Final Drive Stud Shearing

Are ya having a problem with your rig? We'll try to help. Share your tech tips and experiences here. Dr. Billy Glaser, author of the "Unofficial 750 Ural Service Manual" site myural.com, is moderating this section.
Forum rules
Here is the place for you to ask questions about or share your experiences about servicing or repairing your Ural or Dnepr. Please post topics concering modifications or accesories in the "Modifications and Acessories" section. Please post oil related questions in the "Oil Threads" section.
User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 9:57 am

Good (not really) Morning All,
I have been riding my 2012 Yamal on a near-daily basis since January 2018. Nearly eight weeks ago I noticed the lowest (of four) mounting studs missing. I thought it had spun and dropped out BUT in fact, the stud has sheared off leaving only the threads in the FD case half. I had a local machine shop remove the broken piece and ordered a set of new stud, nylock nuts, and gasket. Everything was nice and clean for reassembly and I did not rush any part of the job.
Last night I saw that gear oil had leaked all over the rear tire and was dripping from the nut on the lowest stud. It came off in may hand - sheared again!
From my perspective, there does not seem to be much variation/adjustment in alignment with mounting the FD, which would be my first area of concern.
I am feeling less than stellar about the situation and am looking for some perspective.
Here are some additional pieces of information:
The circlip on the rear drive shaft splines is in the middle position (where it was when I removed the FD)
I replaced the donut at the same time since the circular holes were in fact oval and rubber tendrils were sloughing off
I have been running Red Line gear oil per the previous owner
I typically ride 12 - 15 miles a day commuting to work and running other errands.
The current mileage is nearly 22K km.
TIA,
Kevin
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

User avatar
Lokiboy
Hero of the Soviet Union - 2020
Hero of the Soviet Union - 2020
Posts: 4333
Joined: Fri Apr 29, 2011 9:58 pm

Re: Final Drive Stud Shearing

Post by Lokiboy » Wed Dec 04, 2019 11:09 am

Sorry for an obvious question. Are all the nuts on the FD tight? Being slightly loose the only thing I can think of that would allow the side force on the stud. Does the FD normally slide easily into the swing arm?

As a side, when you are inserting the axle, do you leave the FD nuts loose so the axle slides in easily, then tighten the FD nuts?
Last edited by Lokiboy on Wed Dec 04, 2019 11:22 am, edited 2 times in total.
2011 Gear Up - "Erika"
Yorktown, VA

Mains: 127, Idle: 40, Needle: 1 shim
MKIII air filter
100,000 km and counting

User avatar
Peter Pan
Hero of the Soviet Union - 2020
Hero of the Soviet Union - 2020
Posts: 3658
Joined: Fri Jan 31, 2014 11:30 pm
Location: Heredia, Costa Rica/new speed record 115kmh by son

Re: Final Drive Stud Shearing

Post by Peter Pan » Wed Dec 04, 2019 11:13 am

how much riding in between reassemble and second shear off?
I had on my final drive a certain twist of the final drive "ear" that holds the 2wd FD. With the result, that it was dificult to pass the shaft straight through from left to right. In your case, there might be something more to it, like a crack in the housing.
Sophie Travelair = Patrol 2013
8 weeks 12.000km Oregon-Alaska-Oregon
With a DIY foam air filter the rig runs well even in tropical rain = :moto:
Final drives: 1. at 5000km, 2. at 34.000km(+friction plates) 3. at 42.386km
transmission: 1. 40.000km. 2. installed
Engine: 1. 43.388km crank replacement: Back on the road since 23.Okt.2019 :party:

The Avatar are 2 rice grains stating life's essence:
"The most important you cannot see!"
=> Attitude makes the difference!

rougaroo
Hero of the Soviet Union - 2020
Hero of the Soviet Union - 2020
Posts: 3921
Joined: Mon Aug 24, 2009 8:58 am
Location: NC

Re: Final Drive Stud Shearing

Post by rougaroo » Wed Dec 04, 2019 12:22 pm

Couple of questions:
1. Before you tightened down the nuts on the FD studs, did you notice any slop in the FD/swingarm connection? (i.e. was there any wiggle if you moved the FD back and forth - in the forward/reverse direction?)
2. How does the right rear shock look? Any leaks? Are the bushings ok?

I'm still scratching my head wondering why it's just the one stud that has sheared.

Rougaroo
2003 Tourist - lotsa upgrades
2004 Troyka - work in progress

User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Re: Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 1:06 pm

Lokiboy wrote:
Wed Dec 04, 2019 11:09 am
Sorry for an obvious question. Are all the nuts on the FD tight? Being slightly loose the only thing I can think of that would allow the side force on the stud. Does the FD normally slide easily into the swing arm?

