B7100 Rear Differential/Transmission Rebuild Questions

[woodburner]

Hello,
I recently thought I got a great deal on ebay. I bought a project instead...

So...I'm in the process of rebuilding the manual transmission, rear axles and rear differential on this B7100D. After closely studying the parts and service manual while dis-assembling the tractor, most of the rebuild is pretty straight forward. I'm replacing EVERY bearing, seal, cir-clip, worn bushing etc. I'm also replacing the front U joints, seals, pilot bearing, and clutch while I've got the tractor split. So far I've got about $1500.00 in parts. The transmission and related PTO on this tractor were in pretty rough shape... I've had to replace 4 gears that were worn, chipped and/or missing teeth. I've also had to replace 3 shafts. The PTO shaft was completely broken in two pieces!

My questions are these:

1) To adjust the backlash on the rear differential ring and pinion gear, I realize that you have to vary the size of the shims that are behind the ball bearings on either side of the differential assembly. By varying the thickness of the shims it "moves" the ring gear closer (or further away) to the pinion gear, thereby changing the backlash. Can I simply adjust the size of the shim on either side of the differential assembly to accomplish this; or do I have to have the same size shims on both sides in order to "center" the ring gear on the pinion gear and also obtain the correct backlash?

2) On the PTO shaft the parts list shows three different shims between the PTO rear cover and the PTO shaft rear bearing. I assume that these different size shims are available in different sizes in order to adjust end play on the PTO shaft? However, I cannot find any specs on endplay of the PTO shaft in the Work Shop Manual or reference to using these different size shims.

3) On the very front of the pinion shaft, between the first bearing on the shaft and the rear of the tranmission case, there are again 3 different size shims listed in the parts book, but no reference to these shims anywhere in the Workshop Manual. These shims fit in the bearing recess between the front pinion thrust bearing and the case. It looks like the purpose of these shims is to move the pinion shaft closer to the ring gear? However again, I can find nothing in the manuals about this adjustment?

Anyone that has experience or knows who I can ask about these question I would really appreciate the help.

For fun I attached a few photos of the distressed transmission parts.

Thanks

 

[Egon]

Ohh - that poor little tractor surely seen its share of work.

That is a major project you are undertaking.

 

[Conn]

Woodburner. I've set up plenty of differentials in trucks in my day, but never in a tractor. However, the concept is the same.

1.Just by adding a shim to the left or right side of the differential, you're going to alter the bearing pre-load a bit, and change the orientation of the differential to the pinion gear. If it were me, I would install the new bearings and re-use the shims. If you CAN'T re-use the shims (destroyed, broken, bent, whatever), try to measure the thickness, outside diameter, and inside diameter and replace them with the EXACT same thing as the old ones.

Moving .010 from the left to the right is going to just move the differential and do nothing to the pre-load (What I would suggest).

Just sticking a shim on one side is going to alter the pre-load and teh differential location.

In my experience, it was best to start with what the factory had in it, and make adjustments from there. Are the shims located between the bearing races and the case? Or are the shims pressed between the bearing cone and the differential?


2.I'm having a hard time visualizing this PTO one, there again, in my experience, start with what the factory gave you, and make adjustments as necessary.

3.Are the shims you're refering to located closer to the head (geared) section of the pinion, or towards the splined (input) section of the pinion?

If they're towards the geared side, they are pinion depth shims. If they're towards the splined section, they're more than likely pinion pre-load shims.

If you don't adjust your differential backlash, don't adjust you're pinion depth. They work with each other. If the pinion depth is too much, the backlash will decrease, and vice versa. It's all about contact pattern between two. Manufacturers want the pinion and ring gear to mesh PERFECTLY for the most even stress distribution in the part.

Go to Randy's Ring & Pinion for technical help. They can probably get you additional shims if needed.

Don't get too carried away with it. I'd start with replacing the bearings, while using the exact same shims that came out of it, in the exact same configuration they were in.
Anyone that has experience or knows who I can ask about these question I would really appreciate the help.

 

[woodburner]

Conn,
Thanks for the reply. The only adjustment that the Kubota Workshop Manual refers to on the ring and pinion is the backlash measurement between pinion and ring gear. There is no mention at all of pre-load? When I measured the ring and pinion backlash before I disassembled the rear end, it was excessive by about .010, so I figured I would add a .010 shim to the ring gear side of the differential and then recheck the backlash? These shims are located between the bearing races and the bearing holders which are bolted to the case and hold the bearings in place. The only adjustment that the Workshop Manual refers to is the backlash adjustment and the manual simply states " if the backlash is excessive, adjust with shims"? This leads me to believe that I simply install shims to move the ring gear closer (or further) away from the pinion gear to obtain the correct backlash and it's done?. Is that all there is to it? I do have the original shims that I removed when I disassembled the differential and have kept them marked on there respective sides of the differential. However after further measurements, I've decided to replace the differential assembly complete which includes a new ring and pinion gear, so I figure I need to re- adjust the shims as the tolerances are probably going to be different then the original differential?

