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980H Pilot Pressure Problems

JakeHarrington

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Oct 5, 2016
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77
Location
Long Island NY
Also i forgot to mention this. I hooked up a second gauge today after we got the bucket moving. I hooked it up to test the pressure of the pilot pump goin to the brake valve. It gets to about 2100psi and then drops as the same time as when the pilot pressure up by the valves drops and spikes back up when you touch the brakes. Exactly like the pilot pressure except the pilot pressure is only at 450-500 psi
 

Nige

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Jun 22, 2011
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G..G..G..Granville.........!! Fetch your cloth.
You need to get one as close as possible to what you have right now. If it can be from another JMS-prefix machine so much the better, it really needs to come from another 980H at the very least
If it's not from a JMS machine, post the S/N it's coming from and I'll take a look to see how compatible it's likely to be.
 

JakeHarrington

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Oct 5, 2016
Messages
77
Location
Long Island NY
I haven't tracked down an ecm yet.
I did buy a new shuttle valve today and tried that. It made no difference.

I brought a mechanic in. and he went over it. he thinks that all the electrical stuff checks out and thinks the problem is the brake accumulators are shot. he wants to try recharging them tomorrow

Any thoughts?
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
It's worth a shot. Try a quick and dirty test of the accumulator efficiency. Start the engine and run at half speed for a couple of minutes to allow the accumulators to build up charge. You may even be able to hear the pump change note when they are fully charged. At that point stop the engine then afterwards turn the key back to the ON position. Press the right brake pedal to the floor then release it. Keep doing that, counting how many brake applications you make until the low brake pressure warning sounds. If the warning sounds in less than five cycles of pressing the brake pedal then the accumulators need recharging.
 

JakeHarrington

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Oct 5, 2016
Messages
77
Location
Long Island NY
I can tell you already before i even get back to the machine the alarm will sound in probably 3 pumps of the brake pedal.

What would you say a perfect accumulator amount of pumps are for a new accumulator?
and how hard is it to recharge then myself? I can definitely get my hands on some nitrogen cylinders?
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
Sounds like the accumulators are down on precharge.
It's not the nitrogen that will be the problem, it's the tooling that is needed to connect the nitrogen cylinder to the accumulator. Did the mechanic who was at the machine today say he had that tooling..?
I sent you a PM.
 

JakeHarrington

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Oct 5, 2016
Messages
77
Location
Long Island NY
He said he has everything just not sure what its all going to cost. Also not sure if its going to work. He thinks the accumulators will probably going to have to be replaced if they dropped the charge. Sounds like its gonna get expensive really fast if he is gonna be charging then replacing and then recharging and this might not even be my problem
 

Nige

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He said he has everything just not sure what its all going to cost. Also not sure if its going to work. He thinks the accumulators will probably going to have to be replaced if they dropped the charge.
These are piston-type accumulators and they work in a very simple way. Generally speaking they are very reliable. Also they are easily overhauled - if they need to be that is.
First thing to try would be a nitrogen gas recharge. I would say that in 99% of cases that would be all that was required.
If they do need to come apart and be re-sealed a kit is available. Parts manual page on the way.

Also this is potentially a safety issue. You need those accumulators working correctly in order to have a safe, correctly operating brake system.
 

Jonas302

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Jan 4, 2015
Messages
1,197
Location
mn
My thread on cat cylinders shows resealing the accumulators these would only hold one pump of the brake pedal I had charged them a few times last year to keep going until the off season if oil comes out the Schrader valve on the bottom needs reseal for sure

https://www.heavyequipmentforums.co...ylinder-bench-the-easy-way.81661/#post-878574

I got my nitrogen charging setup on ebay around $150 no regulator on the tank
 

JakeHarrington

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Oct 5, 2016
Messages
77
Location
Long Island NY
Thanks guys thats all very helpful. i took all the guards and stuff off the accumulators.
still waiting on this mechanic to come with his nitrogen setup. If he doesnt come monday im just going to buy tht setup off ebay.

i will definitely rebuild these myself if they dont hold the charge.
typica cat guy telling me to buy new accumulators for 1200 a piece rather than just resealing them. thanks for saving me on that.
 

Nige

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In conversations with Jake I recommended a seal kit, a replacement charging valve core (or indeed the complete charging valve), and the O-Ring for the charging valve that is not part of the accumulator seal kit. Even if only the valve core was replaced I would still remove the valve assembly and replace the O-Ring between it and the accumulator. That ought to cover every eventuality.

Seal kit appears at around $170, complete charging valve (includes core) $60, O-Ring $1, charging valve core alone $12.
 

Dbrg68

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May 8, 2019
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Usa
Where did you hook up the second gauge to see pilot pump oil going to the brake valve?
 

Mobiltech

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Jan 14, 2014
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Sask.
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Self employed Heavy duty mechanic
We have trouble in the cold weather with accumulator piston seals leaking. The pistons are aluminum on the ones I’ve rebuilt and they shrink faster than the steel tube they’re in so if the seals aren’t like new they leak down.
I’ve also noticed the aluminum piston will have a groove worn in them where the seals sit. If the groove is bad you will need to replace the piston.
You are also supposed to put some oil on the nitrogen side to lube the seals as they slide.
 
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