TT-A vs TN Differentials: is one better than the other?
- Thread starter itr674
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AGRIMAN
Platinum Member
The difference is simple, but may become hard to explain so hold on!
What your dealer is referring to is what's commonly called the "bull gears". Every tractor has a rear differential which consist of the ring an pinion gear which transfers the power from the transmission outward to the axles. Every tractor uses some kind of gear deduction to increase the pulling power of the tractor. In the early days (20s 30s 40s) one of the common methods (for some manufactures)was to use external "Bull Gears".
What this means is that the gear deduction is done externally (on the wheel and Tire end of the axle housing) by using a separate gear box which attaches to the axle housing. The reduction is basically done by using a smaller gear to drive a larger gear. Power is transfer from the axle into the reduction box (drop box) then to the wheel. Here are a few ways to identify what method your looking at. Stand behind the tractor and take notice of the axle houses and the inside of the rear wheel. On tractors using the external bull gears you will notice that the axle housing is not inline with the center of wheel, but is off set by the gear deduction box. This is because the wheel bolts to the reduction box and not the axle. You will also notice the somewhat large reduction box takes up the majority of the inside of the rear wheel.
On tractor using internal "bull gears" the same gear reduction is done internally (on the transmission end of the axle housing) and most use a internally mounted sun gear arrangement which eliminates the need for the separate reduction box. On tractors using this method the axle housing is aligned with the center of the rear wheel and the wheel bolts to the axle itself. You will also notice the inside of the rear wheel is mostly open except for the center, where the axle and wheel meet.
As far as which one is the best... Well the external gears have been around for ever and are a proven design and don't give much if any trouble, but they tend to be noisy and it can increase with age. Today they are commonly only used on low cost units. The biggest problem with external gears is they image. They are widely recognized as being old school and a cheaper/weaker design but, have proven themselves reliable.
Internal bull gears are the newer and most common method used today and are also proven. With the use of the sun gears they are quieter and the better of the two designs, but ether will provide reliable service.
External Bull gears mostly died out in the US by the late 50s but started making a come back in the late 70s with the introduction of the Japanese units. In today's market, low cost manufactures like Kubota and Mahindra are returning to this design because they are still widely used in other developing countries and offer a reliable, but low cost design for the growing US economical tractor market.
New Holland has recently enter this market with their TTA series tractors which are built at their plant in India. They are based off of existing models which thousands are built and sold in several countries every year. The design maybe old but it has never when out of production so that should tell you something about it's reliability.
One note: The TT45 and TT50 use the ISM engine (borrowed from their compacts) which is only used for the NA market.
What your dealer is referring to is what's commonly called the "bull gears". Every tractor has a rear differential which consist of the ring an pinion gear which transfers the power from the transmission outward to the axles. Every tractor uses some kind of gear deduction to increase the pulling power of the tractor. In the early days (20s 30s 40s) one of the common methods (for some manufactures)was to use external "Bull Gears".
What this means is that the gear deduction is done externally (on the wheel and Tire end of the axle housing) by using a separate gear box which attaches to the axle housing. The reduction is basically done by using a smaller gear to drive a larger gear. Power is transfer from the axle into the reduction box (drop box) then to the wheel. Here are a few ways to identify what method your looking at. Stand behind the tractor and take notice of the axle houses and the inside of the rear wheel. On tractors using the external bull gears you will notice that the axle housing is not inline with the center of wheel, but is off set by the gear deduction box. This is because the wheel bolts to the reduction box and not the axle. You will also notice the somewhat large reduction box takes up the majority of the inside of the rear wheel.
On tractor using internal "bull gears" the same gear reduction is done internally (on the transmission end of the axle housing) and most use a internally mounted sun gear arrangement which eliminates the need for the separate reduction box. On tractors using this method the axle housing is aligned with the center of the rear wheel and the wheel bolts to the axle itself. You will also notice the inside of the rear wheel is mostly open except for the center, where the axle and wheel meet.
As far as which one is the best... Well the external gears have been around for ever and are a proven design and don't give much if any trouble, but they tend to be noisy and it can increase with age. Today they are commonly only used on low cost units. The biggest problem with external gears is they image. They are widely recognized as being old school and a cheaper/weaker design but, have proven themselves reliable.
Internal bull gears are the newer and most common method used today and are also proven. With the use of the sun gears they are quieter and the better of the two designs, but ether will provide reliable service.
External Bull gears mostly died out in the US by the late 50s but started making a come back in the late 70s with the introduction of the Japanese units. In today's market, low cost manufactures like Kubota and Mahindra are returning to this design because they are still widely used in other developing countries and offer a reliable, but low cost design for the growing US economical tractor market.
New Holland has recently enter this market with their TTA series tractors which are built at their plant in India. They are based off of existing models which thousands are built and sold in several countries every year. The design maybe old but it has never when out of production so that should tell you something about it's reliability.
One note: The TT45 and TT50 use the ISM engine (borrowed from their compacts) which is only used for the NA market.
RickB
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Agriman has given very good info. I will add the cost factor. The closer the final reduction is to the wheel, the less low-speed, high mass components are required to transmit an equal torque value. Less high-mass components (as with outboard final drives)=less manufacturing cost.
Well I have the TT-50A and use if for hay, bush hog and for dragging logs and other general farm stuff. Will be getting a loader for it this summer. Didn't need or want 4X4 as all flat land here, so far very pleased with it. Runs great and no problems at all. Have the 2 rear remotes from factory with it too.
Agriman--thanks a bunch that's just what I wanted to know.
RickB--thanks for the additional info.
bondo--thank for real world experience.
I like the "cleanliness" of the internal gears but cost will problable drive me the other way.
I had an IH 674 but had to sell it 4 years ago and am looking a replacement just want to find something that will be as strong as that tractor was...
RickB--thanks for the additional info.
bondo--thank for real world experience.
I like the "cleanliness" of the internal gears but cost will problable drive me the other way.
I had an IH 674 but had to sell it 4 years ago and am looking a replacement just want to find something that will be as strong as that tractor was...
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