13" Rear Discs with BAER Brake Valve

[bry593]

After I installed 13" rear discs on my '71 C20 Chevy pickup, any panic stops resulted in the rear brakes locking up. If you ever had this happen when trying to avoid a wreck, you know why I chose to install a BAER proportioning valve, p/n 2000035.

https://baer.com/Baer-adjustable-pro...e-2000035.html

Turns out, the valve wasn't enough. I adjusted it all the way out and still mildly skidded the rear tires. I swapped pickup to van calipers thereby reducing piston size from 2.00" to 1.75". Now the braking is excellent and all parts are genuine GM aside from the USA made brake valve.

More info can be found at this video:
https://www.youtube.com/watch?v=_WWka224rgs

[RichardJ]

TTT

Excellent explanation of the operation of the Proportioning Valve. I would argue that it is even better than the videos offered by most, if not all the people that sell those valves.

Your pressure graphs based on your own pressure testing blew me away.
Outstanding.
I was surprised that the second knee point wasn't higher with the two valves in series.

You missed an opportunity to explain how a Residual Pressure valve on the output of the MC would have eliminated any problem resulting from the installed height of the PV and plumbing.

Lack of comments by others on this forum is disturbing.

[bry593]

Thanks brother, I appreciate it.

You are correct, a residual would prevent fluid drain back to the bowl. However, I suspect fluid would not really drain back unless there is a leak. For instance, next time you drink a coke, push the straw down into the beverage and put your thumb over the end. Lift it up and the Coke stays in the straw. Even so, a good design will have the lines lower than the reservoir.

Being that I retained my original combination valve, I get to keep three things:

• Pressure relief valve on front circuit ensures back brakes hit first, reducing brake dive
• Brake warning light warns of pressure loss in front or rear circuits
• Original pressure reducing valve which compounds the effects of the BAER valve

[RichardJ]

>> I suspect fluid would not really drain back unless there is a leak.<<

That leak would be air entering past the wheel cylinder seals with a MC mounted below the floor and require a 10# residual Valve or 2# with disc calipers. It wouldn't so much matter the height of the plumbing, but the MC height vs the wheel cyl/caliper height.


>> * Pressure relief valve on front circuit ensures back brakes hit first <<
Hold-back or Metering Valve.

[bry593]

Originally Posted by RichardJ

>> I suspect fluid would not really drain back unless there is a leak.<<
>> * Pressure relief valve on front circuit ensures back brakes hit first <<
Hold-back or Metering Valve.

Exactly. In '69 it was a hold-off valve, but in '70 a metering valve. This is when GM began eliminating residuals in the master cylinder rear brake port. The '71 C20 did not come with a residual. That said, you never know what the aftermarket will do and so I verified there was no residual valve during the disc swap.

[geezer#99]

After the change to the rear calliper size, where did you end up in the adjustment on the prop valve. You were all the way out, where is it set now?

[bry593]

Backed all the way out (ccw), then in four full turns.

I nice feature is being able to turn it in a couple turns when towing a trailer.

[geezer#99]

How many turns from all the way out to all the way in?
Just curious.
I used one made by wilwood on my 56 210 disc/drum. Found it to be a bit touchy in the setting.

[bry593]

Originally Posted by geezer#99

How many turns from all the way out to all the way in?
Just curious.
I used one made by wilwood on my 56 210 disc/drum. Found it to be a bit touchy in the setting.

I don't remember exactly, but it was more than you'd expect. Maybe 10 turns...

[MikeB]

Pressure reducing valve? I've always heard them referred to as hold-off valves that delay the application of full pressure to the front calipers.