Engine/Transmission (1998.5 - 2002) master cylinder??

[cmills]

Let me try to describe this problem see if anyone can help. The rear brakes on my truck seem to have a mind of their own, they will work perfectly fine one stop, and then the next time I stop they will seem to be working fine and then its like they all the sudden release and all I have is the front brakes for a couple seconds then they might start working again until I finally come to a complete stop. And other times it seems like they are grabbing and then releasing very rapidly to the point where the whole truck starts "bucking or shaking". I thought this might be caused by the drums being out of round but if it was that I would think it would do it all the time, right?



Could the master cylinder be bad and be causing these problems? Its the only the thing left that I know to check. It does have new wheel cylinders on it and nothing is leaking and getting on the brakes like brake fluid or gear lube.



Any help would be appreciated,



Cory

 

[B.G. Smith]

Sounds like tha ABS system might be acting up. Have you had the ABS red light come on? You don't have different size tires front to back do you? I think on the 3/4 ton there is a little mechanism attached to the left rear spring and the frame that varies the braking to the rear wheels according to the load being carried. Don't think the master cylinder would cause those symtoms. bg

 

[cmills]

Thanks, No, the ABS light has not come on at all, the tires are all the same size and the proportioning valve ( not sure what the correct name is) is hooked up and looks ok.



I'm just looking for ideas because I sure don't have any.





Thanks again,

Cory

 

[B.G. Smith]

You might consider taking it to an auto parts place and getting them to check for fault codes, might be something there if it is the ABS?? bg

 

[wcjp]

You have ABS and new rear brake wheel cylinders. Is it necessary on this truck to hook to a scan tool to cycle the ABS pump to purge of air? Opening the brake system on some newer vehicles requires a trip to the dealer. I recommend consulting the manual on purging the brake system with ABS.

 

[cmills]

according to the manual I should only have to bleed the rear brakes since that is the only place I had lines disconnected and since the master cylinder never ran out of fluid. As soon as I can I'll take it and see if it has any codes stored.

 

[Road Dog]

It sounds like the ABS on my '98. If it has rear-wheel ABS (standard) then the ABS sensor is the speedo sensor is on the rear diff. The next time it happens check your speed -- if it's fallen to zero then there's no signal and the sensor or connector needs work. Sometimes a good connector cleaning is all it takes.

 

[cmills]

yeah, I've had the sensor fail a couple of times causing the speedometer not to work, but its working fine now, so I think its something else.

 

[Hackamore]

Check your front calipers and pads. Mine was doing the same. Also had a bad wheel bearing in the right front and it would buck and hop on take off. Replaced bearing and lubed caliper slide bolts and works like a champ, again. Hope this helps, Fabian

 

[TBartlett1]

The sensor for the rear abs is on the top of the rear differential and gets it's signal from a tone ring behind the ring gear.

It's possible there is contamination on the sensor from gear wear. Pull the sensor & check for contamination. If metal is found clean & reinstall & test drive. If it solves the problem great. In either case you should drain, clean & refill the differential or repair if there is gross contamination.

I would also check all connections for corrosion, especially those under the truck and use dielectric grease when you reassemble them.

tim

 

[cmills]

my problem is definitely coming from the rear, I could check the sensor, but the other times I have had problems with it the speedometer would bounce around and the ABS light would come on.

 

[TBartlett1]

It certainly is not the master cylinder from your description.

It sounds like the Speedo & abs may share a signal or a ground.

Get a manual with a complete wiring diagram or go to Mitchell auto repair & down load and print out the complete wiring diagram then start troubleshooting to find where the abs & Speedo share a common source or ground.

The wiring diagram will also tell you where all the ground points are located. A ground may look ok but may be bad, clean & grease all external grounds.

Having owned mine since new in 1990 I have had spliced connections buried deep in the wiring harness corrode and create intermittent problems, they are impossible to find without a shop manual or complete wire diagram.