Hydrolic park brake switch. | MotorhomeFun | The Motorhome Support and Social Network

Hydrolic park brake switch.

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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
 
Feb 2, 2015
1,603
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we are still learning
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

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Aug 26, 2007
38,315
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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.

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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
should have said 1993 fleetwood bounder 5.9 cummins oshkosh chasisjonathan and RV parkbrake picture 213.JPG jonathan and RV parkbrake picture 214.JPG
 
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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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
 
Feb 2, 2015
1,603
3,880
Staffordshire
Funster No
34,975
MH
A motorhome!
Exp
we are still learning
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

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Aug 6, 2013
9,271
9,197
Kendal, Cumbria
Funster No
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Exp
since 1999
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

LIFE MEMBER
Aug 10, 2008
75
69
Funster No
3,630
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

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Aug 26, 2007
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Since 2005
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.

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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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
 
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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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.
 
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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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

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pappajohn

LIFE MEMBER
Aug 26, 2007
38,315
29,929
Dark side of the moon
Funster No
172
Exp
Since 2005
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

LIFE MEMBER
Aug 26, 2007
38,315
29,929
Dark side of the moon
Funster No
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Exp
Since 2005
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.
 
Last edited:
Aug 6, 2013
9,271
9,197
Kendal, Cumbria
Funster No
27,352
MH
A Class
Exp
since 1999
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 :D. 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.

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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
Weird American stuff :D. 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.
 
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PeterCarole29

PeterCarole29

LIFE MEMBER
Jul 23, 2013
167
53
Colchester
Funster No
27,084
MH
Renault Master Fleetwood
Exp
20 years
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
 
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