Hydraulic Parking Brake on '98?

[EngineerMike]

Got a call from a Cincinatti 98 Alpine owner who says he's got a hydraulic oil leak coming from his parking brake.
Anybody w/a '98 that can tell me what kind of parking brake you have?

[Wil Rathke]

We had a '99 that had a parking brake with a hydraulic cylinder that used pressure from the PS pump to compress the spring and release the parking brake. Never had a leak problem but the parking brake did not hold very well.

[Old Trucker]

Originally Posted by EngineerMike

Got a call from a Cincinatti 98 Alpine owner who says he's got a hydraulic oil leak coming from his parking brake.
Anybody w/a '98 that can tell me what kind of parking brake you have?

I am not sure on a 98, but I had a 99 and it was air activated. The Peterbilt shop in Cincinnati seemed to be familiar with this. Old trucker

[Algoma]

The basic operation of the hydraulic release is shown in Figure 2 of the Bendix TW-12 Service sheet.
The difference is that the Alpine uses a TW-11 control valve and the HR-1 relay operates a single transmission drum brake not the 2 axle brakes shown on the diagram. The Alpine also has a pressure switch connected to the TW-11 that operates the parking brake lamp on the dashboard. In fact I thought I had a leak in the control valve but it turned out it was the pressure switch that was leaking due to corrosion, so I would start with that.

[EngineerMike]

John- did you have luck finding a replacement pressure switch? If so, where, cost & part#?
Thanks for the doc, it explains operation very well. Mike

[Algoma]

Mike, I could not find an identical replacement but NAPA had one that fitted. It is part # 701-1606.