Have a rare 4x4 a25c that has been working in a quarry, has recently developed a problem where it starts to bounce uncontrollably when it gets into the higher gears, you can also notice the machine making this motion in first and second but would throw you from the seat when you get up to speed Have also noticed the front tyres wearing suddenly very quickly, disconnected the feed for the front diff thinking that this had maybe stuck on but nothing changed Any ideas what this could be?
bent wheel, bent axle, out of round tire?
Front diff locked up.?
This or a few teeth missing off one of the ring gears, or the bull gear in the diff lock on #2 axle. Have you checked propshaft u-joints and slip yokes? Checked axle and dropbox oils for "babies?" Are you on hard packed clay or sloppy slurry mud or sand? Have someone film the machine from a safe distance from either side. See if you can observe a wheel experiencing lock-up or being impacted with forward momentum. Is your air pressure constant or is it dropping out ? Do each of your locks work properly. Longitudinal diff lock, inter-axle diff lock, 6x6 full lock. Are your A-stay bushings clapped out, what about the hitch? When was it last checked and adjusted? Just re-read your original post, 4x4. Same things to consider, just 1 less axle.
Had similar issue with an A35D. Turned out to be the A-Stay. Your issue sounds a little more violent than the one I worked on though. If you have a boom truck,crane ,forklift or even a loader to pick up on the nose to check/adjust the hitch/a-stay and other attachments to the axle rule that out. If there really bad you would probably hear/feel it banging when it was bouncing.
That symptom sounds to me as though the front diff isn't differentiating, or whatever. I came across the exact same weird (and very rapid) tyre wear symptoms once but on a rear axle. The diff was shot. Have you tried draining the front axle oil or at least inspecting the magnetic plugs.?
Thanks for the reply’s, The machine usually works in a clay environment but has been working in a quarry lately which has really brought the problem to light due to the better traction Tyres all correct size, nothing bent or twisted Prop shafts all straight and all hardy splicers are tight with no play Checked Dropbox, transmission, front and back diffs, all good oil levels and no shinny deposits, air supply seems to be fine and checked diaphragm in longitudinal diff lock all seems fine Getting air pressure to front and rear diffs at the axles When turning the machine you can feel it tight to turn almost as if the rear diff is locked on for half a revolution then releases However noticed steering had gotten heavier so disconnected shaft to front diffs from Dropbox and the problem went away To me this either means the front diff is giving bother or the rear diff is locking up and pushing the nose straight (maybe causing excess tyre wear) Any thoughts? Thanks
Also lifted the machine off the ground with two excavators and drove it in all gears, all diffs seem to work as supposed to, no banging or unusual sounds
With wheels off the ground, if you spin one wheel on an axle, the opposing wheel should counter-rotate. If a dog clutch is hanging the wheels will try to rotate the same direction. With prop shafts disconnected. If the props are still attached, they simply won't turn. Good luck How about, for testing, capping off air lines to axle locks. Maybe the solenoid valve is allowing unwanted air and applying on the fly.
Opened front diff bung again this morning and found this
Otherwise oil was clean with no fillings or bits
I wouldn't sweat that fuzz. As long as you can drag a magnet across the bottom and not hook " a big one" I'd write it off as normal shedding. No chunks, no sweat. She's an old girl after all.
Checked diffs again this afternoon with the machine lifted off the ground, everything working both with diffs on and off Coming to the conclusion that it’s the longitudinal diff lock is stuck on, getting a good air supply to it but is is a possibility that it’s stuck on? Is it spring returned? If so has anyone a parts diagram of this? Can it be stripped from the top of drop box or is it a box out job? Thanks
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A25c 4x4 Sn 5350v9047
Can you confirm that you checked the diffs as per FWF's post #9 by first removing the prop shafts to both front and rear diffs. When you rotated a wheel in one direction the opposite one rotated the other way for both front and rear axles.?
Nige, with machine off the ground both diffs have one wheel rotating foward and one backwards once spun my hand, once diff locks are engaged they both spin the same direction, once locks are disengaged they go back to previous, to me this would rule out that the diffs sticking? Also checked for air trying to activate on the fly but nothing unless the diff locks are applied
With mechanical inspection of the driveline complete, we're gonna have to look at less obvious possibilities,. Is there a possibility that the trans retarder is coming in? Volvo's trans retarder is pretty strong and doesn't really make a sound unlike the exhaust retarded. Does the contronics display work on your machine? Are there error codes present? Holy crap!!! I just remembered, on the 40s this was common, I don't see the 25s being any different. The output speed sensor on the dropbox. If that rascal goes bad, the computer doesn't know what's going on and tries to go to 2nd with the trans. It was usually pretty violent. The resistance should be 1020 +/- 10% depending on temperature. Its a simple pulse sensor. Easy to check, pain in the *** to do it. The connection is just bullet points with a rubber/plastic umbrella. It might be loose. We're branching out into possibilities because you haven't discovered a mechanical failure in the obvious places. Please advise on the contronics. Good luck and happy hunting
I’m not sure if someone has doctored the contronics or if she never came out with one but it doesn’t seem to exist How is the trans retarder activated? Is there an easy way to check this?
It would have been in the overhead. It was an option. They would tell you what the computer sees. The only other methods I can think of are measure voltage to retarder valve or measure pressure for retarder. I don't have the port location/ID in front of me this moment, I'll look later this afternoon.
Looks like port P5. See notes in attached document. I've also attached electrical checks for the trans solenoids. The measurements should be at the fuse/PCB connectors. Hope this helps Good luck.
Thanks for the help much appreciated! The machine is away to work today but will be back tomorrow and get it checked We have removed the front driveshaft to the front axle and the problem has disappeared To me I think that the longitudinal diff is locked on causing the machine to fight with itself on good ground where grip is no issue, the steering is light compared to very heavy with the shaft connected, however I will check the trans retarder and see what it says I might be wrong but my gut feeling points me to the drop box, however it’s only a guess