New to CAT and this forum. Recently purchased '06 CAT 420D (4200 hrs, 4WD, FNR shifter, 4 speed) that has strong and very responsive hoe and bucket hydraulics, but slows to a crawl when climbing even a very modest incline at full power. RPMs hold steady under load, but will only climb an incline in 1st gear; 2nd gear will bring it practically to a stop. Speeds and responsiveness seem normal on level ground, with AWD engaging as it should. Transmission fluid (TDTO-30) and filter were changed, with screen cleaned, but fluid looked/smelled good with no filings on magnets. I sure hope this isn't normal for a CAT backhoe, but don't believe it is. I'm not sure where to start looking to diagnose/fix the problem. Suggestions very much appreciated.
sounds like torque convertor is going out clean strainer on shuttle and see if it helps
The screen at the bottom of the transmission pan was essentially clean, with very little sediment and no apparent debris from internal parts. Is that the screen you're referencing?
I believe I would check clutch pressure
yes
OK. Thanks!
How good did the fluid look? Could be previous owner was having issues and pulled pan and screen was full of clutch material and cleaned and refilled. Then sold.
Is the oil light or dark in colour.? Does it smell burned..?
I've wondered the same thing. It did look to be in good shape, with no burnt smell to the oil, and the filter had clearly not been changed in a long time. So, it appeared somebody changed the oil, but not the filter.
The oil seemed to be in good condition, with no burned smell. Filter looked like it had been on there for quite a while, so it's possible they just changed oil and not filter.
I had a local repairman tell me that it might be due to a dirty fuel filter, not allowing sufficient fuel flow when needed. I intend to change it tomorrow. If that doesn't help, I'll move on to clutch pressure. Thanks.
What does the air filter look like? Do you have any exhaust leaks before the turbo?
How much time on a backhoe?
Did you check for leaks? if the transmission sucks in air you have the same effect. after replacing leaking seals on the transmission you lift the axles in up and let the wheel spin slowly in all gears and forward and reverse to bleed the air out of the system. As you don't know what happened to the machine before the chance that this is the solution is not too likely , but it is much cheaper than a rebuild
It seems very unclear if you have a engine problem or a transmosson problem. Is the engine lugging down or is the machine just slowing and the engine rpm holds steady
he said rpms hold steady under load
4200 hrs
Air filter is good; haven't checked for exhaust leaks, but will do so today. Thanks.
I seen but hes also got advice to change the fuel filters
To all, I replaced the fuel filter today and it made a huge difference. I'm not certain that I've resolved all of the problem associated with lack of power under load, but it went a long way toward bringing the ground speed back up to about what i believe should be normal. Thanks to all. P.S. It solved one problem, but raised another, which I might start in a new thread if i can't figure it out. Thanks, again. This forum feedback has been quite helpful.
420 have past the weight of a Cat 436. The horsepower of 85 to weight 8 tons could be making it feel gut less sounds like it was cared for. Common to have to shift don't think about doing it while shuttling dirt, 420f I was on 17000lbs & bump in power still fall on it face on inclines.
Good point. I had thought about moving up to a heavier unit with 100+ hp, but was concerned that it might be too heavy for my pastures, etc. on the farm. I have a 115 hp tractor for most of my farm work and even it is challenged on these Ozark hills when pulling a load.
I've thought a lot about your comment and do think the relatively low HP is hurting me on my hilly ground in the Ozarks. My main tractor is a 115 HP AWD (~5 ton) and it strains hard to pull a 15' Bushhog up these hills with any speed at all. If I ever trade up, I'll be moving up to a 100 HP machine or better! I really appreciate your help.
Past company,boss had a big new Cat 450 rental hoe 200hrs dropped off at his ranch to use & from there I had to drive it out to the site 20mi/32km boy that hoe was a heavy dog 29k lbs with 130hp same 4.4L engine as 420f. The 450 in 4th/3rd was working the whole way going down the road having stop once water temp pegged out start of small hill 1st was it, slow crawl.4spd doesn't help on hills 1&2 work jump to 3&4 road speed need a 2 speed rear end like the old old John Deere hoes were industrial farm tractors with twin stick high/low+4spd or 500A was a 8 speed power shift. 420D is a fine digger just roading with new hoes is not great.
Don’t forget to replace the fuel pick up tube filter.