Brake operation

[Wykid]

So I'm looking buying a 07 shorty with international motor Allison transmission with 75000 miles. So what I found out is the yellow parking brake was acting up so he cut the cable in back to move it. I'm confused on how this system works when it's hydraulic and the yellow button is air. Anyone give me any input on this. I'm not stupid by any means but does it got a separate air system just for parking brake? Thanks all

[Seb1]

Hi Wykid, if your brake system is hydraulic, your parking brake switch on the dash is not pneumatic. It is electric. If your brake system is Wabco (most likely), when you pull the yellow knob to put parking brake on, it sends signal to the Wabco control module to release hydraulic pressure to the SAHR canister, which then, by the mean of a powerful spring, pulls the cable that activates the parking drum brake on the prop shaft.
Which cable was cut ? The cable from the SAHR canister to the parking drum brake on the prop shaft, or the cable from the dash mounted brake switch ?
In both cases, it is worisome, as you would not have any parking brake at all !
Seb

[Wykid]

I am not sure what one he cut yet. All he told me pretty much is the yellow button was acting up so he cut the cable in the back. A shop in n town told him it'll cost 1400 to fix. I've driven trucks for years with air brakes but hydraulic with this Wabco and SAHR is something new to me. Is it difficult to to work on and or fix? I'm hoping to get it home this week and it's not going any where for awhile snow coming for 8+ months. Thank you for the reply

[Seb1]

Check my thread on the topic of wabco hydraulic system. System by itself it not very complicated from a schematics standpoint point, but 2 components are expensive to replace if they fail : the parking brake SaHR canister (most likely what was quoted to him), and The complete system Hydraulic Control Unit (>$4000…). I have not replaced these myself, but got work done by the dealership service as this is safety related, so I cannot tell you how hard it is to do it yourself.
But again, it sounds like you have no operating parking brake. Danger !