As a side, when you are inserting the axle, do you leave the FD nuts loose so the axle slides in easily, then tighten the FD nuts?
Lokiboy,
As far as I know, yes, the nuts were all tight and as close as possible to the same torque (tight quarters meant by "feel" for the two closest to the exhaust but compared to the more accessible nuts).
Curious, could you comment on keeping the FD nuts loose before inserting the axle? I see it making a difference but would still like your thoughts.
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Re: Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 1:08 pm

Peter Pan wrote:
Wed Dec 04, 2019 11:13 am
how much riding in between reassemble and second shear off?
I had on my final drive a certain twist of the final drive "ear" that holds the 2wd FD. With the result, that it was dificult to pass the shaft straight through from left to right. In your case, there might be something more to it, like a crack in the housing.
Distance covered...probably 120 - 150 miles since the reinstallation of the FD in early November.
I'll reexamine the FD but there weren't any cracks in the cases at all when I had it on the bench
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Re: Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 1:10 pm

rougaroo wrote:
Wed Dec 04, 2019 12:22 pm
Couple of questions:
1. Before you tightened down the nuts on the FD studs, did you notice any slop in the FD/swingarm connection? (i.e. was there any wiggle if you moved the FD back and forth - in the forward/reverse direction?)
2. How does the right rear shock look? Any leaks? Are the bushings ok?

I'm still scratching my head wondering why it's just the one stud that has sheared.

Rougaroo
Rougaroo,
I am with you on the why...it doesn't add up for me. I don't recall any slop/movement between the FD and swingarm "ear" but I will reexamine soon enough. Likewise, I'll take a closer look at the right rear shock. Thanks
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

User avatar
Msblu79
Order of Lenin
Order of Lenin
Posts: 1987
Joined: Mon Sep 13, 2010 8:00 pm
Location: Invading Upstate NewYorkastan

Re: Final Drive Stud Shearing

Post by Msblu79 » Wed Dec 04, 2019 1:51 pm

If the FD has been removed from the swingarm the 4 nuts must be left loose until the axle is slid through and the various sections of the FD are aligned. Then tighten the 4 FD nuts. The nuts should be torqued to stretch the shanks enough to prevent movement and "working" of the shank. Not sure what the torque value is offhand, would also suggest using washers under the nuts to spread the load over a greater area. Odd that only one is having issues, try using a grade 12.9 hexhead bolt instead of the studs & nuts if the problem continues.
2010 Black Patrol 94,000km's
Modtop airbox, 2013 branch pipes, Perch rings, Yamaha petcock, Drilled slides, Gossie needles, 145 mains, 45 pilots, insulated manifolds, Modtop pushrods & Airbox, Dual FMF exhaust, PA Multi-spark system w/ VOES, Spin on filter conversion, 33mpg, Royal Purple fluids.

User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Re: Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 2:43 pm

Msblu79 wrote:
Wed Dec 04, 2019 1:51 pm
If the FD has been removed from the swingarm the 4 nuts must be left loose until the axle is slid through and the various sections of the FD are aligned. Then tighten the 4 FD nuts. The nuts should be torqued to stretch the shanks enough to prevent movement and "working" of the shank. Not sure what the torque value is offhand, would also suggest using washers under the nuts to spread the load over a greater area. Odd that only one is having issues, try using a grade 12.9 hexhead bolt instead of the studs & nuts if the problem continues.
Thank you for the thorough explanation. Given the detail you shared, I doubt I followed that procedure. Good one on the washers (I have been using them) and an even better one on using hexhead bolts.
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

User avatar
Msblu79
Order of Lenin
Order of Lenin
Posts: 1987
Joined: Mon Sep 13, 2010 8:00 pm
Location: Invading Upstate NewYorkastan

Re: Final Drive Stud Shearing

Post by Msblu79 » Wed Dec 04, 2019 3:16 pm

Oh, I forgot to mention one other problem I have encountered with a recent FD casting. A while back the ring gear bolts failed and wrecked the FD casting. I had to replace it and the new one did not quite fit right. The milled clearance around the bolt holes was not done wide enough and when I tried to install the FD it would not sit tight against the swingarm. I had to Dremel away some material to get them to sit flush against the swingarm and be able to torque the nuts. Something must have changed since 2010 on the swingarm or the new castings since I had to modify it to fit. This should not be a problem for you I think but worth a check to make sure the FD casting is flush against swingarm. :)
2010 Black Patrol 94,000km's
Modtop airbox, 2013 branch pipes, Perch rings, Yamaha petcock, Drilled slides, Gossie needles, 145 mains, 45 pilots, insulated manifolds, Modtop pushrods & Airbox, Dual FMF exhaust, PA Multi-spark system w/ VOES, Spin on filter conversion, 33mpg, Royal Purple fluids.

User avatar
Lokiboy
Hero of the Soviet Union - 2020
Hero of the Soviet Union - 2020
Posts: 4333
Joined: Fri Apr 29, 2011 9:58 pm

Re: Final Drive Stud Shearing

Post by Lokiboy » Wed Dec 04, 2019 6:49 pm

mod_rocker wrote:
Wed Dec 04, 2019 1:06 pm
Lokiboy wrote:
Wed Dec 04, 2019 11:09 am
Sorry for an obvious question. Are all the nuts on the FD tight? Being slightly loose the only thing I can think of that would allow the side force on the stud. Does the FD normally slide easily into the swing arm?

