Tomos A3 First Gear vs A35 First Gear

Hi guys,

I just noticed something and wanted to run it by the board. The A3 first gear doesn't appear to have a bushing pressed into it's center and the A35 first gear does.



Aside from the A35 have substantially larger straight cut gears, it looks like Tomos added a brass bushing to gear shaft surface.

That gear is supposed to slide over the shaft and allow the shaft to spin at full speed through it after second gear is engaged. I recently overheated an A3 and the gear is so tightly seized to the intermediate shaft that I can't beat it off with a sledge hammer. I don't want future failures, so I'm considering whether I should have a bushing installed at a machine shop down the road.

In this video you can see the gear being slide over the shaft with a little bit of shaft play. Unless I'm missing it, the A3 first gear has no bearing surface, so the contact surface is iron to steel.

Important part at 59 seconds:


Re: Tomos A3 First Gear vs A35 First Gear

Maybe freeze it and then torch just the hub area and then whack it.

Re: Tomos A3 First Gear vs A35 First Gear

Or I could just throw it in a press and press the gear off. I dont want to save any of it, its trashed. Im asking for future builds. Would it be a good idea to add a bushing to the a3 first gear?

Re: Tomos A3 First Gear vs A35 First Gear

Yeah, I think its a good idea. The sleeve you see in the A35 isn't even brass, its a coated steel sleeve. Better as a replaceable part but still not as good as it could be, even brand new they have more slop than I like. Would be rad to have a large needle bearing but even a brass bushing with a more snug fit would be awesome to try.

Re: Tomos A3 First Gear vs A35 First Gear

I'm digging deep here tryin to remember. That bushing is pretty common to go bad, like probably 3/4 of the engines I've rebuilt it's been shot. I don't think it's coated steel, I think it's a sintered babbitt type material but I might be wrong. I've never replaced it, I just swap around countershaft assemblies to put together all good parts.

Per that other thread, the a3 gears are a harder steel or iron and might be ok as is, as a bearing surface. You can get away with steel on iron/ steel as long as there isn't a lot of pressure, and they obviously put 4 big oil grooves in there. I think if you wanted to upgrade the bushing on either of them to oilite or maybe even aluminum bronze, you could but probably not necessary since when you are in first gear and seeing radial load, it's not spinning, and in second gear there is no radial load since the torque is running through second gear.

This is why I like to run the rotella with zddp. I don't know if ATF or different kinds of ATF have the zddp in them but that's what you want for any steel-on-steel plain bearing situation. If stock tomos was designed for 2 HP and 30 mph, pushing it to 7+ HP and 50 mph, the additives can keep things in the safe zone.

Re: Tomos A3 First Gear vs A35 First Gear

Thanks for chiming in Graham. You've obviously got a lot more experience in this area than me. Since you recall seeing so many worn bearings I think it's obvious this surface endures a great deal of wear when the first gear disengages and the second gear drives the shaft while the first gear idles.

I really like the idea of switching to motor oil with a high amount of ZDDP, I think that's going to be the ticket when using the A3 clutches - since it would destroy the cork lined clutches. I just did some reading from past threads you've contributed to on the subject of motor oil in the transmission. If I have another shaft seize while using motor oil I'll start thinking about pressing in a bearing.

Re: Tomos A3 First Gear vs A35 First Gear

Usually people get black wheel of death either from boogering up a sprocket swap or wear on the pedal shaft and they loose all their trans oil which pooches the bronze bearing I think. Like I said, that joint isn't taking high radial load while it's under power so it shouldn't be a weak point as long as it sees oil.

I think the rotella is just fine in the cork clutches too, I have a a35 with stock clutches that has had it in there for years.

Like 99% of tomos problems are pure neglect and abuse, they are incredibly durable motors but people just fuck them right up. When I build them to take a mild kit I basically just go through everything to make sure it's good, reline the clutches, put in stronger clutch springs and that's it.

It's like 8 screws and about 15 minutes to pop the clutch cover off, you do that once every 500 miles or so, change the oil and check the clutches they will run for thousands and thousands of miles even going 50+ with a kit. If you run them dry or let the clutch shoes wear out, they will destroy the rest of the trans in no time.

Re: Tomos A3 First Gear vs A35 First Gear

Got it back together. The engine I bought from Satan666 had some really high quality parts in it, everything feels brand new. I moved everything over to my old engine case so all the registration matches up. Then I drove all over town until I could find Rotella, there's a shortage of diesel oil apparently. The leather clutches are a lot less grabby now, feels smoother not using the ATF fluid. But I have piece of mind knowing all the new gears are getting lots of zddp.



Re: Tomos A3 First Gear vs A35 First Gear

Awesome! Always nice to see someone come back and post the resolution.

I hope we're not running out of rotella! I just used up my 5gal bucket and the tractor needs an oil change before winter. Usually they have it at the farm store, fleet farm or farm and fleet up here in WI.

Re: Tomos A3 First Gear vs A35 First Gear

Do I spy a fiero gt in the background?

Re: Tomos A3 First Gear vs A35 First Gear

Glad that engine worked out for you. Happy to see some of my old parts bring new life to projects.

Re: Tomos A3 First Gear vs A35 First Gear

Our fleet store had it in Gallons, the trick was finding a quart of it. Finally found a single quart at an Autozone. I also hope there's not truly a shortage. Glad I don't have a Detroit or CAT to maintain right now.

>>Fiero GT

Shhhhhhhhhhhhh. *whisper* Don't tell anyone.

Re: Tomos A3 First Gear vs A35 First Gear

♣Slew Foot♣ /

I think they are plain thin brass

Even when they stick you can use a puller it will stay on crank or pop out when a socket extender of the right diameter is used to power it out of the bell.

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