Need for Speed (Gearing help)

[CartMan007]

Hey guys. First off, everyone's been a huge help. Thank you.

Working on a golf cart project. Finally got things hooked up for quality test drives. It seems really slow though. I've got speed at takeoff and response is great forward and reverse. Granted, I don't want to go really really fast I just want to be able to cruise and be in the street without being absurdly slow. I will get some actual measurements on speed and update this post. I feel like I'm maxing out at 12 mph where the RPMs are high, but I'm not getting any faster. I'm keeping it stock. Open to suggestions. I've tried online gearing calculators and 'm a math guy, but I was getting numbers like 2,000mph max speed, so I know I was doing something wrong. Specs below:

Ezgo Marathon Golf Cart 1989(?) maybe 600/700 lbs according to google
Predator 420cc governed, stock everything
40 series toque converter, comet 780 clutch
40 series gearbox with 10t sprocket
18t rear sprocket
40 chain
22x11x10 tires
Vegas Carts muffler that came with the kit

I saw something that said it would be helpful to upgrade the 10t to a 12t. I also know most go carts have larger rear sprockets (40t/60t) for torque/power? I'm not trying to do wheelies in this but I am trying to not roll backwards down a hill if I have four people on it with me. Also, if I need to be kicked out because this is specifically for go-carts, let me know! Thanks for the help.

 

[ezcome-ezgo]

Do you know the gear ratio of the diff? I seem to recall it's like 8:1, maybe? Mark a tooth on the sprocket and turn the rear wheels while counting the revolutions. When the marked tooth returns to its original spot where you started, do the math, or vice versa, my brain is mush.

 

[Edwin Spangler]

Those gearboxes also have a strange in/out ratio. Its usually not 1:1.

Karts have larger sprockets because there isnt any reduction first (gearbox and diff).

You need to find out the exact ratio of the gearbox and diff unless you want to just shotgun different sprocket sizes.. I would start with a 12t on the driven and 14t on the axle, maybe 16t?

 

[CartMan007]

Thanks for the quick replies. You both said what I feared which is that I may have to consider additional diff gearing. Here's what I found.

Gearbox --> Forward is 1:2 and Reverse is 1:2:6 (according to website)
Rear Diff --> 12 to 1

Not a gearing expert, but with these numbers, is there a way to work with my rear diff to get the speeds in wanting without spending what looks like $400 on new rear diff gears? I paid $400 for the whole cart! LOL

 

[Denny]

You could try a 10 tooth to 10 tooth and see how that works for you.

 

[ezcome-ezgo]

Wait, so for every 1 revolution of wheels the engine turns over 24 times?

 

[CartMan007]

Feels like it. But these are all the measurements of my setup currently.

Wait, so for every 1 revolution of wheels the engine turns over 24 times?

 

[panchothedog]

I'm not going to comment on your gear ratio, but from the picture of your clutch, you need to change the spring in the driven unit. The points or cam on the outer part of the clutch need to be on the front side of the plastic stops for the unit to function properly. Yours are on the back side. You need a reverse wound spring. That will get the outer part of the clutch oriented properly. Not difficult to install.
OMB Warehouse sells them for about $15.

 

[Denny]

Pancho is way right also. Better listen to him too.

 

[CartMan007]

I'm not going to comment on your gear ratio, but from the picture of your clutch, you need to change the spring in the driven unit. The points or cam on the outer part of the clutch need to be on the front side of the plastic stops for the unit to function properly. Yours are on the back side. You need a reverse wound spring. That will get the outer part of the clutch oriented properly. Not difficult to install.
OMB Warehouse sells them for about $15.

Thanks! So just to confirm before I hit buy: that spring is different from the green spring that came with the kit (see picture)?

Update: I figured something else was off because during my “speed test” I’ll take off like I’m about to hit 25mph top speed and end up topping at 5-7mph at full throttle. Looking forward to changing the spring and finding out.

 

[CartMan007]

The more I learn the more pain I feel. watched several YouTube videos on spring replacement instructions. So my torque converter is Blast LED which according to google is the Chinese knockoff. Main issue is that I ordered the spring but now I wonder if it’s going to fit because there’s no hole like the comet clutches. Anyway, going to preload (somehow) and put it back on with the cam position correct and report back.

