# Calling GR gurus!



## peterf225 (Jun 21, 2013)

Guys,

I'm looking for options and opinions for a gear reduction for a 09 420 AT. I am going to run 27" mega mayhems. Don't need anything radical just functional. I just need to spin them in the occasional PB mud. Don't have any other mods done to the bike. 

Thanks guys in advance,
Peter


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## mud PRO 700* (Nov 30, 2012)

Im defiantly not a guru, But since you have the AT I would suggest getting the 420 SRA gears to put in it. They are geared a little lower from the factory and should be a cheapish easy mod to help turn those tires!


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## peterf225 (Jun 21, 2013)

mud PRO 700* said:


> Im defiantly not a guru, But since you have the AT I would suggest getting the 420 SRA gears to put in it. They are geared a little lower from the factory and should be a cheapish easy mod to help turn those tires!


That is definitely one option. I have been thinking hard about this option, just need the part numbers for the gears.

---------- Post added at 09:00 PM ---------- Previous post was at 08:59 PM ----------

BTW the GR from highlifter is out of the question at $650.


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## Polaris425 (Dec 16, 2004)

Talk to lilbigtonka


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## biggwill (Mar 15, 2013)

you could just find a local machine shop to build you one all you need are the gears from a 300ex and have a shop machine them to fit it adds up to a 35% gr. we just did this to a friend of mines sra 420 and hes spinning 30's now with ease.


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## lilbigtonka (Dec 30, 2008)

You need a ring and pinion gear for the rear only ring is 41431-HP5-600 and the pinion is 41421-HP5-600
The front has the same tooth count on both SRA and IRS bikes
You will be going from a 41 tooth ring and a 13 tooth pinion to a 41 tooth ring and 20 tooth pinion.....the ring gears are different though so you need to order both

There is no need to do a full gear reduction with only 27" tires especially if they are not heavy....you will love the way the sra gears are in your bike once it is said and done i believe....


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## peterf225 (Jun 21, 2013)

lilbigtonka said:


> You need a ring and pinion gear for the rear only ring is 41431-HP5-600 and the pinion is 41421-HP5-600
> The front has the same tooth count on both SRA and IRS bikes
> You will be going from a 41 tooth ring and a 13 tooth pinion to a 41 tooth ring and 20 tooth pinion.....the ring gears are different though so you need to order both
> 
> There is no need to do a full gear reduction with only 27" tires especially if they are not heavy....you will love the way the sra gears are in your bike once it is said and done i believe....


So no need to do a secondary GR? The 27x11-12 mega mayhems weigh 33.7 lbs each and the 27x9-12 weigh 30.1 each. I'm mounting them on factory Rincon aluminum wheels. Just go and change rear diff gears?


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## lilbigtonka (Dec 30, 2008)

Change the rear gears first then if you aren't happy add the gear reduction either way that thing is to high from the factory.....I believe you will like it though as our 420 turns wide 28 zillas in most everything


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## peterf225 (Jun 21, 2013)

lilbigtonka said:


> Change the rear gears first then if you aren't happy add the gear reduction either way that thing is to high from the factory.....I believe you will like it though as our 420 turns wide 28 zillas in most everything



I really appreciate all the help and info but, I want to do this one time and from what you are saying I don't know if the rear diff gear change is going to be the problem solver. 

Looking at just the weight of the tires the 28" wide zillas weigh right at 28 lbs. if y'all bike spins them in just about everything with just different rear gears I might still be a little skeptical about trying to turn these mega mayhems just because they weigh about 5 lbs more each and have a 5/16" deeper lug. Some places we go, we are going through PB mud with no water and no bottoms it seems like. We are always loaded down with gear also.


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## duckincrazy92 (May 24, 2011)

My cousin has a sra 420 and he's turning 28 ol2's pretty good with just and epi clutch kit. Even in the thick mud it turns them very well. Put the 27s on it and I think you will be surprised.


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## lilbigtonka (Dec 30, 2008)

Well do a full gear reduction I was just stating what I think would work but go for whatever you want it is your bike....


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## peterf225 (Jun 21, 2013)

Lilbigtonka,

I appreciate all the info. What in your opinion would be a good secondary GR? Would a secondary gear set from a SRA be more than enough for what I want/need?


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## lilbigtonka (Dec 30, 2008)

The secondary gear reduction is more complicated then the primary if your gonna do a gr then just do a primary one and be done with it 


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## peterf225 (Jun 21, 2013)

I have read they don't make a primary GR for the AT models. But then again I've been wrong before.


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## lilbigtonka (Dec 30, 2008)

Well I ain't positive on the at models as I am not a fan of the Honda matic tranny but just get the 15 secondary then but I would do the sra gears just my .02 tho 


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## biggwill (Mar 15, 2013)

Being that it's basically the same tranny as the rincon couldn't he just get the gears from a big red and put them in?


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## peterf225 (Jun 21, 2013)

When people do a SRA gr in an IRS are they just installing the final drive gear and final driven gears? The gears out of an 09 420 ES are 22T and 40T while the gears in the 09 420 AT are 25T and 37T.


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## dodge2500 (Jan 3, 2013)

*just my .02 u can put the primary gr from a 420 sra in the at u just will not get a true 35 unless u do the rear gears in rear end*


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## gotmuddy (Jul 15, 2011)

I dont think a single person in this thread knows anything about the 420at. The AT is a completely different animal than any other honda. The auto tranny is nothing like honda ever made. It uses a two stage clutch that seamlessly shifts a normal 5 speed transmission. You have three options for gear reductions. a 40% primary that will be too much for what you need, a 35% secondary and SRA gears out of a 420 foot shift. Changing pinions in the rear end wont do anything either since both have a 13 tooth pinion(the parts fiche is a typo). the SRA gears will likely do what you want, it should be a 21% reduction.


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## peterf225 (Jun 21, 2013)

Gotmuddy,

I was wondering about the pinion gears because they also look to be different in design. Thanks for clearing it up. Looks like a SRA gear reduction in the near future.


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## peterf225 (Jun 21, 2013)

Well I got my SRA gear reduction installed today. Took about 10 tries to get the speed sensor to work correctly once the bike was back together. Tomorrow I plan on trying it out with the 27" mega mayhems. But I could notice a big difference when loading it back up.


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## peterf225 (Jun 21, 2013)

I was able to get out today and test the bike. The GR made a 100% improvement. No more lugging down in the mud. Made for a much better experience riding today. I can take off in 2nd gear and not hesitate at all.


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