Under power the cart and motor are quiet. When coasting downhill and at the limits of cruise speed when not under power, it has a vibration like hitting the rumble-strip at the side of the highway. Give it power and it goes silent. I tested it by turning off the power while coasting, and the vibration quit. 7.5 HP GE motor, 2012 GEM E2 cart 88.8 Gigawatt Di-Lithium power cells from L-God. Love the range! I do have a 5hp motor available to swap into it (if needed). Thanks for your thoughts.
Normally Iâd say it is your gearbox/motor spline coupler showing signs of wear and getting a little sloppy. Your observation of the vibration going away when KeyOFF is interesting and may be pointing to something else.
Backstory-
The motor only has one bearing, supported at the brush end only. The coupler end is supported by the gearbox bearing through the coupler/input shaft.
When under load, pressure under accel more/less locks it into a position where the armature is inline and happy (possibly due to the magnetic field?)
When under Decel/downhill two things might be happening:
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When coasting/low load, the armature sags a bit and allowed to wander around(off center) in the housing and slop around on the gearbox input spline.
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Under Decel, the controller is actively trying to slow the car (either through Plug braking or Regen). This may be either causing the armature to go off center, or pulsing the motor and it is rattling the car.
The motor experts are free to jump in on the thought. It might be worth looking at some numbers in the controller and see if heavy regen might be a contributor to this.
Spend some time in the archives and you will find the normal suggestion for a âVibration on Decelâ is to change out the rubber damper/bumper in the coupler. This may be a fix. I am not too much of a fan of this as it might be more of a band-aid covering up a bigger issue. I believe this simply loads up the bearings on each end (gearbox and motor) and if overdone, overheats the bearings (usually the motor end) because they are not thrust bearings designed for that.
Itâs something you can check tho. Pull the motor, replace that bumper, and give the spline a dab of coupler grease.
Thanks, as always, for your thoughtful and prompt answer. I agree that probably this is a supporting bearing on one end of the motor. I have a 5hp motor that was changed for the 7.5 one on it now. It can be examined (bearing) and swapped back onto the cart to test. Question; how big of a job is it to change the bearing in the tranny, compared to changing out the wheel bearings? Thanks again!
R.
Interesting how you somehow took away that I was blaming the bearing.
I re-read your reply, and went back through the archives to a Rum-Rum-Rum sound from 2017 and their rubber damper and tranny bearings/seals and input shaft comments. Still gathering data points before diving in. My concern has been the cost of negligence if I avoid this repair for a while. For now it seems like an annoyance more than a harbinger of catastrophic failure afoot.
I remember noticing a lot of side play on the input shaft when installing the ânewâ motor. Shouldnât the input shaft be immovable except in rotation?
Yeah, there should NOT be much side-side play on the input shaft.
It would probably be worth looking more into that.
Is there much noise coming from your gearbox? How is the oil level.
If you lose a bearing, the chunks and metal bits will destroy the rest of your gearbox.
Worn input shafts / bad input bearing are not uncommon on GEMs with higher mileage.
Itâs an easy job. Disconnect / remove whatever you have to get the motor out, pull the motor, remove the internal C-cip holding the input shaft seal in place, pull the oil seal, grab the input shaft with a rag and vicegrips and yank. No timing marks or alignment / shimming to worry about when you install a new one.
Rodney usually has them in stock. You will need to know your transmission ratio, you can look this up by the Dana part number on the sticker.
When you reinstall, take a pick and make damn sure there isnât a wafer-thin bumper stuck up inside the motor collet. If you end up with two bumpers in there or a bumper and a dime, youâre going to smoke a bearing. Probably the end bearing in the motor.
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Hereâs an edit of what I know âfor certainâ. The rumble happens only under deceleration under power. If I switch off the ignition (going down hill, and pull on a click or two for the handbrake to kill the buzzer) the rumble instantly quits. Key back on (and handbrake off) and it will resume. Hence, it is a motor and power related issue and maybe not yet attributed to the gearbox. I will check that oil. Does Plug Braking, or Regenerative power make a pulsing sound?
Thanks, I figured as much . . . and will watch out for the too-fat bumper problem. What is Rodneyâs firm?
Your attempt at clarity has introduced a bit more mud into the water.
Do you need to do BOTH actions to get the rumbly to stop? (turn off key, pull up a couple clicks on brake?)
Or is the brake just so you can shut off the (eardrum splitting) beeper so you can verify the vibration has indeed stopped?
Is this also at Pedal UP condition? Does it go away when pressing the pedal down just a little bit?
I have always assumed the Regen was a straight DC action (not pulsed). Your observation after depowering the car still makes me want to look into this further.
Q- When you last did the motor swap, Did you also put a little spline grease on the coupler? Or did you install the motor dry?
Rodney goes by the handle @Old_Houseboater here in this group. Click on that tag (if he does not show up) and send him a personal message asking about status of a new input shaft kits.
Mud is my middle name! Handbrake is only to stop buzzer and doesnât come close to braking at 2 clicks, cart rolls freely. Key off is enough to stop rumble. Handbrake just makes it easier to verify. Yes, Pedal UP condition on a hill will generate rumble, as will the forced coasting when at V-max when the limiter cuts in (about 25mph.) Yes, pressing the pedal can terminate the rumble (when Iâm slow enough and have headroom to accelerate). On motor swap, yes to spline grease and yes to double check rubber bumper. Going out to check oil levels now. Thanks again, keep those questions/ideas coming.
keep those questions/ideas coming.
What is the airspeed velocity of an unlaiden swallow?
Have you tried switching out the gear oil? Use a heavier 85w-140. It quieted mine down.
Yes, just drained and changed to your suggested oil and will test. Actually, a next step after that is to swap back my 5 HP motor for the 7.5 on it now. That way I can also check the play on the input shaft (and replace if needed). Thatâll remove 2-3 variables.
Meters or Feet per second? 
African or European?
African or European?
Huh? Well, I donât know.
Whiff!!!
AAAAaaaaaaaâŚ
Update: today I pulled the motor, and checked the tranny input shaft for wobble. Itâs firm and wobble-free. Checked the rubber damper disk in the splined coupler on the motor, swapped it for a fresher one on my spare motor and cleaned and lubed all those surfaces before reassembling. Still rumbling. However, now we can eliminate the tranny input shaft question.
I did recently replace the wheel bearings and CV boots and âMightâ have noticed the output cups at the transmission that drive the CV joints âMayâ have had some slop. Couldnât find a detail or torque spec. about them. Ideas? It is a PITA to have to pull the half-shafts to tighten a bolt if there is one inside that cup to the tranny output.
CV/Axle assembly is not turning fast enough to generate a vibration.
I think you were also going to try swapping to the other motor?
Do you have a Magic Magnet on this car? (to allow faster speeds)