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Discussion Starter · #1 ·
Hi Everyone,

I’d like to see if someone could give me advice on a couple vibration issues i’m seeing. Here are the two issues:

1) When I’m going between 38-42 mph I’m experiencing a vibration that appears to increase with acceleration and is most intense at 40 mph. From what I have read it seems like possibly misalignment between motor/transmission or transmission/driveshaft? It has a 2 speed IE Drives transmission (based on Lenco drag racing trans). Since I bought the truck used I don’t have knowledge of the mating design between motor/trans/driveshaft. I've asked Jeff Barber at IE Drives (he has been extremely helpful) about the transmission, but I thought I would ask here in the meantime.
Here is a video showing the vibration at 40 mph: 40 mph Link

2) I’m also seeing a higher frequency vibration when amps are closest to zero and is independent of speed. I can feel it in the pedal and it feels more like an issue between the controller and motor. Here is a video showing the vibration at 0 amps: 0 amps Link

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Hi 1 Has this vibration been there from when you bought the vehicle, or has it just developed? if so its possibly a wear issue looseness has developed, spline/bearing or bolts loose. The vibration also on low amps is possibly as the slack had not been taken up, as once loaded, this helps no end, until 40 mph, this can then be part harmonics, if it subsides at higher speed, more likely better prop shaft support required ,but if worse both, or indicate wear/issues.
2 It looks a good job from the pics, but bringing the male spline further into the prop wont harm, as i assume the slider portion is located further back. 3 Are the UJs in good condition, especially the one in the photo, as its only supported by the gearbox drive shaft, and it may be possible to fit a bearing support to help, fit the type with a rubber mount in the centre section, slip this over the shaft, and then shim up to the bodywork to suit, which may involve having to machine an angled plate if it does not run parallel to bodywork fore and aft. Its unlikely the coupling housing is wrong, provided it was done in one setting and not removed from the chuck jaws and turned round, always a possible issue. If all else fails and lets say the housing machined diameters are not correct, clean of all crud first to prevent anything getting in the gap, and back off the bolts just a few turns, jack up one side solid, and jemmi the other end with a piece of wood, if it drops down an 1/8" of an inch, it is not good at all, but even then, if you can measure with a DTI the actual amount of gap up down, and it will be the same left/right, reset as best as possible, and try it out. If it drives ok job sorted, get back underneath and drill and tap a few more holes in the housing using taper lock pins etc, to ensure it stays in place, and it should be fine, that or strip it down completely and make a fresh adaptor plate a much longer job. Good luck. Dave
 

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Discussion Starter · #4 ·
Thank you David. The vibration was there from the beginning, but I didn't know it when I bought the truck because it had other issues and wouldn't go more than 5 mph. The spline does look like it is not inserted fully but I wasn't sure how much it should be. I just checked play in the spline and it doesn't look good. I took a video:

I think I'm going to take the drive shaft off and check things out.
 

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The outside of the female spline shaft is a turned and ground machined surface (until it rusted over in your case) designed to fit in a bushing located in the original transmission tail shaft housing. This close fitting bushing provides much better support than the normally looser fitting spline. The female splined shaft moving around sideways is probably causing the vibration you feel. You'll need to add, I think as mentioned, support bushing(s) or bearing(s) to support the female splined shaft- possibly with a modified original tail shaft housing.
 

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Why is the shaft joint at the motor so massive? A slip yoke is normally just one piece and doesn't need to be that bulky.

I don't know which Lenco this is, but the basic design is the CS1. Regardless of the model, they all appear to have a plain output end, without the tailshaft housing which is typical of a street transmission; in a more typical installation the housing surrounds the forward part of the slip yoke, presumably sealing against it and perhaps stabilizing it as electro works mentioned, but the Lenco doesn't have that housing.
 

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The large cylindrical piece of metal is a rubber mounted, torsional vibration dampener, similar in function(I guess) as the ones on ICE crankshafts. DIYDAN, you might try replacing the drive line with one that does not have a dampener and see if the vibration is reduced. Keeping the splines packed with heavy grease might help. Most set-ups like this, with exposed splines, have a grease fitting to pump in grease and a vent hole to prevent a hydraulic lock as the shafts work back and forth.
 

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The large cylindrical piece of metal is a rubber mounted, torsional vibration dampener, similar in function(I guess) as the ones on ICE crankshafts.
That makes sense, but it shouldn't be required and it would need to be tuned correctly to work... tuned incorrectly, it could cause torsional vibration problems. Even tuned properly, it seems likely to aggravate any problems with the shaft bending or the yoke moving laterally within the play allowed by the spline fit.
 

