Brake pedal vibrating at a stop

[Ranger305]

2000 3.0 Ext cab, 2wd Auto with 148k miles, 2 wheel ABS only. When you come to a gentle stop, quite often the pedal vibrates and there is a clicking in the dash, ie. the ABS seems to kick in, but the vibrations are not as hard as if ABS fully kicked in. The vibration happens for a few seconds, then stops, but the clicking continues. Once it stops, on occasion while holding the pedal, it will drop a small fraction of an inch quite suddenly then not do it again. It did all this before, but I just changed the pads, rotors, calipers, and flex hoses. No help (but needed doing). I also replaced the ABS sensor in the rear diff, no help.

That leaves Master cylinder, controller, and the ABS valve? There are no lights apparent anywhere either when it happens or afterward.

I've read a few threads in various places about this, but haven't found one with a solution yet. Any ideas?

 

[Dirtman]

The best way to fix or diagnose a RABS system issue is to bypass the valve and chuck it in a river...

 

[Ranger305]

This thread describes exactly where I am, , down to the VSS replacement years ago- https://www.therangerstation.com/fo...rake-pedal-pulsing-and-clicking-sound.154752/

 

[RonD]

RABS(Rear ABS) valve is located on drivers side frame rail under firewall area

Looks like this: https://images.whisystems.com/smartpages/partinfo_resize/A1C/122028-lef.jpg

Unplug its 4 wire connector
Go for a drive and see if the pulsing stops, ABS light will be on, you are just testing if RABS is causing the pulsing

If pulsing stops then it is RABS issue
Can be caused by rear axle ABS sensor, in 1992 this sensor is only used by ABS so changing it is a roll of the dice, but cheaper than changing the ABS module under the dash

You can clean the RABS valve, seen here: https://www.therangerstation.com/fo...-back-brakes-proportioning-rabs-valve.133050/
Very expensive to replace

RABS module is in the cab on firewall usually above gas pedal area, and hump/tunnel

 

[Ranger305]

I don't wholly disagree with you on these trucks, but since this is for a 16yo new driver, I'd rather it work for him.

I also learned that the brake Control module in the dash (GEMS?) was replaced and it didn't fix the issue.

 

[Ranger305]

Ron, that is great info on cleaning the RABS unit. I hadn't seen that before. I ended up replacing it on my '92 when it failed. On this 2000, I don't even see them available to purchase.

 

[RonD]

GEM(generic electronic module) is used as the Body computer(BCM) no connection to ABS

Gem does run wipers, power windows/door locks, interior lights, 4x4

ABS is an autonomous system no connection to other systems except 12v and ground

Here is the 1998 RABS wiring which will be same as 2000

 

[Dirtman]

I was joking about not fixing it, kinda. Even when working 100% properly they didn't do anything beneficial since the system isn't on the steer tires where ABS actually matters. Front wheel ABS was just too complex and expensive to bother with on those older trucks so they stuck a half assed crappy system on the back just to be able to claim "this has ABS!".

If you want to replace the valve it's a crapshoot. You won't find a new one but "usually" you can find remanufactured units and that's where the crapshoot comes in. A reman unit has almost the same chance of being bad out of the box as the one you have now. You are gambling plain and simple.

As sad as it sounds, it might be worth going to the junkyard and finding one where the system looks clean and grab the valve and any parts you can (sensor, control etc). Just check that the master cylinder and all the brake lines are still sealed. If anything was open just pass and keep looking. Shouldn't cost you more than $20-30 bucks at a u-pull yard if that for all the ABS components for ranger a RABS system. Sometimes junkyard stuff is literally just a better option than remanufactured parts. Still gambling, but you can check parts out first and it's about 1/10th the cost to take the chance.

 

[Ranger305]

So after some trial and error, as well as noticing I don't like the feel of the brake pedal (sometimes feels a little soft, other times ok), I unplugged the RABS valve on the fender and the vibrating/dropping pedal is gone and the pedal is more consistent. I'm also not fully convinced the back brakes are fully working. From all that, I suspect the valve is gunked or rusted up internally. I can clean this one and hope for the best or I can replace it. I'd prefer to buy a new/reman one, but it looks like they are NLA, even though the Cardone 12-029 for 89-98 trucks looks like a perfect match. Anyone swap one of these things on a later truck? 2000 was the last year of this system it looks like.

 

[Ranger305]

After digging around, the part number for all years is the same if you drop the year codes off the front and the revisions off the end.

 

[RonD]

After digging around, the part number for all years is the same if you drop the year codes off the front and the revisions off the end.

Yes, Ford has the actual part number in the middle (year/model)-(part number)-(revision)

In this case, RABS valve is the part, same number can be used for any Ford Vehicle of any year, and Rangers might be totally different than F250 but has the same (part number)

So the year and model can matter when looking for matching parts

 

[Dirtman]

The river option is looking better and better ain't it?

 

[Ranger305]

I thought about it for a minute, lol. Just part of working on these things. I just finished restoring my '92 that I've had for 27 years. This 2000 isn't going to beat me that easy.

Just to update this story and add the fix for anyone who finds this searching for solution-

Talked to Ford parts, and, as expected the RABS is NLA, there are none left anywhere, and there is no alternative.

Went to the local you pull yard this morning (I can spend hours there, and have) and pulled 2 RABS units, one from a 99 and one from a 2000. Yard charged me $5 each. Side score- the cruise on this truck hadn't gotten the recall fuse link yet and one of the donor trucks had it. Side score 2- same donor truck had the throttle cable I needed to complete my list of parts needed to swap a later model plastic plenum on my '92 3.0 to get a bit more torque.

Stopped on the way home and picked up a couple new rear wheel cylinders.

Put one of the RABS units in, replaced the wheel cylinders (old one weren't frozen, but had water in the boot and the bore was rusty. Flushed it all out with synthetic Dot4.

Most importantly, fluid is now flowing to the back brakes, they seem to work properly, and the truck now stops like it should. The pedal now feels much more consistent on firmness.

Secondarily, the clicking in the dash is gone. On a slow, dragging stop, you feel the solenoids "click" once through the pedal and the wheels stop. On a harder stop, it doesn't happen. I never got an ABS light through any of this, and still don't have one.

Looked at the old unit and there is fluid under the rubber cap on the end indicating that fluid was seeping past the accumulator oring. I'll probably disassemble it and see what I find one day if I get bored. Going to go ahead and order new shoes, drums, and spring kits for it. They aren't worn out,, but wasn't excited about the condition of the shoes or drums. I'll feel much better refreshing the back brakes before I turn my Son loose with it. I did the front already.

That said thanks for the help everyone.

 

[RonD]

Good work

And thanks for the update

 

[Dirtman]

Drum brakes require routine adjustment and lubrication. People think they last forever so they never maintain them. When you don't maintain them they don't work, when they don't work they don't wear out, they don't wear out and people think they last forever...it's a viscous cycle of neglect...

Drums need love too!