Hydrolic park brake switch.

[PeterCarole29]

My handbrake has never worked. It had this fault when i bought the RV,but was told the brake shoes were worn out .This was not the case when i got it home found the cable from the auto gear change lever had snapped but there is something else wrong as when i got underneath pushing the lever rocker piece it still did not activate the hydraulic handbrake.
Can any one explain if the hydrolic switch is just a pressure switchto act as a warning of low pressure or does it play a part in activating th hand brake. my switch has the terminal broken.
Also do you need the engine running to work it

 

[Carolyn and Kev]

Hi there. I was under the impression that the parking brake (Handbrake) was actually a band on the drive side of an auto gearbox? It has nothing to do with the rear brakes if its an automatic. Hydraulic operation is applied to the drive shaft only on an auto gearbox. By that ..it clamps up the drive output shaft in the gearbox. Preventing drive until the switch to release the shaft is operated.
This prevents roll away and thus...acts as a hand brake

kev

 

[pappajohn]

Always thought a handbrake had to be failsafe.
If you have a fluid leak the handbrake will fail.
Mechanical brake is cable and air brakes default to ON if air leaks out.

 

[PeterCarole29]

should have said 1993 fleetwood bounder 5.9 cummins oshkosh chasis

 

[PeterCarole29]

Hi there. I was under the impression that the parking brake (Handbrake) was actually a band on the drive side of an auto gearbox? It has nothing to do with the rear brakes if its an automatic. Hydraulic operation is applied to the drive shaft only on an auto gearbox. By that ..it clamps up the drive output shaft in the gearbox. Preventing drive until the switch to release the shaft is operated.
This prevents roll away and thus...acts as a hand brake

kev

Yes this system works brake shoes inside its own drum on the prop shaft

^{_{Subscribers  do not see these advertisements}}

 

[Carolyn and Kev]

Yes this system works brake shoes inside its own drum on the prop shaft

With what you have said then..its not acting on an Auto gearbox ? So As Pappa john says.Always thought a handbrake had to be failsafe.
If you have a fluid leak the handbrake will fail.
Mechanical brake is cable and air brakes default to ON if air leaks out.

Basically...The switch you have is a "Pressure switch". It will see pressure when the ign is on. If the switch is on or has failed, it will either show light on or off dependent on how it failed. It will have a single terminal that will make and break contact . It may be set up ( DEPENDENT OF YOUR TRUCK) to be open or closed when ignition is on or off. Basically..engine running and system pressurised..light off. What truck do you have? When you say the parking brake is not working..Is it the light or the brake system that does not function correctly?
Sorry for all the questions..

KEV

 

[tonyidle]

Auto gearbox parking systems I have seen have nothing to do with hydraulics, drums, or shoes. The Park position on the autobox selector lever moves a pawl into engagement with, effectively, the gearbox output shaft to lock it in position and prevent rotation. It most definitely isn't any sort of brake and no attempt should be made to use it as such - it will protest quite loudly and may be damaged. The handbrake on the other hand, is a brake and can be used in an emergency to slow the vehicle. It will be cable operated and will be connected to a disc brake or a drum brake. If the main rear brakes are drum it will operate them mechanically; if they are discs it will operate the pads mechanically or operate an auxiliary drum inside or inboard of the discs. Electrically operated handbrakes work in the same way except the mechanism is operated by a servo - most often still via a Bowden cable.

 

[poacher]

Might be useful to post over on sister site - RVOC
Lots of Americans over there and am sure somebody will have the answer (have seen your make / model mentioned in other threads)

 

[pappajohn]

The handbrake on my RV was a total waste of metal.
It was Ford F53 chassis with a drum on propshaft brake.
How a single 10" drum brake is supposed to hold 7.5ton on a gradient is beyond me. It was only tested once at MOT, I didn't know any better at the time.
I was stood on the pedal and pulling on the steering wheel with all my might to reach the pass mark
I later found out its quite possible to rip out the gearbox rear extension casing doing that so subsequent tests they were told by all means test it with a decelerometer but it ain't going on the brake rollers.
They simply asked if it worked to which I obviously said yes.
It's a big job to replace/service the shoes, requiring removal of the gearbox extension casing and output shaft & bearings just to remove the drum.

 

[PeterCarole29]

With what you have said then..its not acting on an Auto gearbox ? So As Pappa john says.Always thought a handbrake had to be failsafe.
If you have a fluid leak the handbrake will fail.
Mechanical brake is cable and air brakes default to ON if air leaks out.

Basically...The switch you have is a "Pressure switch". It will see pressure when the ign is on. If the switch is on or has failed, it will either show light on or off dependent on how it failed. It will have a single terminal that will make and break contact . It may be set up ( DEPENDENT OF YOUR TRUCK) to be open or closed when ignition is on or off. Basically..engine running and system pressurised..light off. What truck do you have? When you say the parking brake is not working..Is it the light or the brake system that does not function correctly?
Sorry for all the questions..

