Another Drott 40 Track issue

I'm considering the purchase of a 1985 case drott 40 excavator. It has 5326 hours and has been sitting for a bit. The motor was rebuilt 10 years ago. It's sitting on a ranch near where I live. If I can get it fired up without any issues, I know one of the tracks will not engage. The owner seems to think that one of the valves is stuck but based on what I've read it seems more likely to be a "broken shaft" issue? It's a fairly clean excavator. I would use it to clear my ranch of maple trees. It has the detroit 6v71 motor in it and again it has been at least a year since it ran. I will be able to get it for somewhere between $3-4k. What will it cost me to get that track fixed and is it worth the hassle?

Each final drive has a hydraulic motor then a hydraulic brake that is applied by spring pressure. if the engine loads up when that side is engaged the brake is locked up if no change in rpm you can unbolt hydraulic motor and see if it turns if drive going into final turns problem is in final. i have had the finals apart on mine to replace drive seal and they are very easy to work on just reduction after reduction and more reduction gears. unless it's been ran low on oil the final are very reliable except for seals.

a 6v71? a repower? our 50 had a 6v53

I'm guessing its a 53 series engine. They look similar. If the valve cover bolts are around the outside of the covers on the flange, its a 53 series. If it has the big knuckle type knob thru the top of the cover bolts its a 71 series. A 6V-71 series at over 200 HP would be a bit of power overkill but one never knows. Either way if it ran when parked it will more than likely start right up. It sounds like it could be a very fair price for the machine if you are a bit handy with the wrenches.

our 40's had 4-53's in em

I have repowered them with 4BT Cummins. Worked out pretty good.

old excavators...

dad started with hoptos, retired with drotts.'

always had spare hydraulic hoses, and at least 2-5 gallon pails of hydraulic oil with.

My Drott 40BLCW went from driving one day to not driving on one side the next. Operating the drive foot pedal I could hear the engine slightly load but that was it. Nothing happened. If I picked the dead side up off the ground it would move.
Come to find out - with the help of a friend - we found that the transmission output shaft was spinning inside the drive sprocket. The spline is stripped. Replacement output shafts are available for about $450 but the drive sprocket is a different story. Case does not offer them. I have not found an aftermarket source for a sprocket. Sprocket is p/n S953545
Looks like the Drott 40, Drott 50, Case 1280 and Case 1187 used the same sprocket.
Southern Tractor wants $3500 for a used transmission with sprocket.
I'm trying to figure out a means of making the drive function enough to work for a year. Set screws? Remove the outer pillow block bearing and drill holes into the stripped splines then use dowel pins as keys? I need suggestions.

I'm confused, do you mean sprocket or internal spline? A sprocket can be cut on a CNC or pattern tracer plasma or oxy/fuel torch and flame hardened if required. If it's a spline, what spline? Maybe something from an AG tractor could be made to work. Pics. would be a BIG help.

Welder Dave said:

I'm confused, do you mean sprocket or internal spline? A sprocket can be cut on a CNC or pattern tracer plasma or oxy/fuel torch and flame hardened if required. If it's a spline, what spline? Maybe something from an AG tractor could be made to work. Pics. would be a BIG help.

