Hey everyone I'm looking for any help or advice I can get. I have a case 850g that will operate for a short period then suddenly lock up as if the parking brake was thrown in. We've pulled pressures and think we've narrowed it down to the transmission control valve part number 125588a4. This is the control valve that has the modulator. unfortunately this part is no longer available through case as the dozer is over 15 years old. Finding one of these has proved to be an impossibility. Does anyone know anybody that can repair this valve, anywhere where I might find one, or a work around solution? By the way we have replaced the parking brake solenoid already.
They like serial number to help,good luck.
Welcome to HEF @Hayden W "We've pulled pressures" ?? - are you saying you have tested the transmission pressures? If you have tested them - please let us know what you tested & what the pressures were. The park brake needs system pressure to overcome the spring plates in the brake housings. I would be teeing a gauge into that circuit to see what was happening & how that compares to main system pressure.
The Serial # on the machine is JJG0254687.
Thanks so much for the welcome ALR. the real issue seems to be transmission system pressure-no more than 100 lb full rpm in neutral measured at test port on filter. Torque converter and charge pump have been replaced-suction screen cleaned and ckecked for leakage. Pump relief checked. Main line from control valve plugged-pressure reading 400lb-system relief also replaced with new. Can torque converter relief or cooling and lube circuit be dumping pressure? If drain line from system and torque inlet valves is removed should there be drainage? What further steps should be taken?
I have seen the modulation spools in the transmission control valve give trouble. I can't recall the exact symptom I dealt with, but there was a problem with spring tension on one of the many springs located in the spool. Comparing springs between the two spools was required & until a new spring/s were aquired a simple stretch of the suspect spring made a difference to machine operation. There are two different types of spool used, depending on what you have in your machine. I can't recall exactly which spring was at fault, hopefully the culprit will be obvious to you......
If the modulation spool was leaking by wouldn’t it do it with the line blocked at the converter? With my pump deadhead test I have 400lbs
The circuit in this test includes pump filter and control valve.
Maybe there is a bad hemerage in one of the transmission seals (ie brake piston) causing loss of pressure? With the test gauge fitted try different gear shift ranges - all gears/ranges should read the same pressure. Maybe cap off oil supply to the park brake release fittings so that those seals are eliminated from the equation?
Doesn't seem that old that parts should be obsolete. I guess I'm fortunate my 86 machine is a Cat. Some parts are discontinued but I don't think powertrain components are a problem for getting parts. Hopefully it's nothing major you need to replace.
Cat will never let you down on parts
The neutral park applied reading is low
I wouldn't say that. People on here have stated Cat doesn't support older machines as good as they used to.
The have a vast search mechanism for used and even some new old stock, they'll go the distance to try and find what you need. When yo can't buy new....used seems like a good option.
I'm sorry Hayden, your diagnostic descriptions are a little brief, you have to remember were on the internet here bro... - did you say you fitted a new pressure regulator valve (#19)? - This "main line from" ? can you please describe more clearly what was done here, using the diagram below? I'm guessing you removed the hose marked #11 & fitted a gauge? Correct?
Cat is probably the best for supporting older machines but that doesn't mean everything is available that you might need. JD used to have a used parts network but not sure if they still do.