The old girl is coming together....

[Rob-D]

I'm going to have to respectfully disagree with this logic. The driveshaft is mechanically fastened at both ends.... yoke clamped at transmission and engine end bolted to the rubber isolator on the flywheel. So, any and all expansion or contraction is going to be taken up in the rubber isolator. Further, the coefficient of thermal expansion for steel is 0.00000645in per inch per degree F. So even if the driveshaft were experience a totally absurd and unrealistic 1000F difference in temperature, the total difference in expansion/contraction for a d-shaft 1/2" shorter would be 0.003225 inches. That would be easily taken up by the rubber isolator.

Since actual temperature difference would be much less than 1000 F, the total change of length would be much less. I just can't see a 1/2" making any significant difference.

You're right about the low COE of the drive shaft but you also have to take into account the flex of the chasis and the TOTAL length of the shaft itself. The shaft does get hot, not 1000F, but engine and gear friction on a hot day cold easily bring it up to 130-150F. A 36" shaft will expand about 1/32" plus the flex of the chasis which is likely much greater. Also the expansion of the gear cases and any aluminum involved which has a higher COE. I would say Deere made the shaft long for a reason. Your 1000F shaft would expand .00000645 x 1000 x 36 = .232" or almost a 1/4 of an inch not 0.0032". You have to take the length of the shaft into account when calculating expansion not just the extra 1/2".
Let's say the total length of metal expanding and contracting between gear cases, etc. is really 55". Now we have .00000645 x 55" x 1000F = .354" or almost 3/8". While I don't think the shaft will ever reach 1000F, I do think it could get quite hot, even over 150F on a hot day pushing the tractor in the field, now add the dynamics of tractor flex.

My two cents,

Rob

 

[kimodc]

Mechanos,
I have taken the drive shaft out of my 855 a couple of times and never had a problem. If I recall correctly, I would grease the splined end up real good and slide it all the way on (past the spot where it is actually tightened in), which would actually give you about 1/2 inch play on the isolator end. At least it was this way on my 855. If you were to cut it, I would be worried about getting it exactly balanced and straight when rewelding it. I'm sure any imbalance would give you a pretty good vibration.

Kim

 

[Mechanos]

Mechanos,
I have taken the drive shaft out of my 855 a couple of times and never had a problem. If I recall correctly, I would grease the splined end up real good and slide it all the way on (past the spot where it is actually tightened in), which would actually give you about 1/2 inch play on the isolator end. At least it was this way on my 855. If you were to cut it, I would be worried about getting it exactly balanced and straight when rewelding it. I'm sure any imbalance would give you a pretty good vibration.

Kim

I would have it balanced at a driveline shop.

 

[Mechanos]

I'm going to have to respectfully disagree with this logic. The driveshaft is mechanically fastened at both ends.... yoke clamped at transmission and engine end bolted to the rubber isolator on the flywheel. So, any and all expansion or contraction is going to be taken up in the rubber isolator. Further, the coefficient of thermal expansion for steel is 0.00000645in per inch per degree F. So even if the driveshaft were experience a totally absurd and unrealistic 1000F difference in temperature, the total difference in expansion/contraction for a d-shaft 1/2" shorter would be 0.003225 inches. That would be easily taken up by the rubber isolator.

Since actual temperature difference would be much less than 1000 F, the total change of length would be much less. I just can't see a 1/2" making any significant difference.

You're right about the low COE of the drive shaft but you also have to take into account the flex of the chasis and the TOTAL length of the shaft itself. The shaft does get hot, not 1000F, but engine and gear friction on a hot day cold easily bring it up to 130-150F. A 36" shaft will expand about 1/32" plus the flex of the chasis which is likely much greater. Also the expansion of the gear cases and any aluminum involved which has a higher COE. I would say Deere made the shaft long for a reason. Your 1000F shaft would expand .00000645 x 1000 x 36 = .232" or almost a 1/4 of an inch not 0.0032". You have to take the length of the shaft into account when calculating expansion not just the extra 1/2".
Let's say the total length of metal expanding and contracting between gear cases, etc. is really 55". Now we have .00000645 x 55" x 1000F = .354" or almost 3/8". While I don't think the shaft will ever reach 1000F, I do think it could get quite hot, even over 150F on a hot day pushing the tractor in the field, now add the dynamics of tractor flex.

My two cents,

Rob

0.00000645 x 1000 x 36 = 0.2322
0.00000645 x 1000 x 35.5 = 0.228975
0.2322 - 0.228975 = 0.003225

I stand by my original statement. The total difference in expansion between two shafts (one 1/2" shorter than the other) is 0.003225 inches. Actually, the shorter shaft would have less expansion than the original, so if anything it would be considered "more stable" in that the total change due to temperature differences would be smaller.

 

[Rob-D]

0.00000645 x 1000 x 36 = 0.2322
0.00000645 x 1000 x 35.5 = 0.228975
0.2322 - 0.228975 = 0.003225

I stand by my original statement. The total difference in expansion between two shafts (one 1/2" shorter than the other) is 0.003225 inches. Actually, the shorter shaft would have less expansion than the original, so if anything it would be considered "more stable" in that the total change due to temperature differences would be smaller.

