Marathon 36v Jerks repeatedly but does not go. I think it is the motor.

[kevinclark93]

Okay I am looking for a sanity check. I have an old marathon serial no 542608 and manuf. code H13893. It is new enough to have a controller, but not sure of the year.

If you hit the gas in forward or reverse the tires will rotate a few degrees and then bang and then rotate again repeatedly in a jerking motion. The tires will do the same thing off the ground on jack stands. It sounded like something mechanical so here is what have have done.

- Pulled the differential pan off and everything looks good. Nothing stripped and no shavings. Everything works as it should if you spin my hand.
- Pulled the motor off and the spline gears look good. There is a classic burned smell from the motor. If I spin the input shaft of the differential by hand the tires spin as they should.
- At this point I think it is the motor. I un-wired the motor and jumped it with jumper cables to rule everything else out. The results were the same tires spin in a jerking motion a few degrees at a time.

I want to get a sanity check that it is the motor before I buy a new one. The motor is series wound. Also as a side note when removing the cables from the motor the studs spun and that cant be good.

Thanks in advance

[billythekid13]

check your battery posts. i bet one connection is loose or a post is broken. what is the voltage on your battery pack?

[biphase]

Sounds like a power delivery issue. Check batteries under load while driving the cart. Jerking is caused by battery voltage dropping below the controller cut-off voltage.

[kevinclark93]

Battery pack voltage is 37.6 V. I tightened everything up and the same result.

[kevinclark93]

I bypassed the controller completely with the jumper cables. I jumped strait from the batteries to the motor and the same jerking result.

[kevinclark93]

Let me know if this video of the jerking works.


https://drive.google.com/file/d/1N5S...ew?usp=sharing

[biphase]

Originally Posted by kevinclark93

I bypassed the controller completely with the jumper cables. I jumped strait from the batteries to the motor and the same jerking result.

It jerks because you have a battery problem even when you bypass the controller. Get a voltage reading while the cart is jerking. You will probably see the voltage drop below 30 volts as the jerking occurs.

[kevinclark93]

Okay the pack is 34.4 volts while jerking and no single battery was less then 5.8 while jerking.

[biphase]

Originally Posted by kevinclark93

Okay the pack is 34.4 volts while jerking and no single battery was less then 5.8 while jerking.

OK, charge or replace the batteries and see if the jerking stops.

[kevinclark93]

Originally Posted by biphase

OK, charge or replace the batteries and see if the jerking stops.

Alright I have another set of batteries that were reading 38 volts that I jumped over to the existing battery pack in the cart and I am getting the same result with the tires jerking. As mentioned before the studs coming out of the motor are a little loose is that normal.