GPM Driveshaft Defect

[GraciousOne]

Hey guys.

Recently I purchased a set of GPM Axial driveshafts (from AsiaTees), part number SWR037. But when I took a look at the darn things, the u-joints at either end don’t line up. I.e. on any Axial/Traxxas driveshafts there is a mark on either end of the driveshaft that you have to line up when you put the two halves together. This aligns the u joints the same at either end. But the GPM ones don’t line up. One is off only a bit, but the other isn’t even close. Anyone else have this problem?

I'm confident I can return them, but the question is whether to ask for another pair or a refund/store credit. If a thousand other people have had the same problem, I'll get the refund....

Thanks.!

[ZippoMan]

I say get a refund and buy MIP's!! Then you never have to worry!!

[GraciousOne]

I understand what you're saying, man. But I can tell you, the GPMs are tough - one of our local guys who runs 3S brushless, and breaks drivetrain parts on a regular basis has NOT been able to break these. So, aside from the alignment issue, they seem to be good quality. But for sure, I will check out the MIPs - the more options the better.

[doublej]

Why is this a problem? Does the drive shaft work as needed?

[GraciousOne]

U joints have to be installed with the correct alignment as the rotational speed is not constant. The gearbox output turns at a constant speed (because it's driven by the motor), but the SHAFT does not spin at a constant speed (i.e. it speeds up and slows down) because of the way the u joint works. If another u joint is put at the end of the shaft that goes into the diff (with the correct alignment), it reverses the effect (speeding up and slowing down) of the u joint, and thus the diff (and hence axle) gets a constant rotational speed input. So, the u-joints at either end of the shaft have to be aligned correctly to cancel this effect out. That's why all Axial and Traxxas driveshafts have those alignment marks.

Is it harmful? Well, it will be that much harder on your drivetrain, and it may not rotate very smoothly. I also think it would wear the u joints out much faster. But to be honest I have no intention of "testing" it on my truck. The part is defective and it ain't going on my rig.

I suspect the strain on your drivetrain is increased on a high grip surface and reduced on a low grip surface, just like locked diffs and overdrive/underdrive setups.

[Calderwood]

Originally Posted by doublej

Why is this a problem? Does the drive shaft work as needed?

If the joints are out of phase they create a pulsing effect. A non constant velocity joint has a speed oscillation. When the joints are in phase one is slowing down as the other accelerates thus canceling each other out.

Edit: G O beat me to it. I got a phone call in the middle of my reply.

[OSRC]

Got them on a rig I picked up in a trade. I've been running them for months with no issues. Not sure on the joints, I never really looked. I kinda expected to have some issues with them, but so far so good.

I had no idea on this, I assemble my wild bores on my rigs willy-nilly - never even thought of lining up the joints.

[67mustang]

I don't see an issue with the joints being out of phase. Unless you are going for serious wheelspeed the worst thing that could happen is a little accelerated wear on the supporting bearings. If you have experience with traxxas shafts why use a gpm? Asiatees is cool and i spend money there, but I choose traxxas over gpm when it comes to shafts.

[GraciousOne]

67mustang - there was just someone local who could 100% certify that they were bomb-proof, given his attempt to destroy them on 3S. Certainly not to say there aren't a bunch of other options out there, like Traxxas. At the moment, just trying to find out if the issue I had is widespread or just very bad luck.

[GraciousOne]

And please note - there are lots of manufacturers that claim their driveshafts are constant velocity (or CV, or CVD) that are NOT. They are just variations on the u-joint. The MIPs I saw for the Wraith are not CV joints.

And I agree that this misalignment MAY not cause a problem. However, the effect is real, and it's detrimental. My only point was I'm not exposing my truck to extra wear and tear because of a faulty part just to see if it may or may not cause a long term problem.

[Natedog]

Originally Posted by GraciousOne

U joints have to be installed with the correct alignment as the rotational speed is not constant. The gearbox output turns at a constant speed (because it's driven by the motor), but the SHAFT does not spin at a constant speed (i.e. it speeds up and slows down) because of the way the u joint works. If another u joint is put at the end of the shaft that goes into the diff (with the correct alignment), it reverses the effect (speeding up and slowing down) of the u joint, and thus the diff (and hence axle) gets a constant rotational speed input. So, the u-joints at either end of the shaft have to be aligned correctly to cancel this effect out. That's why all Axial and Traxxas driveshafts have those alignment marks.

Is it harmful? Well, it will be that much harder on your drivetrain, and it may not rotate very smoothly. I also think it would wear the u joints out much faster. But to be honest I have no intention of "testing" it on my truck. The part is defective and it ain't going on my rig.

I suspect the strain on your drivetrain is increased on a high grip surface and reduced on a low grip surface, just like locked diffs and overdrive/underdrive setups.

I agree completely, don't run them, return and get a good non-defective pair or a refund.

Originally Posted by Calderwood

If the joints are out of phase they create a pulsing effect. A non constant velocity joint has a speed oscillation. When the joints are in phase one is slowing down as the other accelerates thus canceling each other out.

Yes.

Originally Posted by GraciousOne

And please note - there are lots of manufacturers that claim their driveshafts are constant velocity (or CV, or CVD) that are NOT. They are just variations on the u-joint. The MIPs I saw for the Wraith are not CV joints...

