I replaced the transmission pump on a 2006 988H because the pump was leaking. The machine sat for about a week because the radiator cores were being repaired got everything back together moved the loader 20 feet to the lube area topped off the transmission then serviced the diffs and finals moved the machine as it goes forward fine then I went to put it into reverse and it when into reverse a few times when I was draining the finals the last final the machine wouldn't go into reverse. I shut down the machine started it back up and the machine went into reverse. I messed with it today hooked up ET and there are no active codes. I noticed that it will go into reverse at first start up but after a couple forward and reverse application it won't move when placed into reverse. I did go through the gears manually and I could feel the transmission shifting but it wasn't moving. The machine moves fine in forward. So I was wondering if there could be air in the system since I just changed the pump? I am stumped on what to do I am pretty confident its pressure problem but I doesn't understand why it will go only in forward but not reverse. Also if anyone has any info on hows these transmission work that would be awesome. Please any help is much . Thank you
Did you check the clutch pressures at taps located behind cab?
Have you checked the transmission oil level with it running? Would need to look at the sight gauge but think it should be about 1/4 to 1/3 of the way up when running. Also when shifting through gears does the driveshaft between the converter and transmission stop spinning when shifted into gear, both when it does move and when it will not move? You have ET so have you run the clutch calibration?
So, out of curiosity, when you put it in reverse, and it doesn't go, what gear does it say it is in on the digital display? If it says it's in reverse, completely disregard this.
Sounds like a sticking modulation valve for the reverse clutch. I would try swapping the valves from another clutch. These electric modulating valves are very touchy and don't take much to make them stick. They won't throw a code if it's a problem on the mechanical side of the valve. What is the serial number?
Swapping the valves is not so easy to do on a 988h The cab needs removed So checking pressures would be my first step for the problem Here is a picture of one I worked on a few months ago
Mechanic1, We had a 988H where I just retired from, the valve body on top of trans. was just starting to leak a little oil probably from dried out orings. So as I'm not there any more I missed out on that project! How big a job is it to pull the cab? I had one off a 980G II a couple years back and that was not really that hard. Disconnecting the AC hoses without loosing charge was the worst part, quick connects had never be apart! On the 988H did have to replace all the hoses in the area between the TC and Trans. including a reman trans pump and input shaft seal on trans. a year ago. That eliminated 98% of the drips.
That was a day and a half to remove cab trans and converter Machine had #6 clutch failure
So not too bad a job! Hard to tell from picture but looks to be a pretty clean machine. Sucks that you had to do it outside, nice work on sunny day but might not be so nice when going back together!
Wasn't to bad coming out,had to hustle though because trans was being picked up the next day 1st thing in the morning I do all outside work. The weather was about 95 and very high humidity that day. The bad part was I vent on vacation and the first day back I had to put it back in. It took 2 and half days to install and do the calibrations
So I wonder if he got the cab off and the modulation valve replaced yet. If it's like the cab on the 980g it takes very little time to remove it. Unless you get a stubborn cab mount bolt.