1993 EZGO - Reverse is fine, Forward is a problem. It's NOT the FNR.

[SanJoseMichael]

I recently bought a 1993 Ezgo Marathon (Ezgo web site shows S/N 782159 = 1993 while MFG A07974 suggests 1994, so it may be a 1993 1/2). Ran fine when I got it, and it has recently developed a problem: it will run in reverse just fine, but foward is problematic.

It would sometimes not go forward, the after many presses of the pedal, it would jerk forward at a high speed and then work fine after that with forward acceleration controlled by the pedal as expected. Lately, it will not go forward at all, though with many key switch on offs, forward and reverse switch flips and many pedal stomps, it may end up working in forward, but sometimes not at all. Solenoid activates just as well in forward as it does in reverse.

Based on a few wiring diagrams found on line, it looked at though it might the Forward Neutral Reverse (FNR) switch was bad. I dissassembled and cleaned the copper studs on sides, reassembled and it test fines. Through the wiring studs, across internal contacts, across the bus bar and back out, continuity is fine and resistance about .2 or .3 ohms through the path.

All control wires have been checked and cleaned, continuity test fine, resistance about .2 or .3 ohms across the length of the wires. Key switch, all microswitches fine, potentiometer in the pot box measures 0 to 5K smoothly, pedal linkage properly adusted to allow full potentionmeter travel. Solenoid resistor is 5 watt size, measures 250.7 ohms. Solenoid diode was missing, schematic calls for 3 amp, 100 volts, I used 2.5 amp 1K that I found in my spares. Metal oxide varistor present, schematic calls for 75 volts, the one installed is a Maida 150 volt 20mm.

One wiring diagram shows FNR B goes to Motor S2 with FNR D to motor S1, which is how I am connected. Another diagram shows FNR B to Motor S1 with FNR D to Motor S2, but I can't imagine this would matter.

Since it works just fine in reverse, I'm not thinking it's the controller (a Curtis 1204 I think, with this series motor) though it could be.

So, any ideas or suggestions?

[SanJoseMichael]

Just reversed the B and D position wires on the FNR and now it runs just fine in forward, but the intermittent problem is seen in the reverse function. This continues to point at the FNR, but it's a clean as can be, and alignment is good.

[cgtech]

Well, as far as goes/doesn't go, a series controller doesn't know or care about if it's in forward or reverse, so we can pretty much rule the controller out as the source of problem. Microswitches is a different story. When it refused to go in forward, did the solenoid click? If so, we are back to F&R contacts. If it did not click, one of the microswitches is not dropping down far enough to engage.

[SanJoseMichael]

Solenoid clicks in either direction.

Microswitches all check out fine, click as expected, position relative to FNR cams is okay, microswitch on pot box is fine.

I did read elsewhere on the forum where FNR repair efforts involved sanding the cam contact stud surfaces flat on a sheet of sandpaper laid on on glass (or a similar hard, flat surface) as studs may be at uneven heights. Even though each stud is spring loaded, and setting rotating cam pressure as high as I can with additional washers, it may not overcome the uneveness of the cam studs or the contact plate, hence bad contact somewhere.

Next up is disassembly of the FNR again and measuring surface flatness on all contact surfaces.

[yurtle]

Make sure the FNR is going all the way to the stops. Easy to remove the linkage and rotate the cam by hand. If this fixes the problem, then all you need to do is rotate the cam to exactly halfway between F and R, which is N (neutral), then loosen the bolts connecting it to the frame. Slide it back and forth until the handle is exactly straight up. Assure the FNR goes all the way to the stops.

If that doesn't fix it, you can try sanding the part that does NOT have spring loaded studs - second picture.

EDIT: tighten the center nut until it is kind of hard to turn.

[SanJoseMichael]

It was the FNR after all. The studs on the back plate (contact board) were aligned to the studs on the rotating cam perfectly, continuity was correct, resistance was low (0.2 or 0.3 ohms). All cam studs were measured with a micrometer and found to be the same height, within reason.

I had concluded it was good but it was clearly not working correctly.

I did a complete teardown. The cam side studs had worn a clean "trough" into the plate side, and the plate side studs were "cupped" as well. I taped a piece of sandpaper to a scrap of quartz countertop to make a poor man's surface plate, and then sanded the plate until smooth. I put the studs into a drill press and just cleaned the surace of the studs slightly as I did not want to reduce their height. Reassembly showed the plate side studs to be slightly higher than the plate.

Works perfectly now. Big thanks to Yurtle for the suggestion!

[Raystar57]

Nicely done! I give that a big

[scottyb]

Originally Posted by SanJoseMichael

Just reversed the B and D position wires on the FNR and now it runs just fine in forward, but the intermittent problem is seen in the reverse function. This continues to point at the FNR, but it's a clean as can be, and alignment is good.

Per your tests = Either the high amp cable or the F&R is bad.

[yurtle]

Originally Posted by SanJoseMichael

It was the FNR after all. The studs on the back plate (contact board) were aligned to the studs on the rotating cam perfectly, continuity was correct, resistance was low (0.2 or 0.3 ohms). All cam studs were measured with a micrometer and found to be the same height, within reason.

I had concluded it was good but it was clearly not working correctly.

I did a complete teardown. The cam side studs had worn a clean "trough" into the plate side, and the plate side studs were "cupped" as well. I taped a piece of sandpaper to a scrap of quartz countertop to make a poor man's surface plate, and then sanded the plate until smooth. I put the studs into a drill press and just cleaned the surace of the studs slightly as I did not want to reduce their height. Reassembly showed the plate side studs to be slightly higher than the plate.

Works perfectly now. Big thanks to Yurtle for the suggestion!

Make sure you adequately tighten the center cam nut. I keep mine tight enough to be a little hard to move. You can use a dielectric grease or vaseline to lubricate it.