During the last storm my sons Case 621B (Ser # JAK0020131) approx 1995 vintage stopped moving forward unexpectedly while moving snow at a theater. No previous issues or symptoms with forward gear. Reverse gear works fine. First step was trying to identify which solenoid was the Forward on the valve body. I have a screen shot of a YouTube video in which a 621 trans was repaired and in fresh paint someone used a paint pen and wrote F, R, 1,2,3 near the solenoids - see image. So my assumption is the upper solenoid closest to the engine is the F or forward solenoid. Problem is that the upper solenoid box is near frame rail and the cab mounting post. Access is extremely difficult and basically only with one hand. Verified fuse to transmission is good and that one side of each solenoid is getting 28v. Since the machine is outside in a mall parking lot and in Michigan winter i did not want to attempt complete removal of the solenoid enclosure till I was more confident of the root cause as re-install with wiring connections to solenoid was going to be a major challenge due to accessibility. Tried jumping the Blue wire to ground on the F solenoid to simulate control signal (F_N_R in F with engine running) but got no forward movement nor arc when grounding the test lead. My suspicion is that the coil is open circuit. I measured about 48 ohms across the F solenoid with all leads connected but really want to remove one lead to isolate any parallel ground paths to get a true coil resistance reading - problem is cold fingers and tight space trying to reinstall eyelets made me wonder if the juice was worth the squeeze. Can anyone familiar with the machine and ZF trans verify the F solenoid is top rear most solenoid in valve body? Is there a controller or ECU that actually makes the ground path available to the solenoid to engage it or does the dash shift lever provide the ground to the solenoid? Do people agree that with the engine running, park brake off, and operator in seat with gear shift in F if I ground the Blue wire at the "F" solenoid the machine should move forward? Any better suggestions on diagnosis and access to the extremely tight packaging to make a fix if the solenoid needs replacing? Thanks in advance. Tony Tony
The last photo is Clark trans you have a ZF Did any others gears work? No one solenoid controls one range Except 4th . It has a controller behind the seat a panel there first turn off master battery and turn if back on and try it. they used two shifters Clark has straight handle zf is tilted You could have a shifter problem.
Steve - thanks for the initial reply, So I assumed it was a ZF in my loader - the last picture in my post was from a YouTube video that was the closest match to what i appeared to have. Went back to the machine and looked closer found a blue tag near front lower part of trans - looks like it a CLARK. The machine will not move Forward in any gear selected from the F-N-R lever. The machine will operate in reverse only. Transmission fuse is good. Not aware of a controller behind the seat. Does CLARK use a controller? CLARK model # from tag 13HR28443-501 Serial # HUSA22789
So you have what I believe is what they call a Clark 28000 Series transmission. They used tons of them in the mining industry and also in Timberjack Skidders. I have done a total rebuild on 1 of them. They usually have a valve block with mutiple solenoids that give the gears desired. One of the solenoids could be burn't or the valve is jammed. Dont take any of it apart without first cleaning really good with varsol or brakleen and high presssure air to blow dirt away. The little spools in the solenoids do not like any dirt. Have you removed the transmission filter and cut open the filter to examine the paper, would be a good idea. The one I did had one clutch with a blown seal and transmission was no go till fixed. You will need to check for charge pump pressure, as low pressure is hard on clutches. Would be handy to have manual on it. Simon C
Hi Simon - thanks for your input. I found some info online but the CLARK manual calls out 28000 series buts its a 1968 manual. So its close but valve body slightly different - the 621 Loader is a 1992-1993 vintage its close but not exact. Still trying to determine how those 28v solenoids are activated - does the dash mounted F-N-R provide a ground to one side of the solenoid or is there a controller (ECU) running the solenoids. All was running fine with no prevent symptoms. Still searching for a wiring diagram. Tony
What does the trans pressure gauge show in dash??when shifted to different gears? //