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Discussion Starter · #9 ·
The outside of the female spline shaft is a turned and ground machined surface (until it rusted over in your case) designed to fit in a bushing located in the original transmission tail shaft housing. This close fitting bushing provides much better support than the normally looser fitting spline. The female splined shaft moving around sideways is probably causing the vibration you feel. You'll need to add, I think as mentioned, support bushing(s) or bearing(s) to support the female splined shaft- possibly with a modified original tail shaft housing.
Thank you electro wrks. So I'm missing an essential support for the slip yoke! wow.
There are places on the transmission support bracket where I can envision mounting a support. I did some searching and found carrier bearings for driveshafts like this: link I'm wondering if this would allow too much radial movement given the rubber housing. If I went with a modified tail shaft housing are they typically filled with oil? or would I just be using it for supporting the shaft?
 

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Discussion Starter · #10 ·
I don't know which Lenco this is, but the basic design is the CS1. Regardless of the model, they all appear to have a plain output end, without the tailshaft housing which is typical of a street transmission
Thanks Brian,
Do you know what drag racers use to support the slip yoke? Is the support just not needed because of a completely different driveshaft design?
 

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Thanks Brian,
Do you know what drag racers use to support the slip yoke? Is the support just not needed because of a completely different driveshaft design?
I spent some time looking for examples, and I only found a couple, but they simply had what you have, but with a simpler slip yoke (no dampener) slid further onto the transmission's output shaft.
 

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Discussion Starter · #12 ·
I spent some time looking for examples, and I only found a couple, but they simply had what you have, but with a simpler slip yoke (no dampener) slid further onto the transmission's output shaft.
Thank you for looking.
I got the driveshaft off. I took measurements and I’ll be looking for a simple yoke as was mentioned. I measured 3.69” spline engagement, and the transmission spline length is about 4.5”. Here are some photos.

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I took measurements and I’ll be looking for a simple yoke as was mentioned. I measured 3.69” spline engagement, and the transmission spline length is about 4.5”. Here are some photos.

View attachment 119960
So the transmission output shaft is quite long, and the spline engagement is fine as it is (you need some allowance for shaft plunge anyway)... it's just the size of that dampener that made it look questionable to me. Maybe without the flex and mass of the dampener it it will be okay, although we're still guessing at causes of the vibration.
 

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Looks to me like the rubber in that damper has seen better days. If this was my setup, I'd cut the outer ring of that damper off, and get rid of all that rubber. All you need is the slip joint and yoke. Quick, I think harmless/beneficial, mod to see of the vibe goes away.
 

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Discussion Starter · #15 ·
Looks to me like the rubber in that damper has seen better days. If this was my setup, I'd cut the outer ring of that damper off, and get rid of all that rubber. All you need is the slip joint and yoke. Quick, I think harmless/beneficial, mod to see of the vibe goes away.
Thanks for the input. That’s exactly what I started doing today! I got the damper off and I need to get the rest of the rubber off. It seemed pretty impossible to find just a yoke that was the right dimensions anyway. I hope to have it back on tomorrow.
 

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Thanks for the input. That’s exactly what I started doing today! I got the damper off and I need to get the rest of the rubber off. It seemed pretty impossible to find just a yoke that was the right dimensions anyway. I hope to have it back on tomorrow.
The problem with this move is that everything has been balanced as a unit, judging by the drilled balancing holes in the outer weight. If you still have a vibration problem, a drive line shop can rebalance the drive line. To answer your question about using a modified tail shaft housing and bushing to support the female splined section: Yes, you would have to provide lubrication for the bushing and rubber seal in the housing. This could be separate or with the oil from the gear box. Check with the box manufacturer or supplier.
 

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The problem with this move is that everything has been balanced as a unit, judging by the drilled balancing holes in the outer weight. If you still have a vibration problem, a drive line shop can rebalance the drive line. To answer your question about using a modified tail shaft housing and bushing to support the female splined section: Yes, you would have to provide lubrication for the bushing and rubber seal in the housing. This could be separate or with the oil from the gear box. Check with the box manufacturer or supplier.
That balancing is to compensate for tolerances in the rubber damping insert after it got molded. Not to balance the driveshaft assembly.
 

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It's doubtful that the manufacturer of this drive line would go to all the trouble and expense of balancing it twice. Once before the dampener was added; and for the second time after it was pressed on. You should be able to tell after the dampener is completely removed. There would be a second set of balancing holes drilled in the remaining parts, if it were balanced twice.
 

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Discussion Starter · #20 ·
I got the damper and all the rubber off the driveshaft and got it back onto the truck. It still has the same vibration at the same speed. One thing I noticed before and after removing the damper is that the vibration goes away if I'm accelerating uphill and comes back if I don't accelerate uphill. It seems to change based on the angle of the truck. I'm still trying to do tests on hills but I'm sure of the uphill phenomenon. I'm wondering if there is some instrument I could install to confirm it is at the driveshaft, like a camera, vibration sensor or maybe something simpler.

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