what Proportion valve to use

[[email protected]]

If we change our obs trucks to rear disc. Mine is a 1997 Tahoe .So it came with front disc and rear drum brakes. So if I add rear disc brakes what proportion valve should I use and keep abs.
Thanks in Advance

 

[spitanddirt]

I'm not completely sure that you would have to change anything with a rear disc conversion and factory equipped ABS on a 97. The ABS functionally takes the place of a proportioning valve. Your truck should not be equipped with a proportioning valve just like my 1996 is not. The casting is forged to accept the machining for a proportioning valve in the upper right hand corner in the picture, but it's just blank.

The metering valve, however is technically non-adjustable. The only way to make an adjustment would be to install a stiffer spring if one was available. A stiffer spring would effectively increase the pressure sent to the rear brakes before the fronts started to engage. The problem is that there is no documentation on this. These are only my observations after disassembly and examination of my ABS module during my brake line refit.

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[[email protected]]

This what they used on the bigger trucks that came with rear disc brakes, I was looking through a shop service manual and saw that they came with disc brakes on the 2500.

 

[delta_p]

The make disc/disc combination valves. That's probably what i would use for my 96 C1500 and i would remove the ABS. For the rear proportioning, I don't think you want it with rear discs since much higher pressure is needed than for the drums.

I know in the old SSBC disc conversion kit, they have you remove the proportioning valve from the combination valve block, take out the seal and the spring, and just put the valve stem back in. So it has basically been removed.

https://www.catalograck.com/ImgVD/SSB/A126-2.pdf

 

[Gibson]

The ABS functionally takes place of a proportioning valve.

Not so, ABS acts to dump pressure to a circuit that is locking up.
If the brakes are not locking up the ABS does nothing, and it has nothing to do with any proportioning between front and rear brakes.

The make disc/disc combination valves

This is the correct choice when changing the rear drums to discs.
With discs you want full line pressure available, the combination valve in a disc-drum setup is set to limit the rear line pressure to a certain amount to TRY to limit rear wheel lockup.
With rear discs you feed them the pressure, and let the ABS worry about lockup,, (that's what it's for).

 

[Schurkey]

The more-important question is why you'd convert to rear discs in the first place.

A rear-disc conversion is a whole mess of troubles; aftermarket conversions are generally horrible due to lack of caliper support from the cheap, flat brackets. And then there's the issues with the parking brake.

Better/simpler/cheaper to use upgraded rear drum brakes--dumping the "10 inch" leading/trailing shoe design for the bigger Duo-Servo system makes a nice and SIMPLE improvement, for example.

 

[Erik the Awful]

Drum brakes work fine, they just require more maintenance.

 

[[email protected]]

I went with the nbs rear disc brakes not aftermarket

 

[Pablo8100]

If we change our obs trucks to rear disc. Mine is a 1997 Tahoe .So it came with front disc and rear drum brakes. So if I add rear disc brakes what proportion valve should I use and keep abs.
Thanks in Advance

Did you ever figure it out? I did the little shop disc conversion, changed the booster, upgraded to NBS master cylinder, and took it too a shop to get it bled correctly and my brakes are still so spongy. This is the last thing I think will help me with my problem but was just wondering if it helped you changing the proportion valve

 

[Schurkey]

WHAT VEHICLE? What was the original brake code?

I did the little shop disc conversion,

You have my sympathy.

changed the booster,

To WHAT? FROM what?

upgraded to NBS master cylinder,

Unless you also got rid of the low-drag front calipers, this was another big mistake.

'Course, maybe your truck didn't have low-drag calipers. (JB/JD7 and higher as used on 2500/3500.)

and took it too a shop to get it bled correctly and my brakes are still so spongy. This is the last thing I think will help me with my problem but was just wondering if it helped you changing the proportion valve

Unless they've got trapped air--and that's really unlikely--a proportioning valve, or a combination valve is almost certainly NOT the problem.

Did they bleed the ABS with a scan tool? Did you properly bench-bleed the master cylinder before installation? Bench bleeding takes a lot more effort than most folks put into it.

Is the instrument cluster "BRAKE" or "ABS" light lit-up?