The PTO shims I'm speaking about are located at the back of the PTO shaft between the bearing and the PTO shaft cover. In the parts manual there are three different size shims available so I'm sure they are there to adjust end play, just no reference to shaft endplay in the manual.

The shims I'm referring to on the pinion shaft are located at the splined end of the pinion shaft between the case and the first bearing on the pinion shaft. In effect installing these shims moves the entire shaft towards the rear of the tractor and "into" the ring gear. Once again the Kubota parts manual offers three different size shims, so it must be a tolerance that requires adjustment? However once again there is no mention of this adjustment anywhere in the manual.

The lack of information in the Workshop Manual is frustrating. I have an older manual, if anyone has a more recent manual and find any information on these adjustments please let me know.

Thanks

 

[BotaBigot]

I went thru this same exercise with a B6000 I had years and years ago, so I'll begin by saying your 7100 may be different...but I doubt it.

Being a gearhead, and having dealt with auto diffs, I initially approached the tractor diff the same way. I was baffled by the relatively simple setup instructions in the Kubota manual...until it occurred to me that I wasn't dealing with the kind of tolerences necessary for sustained 60MPH operation. My tractor was a low-speed/low-tech machine with a straight bevel gear diff...not a hypoid, with its acceleration/deceleration loadings. So, I set it up by the Kubota book with no problems.

In your case, I think the pinion shims are for good gear face contact. Then, side shim for stated clearance, and you should be done (but, remember my caveat above... ).

 

[Retlaw 66]

The shims I'm referring to on the pinion shaft are located at the splined end of the pinion shaft between the case and the first bearing on the pinion shaft. In effect installing these shims moves the entire shaft towards the rear of the tractor and "into" the ring gear. Once again the Kubota parts manual offers three different size shims, so it must be a tolerance that requires adjustment? However once again there is no mention of this adjustment anywhere in the manual.

Thanks

I haven't done this on a tractor, but have done it on a few Buicks!
Those pinion shims adjust the 'pinion depth'. It can be checked two ways...measure it with special fixtures, or put it together and check the 'gear contact pattern'. I'd suggest the 2nd option. Just smear the teeth on the ring gear with some white grease, and turn the gears a few revolutions....that will show a gear 'contact pattern'. It should be centered on the ring gear tooth, and not halfway off either end of the tooth.
If you have the old shim, start with that.

The shims for the ring gear are to adjust backlash. The last shim usually needs to be tapped into place. It should be tight. If it just slides in easily, it will allow the bearings to move around too much.... that would be considered to have NO bearing preload. However, a shim that goes in tightly, will put some pressure (preload)on the bearings...and bearings like that.

Start by measuring the total thickness of the old shims from both sides together. Try to maintain that total. To change backlash, put a thinner shim on one side, and a correspondingly thicker shim on the other side.

And again, my experience is with Buicks, but the principles are the same!

Try a Google search for 'setting up ring and pinion' and you'll get some hits that explain it in detail.

 

[woodburner]

Thanks for the posts, they certainly help and I'm learning a lot about setting up differentials. I've rebuilt manual tranny's before but the differential on this tractor is the first differential I've set up. Botabigot, you're right, this differential is not subject to the pressure that hypoid differentials experience. It's a relativly slow turning bevel gear and the clearances probably are a little more forgiving in the tractor diff opposed to a 70 mph car or truck, I'll keep that in mind.. At any rate, here's my plan to determine required shim thickness:

1) I will first measure the dimension between the inside of the bearing holders when they are assembled on the diff case. (Between the axle shafts)

2) Then I will measure the outside dimension of the assembled differential including the bearings.

3) The difference in these measurements will tell me how much space I need to fill between the bearing holders and the bearings.

4)Add an additional small shim to slightly "tighten" the bearings.

5) Finally, completely assemble the differential and move the shims from left to right as necessary until I get the proper backlash adjustment between ring and pinion gear.

With regard to the pinion shaft. I will basically make the same measurement, calculation and adjustments as I did on the axle side of the differential.

1) Assemble the empty transmission case to the empty differential case and measure the bore between the first and last bearing recess between the cases.

2) Assemble the pinion shaft completely and measure the outside dimension between surface of the first and last bearing on the pinion shaft.

3) Make the same measurement and calculation as I did above.

4) Add shims as necessary to fill the gap adding one small shim to the overall "gap" to tighten the bearings in the recess.

5) Assemble the transmission and differential in there respective cases.

6) Assemble the transmission case to the differential case.

7) Apply the marking grease (like Retlaw 66 suggested) to the ring gear and spin the pinion shaft. Check the marking grease on the ring gear for correct placement of the pinion shaft on the ring gear.

8) Re-adjust shims as necessary in the bearing recess bores in order "adjust" the pinion shaft as necessary according to where the pinion shaft rides on the ring gear in step 7.


