RPM and Popping Dog Bones

[Lazy Bushman]

Guys there is a bit of a consistent issue that I have noticed has gaining some traction over the past few months which is to do with dog bones popping our to the diff cups. I thought I could consolidate the issues on to one thread. I have also pinged RPM and email inviting them over as well. I won't aim to relitigate all the discussion in the past, but for people who may not be across this issue below are a few links to previous postings:

https://www.arrmaforum.com/threads/kraton-axles-popping-out-of-diff-cups.11440/
https://www.arrmaforum.com/threads/cvs-popping-out.10590/

I have also included some recent pics, one mine and the others from @olds97_lss and @slick2500 of how the shafts are sitting in the diff cups.

Suggested fixes today seem to be around shortening the arms and/or removing the pillow ball spacers.

For me it has only got worse more recently after I replaced the stock knuckles with GPM due to a pillow ball being pulled through the stock knuckle as a result of a crash. It could be coincidence. I also switched to the GPM turnbuckles and dog bones at the same time. I will return one side of the truck to stock (apart from the RPM's I will leave them there) and keep the other side as it now is and get some comparative pics. Right now I'm thinking the fix for me is to go back to stock. Stock snaps, RPM hasn't for me. Stock retains dog bones, RPM I don't think does for me...hopefully I'm wrong about that.

I think @Notorious J runs the MIP shafts if I recall correctly (but I could be wrong). Are the MIPS any longer than stock at all or just thicker?

Anyway if others have thoughts, idea's or experiences please let us know here. I figured if we give the issue its own space and RPM do come along then it will streamline things more efficiently.

 

[olds97_lss]

My comments with photo's from the other thread:

That is much deeper than where it sits in @Lazy Bushman's truck. There has to be a difference in the tolerances of these parts.

Yeah, mine don't sit near as deep. I recently removed the washer off the bottom ball end and put the shim from the top on the bottom just to close up the gap a bit. I'll take some photo's later with it full extension and compression with the tires pointing forward to show where the bone sits. Under full compression, they are near the edge of the cup if I remember right.

Fully extended (arm set screw stopping near full shock extension):

Compressed with the bone parallel to the chassis:

Compressed with the bone perpendicular to the chassis:

You can see how the bottom ear is almost out of the cup when in that last orientation. Now extend it out a bit further due to impact stretching/bending the arms and BOING!

This is with the lower shim/washer removed and replaced with the upper shim. The upper doesn't have a shim at all now.

Looking at the photo... wonder why the left cup is more chewed up than the right one... odd. Well, the right one in the photo, but it's the left side of the truck when it's pointed away from me.

 

[Notorious J]

I think @Notorious J runs the MIP shafts if I recall correctly (but I could be wrong). Are the MIPS any longer than stock at all or just thicker?

Nope, I do not. All stock on the front of my Noto, but drive shaft issue is the same. Short term remedy was to remove the camber spacers completely. Following to see how others are tackling the issue before switching to RPM up front.

 

[olds97_lss]

If I continue to have the issue, I'm going to shave a mm or two off the end and make sure the remaining hole is deep enough.

Funny, I never had this happen on 4S... 6S speeds are causing harder hits. Then again, it could just be due to time and slop as the hinge pin holes are pretty sloppy. Still, if it continues, I'll shave them down as long as the dog bone doesn't bottom out in the cup, which I don't see that happening for a few more mm at least.

 

[Notorious J]

If I continue to have the issue, I'm going to shave a mm or two off the end and make sure the remaining hole is deep enough.

Funny, I never had this happen on 4S... 6S speeds are causing harder hits. Then again, it could just be due to time and slop as the hinge pin holes are pretty sloppy. Still, if it continues, I'll shave them down as long as the dog bone doesn't bottom out in the cup, which I don't see that happening for a few more mm at least.

This will be my next step if the removed spacers doesn't accomplish the task.

