Here's one for the HEF TLB Board... Our FDP08XXX CAT 420D 4x4 TLB has had an intermittent reverse issue for about 3 years now. In the beginning, I could get reverse engaged and working after warming up the Power Shuttle Shift tranny by moving forward. Once the fluid was hot, reverse would engage and work as long as the machine wasn't switched off for more than roughly 20 mins. As time went on, I had to lift all four wheels off of the ground, shift into 3rd or 4th and engage the reverse shuttle shift. At first, the wheels didn't spin backwards, but, after some time at a fairly high RPM, the reverse would engage and I could lower the machine and move the machine backwards. Like before, the machine couldn't be switched off for more than about 20 mins. If it was kept running, for example, the reverse would work all day long. Back when this first started to interfere with our mill work, a couple of years ago, I replaced the reverse hydraulic solenoid, at the solenoid block (under the front floor plate). As this didn't work, I checked the 12VDC signal that comes from the shuttle shift switch assembly itself and confirmed that the 12VDC voltage was where it was supposed to be for both directions - forward and reverse. Forward has always engaged, so, obviously, the 12VDC voltage was present each and every time the tranny was shifted into Forward. The interesting bit here is that the same 12VDC signal was also present when the shift assembly was shifted in Reverse! I'm no CAT tranny genius, but this tells me that the enclosed shuttle shift switch, mounted to the steering column, is doing what it's supposed to. This being the case, I pulled the metal filter screen from the bottom of the (English Built) CAT 192-0844 4x4 transmission and found a few pieces of rubbery debris trapped in the filter. I even swapped the solenoids at the solenoid block and forward would still engage immediately. I didn't really know what to make of this, so I replaced the tranny fluid with the appropriate (Ultra $$$) CAT transmission fluid and tested the trans out. It seemed to work fairly well, right away, but the intermittent reverse issue quickly flared up again: so the solenoid replacement ended up as fail. After a fairly hard Winter 2025 season here, near the Berkshires of western Mass (USA), I started the machine. As usual, it started up fairly quickly (no heating element required). However, I had the machine lifted up off of the ground, shifted into 3rd gear reverse for about 20 minutes: and absolutely no reverse operation in the early days of Spring 2025! As I'm not exactly sure about how to do it, I haven't pressure-tested our 192-0844 yet. I don't have a service manual for the machine, but I ordered one - and it’s expected be here around April 7, 2025 (this coming Monday). The cheapest new 192-0844 4x4 tranny I could locate cost around $9K - before freight costs - and we simply don't have that kind of money available. Even the cheapest used 192-0844 4x4 tranny I could find would cost us over $4,500: and we really don't have that kind of money for a burnt-looking USED unit. I realize that its looking a lot like there's an internal clutch issue (or pump issue) with our tranny, but I'd still like to ask the CAT TLB experts about this before writing the machine off! It has about 4,400 operating hours on it, but about 80% of that time, to be honest, was as a light source during our long winters. If anyone has any thoughts about this problem, I'd really love to read them. This machine has been a reliable bona fide work tool for us - whether it be as a light source, a snow pusher or as a way to load our modest sawmill with logs (via its folding forks over the clamshell bucket), so it would be a real shame to write it off as a total loss. Thank you kindly for your time. P.S. - I'm not opposed to taking the 192-0844 out of the machine and having a look at the internals, but I really have no clue about what that would take. This is why I'd like to ask the CAT 420 4x4 and/or the CAT 416 4x4 folks before commiting to something that may turn out to be something that would require special tools or other equipment.
This is putting the cart before the horse IMHO. Before making any attempt to remove the transmission the decision to do so should be made on the basis of data-driven diagnostics, not some sort of hunch or the absence of ideas.
Well, it doesn’t sound like an electrical problem and it doesn’t sound like a burned clutch problem. When you changed the oil, did it look dark and smell burned? It sounds like you have internal leakage in the reverse circuit, could be from a sticky valve or something else in the control valve. I’ve also seen control valve gaskets blow out a small chunk and cause low pressure problems in circuits. Im definitely with Nige on this…..don’t pull the transmission without troubleshooting everything else first. The first thing I would do is pressure gauge the reverse port and see what you have in pressure to work with. This could be something very simple, it’s just a matter of finding it.