First reduction gear change

I have a unstyled A JD I have been pulling for some years it pulls ok with some trophies. My question is does anyone have information on changing the first gear reduction to a styled A to give me a slower ground speed? I was told it makes a difference.
 
(quoted from post at 13:30:48 10/09/15) I have a unstyled A JD I have been pulling for some years it pulls ok with some trophies. My question is does anyone have information on changing the first gear reduction to a styled A to give me a slower ground speed? I was told it makes a difference.

Stone boat or transfer sled? You dont want to go slower on a transfer sled. If you want info on changing gears, you may want to ask this question in the John Deere forum.
 

It will make a difference if you are always running out of power. But I suggest building the power to fit your current speed. Back when i had a stock motor and running 1st gear on my late model A, sure I never ran out of power, but I never got to see the second half of the track. now that I have increased HP, I run 2nd gear which is about 3mph and should be about where your 1st gear is. I am much more competitive now.
 
With a old stone boat pulls the lower the gear the better.Its just the opposite with a weight transfer sled the higher gear you can pull it in and stay withen the speed limit if there is one the better you will do.
 
You have a total of 3 ratios for the A's reduction gear sets. The unstyled and early A's should have a 36/86 tooth count set. The late A with creeper gear serial #648000 and above has a 34/88 tooth set. The 620/630 has a 33/89 tooth set. The late A set will slow you down about 8% and the 620 set about 12%. The 620 set has a keyway instead of a splined first reduction gear, but you can put that gear onto the early gear centers by removing the 3 rivets and pressing it on. Good Luck, Mark
 
Thanks for the information I am running a unstyled A JD it turns about 75hp on a dyno. I run out of power in third gear other A JD that I pull against seem to pull third gear fine and I don't think they have more power than I have. I think I am just in between second gear not lugging the motor down enough to much power to the wheels and third gear to much ground speed or not enough power. Maybe I will try a reduction gear next season. Any suggestions?
 
Thanks Mark I located some 620 gears and will try to press the ring gears on my existing ones. Any other tips you have would be greatly appreciated as I have not tried this before.
 
Hi Mark I while ago you had information on first reduction gears on a unstyled A jd. I has some 620 gears pressed on my 1936 A to slow it down a bit, Now I found out the first reduction gear cover is to small because the gear on the transmission is bigger. My question is do know if a styled A cover is bigger or would a 620 cover fit? I hate to buy one just to find out it won't fit anyway. If not I will have to modify the old one enough to make room for the larger gear as always I appreciate any info. Dave
 
(quoted from post at 16:02:37 12/15/15) Hi Mark I while ago you had information on first reduction gears on a unstyled A jd. I has some 620 gears pressed on my 1936 A to slow it down a bit, Now I found out the first reduction gear cover is to small because the gear on the transmission is bigger. My question is do know if a styled A cover is bigger or would a 620 cover fit? I hate to buy one just to find out it won't fit anyway. If not I will have to modify the old one enough to make room for the larger gear as always I appreciate any info. Dave
I ran the 620 gears (33/89 tooth) set up in a styled A using the styled first reduction gear cover then later switched to a unstyled first reduction gear cover because it was lighter and it fit fine. I had a unstyled A that I used the late A creeper gears (34/88 tooth) in and that fit fine also. The covers use the same gasket and some of mine have been milled on the inside by JD to clear the gears. I'll measure the gears that I have next time I get to the shop and see.
 

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