 

[martysmith223]

I had this same issue with rpm arms dog bone destroyed my diff cups and it kept popping out I just went back to factory arms thought I had a bad batch and didn't like the extra flexibility almost seemed to make things worse would even pop out on little wheelies didn't even have to have a hard landing I still have them and one of the diff cups that didn't get eat up all the way i trashed the other one wasn't salvageable... glad to see someone els is addressing the issue I wasnt a forum member back then so I didn't have all the proper know how to have this resolved I'll see if I can find the diff cup if it helps

 

[Lazy Bushman]

The following is the email content I got from RPM not long ago. It's great to see companies be so responsive, though I'm not 100% in agreement with it. someone posted here a comparison (so I thought) between stock and RPM and I thought the difference was greater than 0.025mm which is buggar all.

"We do lurk at the ARRMA forums from time to time but sadly, are limited on the amount of time we have to post (you can imagine how many places we'd have to be to cover all the manufacturers we built aftermarket items for).

Thank you for letting us know about issues you've encountered when running our ARRMA replacement A-arms. Quite honestly, this is the first we've heard of this issue in the 2 years since we first released those a-arms.

After reviewing your forum post and the linked posts within, it sounds like this issue happens with stock a-arms as well (the forum member from your second link shows stock a-arms) so it doesn't appear to be exclusively related to RPM a-arms.

However, it's a very simple fix (which has been mentioned in your forums). Set the pivot balls up as you normally would, then remove the shims and turn both the upper and lower pivot balls in the same amount of turns (I believe the threads on those pivot balls are .7mm pitch so 1 full turn = 0.7mm). Turning them both in the same number of turns will retain the same camber angle but please be aware the toe angle may need to be reset after adjusting. One full turn of each pivot ball would be completely unnoticeable from a performance standpoint and may solve the problem you're experiencing.

Regarding the length of our a-arms in comparison to stock, I did a spot check on our stock version Kraton a-arm and compared it to a production piece and found the length to be identical within .001" (0.025mm).

Take care and thank you for your interest and support of RPM products. If you have any other questions or comments, please feel free to send us another e-mail."

 

[martysmith223]

The following is the email content I got from RPM not long ago. It's great to see companies be so responsive, though I'm not 100% in agreement with it. someone posted here a comparison (so I thought) between stock and RPM and I thought the difference was greater than 0.025mm which is buggar all.

"We do lurk at the ARRMA forums from time to time but sadly, are limited on the amount of time we have to post (you can imagine how many places we'd have to be to cover all the manufacturers we built aftermarket items for).

Thank you for letting us know about issues you've encountered when running our ARRMA replacement A-arms. Quite honestly, this is the first we've heard of this issue in the 2 years since we first released those a-arms.

After reviewing your forum post and the linked posts within, it sounds like this issue happens with stock a-arms as well (the forum member from your second link shows stock a-arms) so it doesn't appear to be exclusively related to RPM a-arms.

However, it's a very simple fix (which has been mentioned in your forums). Set the pivot balls up as you normally would, then remove the shims and turn both the upper and lower pivot balls in the same amount of turns (I believe the threads on those pivot balls are .7mm pitch so 1 full turn = 0.7mm). Turning them both in the same number of turns will retain the same camber angle but please be aware the toe angle may need to be reset after adjusting. One full turn of each pivot ball would be completely unnoticeable from a performance standpoint and may solve the problem you're experiencing.

Regarding the length of our a-arms in comparison to stock, I did a spot check on our stock version Kraton a-arm and compared it to a production piece and found the length to be identical within .001" (0.025mm).