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Hi Dave, I don't have pictures of my parts. I'm not taking the machine apart unless I have means of getting it back together. I need it. I can limp around with it using the boom as a crutch to move the dead side.
I have been asking crawler suppliers if there is a newer sprocket that fits the Case type C chain. Nope. Kind of surprising that they only used this track chain for a rather limited number of years. I'd thought that possibly I could make a flange for the shaft and fit a bolt on sprocket.
From what I've read Dana designed these with a 29 tooth spline on the inside of the sprocket to mount to the shaft. The spline is rather fine and delicate. I don't know what type or exact size of spline it is.
Looking at the shaft photos it appears that the spline is about 2.25" wide and 3 to 3.25 OD. The threaded end is 2.5 inches in diameter.
The drive sprocket appears to possibly pilot on the larger portion of the shaft next to the inner pillow block bearing which is sensible. On the outer side of the sprocket there is a collar that slides onto the shaft and inside a counterbore in the sprocket. It should also be a snug fit - but I do not know this to be true or not. The outer bearing retaining nut presses the outer pillow block bearing against the collar and sprocket against the inner pillow block bearing.
If the sprocket is piloted on the shaft and collar - I believe a rough patch could be done where holes could be made in the sprocket - outside of the webs from the spokes and then plug welds could be used to lock the sprocket to the shaft at the splines. I don't know if they would be sufficient. Woe be the person who needs to access the inner bearing later. I was hoping to not perform such a brutal patch job. I've been told by a crawler supply center that often the shaft can be used on 2 sprockets before it needs replacing. I called the prior owner of my machine to see if he worked on the drives before - he had not. If I could determine what the shaft spline is - I could get a splined bushing and bore the sprocket as needed. Then press the bushing into the sprocket and weld it in via holes in the sprocket. The hub of the sprocket near the outside pillow block bearing appears to measure 5" inches in outside diameter. If the spline is 3.25 OD then an internally splined bushing is going to be roughly 4" in diameter leaving only about 1/2" an inch of sprocket wall thickness for the new shaft collar to support side loads on the sprocket. Not a lot of material. Maybe enough. It would be nice to have a stripped sprocket to rework and have ready to use.
Here are some photos to get an idea of what is there.


This is a new shaft at the sprocket end

You could try multiple keys and or pins. But since the sprocket shaft are toast, can you just weld them up? If the sprocket is tight on shaft (but spinning under load), the have a machine shop bevel into the sprocket so you can get a good penetrating weld that doesn't interfere with your mounts. No idea if you can get the welded up one piece sprocket-shaft back in there...

A couple keys and a shrink fit may work where you have to heat the sprocket to install it.

LCA078 said:

You could try multiple keys and or pins. But since the sprocket shaft are toast, can you just weld them up? If the sprocket is tight on shaft (but spinning under load), the have a machine shop bevel into the sprocket so you can get a good penetrating weld that doesn't interfere with your mounts. No idea if you can get the welded up one piece sprocket-shaft back in there...

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As I posted - one supplier indicated that often the shaft can be reused one time after a failure. So - a sprocket with a good bore could save my day - or - knowing what the spline is so that I can search for a splined bushing to fit into the sprocket.
As for welding the sprocket to the shaft - only the outer side of the sprocket would be accessible due to the sprocket being against the inner bearing. There is already a counter bore in the sprocket for the bushing that is needed to prevent the sprocket from wobbling on the shaft. The bushing possibly could be removed to perform the welding though preventing the sprocket from being welded to the shaft with a wobble in it could be challenging. Of course - this would eliminate the ability to clamp the inner bearing to the shaft with the sprocket and effect the ability to clamp the outer bearing in place also.
It appears to me that welding the sprocket to the shaft is really a job best done in the machine or with the drive still assembled due to the size and weight of dealing with assembling the drive with the entire side of the drive, reduction components and sprocket as an assembly. Supposedly there is some way to get the shaft out without disassembling the drive but I am not seeing a means of accessing the snap ring that retains the final drive gear to the output shaft so that the snap ring can be removed to allow the shaft can be pulled out of the opposite side.
I'd really hoped to find someone who has worked with this situation before.

This whole thread was really very informative, learned a lot. Thanks for asking the question.

I worked for a Case dealership in West Memphis AR back in the 80’s we had a machine shop that made an insert for the sprocket on the 880 Case machines. They bored the sprocket and made splines for the shaft in the insert pressed it into the sprocket and welded it, worked pretty well. If you can find a good shop that may be an option.

