Jegs proportioning valve concerns

[Markmartin01]

Bypassing ABS on the rear only early ABS does not affect proportion. Those ABS pumps only break pressure in the line. Prop valve works the same either way. I'm sure the later OBS worked the same way.

 

[Gibson]

Think back to the old square-bodies,, discs on front, drums on rear, and they had no ABS, just a combo valve.
Every winter, with some snow or slippery conditions, you needed to put some sand bags or other weight over the rear axle to keep the rear brakes from locking-up before the fronts, and sending you sideways.
When you delete the rear only ABS, or the 4-wheel ABS, you're just removing any ability to modulate the rear brakes,, then rear lock-up largely depends upon rear axle weight/load.
The adjustable proportioning valves do nothing to stop this.
One of the main jobs of the combo valves in a disc/drum set-up is to prevent pressure to the front discs until the rear wheel cylinders have been supplied with enough fluid to push the shoes out against the drums to start some braking action,, when the rear pressure reaches a certain point, then the combo valve allows front brake pressure, while "kind of trying" to limit the rear pressure, but it does nothing to prevent rear wheel lock-up with different load or traction issues.

 

[delta_p]

I haven't looked up the ABS delete procedure in full but I know my '96 with 4WAL has a combination valve that the master cylinder routs into and it is bolted directly to the ABS package and then. I can see the combination valve on mine and in the image attached. Seems like an ABS delete would be to simply buy a combination valve and re-route or just make/machine an adapter to bolt to the combination valve on the after removing it from the ABS package.

You must be registered for see images attach

 

[Schurkey]

So I'm deleting the abs on my truck

1. WHAT VEHICLE???

2. WHY? Deleting ABS does not sound like a good plan. Granted, the RWAL on the earlier GMT400s was not a great system.

 

[Chris253]

This is for a 96 Chevrolet k1500.
Reason, The rear brakes suck and I plan on converting to rear discs but I need to drive it a little for now. This is a daily that doesn't tow or haul very often until summer which is mainly to haul my v45 around so not a lot of weight.

From what I read in order to get this to work on my 96 is to tee the front and connect it to the master cylinder and connect the rear to the prop valve and adjust it the way you would if converting to the rear discs (60/40?)since supposedly the prop valve that I bought is for that conversion.

 

[Schurkey]

You'd be way ahead to figure out WHY the rear brakes suck, and then fix the problem.

Rear disc conversions scare me, because typically it means the park brake is no longer functional. When it was me, I slapped a six-lug 3/4 ton axle under my K1500 which eliminated the goofy, tiny rear brakes and got me a stronger axle in the process, without screwing-up the park brake.

 

[Chris253]

The abs module is the problem.

https://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

 

[Chris253]

One of the most unnerving failures that can occur with this system is the loss of pedal when braking. The problem may feel like a bad master cylinder, but it may not be the master cylinder. The real problem may be a bad Electro Hydraulic (EH) valve in the rear wheel antilock brake system.


a small piece of dirt or rust gets into the unit, it may prevent the dump valve inside the EH valve from closing. The dump valve will then leak fluid into the accumulator when the brakes are applied. The misrouted fluid allows the pedal to drop, and the pedal may go all the way to the floor without applying the brakes. No ABS warning light or fault code will be found either because the limited diagnostics on this system can't tell if the dump valve is fully closed or not.

Wagner Brakes recommends the following procedure to find out if the problem is a bad master cylinder or a leaky EH valve in the RWAL system. To rule out a bad master cylinder, disconnect the rear brake line at the master cylinder and install a plug to block off the port. Have an assistant depress the brake pedal about an inch to purge any air from the outlet, then tighten the plug while the assistant holds the pedal in this position. After tightening the plug, continue to apply pressure to the pedal to prevent damage to the primary cup in the master cylinder as the cup moved across the vent port.

If the pedal holds and no longer drops, it isn't the master cylinder that's causing the problem.

Reconnect the brake line to the master cylinder and block off the outlet port on the EH valve. Then apply pressure to the brake pedal again to see if the pedal drops. If the pedal goes down, the EH valve is leaking fluid into the accumulator. The EH valve needs to be replaced.

 

[delta_p]

Didn't the '93 have a separate combination valve before the ABS. I'd use that or buy a combination valve for disc/disc or disc/drum.

T'ing up the front to the master cylinder seems a little rigged. You don't have the benefit of the front metering system found in the combination valve. The slightly delayed front brake apply from the metering is going to help keep the ass end of the truck from sliding out when the fronts grab first in panic because it was T'd to the MC. Even ABS package in the '96 was routed after the combination valve in the brake system.

With the combination valve there's already two ports on it for the front wheels and one for the rear. Or you can block a front port, use one, then T. It has the metering valve already to allow the rear brakes to contact before the front wheels, the limp mode piston to block fluid direction if the front or rear were to spring a leak, the dummy light switch, and the rear proportioning valve to limit rear pressure if the brakes are slammed. The can be bought for both disc/disc setup or disc/drum

I like this ABS delete because he put in the combination valve.

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[Chris253]

Didn't the '93 have a separate combination valve before the ABS. I'd use that or buy a combination valve for disc/disc or disc/drum.

T'ing up the front to the master cylinder seems a little rigged. You don't have the benefit of the front metering system found in the combination valve. The slightly delayed front brake apply from the metering is going to help keep the ass end of the truck from sliding out when the fronts grab first in panic because it was T'd to the MC. Even ABS package in the '96 was routed after the combination valve in the brake system.

With the combination valve there's already two ports on it for the front wheels and one for the rear. Or you can block a front port, use one, then T. It has the metering valve already to allow the rear brakes to contact before the front wheels, the limp mode piston to block fluid direction if the front or rear were to spring a leak, the dummy light switch, and the rear proportioning valve to limit rear pressure if the brakes are slammed. The can be bought for both disc/disc setup or disc/drum

I like this ABS delete because he put in the combination valve.

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I decided to use a proportioning valve off of a 94 pickup that had rwal but took just the valve and the smaller lines, so I'll be doing as you said.