b7800 front drive shaft replacement

Kioti Dave · Mar 3, 2019

Has anyone replaced the front drive shaft on a B7800 without splitting the tractor? My 7800 shaft broke at the u-joint right at the transmission. Want to replace, but don't want to split the tractor. Can this be done, or am I in for a big time job?

mikester · Mar 3, 2019

Most tractors have the front drive shaft in 2 pieces in a tube from the tranny to the front diff. The shaft is splined and joined with a sliding collar. You dont need to split the tractor in this case.

If you see a u-joint then you definitely wont need to split the tractor. Simply split the yolk at the spider.

In any case you could at worst remove the front diff without needing to split the tractor.

It shouldnt be a huge job. I imagine you may need to replace the seals and bearings while you are at it.

orezok · Mar 3, 2019

Here is a cut section of the front wheel drive (6). Did the shaft break on the transmission side of the U joint or the front side?

Ken · Mar 3, 2019

Look at the parts picture and slide back the rubber cover on lower universal joint there is a pin holding the joint on shaft .tap out the pin slide the coupler back and lower to the floor then slide shaft from shaft at rear.
Question did this break from lack of grease. about only way to damage the upper shaft
unless the front pinion or gears in front drive. lock up
ken

Kioti Dave · Mar 4, 2019

U-joint broke right in middle. Some parts left on transmission shaft, some on driveshaft. I read somewhere, that you can drill a hole in top of frame to get at double spring pins. If I can do that, I can remove broken piece and install new parts from bottom. Probably pretty tricky, but if it can be done, would be better than splitting the tractor. Will look at it once it warms up.

orezok · Mar 4, 2019

No need to split the tractor to replace universal joint. All is accessible from below.

Part # is 6C040-57500. About $118 at Messicks.

From service manual. This is for the front universal, but rear is similar.

Tomtint · Mar 4, 2019

I just split my sisters b7510 to replace a motor. Made the mistake of not installing the front driveshaft as we bolted the motor to the bell housing. There is a metal cross member under the motor that makes it virtually impossible to do after the fact. Not sure if yours is the same..

Leejohn · Mar 4, 2019

1st off if you have a loader the sub frame has to come off and there is 28 bolts holding it on. That is the hardest part of the job. The sub frame is heavy and if can get help do it. I'm 78 and did it myself but it was all I could do.
When I split my 7800 to replace the throw out bearing I went ahead and drilled a 3 1/2" hole over the rear joints. Now I get at both roll pins and can line back up easy when going back on. I wouldn't want to split the tractor at the trans, that looks like a real job.
Here are some pictures of where I put the hole and the cover I made for it. See if that helps. If you do this make sure the pilot drill isn't to long and go slow.

Kioti Dave · Mar 6, 2019

Leejohn said:
1st off if you have a loader the sub frame has to come off and there is 28 bolts holding it on. That is the hardest part of the job. The sub frame is heavy and if can get help do it. I'm 78 and did it myself but it was all I could do.
When I split my 7800 to replace the throw out bearing I went ahead and drilled a 3 1/2" hole over the rear joints. Now I get at both roll pins and can line back up easy when going back on. I wouldn't want to split the tractor at the trans, that looks like a real job.
Here are some pictures of where I put the hole and the cover I made for it. See if that helps. If you do this make sure the pilot drill isn't to long and go slow.

That is exactly what I plan to do. What did you use to make the hole? Will make the job much quicker and easier. You tack welded the piece back in as well correct?

Leejohn · Mar 6, 2019

I used a hole saw and no I did not weld back in. Blow the picture up and you can see three screws hold it in. It is flush with the deck.

sixdogs · Mar 6, 2019

I had no idea this was so difficult. Anyone with a shop manual know how Kubota suggests it be done?

Kioti Dave · Mar 6, 2019

Kubota will split tractor. At least $1500 in labour. I know because I already had it done. Cutting an access hole from top will save a lot of money.

Kioti Dave · Mar 6, 2019

Leejohn said:
I used a hole saw and no I did not weld back in. Blow the picture up and you can see three screws hold it in. It is flush with the deck.

Ok see that. Thanks for the photos. They are VERY helpful. Will probably use a cutoff tool and cover with a thin plate. Will post photos as well.

rtrent · Nov 26, 2020

I have discovered similar problem with my B7500HST; I found the rear u-Joint at the transmission end of the front wheel drive prop shaft is really loose/sloppy; just a matter of time I think; middle u-joint seems fine; I guess no zerks for lubrication on these u-Joints?? Not that you can get to them; at least this describes a possible way of replacing without splitting the tractor. But as stated above, you need to remove the loader frame first; I tried sliding the plastic cover back on the middle u-Joint, but the loader frame has a steel brace that crosses there and is too tight against the cover to allow it to slide back.

rtrent · Apr 25, 2022

Leejohn said:
1st off if you have a loader the sub frame has to come off and there is 28 bolts holding it on. That is the hardest part of the job. The sub frame is heavy and if can get help do it. I'm 78 and did it myself but it was all I could do.
When I split my 7800 to replace the throw out bearing I went ahead and drilled a 3 1/2" hole over the rear joints. Now I get at both roll pins and can line back up easy when going back on. I wouldn't want to split the tractor at the trans, that looks like a real job.
Here are some pictures of where I put the hole and the cover I made for it. See if that helps. If you do this make sure the pilot drill isn't to long and go slow.

Hey Leejohn!! This is exactly what I saw on my B7500; my rear universal on the shaft for the front drive is getting bad and saw that in order to get at it you need to remove the loader frame; on top of that, I have a Woods backhoe sub-frame that also attaches to the loader frame; so this hole would make access a lot easier; my question though is can you get the rear universal off the splines without removing the front universal first?? Does it just slide forward when you take the pins out?? Hope you get this message and are able to respond; thank you in advance!!!

Leejohn · Apr 25, 2022

If I remember right, after the front pin is out it well move fwd enough to get the rear off after the pin is out at the rear. I well go back and look at my pictures and see if that helps me to remember.

Update: There is a coupler at front of the main drive shaft. The cover over shaft comes apart after you remove the small screws . I hope we are talking about the same shaft. I can't find the pictures I wanted of me splitting the tractor. If you think I can help anymore and want to call me I give you my phone #.