Cat hydrostatic transmission overhaul.

[Cmark]

Over the next few days, I've got the job of overhauling a Cat 953B HPCU. The 943, 953, 963 and 973 B series and earlier are all much the same.

Anyway, due to the fact that these machines are getting scarce in front line work nowadays, and the relatively high cost of repair I think this may be the last one I ever get to do.

If anyone has any interest, I'll post some photos showing the the insides of one of these mystery boxes and what goes into rebuilding them.

 

[Iceflyer]

Yes for sure, would be very interested in following you in the rebuild of a hydrostatic.

 

[AllDodge]

Count me in

 

[wosama931b]

I will be looking too, Cmark, and a toast to you. on a great idea.

 

[d9gdon]

Me too, I have a 953.

 

[Bob/Ont]

You are right Cmark, haven't seen them in exchange stock for years. Maybe you could put it together and get it filed by it's self so it's easy to find in the future. Post it here and it will get lost as time goes on.
Later Bob

 

[Cat977]

I would love to follow a rebuild. I may end up with one of the pre electronic machines someday.
Shawn

 

[Cmark]

So here we go.

Due to an unfortunate incident involving an Iphone and a puddle, pics of the teardown and start of the rebuild are lost to mankind forever. We join the action as the second pump is being built up. We've already installed the new swash plate bearings and set up the end-float, and the same with the pump drive shafts. The new pistons are being installed. I'll comment as we go along. Any questions, just ask and I'll try my best to answer.

These are the main damaged parts. One of the slippers came off a piston and the retraction plate broke free. Normally you'd suspect some sort of cavitation scenario, but in this case the machine has high hours and was reported to be working normally before the fault suddenly happend, so we're calling it an old age thing.




We have to measure the clearance between the slippers and the swash plate using feeler gauges and adjust it with shim packs under the retraction bearings. The spec is .003"+-.001". For something like this, I like to set up a go/no go scenario, so we're using a .05mm and .1mm feeler gauge. (My tiny set of feeler gauges are metric). If the small gauge slips in the gap and the big one doesn't, we're good.





The swash plate and pistons finished.
Next. Cylinder barrel.

 

[Cmark]

Installing the spring into the barrel. The spring keeps the barrel pushed against the port plate.




And the barrel installed onto the pistons. Can't get an action shot of it happening as it's a three-handed job on a good day
The yellow cover is just for protection. The barrel face is precision finished and any damage or scratches is a big no no. This is the LH pump, by the way.




Inside of the case where the LH pump will go. Here the case is laid down and we are seeing at it as if we were stood at the front of the machine looking towards the cab.




The RH pump already installed.
Next, installing the pump.

 

[Cmark]

The shaft goes up from the botton and the bearing cone is installed on the top end




We screw an eyebolt into the shaft and hang the pump from the crane.




This is one of the servo cylinders. Just a simple double acting hydraulic cylinder that swings the swash plate back and forth. We already stripped and resealed these. The hoses can be a cause of trouble, especially if the machine has been allowed to run hot. They're a bugger to change when the thing's assembled so they always get renewed on a rebuild.




Servo cylinder attached to the swash plate. The black O ring is just to keep the thing under control as it's being dropped into the case.




Lowering the LH pump into the case.

 

[Cmark]

Swashplate bottom bearing.




Swashplate top bearing.




Swashplate top bearing housing installed. Swashplate endfloat is adjusted with shim packs under the top and bottom bearing housings. We adjusted this previously.




Both pumps installled. Gasket in place ready for the pump head.
Note the long guide-bolts. Probably the cheapest tools you can make and they make jobs like this soooo easy.

More to follow. Probably tomorrow.

 

[JBGASH]

Cmark, Thank you for sharing that information with us, I have always wanted to see what that procedure looked like.

 

[ihmusedparts]

Thank you very much for sharing this.

Would you mind if I put a like to this thread on my website so it can help others out too?

Thank you,

Chris Hill
http://ihmusedparts.com

 

[Cat977]

Nicely done. I use loctite gasket eliminator 515 and 520. I am curious what you use.
Shawn

 

[Cmark]

Thank you very much for sharing this.

Would you mind if I put a like to this thread on my website so it can help others out too?

Thank you,

Chris Hill
http://ihmusedparts.com

Personally, I've got no objection to you linking this, but I think you should probably get the go ahead from Steve or one of the mods first.

 

[Cmark]

Nicely done. I use loctite gasket eliminator 515 and 520. I am curious what you use.
Shawn

It's Cat 6V6640 which is Loctite 38364 high temperature flange sealant.

The gasket is steel coated with plastic. (anyone know what the plastic is? Teflon maybe, or some sort of graphite compound?) so strictly speaking, gasket eliminator shouldn't be necessary, and normally I don't use any where the build doesn't call for it.

However, once the unit is installed in the machine, an oil leak here would be a disaster of biblical proportions, so it's just a little extra insurance, to be sure, to be sure.........

 

[Cat977]

I had my numbers wrong. It is 510 high temp. rigid castings ect.. 515 flexible both anaerobic. A fellow helping me used Dow Corning 111 a heavy silicone grease on a 10 psi bearing cover (very rigid stationary pump). Very easy to clean up when you need to go back in for future work. Anyhow thanks for letting us follow along.
Shawn

 

[overworked]

I have had the pleasure of changing those servo hoses in the machine before, not fun, it was a rebuilt unit with low hours from another state, hoses were twisted when tightened up and rubbed through. something I learned from someone else's error. Hope it helps someone

 

[Cmark]

I have had the pleasure of changing those servo hoses in the machine before, not fun, it was a rebuilt unit with low hours from another state, hoses were twisted when tightened up and rubbed through. something I learned from someone else's error. Hope it helps someone

Thanks for the tip. I'll pay extra attention when I hook them up.

 

[Cmark]

Cmark, Thank you for sharing that information with us, I have always wanted to see what that procedure looked like.

Thank you for the feedback.