At least it's a plan.... Am I missing something? I'll let you know how it goes. I'll order my parts next week and with some luck I'll receive them in few weeks. Some of the parts are certain to be back ordered with Kubota so hopefully it won't take too long. In the mean time I have plenty of parts to clean and paint.

My next question is: When I add an additional small shim to the overall length of the shafts in order to "tighten" the bearings, how thick should this last shim be??

Thanks,

 

[BotaBigot]

Your plan looks good. I still have my old B6000 manuals, so I did a quick lookup to see how Kubota addressed the preload issue...and the instructions went something like "...not too tight to turn smoothly or which rattles left and right..." No measurements...just that the diff "turns lightly."

With aluminum cases, my advice would be to keep the preload to a minimum...whatever shim stack accomplishes that...ideally zero preload with zero end play, but err to slight preload.

 

[Retlaw 66]

You could probably skip the measuring of the original parts.
If the pinion gear is like the one in my Buick , there is the gear, followed by a shim, the inner bearing, the outer bearing, then a washer and nut?

If there is a spacer or shim between the two bearings, that would be to adjust the bearing preload. My Buick has a collapsible spacer there....you torque the end nut until the whole gear turns with some resistance....something like 30 inch pounds (which feels like a lot). Some race cars use a spacer there for the same purpose....you change the spacer thickness until the pinion turns with some resistance.
In your tractor, it shouldn't be critical....you just need to eliminate any slop in the bearings, and add a wee bit of pressure....kinda like doing front wheel bearings on a car.
Do that first. Just start with the old pinion shim. You may need to change it out if the final gear contact pattern is way out. (not likely)

So install the pinion gear. Then drop the differential (carrier) unit in. Push it against the pinion gear so there is no backlash. Slide a few shims between the housing and carrier bearing race on the pinion bearing side, and go a bit thicker so you do end up with some backlash.
Now add shims to the other (ring gear) side to fill the space, but still maintaining some backlash.

BTW, what is the backlash spec for your tractor?
0.001" to 0.002" of backlash you will just barely feel. Cars like 0.008" or so....you'll SEE that in ring gear movement.

So, you should still have noticeable backlash...now choose a thicker shim for the ring gear side...something that you will have to tap into place. That'll give you some carrier bearing preload, and tighten up the backlash some more. Now measure your backlash (are you using a dial indicator?). If it's close, then put the grease on the ring gear, and turn the pinion shaft so the ring gear goes around a few times. You'll see a contact pattern on the ring gear teeth. If it's more or less centered, you're good to go!

I have to emphasize this procedure is for an automotive differential... Your tractor might be slightly different. But the same principals still apply.
If someone with tractor experience would speak up, I'd keep my mouth shut! But I wanted to give you something to go on...

BTW, where are you getting your parts?
Most online sources have online catalogs where you can do price-checking...as long as you have the part numbers.

Good Luck!

Walt

 

[woodburner]

Retlaw,
Thanks for the response, it's very helpful. I took a photo of the pinion shaft. The cir-clip on the bearing shown on the right side of the pinion shaft rests against the outside of the differential case. The pinion shaft is shimmed behind the bearing shown on the left side of the shaft. The shims fit between this bearing and its recess in the tranny case. The pinion shaft gear "sticks out" of the rear of the tranny case and into the differential case where it makes contact with the bevel gear. When the two cases are assembled this would fix the pinion shaft in place. When the two cases are assembled this is when the pinion shaft would be pre-loaded? In order to do a "resistance" test of the pinion shaft preload resistance, I'd have to disassemble and re-assemble the tranny and diff cases while changing the shim each time. It also occured to me that because the rear of the pinion shaft has that cir-clip and no other spacers or shims, there is no way to move the pinion shaft closer (or further away) from the bevel gear, that position is fixed by the circlip that rests against the case. There are no shims there at all... So it looks like the only opportunity for adjustment I have on the pinion shaft will be by inserting shims behind the small bearing shown on the left of picture and the bearing recess in the tranny case. This will in effect pre-load the pinion shaft. It should be noted that the small bearing shown on the left side of the shaft is a thrust bearing and carries the rearward thrust generated by the contact between the pinion and bevel gear.
So I still go back to the idea of measuring the tolerance of the assembled tranny and differential case without the pinion shaft in place, then measure the length of the assembled pinion shaft between the circlip and the rear of the bearing. Then add shims to make up the difference and then add 1 extra shim to preload the bearings. So that leads me back to one of my original questions; What size shim should I use to preload the bearings?

By the way I ordered all my parts from Jeff at Messicks. He was very helpful in pricing and updating part numbers on a very extensive parts list that has hundreds of parts, most of them small parts like pins. cir-clips, shims, bearings,as well as major parts like gears and shafts. I was using an older parts book so the part numbers I gave him all had to be updated and priced. The bad news is that Kubota has parts backordered so it could be a couple weeks before I see my parts. I'll be busy cleaning and painting in the meantime.

Also, I left my service manual at my cabin last weekend so I don't know the backlash spec on the ring gear. I'll let you know when I get my manual back in my hands