VAI - how to slow it down by changing gearing?

dpski

Member
Contemplating changing the gearing to slow down my VAI to be more like a VA / VAC.

What exactly would I need to change? Pinion shaft and ring gear on differential only? Or do the Bull Gears need to be changed too?

Do I also have to change gears 1-4? I don't care if the speeds match the VA / VAC exactly, just want to be able to go slower overall.

I should add this would be my first time splitting a tractor. Just rebuilt the PTO and differential brakes, but didn't have to split the tractor for those. So pretty sure I could handle it unless there's all sorts of special tools required.
 
You can slow down the overall speed by changing the bull gears and side gears (brake shafts) to the ones used in the regular VAC with disc brakes. The bull gears will be 66 tooth and the side gears will be 13 tooth. The side gears in your tractor now should be 13 tooth also but it carries a different part # so I doubt it will work. You have to seperate the rear housing from the transmission to change the gears. Also takes some work to get the side gears and carrier shimmed back to specs but it is more time consuming than anything. We can change the bull gears in a couple of hours or less but we have had a lot of practice since we pull a VAC. End up spending a lot of time draining oil to prevent such a mess when you seperate them. Have had good luck with high temp copper sealant when reassembling instead of trying to get or make gaskets. It seems to work without having to let it set and cure which we usually don't have time to wait anyway. After you change the gears you still will not have the same 2nd or 3rd gear as the VAC because the transmission gears are different also, but this will help considerably with the speed overall.
 
Ughh, doesn"t sound like a whole lot of fun.

Here"s what I was able to find from the Case/IH website on the different part#"s.

I"m somewhat surpised that a difference of 3 teeth can make such a difference.

VAI Differential gears;

2 VT3725 Bull GEAR - final drive, 63 teeth
2 VTA-2514 Diff Brake Gear — side, with bushings, 16 teeth (tractors before No. 5555000)
2 VTA2814 Diff Brake GEAR - side, with plug, 16 teeth (Tractors after no. 5554999)
1 VT3421 Ring GEAR, 43 teeth
1 VT3410 COUNTERSHAFT AND BEVEL DRIVE PINION



VA / VAC Differential Gears;
2 VT3422 Bull GEAR - final drive (66T) (44" - 80" tread on VAC)
2 VT3606 Bull GEAR - final drive (65T), Used on special mowing VAC 13 tractors with adjustable front axle after #5570000.
2 VT5467 Bull GEAR - final drive (67T) VAC 44" - 88" tread and VAO 15 (VAC, VAO)
1 VTA587 RING GEAR AND CENTER WHEEL ASSEMBLY W/SHAFT (Includes VT3457 shaft) (No teeth count listed?)
2 VTA2512 Diff Brake GEAR - side (Includes VT3479 plug and 2-VT3765 bushings) Tractors w/disc type brakes
1 VT3410 COUNTERSHAFT AND BEVEL DRIVE PINION
 
If any of you guys have a set of 13/67 pinion and bull gears you'd like to part with please get in touch with me.

casemanaugieATyahooDOTcom
 

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