Bill: Although I'm sure that others will chime in, I'll offer my thoughts regarding the 122 vs. 126.
Bill writes, "Will the 122 engine fit the 126?"
JC: Yes, they're both 12 HP with S/G
Bill writes, "Are attachments, ie deck or blade, etc interchange? . . . Does the 122 have a quick attach system like the 126?"
JC: Not sure, I think the 122 may lack the Quick Attach features of later tractors, others may respond.
Bill writes: "If the 122 is complete and running, should I leave it alone and move the 126 down the road instead, and keep the 122?"
JC: Yes, I would. I value a steel dash over the fiberglass, and according to no less an authority than Forum member and frequent contributor, Tom Hoffman, the 122 is "bullet-proof."
Bill writes: "Also, I think the 122 has internal vs external brakes on the 126 - question is why the change, any advantage to one over the other?"
JC: The internal brakes were used, not used, and used again. I suspect they're cheaper to manufacture. The external brakes were provided from several suppliers. The main advantage to the external brakes is that they act on the wheels and keep the tractor from spinning around while "stopped," which sometimes happens with the internal brakes which acts on the differential. I find the internal brakes fairly bullet-proof, myself; but then again, I'm not accustomed to pulling/stopping heavy tow loads with my tractor.
Bill writes, "I think the 126 has the 19T second gear and the 122 might have the 16T second gear? Which of these 2nd gears is the better mowing gear? Does the difference in speed make one better or worse than the other with a moldboard plow."
JC: Not sure about the 122 and 2nd gear ratios (although I could look it up), I think the slower gear was limited to the 70/100 series, others may contribute, or I'll check my notes and come back. Can't speak to plowing, never tried it.
Bill, your "quick questions" are killing me.
Edit: My notes on Cub Cadet 2nd Gear:
1. By Troy Rutherford (Trutherford) on Wednesday, June 06, 2012 - 08:17 pm:
I have a 70 and a 100 that were both built in 1964 with low serial numbers. I was driving them both today and relized that 2nd gear was about the same speed as 1st gear. But all of my later model 100s and the following models after have the normal 2nd gear that is at the speed between 1st and 3rd I was wondering since they had low serial numbers if this had a factor. Was this an option by the factory. Are these rear ends rare or hard to come by. I haven't seen another 2 cubs like these or any other models with this slow of a second gear. Does anyone have any information on this. Thanks
2. By Paul Bell (Pbell) on Wednesday, June 06, 2012 - 08:54 pm:
Troy R,
Cub Cadets from the beginning to serial number 96765 (70/100 from serial # 65458 to 96765) had a 16/36 tooth 2nd gear set (or 2nd speed as IH liked to call it). From serial # 96766 up to the wide frame models (86/108/128) they had a 19/33 tooth 2nd gear set, and the wide frames and later had a 17/35 tooth 2nd gear set.
3. By Steve Blunier "Mr. Plow" (Central IL) (Sblunier) on Wednesday, June 06, 2012 - 10:07 pm:
16T 2nd is great for mowing with a small HP tractor...otherwise, I find then annoying, much preferring the 19T second for most all other uses.
Mowing with 10-12hp is a 19T job, as is plowing, etc.
4. By Dennis Frisk (Dfrisk) on Thursday, June 07, 2012 - 06:44 am:
TROY, STEVE B. - The 16T 2nd Paul describes is 3.2 MPH @ 3600 RPM, the 19T is 3.9 MPH, and the 17T is 3.5.
My old #70 had the 16T 2nd, was always a great mowing gear unless the grass was over 5-6 inchs tall then the little 7 HP ran out of power. With 10 HP they make a great mower for any condition.
My #72 has the fast 19T 2nd, and I find it just a bit too fast for mowing, but as Steve says, it's great for plowing, both with a moldboard plow and a snow blade, general yard work, towing carts, sprayers, spreaders, etc. I used to mow with it in 2nd, when I had wide open spaces to mow, but now my yard is more like an obstacle course and 1st gear works better. Even with a hydro I find the mowers do the best job around 3 MPH.