Where's the Torque?

[BanOne]

Hey, y'all.

First, big thanks to all of y'all that contribute regularly to this site. The wealth of information available for free is just incredible. Scottyb, I don't know you, but you're one of my heroes! Ha! As I keep learning, I hope to pay it forward.

I'll make a long story fairly short:

I've never owned or messed with a cart until a few months ago. I picked up a 1990 EzGo Marathon (36v, series, controller cart) that had been damaged in a fire as a quarantine project. I spent the better part of a month stripping it down, cleaning, doing body work, and then figuring out mechanical operations. I have tried to keep my budget reasonable considering that it is a 30 year old cart that was in a fire, but all in all, I'm real happy with how it turned out.

I have just one problem remaining: I have zero torque. I mean so little torque that if I'm in the grass, I'm liable to just be stuck there until I pull out the Fred Flintstone technique. I'm wondering if you all could help me think a little?

Here is what I've done mechanically:

1. The battery pack in the cart was new in 2018. It was not damaged in the fire (at least visually). I visually inspected each battery, made sure water levels were correct using only distilled water, and charged properly. At 12 hours rest after full charge the cart reads right at 38.2v. I've tested the pack as well as each individual battery under load in a high amperage situation (i.e. stuck in the grass on a slight incline at fully depressed pedal.). Each battery reads between 6.3v and 6.4v at full charge under rest and holds up with no more than .15v of drop per battery under load. I don't have a proper load tester...just my multimeter... but that's what I got on that. I feel like the batteries are OK. They're not a high end pack... Just 6v batteries from O'Reilly's Auto... But they seem to check out.

2. I replaced all of the battery wires, wires to the F/R switch, wires to the solenoid, and wires to the motor with 2awg wires.

3. I installed a 200amp HD solenoid with 250ohm resistor and diode in the proper direction.

4. I replaced the F/R switch. (Should have went HD... Didn't realize that at the time... but I know I have a good F/R switch...)

5. I disassembled the motor (2hp), polished and cleaned the armature and commutator, replaced the brushes, and replaced the commutator bearing. I cleaned the magnets and they look to be good.

6. I had a high whine in the differential... I happened to find someone selling a 1993 version of the cart that had a broken frame, but it had a few plastic pieces I needed and an intact differential and motor. The price was right. I replaced my differential (which had been exposed to high heat in the fire) with the other. Whine went away. I'm happy with my differential. I've cleaned it and changed the fluid with proper gear lube. I tested the other motor on my cart... Did not fix the torque issue. Don't think the issue is the motor. I'm saving the other as a "back up."

7. I tested the potentiometer and had 1300 ohms of resistance at rest and 4200 ohms at fully depressed pedal. Knowing it had been exposed to some high heat, I replaced it. I now have 0 ohms at no pedal and 5300 ohms at fully depressed pedal.

8. And this brings me to what I think could be the culprit, but I need y'all's collective brains at this point. The cart would not move when I got it. I could not get proper voltage through the controller. (i.e., I couldn't get any voltage when measuring for output across B+ and M-.) I had proper voltage at controller input (B+ and B-). I sent the controller off to someone I found who repairs controllers. Since I was still learning, it seemed like a low cost troubleshooting attempt. The controller came back, I hooked it up, and BOOM... We were rolling. My voltage across B- and M- is near pack voltage at full pedal. But I have no torque...

So, here I am a little stumped. My thoughts are that perhaps something is still funky with the controller and thus causing my problem.

Some other info that might help:
- It's not lifted.
- It is running larger than stock tires and wheels... 205/50s on 10" wheels.
- I've replaced all my brake cables, pulled my drums, and inspected and cleaned everything. I do not have brake drag.
- I've replaced my rear leafs with HD leaf springs and shocks to support a back seat.
- I've installed a voltage reducer and fuse block so that I could wire in tail lights and head lights. The torque problem existed before that and has persisted after, unchanged. All lights are LED.

Maybe most interestingly... My speed in this cart is great. I live in a very flat place, and with no passengers and just me driving the cart will do about 18mph. That's a lot faster than I expected out of it... but then again, as stated, I had no experience. It does not, to the best of my knowledge, have a high speed gear installed. Having the same problem across two differentials probably also helps confirm that.

So, that's it... I know that's a lot... But if anyone sees where I've overlooked something, not considered something, or just flat out goofed up, I would SO appreciate any help y'all can send my way.

My next step would probably be to just go ahead and upgrade to a new 500amp controller... But figure I need to think on it for a spell longer! That purchase will about double what I've spent on the cart all along! Ha!

Thanks so much!!

[cgtech]

When that happened to me, it was a bad controller. But, in the controllers defense, I did put a 48v pack in place of the 36v pack (which worked well for about a month, until I had no torque). I couldnt run over a 1" taller sidewalk without a running start.

[BanOne]

Originally Posted by cgtech

When that happened to me, it was a bad controller. But, in the controllers defense, I did put a 48v pack in place of the 36v pack (which worked well for about a month, until I had no torque). I couldnt run over a 1" taller sidewalk without a running start.

Thanks, cgtech! That's exactly my scenario. If I'm on the flat, paved road I'm rolling without issue. If not, it's trouble and the Fred Flintstone feet have to come out. Ha!

[cgtech]

I could get up to full speed, if I had 3 blocks of flat road to get there.

[BanOne]

Same!

You just replaced the controller and were good to go? I’m not looking to break land speed records here. I mean, my other toy is a KLR650. Clearly I don’t care about speed. Ha!

[cgtech]

I did my 48v conversion without changing the stock 36v controller just to see how long it would last, or even would it work even once. It worked fine for about a month, then no torque. I already had a alltrax sitting at the ready for when the inevitable happened. I tossed the alltrax in, and everything was perfect.