Cat 950h no park brake in reverse

Simon75 · Mar 16, 2016

Hi all
Have a cat 950h at work, just noticed the other day that the park brake does not hold at all in reverse but works perfectly in forward direction. Have had one fitter tell me the park brake is designed to hold in forwards only, and another said it should work in both directions. Park brake has been checked and no faults found. I find it hard to believe cat would make a loader with a park brake that only works in one direction, can any one shed any Light on this?

kshansen · Mar 16, 2016

Simon75 said:
Hi all
Have a cat 950h at work, just noticed the other day that the park brake does not hold at all in reverse but works perfectly in forward direction. Have had one fitter tell me the park brake is designed to hold in forwards only, and another said it should work in both directions. Park brake has been checked and no faults found. I find it hard to believe cat would make a loader with a park brake that only works in one direction, can any one shed any Light on this?

Right off I'd stay clear of that fitter! Sure some parking brakes will hold a little better in one direction than the other but it should hold. I'll have to see if I can access the Cat spec's on the 950H, a serial No. would help or at least the first part with the letters! Quick look at SIS and there are at least 7 different S/N prefixes for a 950H!

PAcattech · Mar 16, 2016

The parking brake should prevent machine movement in both directions. cat spec it should hold in third gear at full throttle . there is and adjustment for the brake shoes but when they don't hold its usually a problem with the shoes and adjusting them doesnt usually help

kshansen · Mar 16, 2016

Here's what I found for one version of the 950H Loader:

Testing Procedure

Start the engine. Raise the bucket slightly.
Engage the parking brake. Place the autoshift control switch in the MANUAL position. Place the transmission direction and speed control lever in the THIRD SPEED FORWARD position.
Note: When the transmission is shifted to the THIRD SPEED FORWARD position and the parking brake is engaged a Warning Category 3 will occur.

Gradually increase the engine speed to high idle. The machine should not move.
Reduce the engine speed to low idle. Place the transmission direction and speed control lever in the NEUTRAL position.
Lower the bucket to the ground. Stop the engine.

Note it does say to test in forward direction but I would say it should hold just as good in reverse.

Mark250 · Mar 16, 2016

I have seen this before, and after dismantling the park brake assembly I have found one brake shoe worn down as compared to the other shoe,
this is only a thought but on tear down of these p/brake assembly's they are full of grease from an over greased drive line centre bearing. I believe the excess grease attracts contamination eg dirt sand or what ever and slowly wears one shoe out in the prominate direction of travel and as the park brake assembly is of the self energising type it is possible to have more brake force in one direction than the other
any way that's my two cents worth
Mark

kshansen · Mar 16, 2016

I was looking through the info on the one 950H I looked up trying to find the procedure for "Burnishing new shoes" I know there is one for the 980G as I had to do it a couple years back on one of ours. I know it involved running at I believe full speed in third gear and then engaging the parking brake and repeating maybe three times then letting it cool down. Could not see that procedure for the 950H.

Nige · Mar 17, 2016

kshansen said:
I was looking through the info on the one 950H I looked up trying to find the procedure for "Burnishing new shoes" I know there is one for the 980G as I had to do it a couple years back on one of ours. I know it involved running at I believe full speed in third gear and then engaging the parking brake and repeating maybe three times then letting it cool down. Could not see that procedure for the 950H.

SOP for the bigger machines Ken. You have to get new brake pads well cooked before they will work correctly.

Echoing what others have posted. The park brake should hold against full RPM in 3rd/4th gear depending if the loader has a 3 or a 4-speed transmission.

No-one has mentioned it here so I will - the park brake has a designed "drive through" facility to be used in case of emergency to extract the machine from a danger situation. It will burn up the park brake at the same time but it gets you out of trouble. The park brake should therefore not be expected to hold in first gear. I note that the OP was not specific regarding which gear he was using when he could drive through the park brake in reverse.

daterplant · Mar 17, 2016

I reckon all the answers you need are in this thread.
Get a competent mechanic let him read this thread, I'm sure he will then fix your park brake.

kshansen · Mar 17, 2016

Nige said:
SOP for the bigger machines Ken. You have to get new brake pads well cooked before they will work correctly.

I was aware of the "burning in" process for some brakes as I had done a similar procedure on the disc brakes of some of our haul trucks in the past. That "burning in" actually would get to the smoking stage. But knowing how good the parking brakes grabbed on the 980G's I had to read through the instructions a couple time to be sure I read it right! I also showed my boss the service manual first just to be sure he did not think I was crazy. After all that it was rather uneventful when I did it. And the brakes worked great in the end. They would hold easy one gear lower than the test procedure required.

Cat 950h no park brake in reverse

Simon75

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kshansen

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PAcattech

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kshansen

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Mark250

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kshansen

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Nige

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daterplant

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kshansen

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