop... Then she calls me... Even when she has a triple A card in her purse.... She ran the truck out of diesel about a month ago... Her thinking about this..... "Well... My Civic runs a whole week on one tank of fuel... Why not the truck"..... What a duma$$ I got on my hands in this one.... I really hope she is teasing me like this...

 

[bikepilot]

I would definitely recommend not driving the truck till its fixed, sounds quite dangerous, especially for others on the road!

For what its worth my truck will lock up the front wheels and will just chirp the rear wheels a little. The pedal stays firm and doesn't mush down even when the ABS is active and the ABS definitely doesn't do anything wrt braking on the front wheels. I had some soccer mom in a little lex mini-suv pull out right in front of me a few weeks ago and got to test the brakes quite well.

Agnem, in general I don't like ABS but I personally wouldn't dump the rear abs on our trucks. I find that on a pickup where the weight over the rear end varies so wildly (at least for me - sometimes I'm empty, other times I've got the bed full, other times I've got trailers of varying weights hooked up) you need either a weight sensitive proportioning valve or rear ABS, else you'll have seriously compromised braking at least part of the time. I'm too lazy to try to rig up and calibrate a weight sensitive proportioning valve (my old 'yota had one, worked pretty well), so I'll be keeping the rear abs

good luck!

 

[Agnem]

Earler trucks (like my 83') had neither a load proportioning valve, nor ABS. I've had mine for 27 years and have never needed it. Not even during the IDI rally when I locked up the rears to keep from plowing into somebody at a red light.

 

[Hybrid455]

You do not have anti-lock in the front, it's rear abs only or for short RABS. The RABS unit is as TowCat says prone to failure, however, if you mess with it just replace it. Don't waste you time trying to work on it. If your rear wheels start to skid then stop and the pedal drops you have just described what anti lock does. As soon as the ABS module sees the brake lock it signals the RABS valve to dump fluid and release the rear brakes. The RABS valve will continue to do this as long as the rear wheels are trying to lock resulting in the kind of braking experience you are describing. If you have a grease leak in the rear it can really drive the ABS crazy because the brakes will try to grab and will lock prematurely. I also wonder how the Hydroboost and larger master cylinder may be effecting the stock RABS valve as it was not designed for the kind of hydraulic pressure that you are undoubtedly making in a panic stop. Another area prone to failure is the rear speed sensor. They drop like flys around here. If the sensor drops out the module thinks it has a lock up and can cause an unwarranted actuation of the ABS. If this happens it will normally turn on the ABS light and set a code.