Yes.

[Johnnysplits]

I had these shafts in my wraith on 4s...never had an issue. I just bolted them in. Driveshaft phasing? Seriously? You would get more vibration from out of balance tires than you would ever get from a driveshaft. And at the speeds these run and being offroad, it would be irrelevant.

[Calderwood]

Originally Posted by Johnnysplits

I had these shafts in my wraith on 4s...never had an issue. I just bolted them in. Driveshaft phasing? Seriously? You would get more vibration from out of balance tires than you would ever get from a driveshaft. And at the speeds these run and being offroad, it would be irrelevant.

Yes, seriously. Any performance gain is worth exploiting. If you ignore all the little stuff, you end up missing a big chunk. Ounces equal pounds.

[WHITE-TRASH]

Originally Posted by Calderwood

Yes, seriously. Any performance gain is worth exploiting. If you ignore all the little stuff, you end up missing a big chunk. Ounces equal pounds.

If this was a 1:1 I'd agree completely but on an R/C car pfffft not a chance. The drivelines don't give half a damn since their weight is so low that any out of phase situation is negligible. Do you whip out your angle finder when setting pinion angle on your R/C's? If not you're not exploiting a gain.

Half the time I don't get my mip's lined up perfectly and I have yet to notice any negative effect.

[GraciousOne]

Originally Posted by Johnnysplits

I had these shafts in my wraith on 4s...never had an issue. I just bolted them in. Driveshaft phasing? Seriously? You would get more vibration from out of balance tires than you would ever get from a driveshaft. And at the speeds these run and being offroad, it would be irrelevant.

No one here is saying that this is the sort of thing that blows a driveline apart the second you hit the throttle. It DOES add unnecessary wear and tear on your driveline, fact.

AND the most important thing to remember is that this is all completely unnecessary. If they hadn't been machined incorrectly in the first place, all of these issues would disappear. A properly machined set of driveshafts would be bombproof AND not induce any extra strain on the drivetrain.

THAT's the point. Just sayin'.

[altd896]

As an idle though, has anyone else noticed that MIPs don't have a master spline or have any reference to joint phasing in their instructions?
Possibility it doesn't actually matter?
I know none of my WB8s or MIPs in SCX10s, Wraith or 2.2Shafty are phased & I have no vibration or binding issues.
Cross style uni joints however, whole different story.

[Calderwood]

Originally Posted by WHITE-TRASH

If this was a 1:1 I'd agree completely but on an R/C car pfffft not a chance. The drivelines don't give half a damn since their weight is so low that any out of phase situation is negligible. Do you whip out your angle finder when setting pinion angle on your R/C's? If not you're not exploiting a gain.

Half the time I don't get my mip's lined up perfectly and I have yet to notice any negative effect.

Oh come on. We have been agreeing on everything lately! and remember just because you don't notice it doesn't mean its not there.

I know that a lot of my idiosyncrasies are habits learned from years of 1:1 playtime. Some stuff is hard to let go. and I might be a little ocd.

[WHITE-TRASH]

Originally Posted by Calderwood

Oh come on. We have been agreeing on everything lately! and remember just because you don't notice it doesn't mean its not there.

I know that a lot of my idiosyncrasies are habits learned from years of 1:1 playtime. Some stuff is hard to let go. and I might be a little ocd.

In 1:1's you're absolutely correct, the u-joints absolutely HAVE to be in phase but that's a whole different animal than a toy truck driveline that doesn't even have bearings or any way to contain a smear of grease.



When I had my scx together I straight up wore a yoke right the fawk out at the front trans output due to the high angle that was required to have any uptravel for the front axle. So yes, high angles surely do wear parts but I don't see any phase issues unless you run short links and terrible angles. If you do that you deserve whatever problems arise.

[GraciousOne]

As mentioned before, MIPs are NOT CV joints, thus they have to be aligned correctly for OPTIMAL performance, whether it's in the instructions or not. I'm NOT saying that if it's not aligned correctly, the truck will vibrate or not work at all.

Not that I make a habit of it, but I have driven my SCX10 on pavement. It never shuddered or vibrated or made grinding noises, etc., but it sure as hell was putting a lot of unecessary strain on the driveline.

[WHITE-TRASH]

Originally Posted by GraciousOne

As mentioned before, MIPs are NOT CV joints, thus they have to be aligned correctly for OPTIMAL performance, whether it's in the instructions or not. I'm NOT saying that if it's not aligned correctly, the truck will vibrate or not work at all.

Not that I make a habit of it, but I have driven my SCX10 on pavement. It never shuddered or vibrated or made grinding noises, etc., but it sure as hell was putting a lot of unecessary strain on the driveline.

You are correct that no one makes a true constant velocity driveline or axle shaft. In order to do so the joint would either be huge or extremely fragile.


I drive all of my rigs on rocks, concrete rubble, pavement, etc etc with no issues so far. Two of them have overdrive front gears and underdrive rear with sticky tires. At best I get increased tire wear but that's the only thing I can blame on the traction.

My best advice is to either send the drivelines back or stop thinking so hard about miniscule amounts of imagined wear and just enjoy running the silly thing.