Bad motor or transmission? 2008 gem

Hey there -

I have a 2008 GEM 4 seater with a 7.5 hp GE motor. Everything is completely stock but I do have the MM installed. The car was in good working order.

Hit about 40-45 going down a hill this morning and something gave way. Heard a bunch of grinding after I let off the accelerator as I slowed the car.

The car still functions but it won’t go over 18mph now and there is some unfamiliar grinding noise when on the accelerator. The power seems to cut around 16-18 mph.

Any recommendations or ideas would be great. Thanks!

Pull the motor. It sounds like you winged it a little too high.
Take pictures. Post results.

Just so we can math out how high it went -
What is your trans ratio?
What is your tire height(diameter)?

Outer tire diameter is 20.5”
Differential 12.44:1 <-> PN 0613-00643

I’m paging around trying to find the max rated RPM is on your motor. Does it say on the label?
I know the 5hp is rated 4100(pushable to 5k). What is the 7.5?

FWIW the MM can be set to limit rpm to a safe level. We push the transmission to 9k rpm all the time.
A brush motor will grenade, as Rodney puts it, over 6k rpm.
Seriously? Tires are that small?
With those tires and 1+3 MM setting, car should have limited to 35mph, actual. Something must have happened before the motor damage.

And how were you judging your speed? Seat of your pants? Or GPS?

But just for shock value- plugging in your given numbers you may have hit 8~9k rpm running down that hill !!!

Speed was the appx reading from the speedometer set to kph. Never tweaked any of the MM settings from the way it shipped. We have some speed radars in my area and generally the reading is slightly less than the radars repot (by ~2mph or so). Last reading I saw before things went kaput was 42, then the screen went blank, then grinding.

Generally the cars top reading on flat level was somewhere around 34-35 . Contributing factor was definitely the grade. I’ve driven it a few hundred times, difference was I was grabbing coffee at 5am and there wasn’t anyone on the road so I tried to set record.

Attaching the label of the motor and double checked the tire diameter.

Ok, Now I gotta see pics of the inside of the motor!

there wasn’t anyone on the road so I tried to set record.

Atta boy!!! Sorry about the apparent results tho.


We have some speed radars in my area and generally the reading is slightly MORE than the radars repot (by ~2mph or so).

bearings are good to 18k ish, so my guess is on severely arc flash damaged commutator. Seen ones that looked like they were wrapped in non skid tape.

Luckily, that motor is pretty beefy. If that is the damage, you can send it out to be turned and if needed, undercut.

This is what happened with my 2013 e6 Interested to hear the result. Did you have any codes when you were running afterwards at lower speeds?

12.44 gears, small tires and 40+ ? You grenaded that thing. those are great ,motors but at 200% of max rpm …

And getting worse as you drive. The springs weaken and act like a governor. I bet. Lifting off the comutator.

I am a bit intrigued by this statement. Why would the screen go blank? Even if he just meant speed went to zero that might mean he exploded a magnet. Speed works after tho because he made it home.

If windings came apart and flailing around inside motor then it might be shorting to case. Would controller see this as over curent and shut down (it kinda does this when doing brake stand test but doesn’t blank the controller).

The power seems to cut around 16-18 mph.

So now a wire shorts out around 18mph. (guessing) But no error codes?

Also waiting for pics…

Are you in the south bay area at Torrance Redondo Beach Manhattan Beach

I believe he is down more south. Oceanside.

He fried 1 or more winding’s on the armature. 1 or more open armature winding’s and you end up at about half speed. Real common on AMD, don’t know why.

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im in north county san diego.

I pulled the motor over the weekend. I will take it apart shortly and post pictures here.