Cat 966 F Brake oil pressure

[pedrocar]

Hi we have a 966f just resealed the front brakes , but the brake oil press light & alarm are going off looking at the book says its the brake oil press overstroke switch that has to be manually reset anyone ever done one ? s/n 8BG02280

 

[kshansen]

Resetting is pretty easy. But the real question is WHY it needs to be reset.

Most common reasons would be loss of brake oil/fluid, bad master cylinder or an electrical problem.

Loss of oil/fluid could be either an external leak from a broken hose, line or fitting. An internal leak could be seals in one or more of the wheel brakes leaking into the axle housing.

Electrical problem could be a bad switch or wiring among other things.

First thing I would be checking is to see if one or more of the reservoirs was low on fluid/oil. One quick way to know where to begin is to look at the master cylinders there will be one for each axle. The section with the problem will have a pin sticking out under the warning light switch. If one is low you then need to learn why it is low and fix that problem! Once that problem is corrected then system needs to be bled and then the switch reset!

Almost failed to mention that the problem could also be a bad seal on the piston near the arrow #11 in picture below

I almost hesitate to explain how to reset as some people think that is the "cure" to the problem and will just go ahead and run it like that till the brakes don't work and someone gets killed!

See picture below, the switch is actuated by the rod(#6) I have colored red. Switch is numbered #3. The reset procedure is to simply push that rod back in flush with the surface of the casting. Some times it will push in hard or not at all if there is lots of dirt or rust on the casting or rod. Also often the switch will not reset even with the rod pushed back in due again to dirt and rust and may need to be replaced.


I can not stress strongly enough that just resetting and running the machine is asking for trouble when you need the brakes in an emergency!

 

[Nige]

Ken,
In my experience a brake pack reseal (as per the OP) and the subsequent brake bleeding operation will usually overstroke the master cylinder and cause the alarm to go off. (New haul trucks you can't bleed the brakes without setting off the overstroke alarm no matter how careful you are.) doesn't necessarily mean that there is anything wrong, but it would be worthwhile to check.
I do agree with you that simply resetting the switch should not be the "guaranteed fix". as suggested the brake system needs a through check, hopefully it is the bleeding operation that has triggered the overstroke alarm.

 

[kshansen]

Sorry don't know how I missed that the front brakes had been resealed. I could make excuses about things going on in my life these days but that would just be an excuse for something that should not happen! My bad!

Hard to believe that someone who has the skills needed to reseal the brakes on one of these has not had the experience or knowledge of how those sensors work. Of all the complicated electronic BS on equipment these days they are one of the easiest to figure out! But if one has never had the problem I guess there would be no reason to know about it!

Like I did say I would not be too surprised if the switch does not reset even with the plunger pushed back in place. I've seen more than a few that end up being a one time use switch due to them sitting for years with no movement. In a pinch, like out in the bush, one could remove the switch and spray some penetrating oil in the plunger end and work it in and out to free it up.

pedrocar, sorry for getting a bit far off from your actual question but maybe someone else will benefit from this thread in the future

 

[Nige]

Hijacking the thread I know but I recall an accident investigation years ago on a haul truck that had lost the brakes where I found that not one but all three of the overstroke switches had been jumpered out of the alarm circuit, so when the rotochambers actually did overstroke the alarm stayed obstinately silent. Hard to believe but true.

Agreed, those switches tend to stick and if it was mine I'd think about pulling the switch(es) and giving them a good dose of penetrating oil before even trying to reset the pins.

 

[pedrocar]

Thanks wasnt sure if sender needed to be removed in order to reset ,will lube up and reset.
brakes are good now stop on a dime .

 

[kshansen]

Thanks wasnt sure if sender needed to be removed in order to reset ,will lube up and reset.
brakes are good now stop on a dime .

If the switch and the rod are in good condition it should take just a fairly easy push with your finger to move back in place.

 

[kshansen]

Here are the Cat Recommended tests for both the service brakes and the parking brakes:

Service Brake Test Procedure
Be sure the area around the machine is clear of personnel and obstructions.

Be sure the steering frame lock link is in the stored position.

Test the service brakes on a dry, level surface.

Fasten the seat belt before testing the brakes.

1. Start the engine, and raise the bucket slightly.

2. Place the transmission neutralizer switch in the OFF position.

3. Apply the service brake and release the parking brake.

4. Move the transmission to third speed forward.

5. Gradually increase the engine speed to high idle. The machine should not move.

6. Reduce the engine speed to low idle, move the transmission to NEUTRAL. Engage the parking brake, lower the bucket to the ground and stop the engine.

Parking Brake Test Procedure
Be sure the area around the machine is clear of personnel and obstructions.

Be sure the steering frame lock link is in the stored position.

Test the brakes on a dry, level surface.

Fasten the seat belt before performing the following brake test.

1. Start the engine, and raise the bucket slightly.

NOTE: The following step will produce a Warning Category 3. The parking brake indicator light will come on, the action lamp will flash, and the action alarm will sound.

2. With the parking brake engaged, move the transmission to third speed forward.

NOTE: The parking brake indicator light should come on.

3. Gradually increase the engine speed to high idle. The machine should not move.

If the machine begins to move, reduce the engine speed immediately and apply the service brakes.

4. Reduce the engine speed, move the transmission to NEUTRAL. Lower the bucket to the ground and stop the engine.

And this one that some might find hard to believe about new parking brake shoes:

NOTE: If new brake shoes were installed, engage the secondary brake to make three successive stops from third speed FORWARD at maximum speed. Allow the brakes to cool to ambient temperature after the third stop, and repeat Steps 1 through 9.

Steps 1 through 9 are the adjustment procedures for parking brake.

 

[pedrocar]

Thanks for all your advice , last owners kept filling up the reservoir to a point where the diff was full of oil because of the bypass the axel has been a reman at some stage when removing the seals the white plastic one has a protruding edge on one side that was fitted incorrectly , new ones fitted correctly brakes all bled now work well

 

[Nige]

Ah-ha - "shaving" the white Teflon brake piston seal during installation. Won't be the first time, surely won't be the last. If you don't have tooling you need about 8 arms to make sure that white seal doesn't get caught when you reinstall the resealed piston back into the housing. I've seen dealer techs who do nothing but rebuild brakes day in, day out do the same thing.

 

[kshansen]

guess that is one "problem" with internal brakes like these, nothing shows on the outside to let you know you screwed up. The old 988 87A loaders with the bladder brakes let you know fast! Shave off one of those little orings on the nipples to the bladder and nice new brake pads soaked in oil the first time you hit the brakes!

 

[Nige]

The internal ones usually tell you there's a problem when you pull the oil level plug in the axle and a gazillion gallons of oil lands on the ground ......

 

[kshansen]

The internal ones usually tell you there's a problem when you pull the oil level plug in the axle and a gazillion gallons of oil lands on the ground ......

True but that can take several days and someone not smart enough to know why the little reservoir needs topping up every day if it is an air over hydraulic system. The straight hydraulic systems can be harder to catch before the oil is pushing out the breather on the axle if there is one!

 

[pedrocar]

Thats how it happened Nige removed the plug got covered in oil