[ScythianNightingale]

just catching up on this thread, that's a clever repurpose of the PPF! glad to see you have this running around now!

 

[Forrest]

Spring break is here! Time to kick back a do nothing for a week.

Just kidding.

First on the list was repairing the mirror that had been wacked off while I was away. Turns out there might have been another problem that contributed to the failure. (This is what I saw when I took the glass out of the mirror).

Bolt replaced and now I am road legal again.

On to the next problem - the vibration I discussed last time.
Facts about the vibration:

• When driving, the vibration occurs when there is no or light load (coasting)
• When the car is up on jacks, the vibration always occurs unless I give full throttle
• The vibration is present on the sled, rubber mounts absorb most of it before it hits the frame.
• The vibration occurs at a frequency equal to the rpm of the motor/adapter/driveshaft
• Vibrations are at their loudest between 35 and 55 mph, at 60 they die down. (With wheels up)
• The problem did not occur with the last version. Tested at 45mph in neutral (last version had transmission), never heard it. So it probably isn't the diff.

Leading Theory: There is some slack between the male spline coming out of my adapter and the female spline in the driveshaft. That allows the driveshaft to wiggle out of alignment with the motor. Here is a video of the extent of the slack.

I felt the driveshaft while it was in motion - the part near the differential was centered and had no wiggle and the part near the adapter had the vibration at the right frequency.

Anyone have any ideas about how to cut out this slack?

 

[remy_martian]

Chevy used a special grease on the early 2000's pickup truck driveshaft splines. Might be worth a try?

 

[MattsAwesomeStuff]

There is some slack between the male spline coming out of my adapter and the female spline in the driveshaft.

It's a bit hard to see in the video, but just to rule out the stupid... the wiggle is not coming from a sloppy u-joint about to fail, right? It wobbles all the way to the splines, right?

Anyone have any ideas about how to cut out this slack?

Remind us again where this compler came from?

If it's that loose and floppy, I'd also be suspicious of it being machined on center and other issues.

The length of the shaft before the u-joint might be a problem. As a bodge, you could do surgery on both. Cut the coupler side shorter and extend the driveshaft longer.

Otherwise... if your coupler is so sloppy I dunno what would make it less sloppy other than adding more material back into it :/ . Super ghetto solution, a shot of JB-weld onto the coupler, squish the two together, try to guess where square is, and hope the JB fills the space appropriately. Then pull it off and maybe do it again in case some wiggled out.

Proper solution: Better coupler.

 

[Forrest]

It's a bit hard to see in the video, but just to rule out the stupid... the wiggle is not coming from a sloppy u-joint about to fail, right? It wobbles all the way to the splines, right?

Yeah, checked this. The u-joint isn't moving. The driveshaft female spline is definitely moving relative to the male spline on the adapter.

Remind us again where this compler came from?

I built the adapter. It is a taper lock on the motor shaft which is welded to a spline shaft. I had a machinist make the piece that the spline shaft slides in. He had the spline shaft when he made it - the shaft was air tight with the adapter before it was welded. He also faced the both sides, notable the one that is up against the taper lock. There isn't any play in this part of the design, and I don't see where it wouldn't be straight. The spline shaft was cut off an output shaft of a transmission. The guy who machined the thickest cylinder has lots of years in the biz and knows his stuff.

Here's an image of what it looked like out of the car.

It seems that the stock driveshaft (female spline) and the stock transmission output spline (male spline) have some play. In the actual transmission there is a bearing (probably two) around the outside of the female spline probably to eliminate this play.

Proper solution: Better coupler.

I guess I thought to myself when designing - what could be better than the OEM transmission output spline to the driveshaft?

 

[Forrest]

Chevy used a special grease on the early 2000's pickup truck driveshaft splines. Might be worth a try?

You know, I did not apply any grease whatsoever to this spline. A quick google search for "miata transmission spline grease" gives lots of online resources - miata specific forums claim it is required. I think for how easy this will be to do I am going to go ahead and do it.

 

[MattsAwesomeStuff]

I had a machinist make the piece that the spline shaft slides in. He had the spline shaft when he made it - the shaft was air tight with the adapter before it was welded.