Take care and thank you for your interest and support of RPM products. If you have any other questions or comments, please feel free to send us another e-mail."

yeah I have to say I'm not happy with the answer either I'm glad they responded but you wont catch me with an rpm on my kraton may used them on my odds and ends spare parts build )0... but I will be sanding the ends down on them just to play around with some different lengths Ill start slowly 1mm at a time... i already removed the little shims behind my pillow balls along time ago after tightening the pillow ball down so many times they just kinda blew out anyway ... they are still to long

yeah I have to say I'm not happy with the answer either I'm glad they responded but you wont catch me with an rpm on my kraton may used them on my odds and ends spare parts build )0... but I will be sanding the ends down on them just to play around with some different lengths Ill start slowly 1mm at a time... i already removed the little shims behind my pillow balls along time ago after tightening the pillow ball down so many times they just kinda blew out anyway ... they are still to long

and 6s definitely makes it worse

yeah I have to say I'm not happy with the answer either I'm glad they responded but you wont catch me with an rpm on my kraton may used them on my odds and ends spare parts build )0... but I will be sanding the ends down on them just to play around with some different lengths Ill start slowly 1mm at a time... i already removed the little shims behind my pillow balls along time ago after tightening the pillow ball down so many times they just kinda blew out anyway ... they are still to long

and 6s definitely makes it worse

for the record I'm not here to talk crap on rpm either they make great products they just didn't work out to well for me on this particular setup

 

[Lazy Bushman]

Agreed @martysmith223, this is absolutely NOT about dumping on RPM. In fact I would hate to see us dump on any company unless there was clear evidence of illegal or unethical practice. This is not that situation. There is a problem and we just need to find a way that fixes it for existing owners of RPM (which could include going back to stock or another product...I hope not). I like RPM, I just need to work this issue out. It could be that they are great out of the packet but overtime stretch too much....dunno but we will work it out.

someone did a side by side shot of stock and their RPM, that pic and the measurements would be useful. I will do mine tonight I hope but need to pack to go camping as well so might not get to it

...BTW I'm not unhappy with their response. Clearly they haven't have sufficient feedback on the issue for it to be a problem. I will ask them to check this thread specifically as non of the pics or comments are stock and in my quick skim of the links in the original post didn't indicate that this was a universal problem with stock either. It is a learning or all

 

[slick2500]

I am currently taking measurements of my stock V1 a arms and the Rpm a arms off the front and I will also measure the cv shafts, I will also install the stock a arms back and the front and take some pictures of the diff cups with those as well. If I have time later tonight or tomorrow night I'll tear apart the rear and get measurements of them as well. I will either update this post or just create another post if needed.


Front stock a arms. Note both lower stock front a arms are bowed, hence the different measurements.

Front Rpms.

CV Shafts.

 

[martysmith223]

Agreed @martysmith223, this is absolutely NOT about dumping on RPM. In fact I would hate to see us dump on any company unless there was clear evidence of illegal or unethical practice. This is not that situation. There is a problem and we just need to find a way that fixes it for existing owners of RPM (which could include going back to stock or another product...I hope not). I like RPM, I just need to work this issue out. It could be that they are great out of the packet but overtime stretch too much....dunno but we will work it out.

someone did a side by side shot of stock and their RPM, that pic and the measurements would be useful. I will do mine tonight I hope but need to pack to go camping as well so might not get to it

...BTW I'm not unhappy with their response. Clearly they haven't have sufficient feedback on the issue for it to be a problem. I will ask them to check this thread specifically as non of the pics or comments are stock and in my quick skim of the links in the original post didn't indicate that this was a universal problem with stock either. It is a learning or all

agreed iv already started sanding my ends flat so not gonna be a good comparison anymore ..I'm down 2mm and it's looking good may do one more after I check my droop and what have you ... had to pack it up for the night aperently baby boy don't like the sound of the bench grinder when hes trying to sleep lol should have seen the wife's face when I said it's only 10pm .... I'm gonna go out on a limb here and say rpm has alittle stretch to it over time I think she grows alittle

 

[slick2500]

Too many pics for one post.

Stock a arms diff cup.

 

[Lazy Bushman]

Thanks @slick2500 that looks about right. I might end up going back to stock still
I checked my RPM's vs Stock and they are pretty much bang on the same (less than a mill difference) except the RPM's do obviously flex more.

