Question Re ABS Systems 99 2500

Hi All!
Seem to recall that there were two ABS systems available on the 99's?? Can anyone refresh my memory on the systems that were available...was one a two
wheel system and the other a full four wheel system??
TIA
Fred
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Yes - standard was the rear-wheel anti-lock, or RWAL. This uses a single rear-wheel speed sensor, and upon impending lockup, it restricts the pressure to the rear brakes. If that doesn't correct the problem, the RWAL dump valve kicks in, which dumps pressure from the rear system. This has the net effect of feeling like the brakes "let go", and isn't very pleasant.
The optional 4-wheel ABS system adds a sensor at each front wheel, and a pump. Whenver wheel slippage is detected, the ABS pump kicks in, which quickly applies/releases hydraulic pressure on both front and rear systems. The net effect is slightly reduced braking effectiveness, but is much more controllable than the RWAL system.
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Hey thanks Tom!
Couple other questions...is there an easy way to tell which system you have without pulling things apart?
Also...just for general maitenance purposes I want to bleed and flush the brake fluid in the system and replace it with fresh fluid...will this cause a code fault on the system that will need to be reset?
TIA
Fred

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Look on the hub of the front...you will see the brake line going to the caliper and an additional black line approximately 1/4" in diameter...well, if you have front anti-lock you will see it...otherwise you won't.
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If there's a big square pump sitting on the driver's side fender, next to the brake master cylinder, with brake lines running to and from it, you have 4WABS. If not, and there' just a slim little black box (maybe 6"x4"x1"), you have the RWAL system.

As long as you don't run the resevoir dry, no. The problem with a 4W ABS system comes when you introduce air into the pump. Then you need a dealer (or a shop with a DRB3 scan tool) to cycle the ABS pump to bleed the air.
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