I can't say I've experienced to much of this problem, I have come across it now and then mainly on older trucks such as Lansing Bagnals FOER where tilt cylinders are located under the truck, when the mast is in the verticle and the cylinder push rod is at 90*
To the mast, then if the driver runs into a solid obstacle then the cylinder rear weld may crack, and valve blocks only had one relief valve set to lift load requirements.
I've seen plenty of forks with toes curled up even banana shape, the best one one was when some wise driver drove a sixteen ton lift into a rail embankment trying to lift a section of rail track the forks broke clean of at the heels leaving them embedded in the embankment, still that may be moving way from the current subject.
I've seen plenty of bottom carriage rollers smashed due to forks being run into solid objects, and I've seen plenty of tilt cylinder rod ends broken of on Yale trucks due to in my opinion rod end being pinned to mast with pin and no grease nipple done for cheapness I suppose this led to rod end seizing to the mast, then when tilt was applied the piston rod flexed and eventually after a time broke at the rod end thread portion, never ever saw a bulletin to modifye and fit grease nipple and pin to sort that problem.

Regards Titus

My own opinion of why the cylinders crack at the tube base weld is because of "mast side sway".
The mast assembly has play in the mast trunnion bushing and mount clamps and this side sway tries in effect to break the tilt cylinder when stressed in that direction.
The tilt cylinder mounting pins prevent any sidewise stresses from being applied to the cylinder in the directions that the pins are free to move, but there are no pins or "give points" to stop the sidewise stresses of mast sway from being applied to the cylinder.
I believe that the sidewise stresses of mast sway weaken the weld enough that a crack begins to develop in the weld.
The crack then begins to spread below the actual surface of the weld and you never know where the crack will finally break through to the outside to reveal itself as a leak.
And rest assured, whatever small looking crack you actually do see on the surface, is only just that.......the portion of the crack that finally broke through.
I have welded literally hundreds of these cylinders on various Toyota, Komatsu, Mitsubishi trucks over the course of about 25 years.
I know from first hand experience that in many cases, the actual crack usually extends halfway (or more) around the weld circumference under the surface by the time it manifests itself to show as an oil leak.
Certified weldor? Yes I am.
The only reliable way to weld repair a cracked cylinder is to completely grind out, or otherwise cut out the old weld so that all material involved in the crack is removed.
That's not all there is to the process but I'm not going into a lot of extra detail about it unless there is a specific request for more.
Some people have blamed the cracking cylinders on "poor welding" by the cylinder OEM.
But I have doubts about that being a reason as cylinders I have welded (that cracked again later), did so only after approximately the same amount of time as it took for the OEM weld to fail. I have had some cylinders that I welded that have not yet (to my knowledge) cracked again.

There are likely a few factors involved in why some companies seem to have higher rates of tilt cylinder cracking than others, but I am betting that these factors result in a lot more brutal sidewise forces caused by mast side sway being applied to the cylinders than by hydraulic forces due to design or operator habits.

heh i suppose this subject can be debatable.
we all run into all sorts of various situations that cause issues like this varying from manufacturing flaws to operator abuse.
i guess my opinion was just one of many here.
But all in all everything that has been said can apply here.
Sure the operator uses the lift everyday and if he happens to notice something wrong he should report it... but in defense to what i said about the PM tech being the responsible party?
Well the driver of the lift is not a mechanic and most of the time he has no clue about these things, the PM tech is the trained person that is trained to recognise these problems and correct them at that time. Thats what i meant about that edward. :o)
As for how the operator drives the lift, sure it could be one of many reasons that would ultimately create the cause of the issue.

opinions are like... well we all know that analogy dont we ;o)

Scoop on the fly....Common to see driver`s pick up a load without stopping. I have seen many tilt cylinders leak at the welds.
Other than that, age, high hours and cold or hot environments are main cause. Many cracked cyls I replaced had bent mounting brackets or broken bolts, obvious impact damage. The reach cyls are affected the same way, as are the main lift cyls on many trucks.
Yes a few are bad welds, but most are excess pressure build up.
A Hydraulic rebuilder showed me how much these cylinders `Bulge`
when pressures hit the roof. These cyls balloon and flex more than we realize. The welds are the spots where there is little flexibility, so leaks will appear there first. I have fixed main cyls for bottom end cap leaks. Spot welds are temporary. A new bottom cap will fix it. The cracks appear with high hour trucks that go `dead head`each time the driver runs the lift to the top and forces it. You will see some blocks leak at welds where the cyl has a flow control valve in the block. That forces pressure too high on collapse as the restriction is biggest at the block. Only the right main cyl and left main free lift cyl cracks on a Raymond 7400 as they both have flow control valves.
We have successfully re-welded these block back on, but spot welding rarely works. The factory approves spot welding.

