Hydraulic parking brake indicating light switch

Pretty much everything on the bottom side of the coach: Steering, wheels, tires, brakes, suspension
jay
Posts: 9
Joined: Mon Dec 20, 2021 5:52 pm

Re: Hydraulic parking brake indicating light switch

Post by jay »

Makes sense. Thanks everyone for helping think it through. Will go searching tomorrow.
LeeTN
Posts: 18
Joined: Sun Oct 27, 2019 5:44 pm
Location: Eastern Georgia, USA

Re: Hydraulic parking brake indicating light switch

Post by LeeTN »

Jay,

I replaced mine (looked just like yours) about a year ago. You are correct in that the switch needs to withstand a considerable amount of pressure (upwards of 1000 psi). There are a lot of switches out there that look like that switch, but a built for pneumatic systems (air brakes) and have burst pressures of around 250 psi. The will work under hydraulic pressure for a time (months), but will blow soon. Mine blew on the interstate and emptied the hydraulic reservoir in just a few seconds. I lost power steering, but luckily the backup breaking system worked.

The only place I could find a switch designed for hydraulic fluid at that high pressure was onlinecomponents.com:

https://www.onlinecomponents.com/en/hon ... 94223.html

That part number has a burst pressure of 1250 psi.

They stock them and have fast shipping. BUT... they are very expensive now ($151.00). When I got mine, they were $50, so I bought two (one for a spare). Looks like Walmart can get them for around $50:

https://www.walmart.com/ip/76068-B00000 ... /879805069

Good luck and I hope this helps.

Lee
'93 40' Continental (Oshcosh Chassis) -- 300 Cummins -- Allison 6spd
Lee
1993 Continental 40'
Oshkosh Chassis -- Cummins 300 -- Allison 6sp
jay
Posts: 9
Joined: Mon Dec 20, 2021 5:52 pm

Re: Hydraulic parking brake indicating light switch

Post by jay »

Hey Lee, Thanks. Could have saved a lot of trouble. Went to 6 different auto parts stores, a bus parts shop and a heavy duty truck repair. The original switch was manufactured by Hobbs Corp. They were bought out by Honeywell. These switches are normally closed and set to open at 35 psi. Rated to 1250 psi. The superseded honeywell p/n is 76063-00000350-01. they have screw terminals so will have to make a couple of adapters since there's no way you'll be able to get to the screws once the switch is installed. I'm taking you're advice and getting 2. Great advice!
Thanks,
Jay
TDJohn
Posts: 552
Joined: Sun Oct 27, 2019 11:34 pm

Re: Hydraulic parking brake indicating light switch

Post by TDJohn »

If you can not reach the screws for the wire terminals, you could easily attach some short wire pig tails, screw them on ahead of time before installing the switch and then attach the wires to the coach using blade connectors. This will make for easy replacement, if the new part ever fails.

One low cost option one can consider in a pinch, if the switch is not readily available is to install, or carry as an emergency backup, a 1/8-27 NPT plug. This would stop the leak and get you back on the road in a pinch. The only thing would be is your parking brake light would stay on, unless you ground out the wire.


Here is a link to the same switch but with blade connectors.

https://www.radwell.com/en-US/Buy/HONEY ... 000400-01/

Here is a Honeywell PDF file for this 5000 series switch. See the notes on the spec sheet, it states that switches under 25psi sensing pressure are only rated for 750psi burst pressure, and the ones that are 25psi and above are rated for 1250psi burst pressure. So if the normal switch is not in stock, one could get a switch that senses a higher pressure without causing any problems. If anything, the higher pressure switch will give you an earlier warning, is hydraulic pressure starts to drop in the system.

https://sensing.honeywell.com/honeywell ... tsheet.pdf
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.
jay
Posts: 9
Joined: Mon Dec 20, 2021 5:52 pm

Re: Hydraulic parking brake indicating light switch

Post by jay »

Hey John,
Pretty much what I ended up doing. Made up pigtail adapters for the screw on terminals and installed the switch. WORKS GREAT! Ordered a spade terminal switch for a spare. I am very appreciative for all the great imputs. Was really stressing over what should be a relatively easy fix. Thanks everyone for the quality help. Thinking of Willie right now since I'm on the road again!
Thanks again,
Jay
TDJohn
Posts: 552
Joined: Sun Oct 27, 2019 11:34 pm

Re: Hydraulic parking brake indicating light switch

Post by TDJohn »

Your stress and concern is warranted, as you experienced, being out of hydraulic fluid is a dangerous nightmare situation and one doesn't want to experience a repeat by blowing out a switch that was not rated for this high pressure application. When in doubt, it is better to temporarily eliminate the switch than risk another disaster. I'm glad you were able to escape disaster.
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.
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