We have to take the complete shaft into consideration when we talk about expansion because the whole shaft expands and contracts over temperature. We're not concerned about the 1/2" particularly, we're concerned about total expansion and contraction in daily use. Shortening the shaft 1/2" can effect how deeply it protrudes or doesn't protrude (dynamically) into the housing. The 1/2" enters in if there is flex or whatever where not enough shaft is in the housing.
Again, several dynamics come into play, temperature, tractor flex, housing metals, etc. It's more than the shaft, other metals are moving, flexing, contracting and expanding.
Remember also there has to be a specific amount of spline overlap for strength. Even if we dismiss temperature altogether we can't dismiss the other factors.

That's how I see it.

Rob

 

[Mechanos]

I'm going to have to respectfully disagree with this logic. The driveshaft is mechanically fastened at both ends.... yoke clamped at transmission and engine end bolted to the rubber isolator on the flywheel. So, any and all expansion or contraction is going to be taken up in the rubber isolator. Further, the coefficient of thermal expansion for steel is 0.00000645in per inch per degree F. So even if the driveshaft were experience a totally absurd and unrealistic 1000F difference in temperature, the total difference in expansion/contraction for a d-shaft 1/2" shorter would be 0.003225 inches. That would be easily taken up by the rubber isolator.

Since actual temperature difference would be much less than 1000 F, the total change of length would be much less. I just can't see a 1/2" making any significant difference.

We have to take the complete shaft into consideration when we talk about expansion because the whole shaft expands and contracts over temperature. We're not concerned about the 1/2" particularly, we're concerned about total expansion and contraction in daily use. Shortening the shaft 1/2" can effect how deeply it protrudes or doesn't protrude (dynamically) into the housing. The 1/2" enters in if there is flex or whatever where not enough shaft is in the housing.
Again, several dynamics come into play, temperature, tractor flex, housing metals, etc. It's more than the shaft, other metals are moving, flexing, contracting and expanding.
Remember also there has to be a specific amount of spline overlap for strength. Even if we dismiss temperature altogether we can't dismiss the other factors.

That's how I see it.

Rob

I would agree with you IF this were a slip shaft that was allowed to move. It is not. As pointed out in my previous post that I keep going back to, the driveshaft in a 955 is fixed on both ends. It does not dynamically protrude into any housing, it does not slip in or out of anything on either end. It is bolted solid at both ends. The rubber isolator between the d-shaft and the flywheel is the only thing that takes up any movement of the d-shaft.

Since in both scenarios, everything is the same..... same transaxle, same transmission... same everything... the only difference is 0.5" of steel d-shaft. Therefore the only difference between the two scenarios is 0.003225 inches less expansion.

 

[Rob-D]

I would agree with you IF this were a slip shaft that was allowed to move. It is not. As pointed out in my previous post that I keep going back to, the driveshaft in a 955 is fixed on both ends. It does not dynamically protrude into any housing, it does not slip in or out of anything on either end. It is bolted solid at both ends. The rubber isolator between the d-shaft and the flywheel is the only thing that takes up any movement of the d-shaft.

Since in both scenarios, everything is the same..... same transaxle, same transmission... same everything... the only difference is 0.5" of steel d-shaft. Therefore the only difference between the two scenarios is 0.003225 inches less expansion.

OK, here's why I said that:

"That driveshaft could be 3/8" to 1/2" shorter and still have full spline engagement at the transmission."

Is it moving in the spline or not?

Rob

 

[Mechanos]

OK, here's why I said that:

"That driveshaft could be 3/8" to 1/2" shorter and still have full spline engagement at the transmission."

Is it moving in the spline or not?

Rob

Not. The transmission input shaft is a male splined shaft. The transmission end of the driveshaft has a split, female splined u-joint end yoke. To install the d-shaft you have to slide the end yoke over the trans input shaft and slide if far enough rearward to get the engine end of the shaft to engage the rubber isolator. Then slide the shaft forward and bolt down the engine end. Then you tighten two bolts on the split end yoke that clamps it onto the trans input shaft effectively fixing it's position. So, it is moving on the spline to install it.... once installed, it does not move.

 

[Mechanos]

Got a few more items taken care of last night. Hooked up a few more oil lines, installed the clutch discs & steels for the PTO inertia brake, installed the PTO brake cover, cleaned up a bunch more parts to be installed. Put a new rear PTO seal in the rear cover and was about to install the rear PTO shaft and rear cover when I noticed a huge groove in the oil seal wear sleeve on the rear PTO shaft.

That pretty much put a halt to that operation since the PTO shaft installs in to the cover before the cover is installed. Of course, my local Deere dealer doesn't have the part in stock and will have to order it. I have an '87, an '88 and a '90 tractors and I don't think they've had a single part for any of them on the shelf except for common items like an oil filter or the such. There is a good chance that they won't have the sleeve until Monday, so I'll have to find something else to work on over the weekend.

 

[Rob-D]

Not. The transmission input shaft is a male splined shaft. The transmission end of the driveshaft has a split, female splined u-joint end yoke. To install the d-shaft you have to slide the end yoke over the trans input shaft and slide if far enough rearward to get the engine end of the shaft to engage the rubber isolator. Then slide the shaft forward and bolt down the engine end. Then you tighten two bolts on the split end yoke that clamps it onto the trans input shaft effectively fixing it's position. So, it is moving on the spline to install it.... once installed, it does not move.

Got it, thanks for the clarification.
Rob