As a side, when you are inserting the axle, do you leave the FD nuts loose so the axle slides in easily, then tighten the FD nuts?
Lokiboy,
As far as I know, yes, the nuts were all tight and as close as possible to the same torque (tight quarters meant by "feel" for the two closest to the exhaust but compared to the more accessible nuts).
Curious, could you comment on keeping the FD nuts loose before inserting the axle? I see it making a difference but would still like your thoughts.
By leaving the nuts loose it allows the FD to flex as you insert the axle. I can spin remove, and insert the axle with my fingers. Then I tighten the four FD bolts and nuts to the swing arm. You can access all of them from different angles.

As another side, for the castle nut I just hand tight and align the axle hole with a castle opening. Insert a reusable retaining clip. No need to do more then that. The swing arm pinch bolt is what really holds the axle in place.

Basically, once I loosen the pinch bolts and remove the retaining clip, I can unscrew the castle nut and remove the axle by hand.

Have fun
2011 Gear Up - "Erika"
Yorktown, VA

Mains: 127, Idle: 40, Needle: 1 shim
MKIII air filter
100,000 km and counting

User avatar
mod_rocker
Comrade
Comrade
Posts: 76
Joined: Wed Jan 03, 2018 6:28 pm
Contact:

Re: Final Drive Stud Shearing

Post by mod_rocker » Wed Dec 04, 2019 7:59 pm

Thank you everyone for the thoughtful comments and questions. Although I can’t get to it tonight, I have a better sense of the potential “why” for the stud shearing in the first place.
Kevin
Washington, D.C.
@sidecar2school
'12 Yamal "Plaustrum"
'73 Triumph Tiger
'68 BSA Starfire "resting in pieces"

CrankyTom
Party Member
Party Member
Posts: 187
Joined: Tue Apr 23, 2013 6:11 pm
Location: Woburn,MA

Re: Final Drive Stud Shearing

Post by CrankyTom » Thu Dec 05, 2019 8:01 am

Double check the washers - on my 2012 Patrol I noticed that on at least one of the studs the threads ended just about level with the top of the washer.
The nut would bottom on the end of the threads and feel tight but it was barely touching the washer and not doing much to clamp the final drive to the swing arm.Just adding a second washer fixed the problem.
I'm a Marxist at heart-you can't beat Groucho,Chico,and Harpo!
2012 Patrol T

User avatar
Peter Pan
Hero of the Soviet Union - 2020
Hero of the Soviet Union - 2020
Posts: 3658
Joined: Fri Jan 31, 2014 11:30 pm
Location: Heredia, Costa Rica/new speed record 115kmh by son

Re: Final Drive Stud Shearing

Post by Peter Pan » Thu Dec 05, 2019 3:40 pm

This should not be a problem for you I think but worth a check to make sure the FD casting is flush against swingarm. :)
IMPORTANT: and when you stick through the axle without the wheel, left swing arm bore and final drive HAVE TO LIGN up perfectly.
If not you obligate the axle and cause wear on the traction spline. That is what I meant with taking up the gap. My right "ear" was twisted from the monkey/nut that conects handlebar and seat. So I left the final drive loose, pushed through the axle, pushed by hand the final drive against the ear, measured the gaps between ear and each bolt base, made for each base a surface ground washer and glued them in place with epoxi.
After that work I could tighten the FD in place, mount the wheel and for the first time in years push the axle right into place without any force at all!
Sven
Sophie Travelair = Patrol 2013
8 weeks 12.000km Oregon-Alaska-Oregon
With a DIY foam air filter the rig runs well even in tropical rain = :moto:
Final drives: 1. at 5000km, 2. at 34.000km(+friction plates) 3. at 42.386km
transmission: 1. 40.000km. 2. installed
Engine: 1. 43.388km crank replacement: Back on the road since 23.Okt.2019 :party:

The Avatar are 2 rice grains stating life's essence:
"The most important you cannot see!"
=> Attitude makes the difference!

User avatar
Snakeoil
Order of Suvarov
Order of Suvarov
Posts: 4798
Joined: Sat Nov 29, 2014 9:45 pm
Location: Upstate NY

Re: Final Drive Stud Shearing

Post by Snakeoil » Fri Dec 06, 2019 10:17 am

Read this last night so I may have forgotten a few detail. Please excuse any repetitive info here. I tool struggle with why the same stud shears. Here are a few thoughts.

- The hole thru the swingarm for that stud has a raised sharp corner that bites into the stud and creates a stress riser.
- The surface is not flat and the other three studs are not truly providing 100% participation in the gripping of the FD and that failing stud is doing more of the work.
- Same lack of contact/flatness between the swingarm and the FD and NONE of the studs are properly holding the FD in place and that failing stud is seeing the torque load from the FD. It might be just the axle and that stud dealing with the torque load.

I'm grasping at straws here. Always tough to find a root cause without actually standing in front of the offending system.
Regards,
Rob
Proud member of the Peanut Gallery
2000 Ural Tourist
40 Pilots, 122 Mains
Before you say something stupid, always ask yourself, "What would Harpo say?".

Post Reply