1950 d25u with 2s blade ?

Do you have it apart?....is it the cup style or ring style piston seal?
If it is the cup style did it blow out or wear out?
I've had to add a back up (teflon) ring to keep the cup seals in the early D4 cylinders.

It just a guess right now the blade would drift down so bypass tested the cyl and they leaked by real bad all pull them apart and let you know the ser.#for the hyd pump is 4w920

thanks

I have a D2 that I am working on that is very similar to yours with the early control unit.I had asked about it on the other Cat site so I will try to put a link up to that- http://www.antiquecaterpillar.net/ACF_v2/showthread.php?p=121473#post121473

Eric,
If you have a good hydraulic supplier/shop nearby, take the piston in and see if you can get new cups for 'em. Quite a lot of stuff like that can be updated with newer parts. Sometimes it takes a quick visit to a machine shop to recut the ring grooves. Also, replace the rod seals and bushings as well. .saves time later on tearing 'em down again.

My parts guy reccommended that I take one cyl apart and mail in all the gaskets and seals and they would be able to replace them that way.

There is no problem getting the parts.....problem is the cup seals for the early D2/D4 (from Cat) don't work. I don't know what has happened, whether they never did fit right or something has changed. It is not a wear problem. The seals are not wide enough to remain captured by the retainer and extrude/blow out without a 0.030 or 1/32 in. back up ring.

By not a wear problem I mean at the seal groove and retainer.....but cylinder wear is certainly a factor. I suspect the seal fit has always been loose (too loose) but managed to work in combination with new cylinder bore specs. At least the back up washer will allow full retention of the seal (without clamping pressure). Kind of a prototype situation.....time will tell.

Ok I should use a back ring with the new caterpillar seals do you get them at a HYd rebuilder our caterpillar thanks for all the help