Combo valves backinaday

[Rust_never_sleeps]

Didn't want to derail the conversation in another thread, so I thought I'd throw this out for discussion, ICAC:

So, were the OEM combo valves from '71 onward actually application specific?
Seems to me that GM being GM, they would have used a generic product and bought them by the freight car

[dmjlambert]

I think they were application specific. Member Keith Seymore has shown us the actual engineering charts for these trucks on a couple of threads, such as this one:
https://67-72chevytrucks.com/vboard/....php?p=8909230
As you can see in the charts, depending on the model of truck there are different specs for the proportioning valve.

[dmjlambert]

I suppose they could have screwed in the appropriate proportioning valve onto the back of a generic combination valve, and the metering and shuttle valves are all the same.

[Rust_never_sleeps]

Originally Posted by dmjlambert

I think they were application specific. Member Keith Seymore has shown us the actual engineering charts for these trucks on a couple of threads, such as this one:
https://67-72chevytrucks.com/vboard/....php?p=8909230
As you can see in the charts, depending on the model of truck there are different specs for the proportioning valve.

Ah, interesting reference, thanks.
So, in '71, all metering valves were 138#, with prop valves at 300# or 470#
but in '72 all metering valves were at 75# and all prop valves at 300#

To slither further down the rabbithole, I wonder what values passenger cars used, and what values the now ubiquitous PV2/PV4 parts use.

[Rust_never_sleeps]

Originally Posted by dmjlambert

I suppose they could have screwed in the appropriate proportioning valve onto the back of a generic combination valve, and the metering and shuttle valves are all the same.

Sure, the components just screw in, and in turn the components prolly use standard housing+valve but different springs, BUT from GM's perspective the combo valves came with different part numbers spec'd from multiple vendors