91 Club Car: Forward Only, No Reverse

[firepuppy]

Wow, NO replies at all for 24 hours, then a flood of good discussion in the last 8...

I finally got a chance to review the replies and run some tests this evening and I have to tell you I thought CTD was on the right track when he kept pointing out my 18V on the purple wire going back to the motor (see photo). To further support his (and my) presumption of a motor issue, what I didn't mention in the original posts was that I had ohmed out the F/R switch during my tests: in the forward position, top bus bar is shorted to purple & bottom left bar is shorted to white (grey in Sergio's diagram); in reverse, top is shorted to my white wire & bottom right bar is shorted to purple; based on that test I was pretty sure the switch was doing what it was supposed to...

So now for the surprise: I was in a bit of a hurry (too many mosquitoes down here tonight!!), so I opted for scottyb's test: it would only take a couple minutes and would eliminate the F/R switch completely. I was stunned when I did the swap and suddenly had a (really fast!) reverse-only cart!!

Ok, so it appears Sergio's hypothesis about an open in the yellow circled area is causing my problem; this brings up 2 more questions:

1. Why did my ohmeter show connectivity from the top right bus bar to the white wire in reverse?
2. If there is just enough connectivity to carry the ohmeter's microamps, but not the XX amps under load, can I take the F/R switch apart & clean up the bar rather than order and wait for a new one to come in?

Thanx again for all the input; hope I can pay it forward some day...
fp

Originally Posted by firepuppy

Wow, NO replies at all for 24 hours, then a flood of good discussion in the last 8...

sorry i was at the beach ... the ladies would not let me alone to get on the net ... lol

yes you can take f/r switch apart and clean it... it might work
look into a heavy duty from scotty b

http://www.cartsunlimited.net/F_R_Switch_Upgrades.php

[firepuppy]

Ok, finally got a working cart today! And the correct answer was... We were ALL wrong! Turns out scottyb's test of swapping the 2 cables on the F/R switch eliminates the motor from the list of suspects; however, there's another part in the circuit (besides the F/R switch) that doesn't get used in that test: the (green in my case) cable from the middle battery (18V takeoff) to the bottom right lug on the switch!

I first took the switch apart and cleaned up all the copper and it looked fine, so before ordering a new one I hooked it all back up and started testing voltages again. I finally found I was getting 18V measured at the lug until I stepped on the pedal; then it dropped to 0 (still showed 18V at the battery end of that cable), so I guess the cable was corroded internally just enough to cause an open when trying to push all the amps through.

Anyway, thanx for all the help from everyone and I hope this thread helps someone diagnose a similar issue in the future!

[Volt_Ampere]

A standard ohmmeter can't measure the low resistance you need for a motor circuit to work properly. You need to be able to measure miliohms. This is why most of this stuff has to be measured under a load. There are special low ohm meters available that incorporate a four wire system to eliminate lead resistance. Most of us don't have one.

[kantuckian]

Good Info