91 RABS light on after new master cylinder

Hello group,
91 Navajo 4WD 353K. It keeps going so I keep driving it. Needed brakes so I
took it in and had the front pads and rotors replaced. Rears were OK. Also
needed a master cylinder which was done the following day. Soon as the
master cylinder was replaced the rear antilock light came on. This warning
light has never come on before. Shop says the RABS module is bad. Searching
around the web, seems like the preferred fix is just remove the warning
lightbulb. My question is, is there something about changing the master
cylinder that might cause the light to come on? Bad sensor on the old one?
New one? RABS module just picked that moment to die?

Thanks for the information. What you're saying makes sense. The guys at the
"brake-o-rama" said the module was bad because it wouldn't give them a code.
I'll see if I can get a flash code off the diagnostic connector and have my
regular mechanic check it out when he gets back from vacation.

"Ashton Crusher" > wrote in message
...
> On Mon, 1 Dec 2008 20:44:25 -0800, "David" >
> wrote:
>
>>Hello group,
>>91 Navajo 4WD 353K. It keeps going so I keep driving it. Needed brakes so
>>I
>>took it in and had the front pads and rotors replaced. Rears were OK. Also
>>needed a master cylinder which was done the following day. Soon as the
>>master cylinder was replaced the rear antilock light came on. This warning
>>light has never come on before. Shop says the RABS module is bad.
>>Searching
>>around the web, seems like the preferred fix is just remove the warning
>>lightbulb. My question is, is there something about changing the master
>>cylinder that might cause the light to come on? Bad sensor on the old one?
>>New one? RABS module just picked that moment to die?
>>
>>
>>
>
> If by "rabs module" they mean the electronic box in the rear side
> panel I would wager that's not the problem. I'm not saying they never
> go back but I've never heard of one going bad. What I have heard of
> going bad is the RABS valve that's on the drivers side frame rail next
> to the fuel filter. I've had to replace mine twice. Also, the speed
> sensor in the differential (top center front area with a wire or two
> attached to it) also goes bad, replace one of those on two different
> explorers.
>
> As to the coincidence of the Master Cylinder repair and the RABS light
> coming on... I don't think it's a coincidence. My experience suggests
> that in normal driving where the rear brakes hardly do anything that
> the system will seem fine. But if something happens to put some
> decent pressure or brake fluid flow thru that valve it moves the
> innards and then they stick and generate a fault. Or something like
> that. One of the times mine "went bad" was when I decided to "test"
> to see if the rear anti-lock was still working!!! After a good hard
> brake application, unlike the way the brakes are normally used, the
> light came on. Turning the truck off and then back on would reset it
> but after that it got worse and worse until almost any braking caused
> the light to go on. Replacing the RABS valve fixed that both times.
> The valves are about $140 if you buy them yourself from a discount
> place such as www.rockauto.com .Installing them can be a pain, they
> are located in a very hard to get to area, especially if you don't
> have a lift. I paid the local shop to put mine in the second time.
> The truck really needs the anti lock working if you want to be able to
> stay in control on wet pavement in a panic stop.