KEV

The park brake system is not working.I am guessing one of the valves must be seized.
i know understand what the pressure switch does so can eliminate that as being the reason

^{_{Subscribers  do not see these advertisements}}

 

[PeterCarole29]

The handbrake on my RV was a total waste of metal.
It was Ford F53 chassis with a drum on propshaft brake.
How a single 10" drum brake is supposed to hold 7.5ton on a gradient is beyond me. It was only tested once at MOT, I didn't know any better at the time.
I was stood on the pedal and pulling on the steering wheel with all my might to reach the pass mark
I later found out its quite possible to rip out the gearbox rear extension casing doing that so subsequent tests they were told by all means test it with a decelerometer but it ain't going on the brake rollers.
They simply asked if it worked to which I obviously said yes.
It's a big job to replace/service the shoes, requiring removal of the gearbox extension casing and output shaft & bearings just to remove the drum.

Yes quite understand it may be useless. It looks like the shoes arent worn out .they are just not being activated via the cable. but would like it to work however bad.

 

[PeterCarole29]

Auto gearbox parking systems I have seen have nothing to do with hydraulics, drums, or shoes. The Park position on the autobox selector lever moves a pawl into engagement with, effectively, the gearbox output shaft to lock it in position and prevent rotation. It most definitely isn't any sort of brake and no attempt should be made to use it as such - it will protest quite loudly and may be damaged. The handbrake on the other hand, is a brake and can be used in an emergency to slow the vehicle. It will be cable operated and will be connected to a disc brake or a drum brake. If the main rear brakes are drum it will operate them mechanically; if they are discs it will operate the pads mechanically or operate an auxiliary drum inside or inboard of the discs. Electrically operated handbrakes work in the same way except the mechanism is operated by a servo - most often still via a Bowden cable.

My system is hydraulic oil pressured to some kind of 2 way valve and a cable in park position should activate some kind of spring that pulls another cable connected to shoes in a small drum on the drive shaft on the end of the auto box

 

[pappajohn]

My system is hydraulic oil pressured to some kind of 2 way valve and a cable in park position should activate some kind of spring that pulls another cable connected to shoes in a small drum on the drive shaft on the end of the auto box

Where is the hydraulic oil pressurised from

 

[pappajohn]

I'm beginning to understand how this works I think.
When you engage PARK with the gear shift a cable attached to the shifter operates a cam which in turn operates a hydraulic valve and piston (I believe the cam and valve are mounted on the chassis rail) from the gearbox which in turn pulls, via a spring, the brake cable to the drum brake.

If I'm correct it could be any of the various links.
The first cable could have broken or come detached
The cam may have broken
The hydraulic valve could be knackered
The spring attached to the piston could be broken
The final cable could be broken.

The only way to find out is crawl underneath with a torch and follow the various items back from the drum to the gear shifter.
Someone should be under there every year anyway to grease the prop shaft, King pins, steering links and steering box drop arm.

Ford are so much easier.
Foot Pedal, cable, drum. Hand lever to release.

 

[tonyidle]

My system is hydraulic oil pressured to some kind of 2 way valve and a cable in park position should activate some kind of spring that pulls another cable connected to shoes in a small drum on the drive shaft on the end of the auto box

Weird American stuff . I've just Googled Oshkosh handbrake & there's a bit of useful info if you look at photos. I didn't look too hard but two systems appear to exist: one uses a spring accumulator to operate the Parking brake & the other has a small chassis mounted hydraulic pump to pressurise the handbrake cylinder & hold the brake off - no pressure & the brake stays on.

^{_{Subscribers  do not see these advertisements}}

 

[PeterCarole29]

Weird American stuff . I've just Googled Oshkosh handbrake & there's a bit of useful info if you look at photos. I didn't look too hard but two systems appear to exist: one uses a spring accumulator to operate the Parking brake & the other has a small chassis mounted hydraulic pump to pressurise the handbrake cylinder & hold the brake off - no pressure & the brake stays on.

Thanks all sorry for not posting back earlier.I have now found the problem.
and it was a valve siezed.
Now i just need to source a new cable from the gear lever to the rear axle.

 

[PeterCarole29]

I'm beginning to understand how this works I think.
When you engage PARK with the gear shift a cable attached to the shifter operates a cam which in turn operates a hydraulic valve and piston (I believe the cam and valve are mounted on the chassis rail) from the gearbox which in turn pulls, via a spring, the brake cable to the drum brake.

If I'm correct it could be any of the various links.
The first cable could have broken or come detached
The cam may have broken
The hydraulic valve could be knackered
The spring attached to the piston could be broken
The final cable could be broken.

The only way to find out is crawl underneath with a torch and follow the various items back from the drum to the gear shifter.
Someone should be under there every year anyway to grease the prop shaft, King pins, steering links and steering box drop arm.

Ford are so much easier.
Foot Pedal, cable, drum. Hand lever to release.

Ford yes might be better but I,m stuck enjoying fixing all my many faults ?
I have now greased every part and will source a cable cheers

 

[pappajohn]

Duplicate post