Okay, well, that's obviously well made, I wouldn't worry about that.

There isn't any play in this part of the design, and I don't see where it wouldn't be straight.

Just to be thorough, even though it's probably not this... even if tightly machined, it could still be either of these, especially after welding:

MS Paints

It seems that the stock driveshaft (female spline) and the stock transmission output spline (male spline) have some play. In the actual transmission there is a bearing (probably two) around the outside of the female spline probably to eliminate this play.

Hmm, yes and no.

I think in a transmission you'll have a bearing on the outside of where the transmission tail shaft goes to support the weight of the driveshaft. The tail shaft of the transmission is obviously floating so that you can slide the driveshaft over it.

It'll also be filled with oil and there will be a seal that runs around the driveshaft to keep that oil in. This oiled and contained area is, in your design, exposed to the air. I was told to avoid this by some car guys, because that tailshaft-driveshaft spline coupler moves constantly every time the car's compression changes (it lengthens or shortens the distance between transmission and diff, slightly).

Since the driveshaft probably slid into the transmission right up to the u-joint, the bearing was presumably supported right there , forcing the driveshaft to stay square the way the transmission wanted it to, maybe allowing some slop in the splines. In your video you can kinda see where the scar is from where the end of the bearing would have been.

Or, perhaps the original two mating surfaces of the splines are now worn. Or, maybe, by driving them when dry, you've ended up using the imbalance as a scraper and wallowed out and exaggerated the wear.

Maybe you could get away with some grease that you replace regularly instead of being sealed in oil.

I guess I thought to myself when designing - what could be better than the OEM transmission output spline to the driveshaft?

Yeah

Well, one thing you could do, if you still have it, is cannibalize the tail housing of the transmission (if any?), bolt that to your motor faceplate, and use that to mechanically support the u-joint as originally designed. Or, come up with something similar. That combined with some grease might help. Maybe by this point you'll need a new transmission shaft. Maybe you could even still flood that area, if the seal on the motor is good enough and you can make a gasket around its face to the tranny tail housing.

Or, machine a whole new shaft that has better tolerances than the original, and pray that it doesn't work its way sloppy. But that seems like a lot more work than just getting a supporting bearing in there.

Also, thank you, because I was debating doing things the same way as you, counter to the advice of my mentors, thinking "bah, the transmission shaft will be strong enough, it'll be fine, I don't need a tail housing."

 

[Forrest]

You know, I did not apply any grease whatsoever to this spline. A quick google search for "miata transmission spline grease" gives lots of online resources - miata specific forums claim it is required. I think for how easy this will be to do I am going to go ahead and do it.

The grease is in. No noticeable changes though. When the spline was off I ran my fingers over the male spline on the motor, not much wear, but some. After not much driving.

 

[Duncan]

If you have the motor with the male driveshaft without the female bit

Just bodge together something that is very close to the splined shaft and rotate the motor - that should show if the spline is central and straight

And how are your motor bearings?

If you grab that spline and heave does it move at all?

 

[remy_martian]

Sounds like it's so sloppy that you need a yoke support bearing, which was noted by Matt.

What I would do is rework the driveline to have the telescoping in the middle of the driveshaft (some vehicles do this, and go for a rigid, zero-clearance attachment to the motor. Second option is to rework a trans tailshaft, but your problem will be keeping that support bearing lubricated.

A fair amount of work to fix this. Mid shaft telescoping splines and fixing the motor side sounds easiest to me.

 

[remy_martian]

Just thought of another idea...pour a "babbit" bearing in place to resize the splines, but lube is still a problem unless you can get away with grease.

 

[Forrest]

pour a "babbit" bearing

Would you elaborate on this? I tried google searching but came up with nothing that seemed like what you are talking about. You mean I should put a layer of metal in between the two splines? They aren't that far apart.

I don't have enough time to do this bit this week, but I think the best idea at this point is to replace the current driveshaft with a new telescoping one that will bolt directly onto my taperlock. Where do I get myself a telescoping driveshaft? On the internet new they seem to run 250-300 plus shipping.

 

[remy_martian]

Some pickup trucks use them.

Not 100% sure, but I think a Gen 5 Camaro might use one.