RonO said:

My Drott 40BLCW went from driving one day to not driving on one side the next. Operating the drive foot pedal I could hear the engine slightly load but that was it. Nothing happened. If I picked the dead side up off the ground it would move.
Come to find out - with the help of a friend - we found that the transmission output shaft was spinning inside the drive sprocket. The spline is stripped. Replacement output shafts are available for about $450 but the drive sprocket is a different story. Case does not offer them. I have not found an aftermarket source for a sprocket. Sprocket is p/n S953545
Looks like the Drott 40, Drott 50, Case 1280 and Case 1187 used the same sprocket.
Southern Tractor wants $3500 for a used transmission with sprocket.
I'm trying to figure out a means of making the drive function enough to work for a year. Set screws? Remove the outer pillow block bearing and drill holes into the stripped splines then use dowel pins as keys? I need suggestions.

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I ended up disassembling it and finding it had 2 5/8 keys fitted at one time. They were long gone. I welded the sprocket bore and bored it. I welded up damage on the shaft key ways and fitted keys. The shaft was straightened and resized with a file and a micrometer.......too many hours to talk about. The sprocket was made to be a .004 inch shrink fit.

Yep, rebuilding spun shafts and sprockets are always (not) fun. Hopefully that works well for you to move the Drott where you need it. I'd just be careful not to load the tracks too much as keys are generally designed to shear before the shaft or other items have catastrophic damage. But then again, I have no idea what size keys and from what material you tossed in there. Either way, best of luck with it not stripping again.

LCA078 said:

Yep, rebuilding spun shafts and sprockets are always (not) fun. Hopefully that works well for you to move the Drott where you need it. I'd just be careful not to load the tracks too much as keys are generally designed to shear before the shaft or other items have catastrophic damage. But then again, I have no idea what size keys and from what material you tossed in there. Either way, best of luck with it not stripping again.

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The material I used for keys were cemented carbide lathe tool bits. They are 5/8" square. Typically a grade 4140 steel or similar. They were full width of the sprocket. The sprocket is a shrink fit onto the shaft.
The friction of the shrink fit provides much drive force from the shaft to the sprocket. The keys are to provide additional drive and help prevent any rotational movement between the sprocket and shaft. Both keys were driven into place. The first was driven in as rapidly as possible before the sprocket shrunk onto the shaft so that it could align the shaft and sprocket as the key was driven in. Nearly all of the key was able to be driven in before it wedged. The other was fitted and driven into place. I didn't like the fit and welded it to a threaded rod so it could be pulled with a puller. Using that key's dimensions as a guide I then made a new key that fit tighter - both in width and height. It was driven in. I had to cut off about 5/16" of the end after it simply would not drive in anymore.
The outer bearing retaining nut was torqued to at least 1700ft/lbs.
I've done what I could to make sure the repair holds. Due to the shrink fit of the sprocket on the shaft and the interference fit of the keys there should not be wear inducing movement like found on the original splined drive.

I ended up buying a parts manual as I wasn't confident in the numbers being given to me for a replacement hydraulic filter. Using the part number for the filter O-ring I found this Russian web site that has many parts manuals on it with free access.

"https://cats.klaxon-parts.ru"

here is the hyperlink- https://cats.klaxon-parts.ru/

This is the Drott section. https://cats.klaxon-parts.ru/casece/90084-/

RonO said:

The material I used for keys were cemented carbide lathe tool bits.

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Yeah, that'll hold and then some. Obviously you have some knowledge of machining with the shrink fit tolerances so glad to know your repair is top notch. I've seen too many folks use slip-fit tolerances on keyed straight bores and then wonder why their keys shear down the road. Any movement, and I mean any movement, between the mating surfaces of the keyway and key drastically shifts the load to become point loads instead of evenly being spread out against a surface. Pressure shoots up and materials at the load points start to flex and/or reach their shear strength. Failure is eminent when there is any slop.

RonO said:

The outer bearing retaining nut was torqued to at least 1700ft/lbs.

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Gott ask: Do you weigh 212 pounds and stand on an 8ft cheater?