I have included a pick of both RPM's and interestingly you can see from the one on the right (which is the left arm when mounted) where it has been coming in contact with the diff cup. Compare that to the other one which hasn't which probably explains why it is the left dog bone that is always the one that pops. Also my GKA dog bones are about 0.3mm shorter than stock as well

 

[Primarrma]

I recently installed new rpm arms they have lasted about 5 or 6 packs, now the dogbones are popping out, this happened with my last set too. They start to get really soft and the droop setting doesn't do much anymore either, the shock can be easily over extended.

 

[bicketybam]

I've been running RPM arms on my Notorious and My Kraton. I removed the spacers and problem solved. I look at it like this: I can run the softer, more flexible RPM arms with no spacers and have then never break or run stock with the spacers and have then bust at the pin or elsewhere. I'd rather have arms that last with no spacers. I'd even shave them down if needed.

 

[Primarrma]

I've been running RPM arms on my Notorious and My Kraton. I removed the spacers and problem solved. I look at it like this: I can run the softer, more flexible RPM arms with no spacers and have then never break or run stock with the spacers and have then bust at the pin or elsewhere. I'd rather have arms that last with no spacers. I'd even shave them down if needed.

I've broken two rear rpm arms at the hinge pin, never broken an Arrma one, I've just stripped the threads for the pillow ball's(on both rpm and arrma arms). Funny how everyone has different experiences with products.

 

[bicketybam]

I've broken two rear rpm arms at the hinge pin, never broken an Arrma one, I've just stripped the threads for the pillow ball's(on both rpm and arrma arms). Funny how everyone has different experiences with products.

To be honest, I don't break a-arms. I would have to have a really miserable landing of a big jump to do it. I did had a crack in one if my stock Talion rear arms so I replaced it with a spare RPM one. I've got the best of both worlds, lol ? One of each in the rear!

 

[Primarrma]

To be honest, I don't break a-arms. I would have to have a really miserable landing of a big jump to do it. I did had a crack in one if my stock Talion rear arms so I replaced it with a spare RPM one. I've got the best of both worlds, lol ? One of each in the rear!

It happens over time, a bad landing does it in, but not straight away, plus my hinge pins are bent now, so that probably contributed. I still run rpm stuff, but I was surprised recently, I broke a wing mount and two rear a-arms. That rpm wing mount has lasted well over a year, you've seen the abuse it takes, wow.

 

[Notorious J]

I am currently taking measurements of my stock V1 a arms and the Rpm a arms off the front and I will also measure the cv shafts, I will also install the stock a arms back and the front and take some pictures of the diff cups with those as well. If I have time later tonight or tomorrow night I'll tear apart the rear and get measurements of them as well. I will either update this post or just create another post if needed.


Front stock a arms. Note both lower stock front a arms are bowed, hence the different measurements.
View attachment 37097View attachment 37098View attachment 37099View attachment 37100


Front Rpms.

View attachment 37101View attachment 37102View attachment 37103View attachment 37104


CV Shafts.

View attachment 37105View attachment 37106

As I have watched you and @olds97_lss posting these pics, I felt that I should mention one thing. The measurements should not be end to end. The plastic could be thinner or thicker where they wrap the hinge pins. On the fronts, the measurements should be taken from where the pillow balls screw in, to the "center" of the hinge pin hole. On the rears, it's from hole to hole. This measurement would give a more accurate distance, and determine if one is truly longer than the other. Agree or disagree?

 

[martysmith223]

As I have watched you and @olds97_lss posting these pics, I felt that I should mention one thing. The measurements should not be end to end. The plastic could be thinner or thicker where they wrap the hinge pins. On the fronts, the measurements should be taken from where the pillow balls screw in to the "center" of the hinge pin hole. On the rears, it's from hole to hole. This measurement would give a more accurate distance, and determine if one is truly longer than the other. Agree or disagree?

I agree with this