 

[MattsAwesomeStuff]

Just bodge together something that is very close to the splined shaft and rotate the motor - that should show if the spline is central and straight

Yeah, that'd be an easy check. Just a dial indiator seeing how off-center it is (like my two earlier diagrams).

I suspect that's not the issue. I suspect the issue are the splined pieces themselves.

And how are your motor bearings?

I mean, I guess check but, what could possible damage the bearings on that giant motor? He did buy it used though, IIRC, so, not out of the question.

It's also possible he wrecked the bearings with the bad spline alignment too, though, not likely.

Those are all quick things to rule out in a few minutes, so, good things to check.

...

Babbit bearings are how they used to do some kinds of bearings... I dunno, a hundred years ago? Yes, specific type of liquid metal poured in through a hole, that fills gaps. Though your gaps are going to be all around every spline, so, I think your odds of success are low.

...

I think Remy's suggestion of a telescoping driveshaft (or paying a machine shop to chop and add one) is a great idea. I didn't know that existed. Then just make sure your splines are well centered and weld the damned thing right up.

 

[brian_]

Whenever a shaft connects to components, either those components must be held rigidly at a constant spacing, or in some way the shaft must accommodate length change. In the stock Mazda Miata/MX-5 the required plunge in the propeller shaft is very small because the Power Plant Frame holds the components on the ends of that shaft apart relatively rigidly. If required, length change can be accomplished by:

• one end connected to a component by a sliding spline (the "slip yoke" of traditional drivetrains)
• a sliding spline or ball spline within a section of the shaft (usually used if both ends have U-joints attached to flanges fixed to the shafts)
• one joint allowing plunge

Universal (Cardan, Hooke) joints do not allow plunge, but some constant velocity (CV) joints do.
In common axle half-shafts, a tripod joint allows a lot of plunge; these are not normally used on propeller shafts.
Some other CV joints allow a smaller amount of plunge.
Flex disk joints (Giubos) allow a very small amount of plunge.

 

[brian_]

I think in a transmission you'll have a bearing on the outside of where the transmission tail shaft goes to support the weight of the driveshaft. The tail shaft of the transmission is obviously floating so that you can slide the driveshaft over it.

There is a seal around the outside of the slip yoke, but a bearing supporting the yoke is only needed if the tail shaft is short and can't provide enough support by itself.

Well, one thing you could do, if you still have it, is cannibalize the tail housing of the transmission (if any?), bolt that to your motor faceplate, and use that to mechanically support the u-joint as originally designed.

The TransWarP motors sold by NetGain (and at least originally made by Warfield Electric) use a tail extension housing:

This motor has a "shorty" tail shaft housing from a Chevrolet Turbo 400 transmission fitted to the drive end-bell (may be ordered with or without housing!) This is because the drive end shaft is not the typical 1.125" single-keyed type, but rather a hefty 1.370", 32-tooth involute spline that is identical to the tail shaft spline of a Turbo 400 transmission. In other words, this motor was designed to replace a transmission and couple directly to a drive shaft!

Note that they use the TH400 housing, but the only shaft in the TransWarP is the motor's shaft, running on the motor's bearings without any additional bearing in the extension housing. This extension housing just encloses the splined area and holds a seal around the outside of the slip yoke.

 

[remy_martian]

I forgot about the tail housing. Anyone know what it used for a bearing and if the tail housing is wet?

 

[brian_]

The TurboHydramatic tail housing is "wet", presumably with transmission fluid rather than grease. As used in the TransWarP it contains only the grease which is applied to the splines. There is a seal at the rear, around the outside of the slip yoke, in either case.

In the TurboHydramatic, the output shaft is short and supported by a bearing at the front end inside the transmission, but like the similar situation in a traditional manual transmission input shaft a bearing is needed at the free end (that's the pilot bearing in the manual input case); the THM uses a bearing (or a bushing in earlier or lighter-duty version) which looks like it is just inside the seal. In the TransWarp there is no bearing in the extension housing, because the motor shaft has two widely spaced bearings and doesn't need an additional one.

Here's an aftermarket THM 400 tail housing, showing the seal and the double-row roller bearing just forward of that:
Reid Racing TH400 Tailhousings