 

[panchothedog]

I have replaced the spring on mine, the only 40 series converter I own. I have no reason to believe that mine didn't also come from China. I own 5 or 6 of the 30 series and I know that all of them came from China.. I don't think you have anything to worry about. However the current spring is attached, the new one will attach in the same manner. As you push down and turn to preload the clutch, you just turn it in the opposite direction. Make sure you have a good set of snap ring plires. That is the key or tool that makes the difference.

 

[Edwin Spangler]

Make sure you have a good set of snap ring plires. That is the key or tool that makes the difference.

One of the most frustrating things you can run into while working with these toys is needing a quality set of snap ring pliers and only having your crappy backup....


-And c-clamps can work wonders with these pulleys when youre trying to reassemble.

 

[CartMan007]

I have replaced the spring on mine, the only 40 series converter I own. I have no reason to believe that mine didn't also come from China. I own 5 or 6 of the 30 series and I know that all of them came from China.. I don't think you have anything to worry about. However the current spring is attached, the new one will attach in the same manner. As you push down and turn to preload the clutch, you just turn it in the opposite direction. Make sure you have a good set of snap ring plires. That is the key or tool that makes the difference.

Good to know. I haven’t had an issue with the TC at all, but hoping the springs work out well. Finished assembling the correct way last night and did a mini test run this morning. Seemed WAY more responsive and I realized when I topped out it was smooth/constant. Feeling this, now I realize that before I would literally take off fast (with the old assembly) then actually slow down while pressing the gas pedal.

Still slow and I think I will have to bite the bullet and change rear end gearing and sprockets.

Yup. Made sure I got snap ring pliers because I had a cheap, interchangeable head version from Lowe’s when I was working on the brake lines and that was so frustrating. The ones I got are still relatively cheap (4 pieces for about $45 from harbor freight) but worked great. Probably need bigger/wider ones but they made it easy.

 

[CartMan007]

One of the most frustrating things you can run into while working with these toys is needing a quality set of snap ring pliers and only having your crappy backup....


-And c-clamps can work wonders with these pulleys when youre trying to reassemble.

Tell me more about the c clamps helping with pulleys? Not sure what you mean but I’m probably experiencing frustra There too.

 

[Edwin Spangler]

Tell me more about the c clamps helping with pulleys? Not sure what you mean but I’m probably experiencing frustra There too.

When you preload the spring in the driven, you use the c-clamp to hold the spring retainer in position so your hands are completely free to put the snap ring back on. If you dont get that retainer back on the first couple attempts, your hands are gonna be too tired to do it again. Then you gotta let go of it all, have some of it fly up in your face, some fly to some corner that you havnt seen in years, and youll spend the rest of the day finding pieces.

Or you can do the 'press and kneel' method but thats not my thing. Id like to have feeling in my leg for the remainder of the day.

 

[CartMan007]

When you preload the spring in the driven, you use the c-clamp to hold the spring retainer in position so your hands are completely free to put the snap ring back on. If you dont get that retainer back on the first couple attempts, your hands are gonna be too tired to do it again. Then you gotta let go of it all, have some of it fly up in your face, some fly to some corner that you havnt seen in years, and youll spend the rest of the day finding pieces.

Or you can do the 'press and kneel' method but thats not my thing. Id like to have feeling in my leg for the remainder of the day.

Oh right! Yea I experienced this last night when I was preloading. Kept losing the lock key!

 

[CartMan007]

In conclusion, I’m going to probably have to just save up and buy the gears. I’ll also try a 10 tooth sprocket on the back. unfortunately I can’t just pick up and throw on sprockets. The rear end input shaft is 19 splines and I have to first find a 1-3/8 bore sprocket that happens to be 10t and then weld it to the coupling that fits the 19 splines.

It’ll all be worth it one day.

 

[CartMan007]

One more question: I know going to the 6:1 rear end gears decreases torque. Not climbing any mountains but want to be able to drive 4 passengers with ease, should I be worried about torque? I assumed with a 420, even with higher speed gears I should have the torque I need, but you know what they say about assumptions.

 

[panchothedog]

6 :1 is the gold standard for karts with 18 to 20" rear tires. That is for small block engines ( 196 to 224cc ). With 22" tires, if it's mostly on flat or close to flat ground, I think you'll be OK. Sorta guessing here, but your 420 makes twice the torque of the small block.