Re: super m brakes

Posted by Janicholson on March 03, 2013 at 07:49:25 from (74.60.94.18):

In Reply to: super m brakes posted by Rick deere on March 03, 2013 at 06:07:54:

The common issues are easy to diagnose:
If the pedal pushes about like the right brake, but does nothing, then these are possible:
1- The left differential shaft )bull pinion) seal is bad and leaking 90wt into the disks.
2- The disks and surfaces are glazed and have so little friction that they do not have any servo action (self help to power through geometry of the ramp and balls of the expander plate system). They will just barely apply.
3- The adjustment (pull rod length shortened) is maxed out and the disks plus wear on the metal surfaces is causing the expander links to pull at a steep angle making the system inoperative. There is a specification for good operation repair.
4- The ramps and balls of the expander are worn with wear pits or non round balls.

IF the pedal is rock hard and doesn"t move:
1- The pedal shaft is frozen in the transmission casting.
2- the left brake pull links to the expander are rusted tight (less likely)
3- The ramps and balls are rusted together. (also less likely)

Fixes Pedal moves:
#1: Remove the rod and housing as described by Bob. Clean things up with brake cleaner. Replace seals on the shaft ( no need to pull the pinion carrier)(use metal screws and a slide hammer to pull out the old seal. Polish the shaft round and round, not in and out, with 320 or finer paper. The new one will be thinner and should be put on an un-worn spot on the shaft, two can be used with chassis grease packed between them to lube the outer seal.
Heating the disks with a propane torch till all the oil is fried out (but not burnt out in a massive fire, control the flame to prevent radical heat).
#2:Deglaze the surfaces with 150 grit silicon carbide paper. Use non directional motion to distribute the sanding pattern evenly.
#3: To be done on all numbers for good action at the pedal. Measure the thickness of the stack of internal components including the two disks and the expander when it is as thin as it will go (relaxed). This can be done with a caliper or micrometer on individual components and added, or the stack can be piled up on the bench and measured.
Next measure the depth of the cover housing from mounting surface to friction surface with a depth gauge, or a pop sickle stick and knife mark then measure with caliper. These should be measured several places and averaged to + or - .005" of accuracy. Add any depth from wear on the bull pinion carrier (tractor surface).
Subtract the stack number from the depth number. There should be between .025" and .060" clearance.
If more, a combination of new disks, and machining of the housing mating surface to reduce this clearance is needed. The pull links must be at a shallow angle to have the correct geometry to pull the expander halves up the ramps on the balls. If the clearance is too great in the stack/housing the links are so far pulled that they have little mechanical advantage.
#4 If the balls are out of round more than .002, they should be replaced. If there are wear pits on the ramp grooves, that cannot be sanded or polished out the expander should be replaced.

Repair if pedal is stuck:
Remove right brake lever from right side.
Unclamp and remove the left brake pedal from shaft (woodruf Key).
Remove the brake actuator and clutch pedal from the left side.
Use PB Blaster or your favorite penetrating juice on the shaft and holes on both sides. Heat the shaft with a propane torch (keeps temps safe) and tap it back and forth side to side with a brass hammer, or an aluminum buffer between a steel hammer and the end of the shaft. Repeat till loose. Polish and remove the shaft. Put new Orings on it grease the opening and replace the shaft and parts.
#2 and #3 Remove and clean the rust and make sure things are free to move.
Always:::
Clean and deburr the splines on the pinion shaft.
Use PTFE (Tri-Flow spray or similar dry powder spray) on the splines. The balls and ramps can be coated with a "molecule" thick film of LPS rust inhibitor, or similar. but not enough to flow or collect dust from the disks.
Make sure the weird little springs on the expander disks are in good shape, not stretched, and not thin from rust.
Adjust the pedal for about one to 1.5 inches of travel (match the other brake) to assure good pedal action.
If the performance changes, R and R the housing to clean as needed. Do not use the tractor with inoperative brakes.

With confidence, Jim

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