Gee, I finally get to disagree with Swoop... ;-) but I do have to agree with his assessment of 'repair vs replace' liability issues
Actually, from where I stand, the PM tech is far less the "responsible party" than the people doing and insuring proper operator training (and thus the operator), as an explanation of what is a a "full and complete" stroke, as part of the required daily inspection that is required as part of OSHA mandated safety training and daily pre-operational check out, just like showing the operator where the brake master cylinder reservoir and the controls are, we have to inform the operators of what to look for as 'not acceptable' ["tweaking" mast when tilting to the end of the stroke, or a side shifter that shifts more to one side and a brake master cylinder loosing fluid among others].
All that said, now back to the mechanical reasons for this. I have to firmly disagree with Swoop, here. The maladjustment of the tilt cylinders does not put more force on the rear of the cylinders, which is where this break we are talking about here, is happening. What it does is extend 1 cylinder further out, making the 1 rod longer, that force is pulling away from the operator. The force at the rear of the cylinder is a force coming towards the operator.
I think you will far more likely find the 'causing stress' {A.K.A. 'root cause'} to be a force pushing against the base of the cylinder, and may be caused by the wrong sleeve/stop and shims on the outside of the cylinder rod, or by the rod bottoming out inside the cylinder, or bulldozing or maybe even a far over expected pressure setting on the relief valve. (can the truck lift the rear wheels when lifting an over capacity load? is so, you may have found the cause),
As far as "the drivers running into something with the forks raised some what and that causes a high pressure spike inside the tube", this is not an operators error, but the relief valve being set too high, even if you overload the truck, if the relief valve is properly set, it would provide relief instantly for an over pressure "spike". A properly set relief valve will not permit lifting more than a 'rated capacity' load.
I also think, when you see this sort of abuse {and this is sure not normal wear}, it is important for everyone's safety, to insure the operators understand that the design of the forklift, (referring to the "Stability pyramid" and how you get out of the stable zone at height much quicker and with far more disastrous results at height than down low, which is required to be understood [as clearly required to be included in the OSHA mandated training]) expects the truck to do virtually all of the tilting when the load is close to the floor, not when it is raised above travel heights. maybe it is time to sell that customer on a more expert trainer's services than their 'in house' trainer (or maybe invite their 'in-house' trainer to "audit" a class of your trainer to help each of them better their training skills, rather than point a finger and admit the 'in-house' trainer is lacking skills), and explain that proper training can greatly lessen the cost of these sorts of repairs.
You may find that a number of these cylinders were previously rebuilt and reused the same nut on the inside that holds the piston to the rod (and that nut backed off and is now hitting the base end of the cylinder jug), or were not shimmed to keep the expected clearances, customer wanted more back tilt so someone ground down a % of an inch off the back tilt spacer, or over time that spacer/sleeve has 'somehow' gotten shorter.
Does anyone in your area use a protractor and a level to check the actual degrees of tilt on a truck?

the rear mount end cap cracking i've seen before too.
when i worked for yale and caterpillar we saw it more then we would have liked, and the reasons for the cracking varied anywhere from just bad welds to stress cracks from mast racking where the cylinders were out of adjustment to operator abuse from running into stationary objects.

It's hard to put a definitive reason on why it happens sometimes but there are things you can look for when inspecting the causes for the damage.
- check the mast and make sure both cylinders travel evenly and bottom out at the same time when fully extended and retracted also. (the mast racking i spoke of and was mentioned by kevin)
- check the forks and carriage for damage from impacts, forks may be curled up on the ends or the carriage bent even in the slightest.
- if you can, watch the operators while they are loading up product in the racks or areas where they work, see if you can find a cause in that area. I have on occasion caught drivers doing the dasterdly deed while i was there at the customer site before.
- check the hydraulic tilt pressure and make sure it is at correct relief, over pressure can also make a cylinder crack over time.

it could also be a combination of all of the above or even something i may have not mentioned here.

As for repairing them? Back in the day when safety was not as clear cut as it is today welding them back up was almost always done without question but in todays material handling world safety is now one of the more prominent factors when working on equipment and welding on 'load bearing' structural components is not the first choice anymore. It generally requires factory approval and should be done by a certified welder. Weigh those factors into the repair and in alot of cases just replacing the cylinder is more economical and cost effective and safer than just welding it back up and getting it certified.

It would pretty much be your decision and your company's and ultimately the customer on wether or not to follow through with the repair v/s just replacement.

But with all that said, most of the time in my experiences we almost always found it to be because of bad weld penetration causing a weak spot in the weld and most of the time the masts were out of adjustment causing a bad racking effect. (something the pm tech should of caught during pm's and corrected)

The weld on back of the tube cracks and then they leak oil real bad while tilting forward. It cracks right in the center of the weld. The cracks range in size from 1/4" to 1". Some I have carefully re-welded and seem to hold up ok (like the TCM which is ridiculously priced). These are on 3K - 5K triple mast machines. I see this about twice a year but I've done 3 in the past couple of months. I can't figure out if it's from pressure in the cylinder or just stress from the mast trying to pull on that welded-on end pin clevis. I think it is from the drivers running into something with the forks raised some what and that causes a high pressure spike inside the tube.

where on the tilt cylinders are you seeing the damage?
is it the rod and eye threads or are you seeing the back end weld breaking?
what is the stroke? "bottlers tilt"?
I consider this an interesting subject, thanks for bringing it up.
I am realizing that I used to see considerably more tilt cyl. damage than I have in the last 3 years or so, but these things seem to run in batches, I might go a year and not change a battery and then have 6 in 2 week.

Is ere any "racking of the tilt cylinders,this is where they are out of adjustment and one pushes out farther than the other..........