FORD 420 backhoe swing boom, loose chain

[icie727]

it's a '78 420 concerning a problem with the backhoe #19-389. the BH swing chain loosens when the boom moves side to side. I have to drain oil from the boom cylinders' equalizer hose to have the pistons draw back in. works for half a day. any suggestions?

 

[icie727]

Hi friends, this is still a problem. the boom cylinders are one way- they both draw in to keep the chain tight. Logic would suggest that a seal/packing is letting fluid into the end of the cylinder to keep the piston from fully retracting. Or is the problem in the combination valve box? I don't want to remove the backhoe needlessly... but would be necessary to remove the cylinders to rebuild. Any ideas?

 

[Sportsman762]

I have this problem with a Ford 550 backhoe. I have put a valve on a tee in the cushion crossover line. Based off my research Ford was aware of this problem and issued a service bulletin for the 550 in the early 80's to replace the swing spool with a stabilizer spool. There is something in the swing valve to provide cushioning and it messes up. I believe the issue is amplified in older machines to internal leakage. My next step is to extend a hose from the Tee up to the operator station and put the valve up were I can reach it without crawling under the machine. Draining the crossover cushion line, then swinging the boom one side to the other and back again to clear them out with the valve open cures the issue for some time. I do not have an answer for you. Perhaps repacking the cylinders would help, however I have not tried it.

 

[icie727]

Hi friends, this is still a problem. the boom cylinders are one way- they both draw in to keep the chain tight. Logic would suggest that a seal/packing is letting fluid into the end of the cylinder to keep the piston from fully retracting. Or is the problem in the combination valve box? I don't want to remove the backhoe needlessly... but would be necessary to remove the cylinders to rebuild. Any ideas?View attachment 690250View attachment 690251

I have this problem with a Ford 550 backhoe. I have put a valve on a tee in the cushion crossover line. Based off my research Ford was aware of this problem and issued a service bulletin for the 550 in the early 80's to replace the swing spool with a stabilizer spool. There is something in the swing valve to provide cushioning and it messes up. I believe the issue is amplified in older machines to internal leakage. My next step is to extend a hose from the Tee up to the operator station and put the valve up were I can reach it without crawling under the machine. Draining the crossover cushion line, then swinging the boom one side to the other and back again to clear them out with the valve open cures the issue for some time. I do not have an answer for you. Perhaps repacking the cylinders would help, however I have not tried it.

Hello S 762, that's precisely what I was considering, but the ford guys couldn't remember what the fix was. A year ago, I asked an independent tractor/hydraulics man about the fix and he suggested operating two specific controls at the same time. It worked like a charm for a year. When the chain loosened this time I called him to get a refresher on which controls tightened the chain/piston and he couldn't remember. old tractor, old repair men, old owner. I'm renewing my search and will keep you in the loop, icie27.