2004 Cat 257b Drive problem

[Nige]

You are correct Nige. I tried to order the motor #222-5662 from Cat. It has been replaced by part # 280-7862 thru Caterpillar.

As complete assemblies the old & new motor Part Numbers are interchangeable, despite the internal parts being different for each one.

There is no need to buy an engine because of two piston seals. I think these seals can be found by selection. And theoretically, the 268-1933 KIT-SEAL (INCLUDES SEALS & GASKET) should contain all the sealing rings and gaskets, including the piston.

The contents of the 268-1933 Seal Kit are as follows: -
1 x 3E-6708 Seal, O-Ring
1 x 207-9718 Gasket
1 x 3J-7354 Seal, O-Ring
1 x 3K0360 Seal, O-Ring

No brake piston seal. Sorry about that.

I am now trying to locate the piston "O" rings but, even Bosch Rexroth is having problems locating. They can't even give me the part number or size of the piston "o" rings.

Can you give some basic measurements of the piston seal; as a minimum inside diameter and cross-section (in millimatres please) as near as you can measure. Is the cross-section square or rectangular.? If it is rectangular then you will need both height and width.
There may just be a Cat piston seal P/N hiding somewhere in the Parts system that might fit as an alternative.

 

[Gregory A White]

As complete assemblies the old & new motor Part Numbers are interchangeable, despite the internal parts being different for each one.

The contents of the 268-1933 Seal Kit are as follows: -
1 x 3E-6708 Seal, O-Ring
1 x 207-9718 Gasket
1 x 3J-7354 Seal, O-Ring
1 x 3K0360 Seal, O-Ring

No brake piston seal. Sorry about that.

Can you give some basic measurements of the piston seal; as a minimum inside diameter and cross-section (in millimatres please) as near as you can measure. Is the cross-section square or rectangular.? If it is rectangular then you will need both height and width.
There may just be a Cat piston seal P/N hiding somewhere in the Parts system that might fit as an alternative.

It is square.

 

[Nige]

Thanks for the measurements. I will go digging but it may take a while and even then I might turn up nothing.

Question. In the photos accompanying Post #59 on the previous page the seal looked a lot bigger than 1.5" Inside Diameter. Can you conform that measurement please.

 

[Gregory A White]

Those measurements are very close. It measures 1 7/16” on the piston groove and that is a tight measurement. The seal itself has the gap in it so it measures 1 1/2”. That gap is for expanding the “rigid” o ring to install it on the piston. And those pictures were zoomed in to get a better close-up view.

 

[Mobiltech]

I think you will have to go to a hydraulic shop that services rexroth for those seals.
Cat is famous for not giving a complete breakdown of parts for items they don't make themselves.
Here is some interesting info on the rexroth radial piston motor.

 

[Nige]

That gap is for expanding the “rigid” o ring to install it on the piston.

Sorry but no it isn't. That seal should be a perfect circle with no break in it. A new one will be much softer than your one that by now has worked for hundreds of hours in hot oil and hardened as a result. The normal way of installing a seal like that is to drop it in some boiuling water to soften it then "persuade" it over the piston until it drops into the groove.

TBH I like Mobiltech's idea of taking the piston and seal to a Rexroth agent and have them try to identify it.

 

[Gregory A White]

Wow Nige, I was fooled again by this thing. Each and every ring has the same gap except the one I took out in pieces. THAT bit of info will make this easier on me IF those rings need to be continuous.

 

[Gregory A White]

With that said, what are the chances the rings for the 268-7862 motor would work? Or is it built the same as this one?

 

[Nige]

With that said, what are the chances the rings for the 268-7862 motor would work? Or is it built the same as this one?

Unfortunately no. The brake piston seal on the 280-7862 is a different size to yours. If you look at the illustration of the two motors they are very different despite being interchangeable as complete units.

 

[ThreeCW]

I cannot locate a part number anywhere on my motor. The diagram Nige sent me is very similar to my motor and the seal in my motor is not an “O” ring. I found a number stamped in the edge of the mounting plate C779956. 10 03 stamped about 2” away. I can’t find that number anywhere on the internet.

Forgot. REXROTH is stamped on it.

Posts #48 and #49 mentioned the only ID on this motor is Rexroth C779956. I had a pretty deep look online and could find not reference to this motor.

What about the drive motor on the other side ... does it have any identification plates on it?

 

[ThreeCW]

I found a really good tear down video on a Rexroth MCR-T Radial Piston Motor.

In the video at about 27:30 min:sec, the mechanic starts to remove the piston assembly. At 28:00 min:sec, he removes a piston and roller and comments that "you can't buy the seal, you have to buy the piston and roller section as a pair".

I have not watched the rebuild video yet, but perhaps you can get some more information when he reassembles the piston assembly.

Based on this video by a mechanic who has done many of these repairs, I'm thinking that the square seal rings you are looking for may not be readily available.

 

[Gregory A White]

This comment #72 will hopefully be the last. I ordered some rings from CRC Industrial. They are supposed to be here 2nd week of November. If it works, great. If not, I’m going to buy a new motor. You gentlemen have been awesome and patient with me. Your knowledge has impressed me tremendously and words can’t express my sincere appreciation. I figure I have made your eyes roll a few times but you stayed the course. That is my opinion of a MAN!
I’ve found myself calling you gentlemen “a friend of mine” more than once.