others be able to say better, but when i went and looked at i want to say 14 specific TLB (tractor loader backhoes) i found off of tractorhouse.com and sister site machinetrader.com and some local papers. i did this all in one day looking at them 20 plus hour day needless to say.
a 3 cylinder diesel vs a 4 cylinder diesel. was a huge difference in power. regardless of manufacture make or model. i mean ya get into them and took them for a test spin up into some dirt piles or like. and just night and day difference in power differences and reaction speeds.
the 555c TLB ended up getting and now have, ((was actually the very last one on the list i was going to look at))
i think is rated for 4200lbs in FEL and 2100LBS for the 12 foot BH.
it is a digging machine for sure.
==================
as far as actually finding a TLB, for what you are wanting, i would be looking for a construction TLB. meaning a single seat that ya pull a lever to switch between driving tractor and backhoe use.
as far as finding out if tractor is worth getting or not. after that day of test driving them all. i would suggest shut your eyes as far as how they look (rust, paint, etc...) ugly looking tractors on interent ran good while others look new barely ran. it was a mix of it all.
some had a lot of slope in the BH (backhoe). when i say slope, ya swing the BH left and/or right. and sudden stop and they would keep on going. or if ya raised BH all the way and sudden drop and sudden stop of levers. and the BH would just bounce all around.
same went with the loaders on them. but the BH are more imporant less slop the better.
as far as transmission, engine, rear end, and hydraulics. get in them, start them up let them idle for about 5 to 10 minutes to let them warm up, do a test drive of them.
run loader into the ground and see how much power there is to keep on pushing into ground to see about digging. run at all gear speeds, then do same thing with full bucket of dirt and see how the power is in all gear speeds. run the backhoe, no need to dig, just work everything 10 to 20 times. to get hot warm oil in all the cylinders and lines.
once ya done with the inital test drive, set the throttle half way to 3/4 and let it set for 30 minutes to an hour like that. then redo all your tests. and see if there is a difference. on a couple of the TLB i tested i remember a decrease in power.
when you are all done with tests, raise the FEL (front end loader) up all the way, and do same thing with backhoe and the Turn OFF the tractor. and wait for 30 minutes and see how far they come down. the more they drop the more likely valves, seals, etc... are worn out.
the 555c just the main largest cylinder for BH has a small leak. and over 24 to 48hour period will drop down to ground. but over the initial 30 minutes you can hear it slowly drop, as it grinds and moves within the joints of it. the lock pin to lock the BH up when driving some were down line before i got it. look like it got hung up on something and tore the pin out. and was never fixed. so i am guessing all the bouncing around. caused extra strain on seals and valves. which is result of this. but beyond that. it all works.
==============
if ya serious about TLB, be willing to drive 3 hours away. and test drive a few older ones. so you get a better idea of things.
once ya get one, get a shop manual, the 555c TLB shop manual i have is about 5 to 7 inches thick and very detailed info in how to tear stuff apart, check things and then steps to put it all back together.
