sundstrand parking brake question

[chorusguy 227]

Certainly no expert here but it seems to me that the fragility of the parking brake is a ***** in the old wheelhorse armor.  I have a question about these.  Several tractors I own the parking brake is inoperable.  On a couple the parking brake lever won't even descend into the drive position.  Any clue what could be causing that?

 

Thanks

Edited February 19, 2016 by chorusguy
misspell

[chorusguy 227]

Funny.  I have been censored by red square.  The word that I typed where the asterisks are is c,h,I,n,k.  I guess it must be a bad word

[Daddy Don 907]

None of mine work either.

[Aldon 4,827]

Not sure if it is Pall or Pawl

 

Not sure if it is true for all models but the parking "Pall" is not built to stand abuse of use as a break but more like a mechanical anchor once motion is stopped. If engaged while moving, the  "pall" can become permanently damaged.

 

I read a thread a few months ago where someone modified and installed a beefed up version.  

Edited February 20, 2016 by Aldon

[953 nut 55,966]

Read over this thread, it may help.

Good info here too.

 

[Aldon 4,827]

The second link is the one I recalled...

[daveoman1966 3,762]

The Parking PAWL is designed to HOLD the tractor in a STOPPED position.  It is NOT to be used (engaged) when the tractor is in motion and only applied when at FULL STOP.  That is to say, NEVER pull up the lever while moving in either direction.   For the same reasons that you wouldn't put your car/truck auto trans  into PARK while moving, you shouldn't jerk up the lever in a PANIC STOP.   (Lecture ends...).

 

Every time the lever is pulled up when moving (when you hear that little annoying GRINDING sound), tiny bits of the parking PAWL (or the trans GEAR that it locks to) gets chipped away and into the trans fluid.  Eventually, the PAWL gets ground off to where is doesn't engage the gear anymore and the parking brake won't work because of that.   This is the likely condition that DADDY DON has with his tractors.   

 

These tiny, even microscopic, bits in the fluid pass thru BRASS components & pressure ports / valves of the HYDRO PUMP and the HYDRO MOTOR where they scar and gouge the mated machined surfaces... namely the 18 Piston Slippers and the 2 Valve Plates (and other parts). 

 

When these brass surfaces become scratched / gouged, the result is LOSS OF HYDRO PRESSURE, especially when the fluid reaches normal oper temps.  If your tractor seems to have good power when first started (cold) then looses power with every passing minute as the fluid heats up....you have worn internals as I am defining herein.

  

Inasmuch as the fluid (oil or ATF) is common to the pump and the motor, similar brass parts of each will become scored from metal chips and that is why it is necessary to rebuild BOTH the hydro pump and motor.  They contain nearly identical machined brass components and, accordingly, all need to be restored.  The pump END CAP and the GEROTOR SET may also be damaged but to a lesser extent as they are steel.  ps...another cause of damage is DIRT in the fluid.  Be extremely careful to keep dirt and debris of any sort from entering the refill spout when topping off or changing the fluid and filter.    

 

Here are a few pics of the damage caused by the floating particles in the trans fluid. Some of these are DEEP gouges and could not be completely removed.  

I've also posted a couple pics of the two types of parking PAWL(s).             

 

Edited February 20, 2016 by daveoman1966
spell errors...bad pic

[chorusguy 227]

Good post.  I know about not engaging thbrake while moving and never do.  When you resurface the mating parts, what compensates for the material you remove? In other words, what causes the two maring surfaces to come together?  Secondly, what is preventing the parking brake handle from descending into the drive position?  I can't push it down. It releases from park position but won't lower into the drive position.  Is it an internal issue or a linkage issue?

[pfrederi 17,913]

The slippers are really pistons. When you remove a bit of them and the valve plate they ride on the piston just moves a bit further out of its cylinder.  There are specs as to how much you can remove in the manual. 

 

The "parking brake handle" I think you are describing does 2 things.  When you pull it up it releases tension on the drive belt so the hydro pump stops and then it engages the parking pawl.  When you push it down it release the parking pawl and puts tension back on the drive belt to engage the hydro pump. You have to remove the drive belt cover to see if you linkages are all working and see if the spring is in place

[daveoman1966 3,762]

Just for clarity, here is the Sundstrand CYLINDER block and PISTON-SLIPPER assembly.  These are very similar for the hyd PUMP and MOTOR sections. 

There is a heavy spring inside the block that applies pressure between the piston slippers and the thrust washer as well as the cylinder block and opposing valve plate.  The whole thing is spring-loaded when the end cap is bolted to the cast iron base.  

The base of the cylinder(s) and the thrust washer(s) MAY also have scoring as well as the valve plate(s)that they ride on.    

Shown here is the HYD MOTOR section....the HYD PUMP components are very similar. 

Edited February 20, 2016 by daveoman1966
spell check

[ztnoo 2,298]

Dave,

Outstanding explanation, great pictures, and very graphic parts identification.

These trannies are still a little like voodoo medicine to me......full of mysteries and yet unexplored paths.

I'm tying to absorb everything offered.

Great posts!

 

Regards,

Steve