D21 Differential

Been there done that. Low transmission/rear end oil levels (all one compartment) is for sure the death of a differential located that high in the drive line. A tractor used for moldboard plowing would have the highest failure rate possibility. Four new matching radial tires across the back and a lot of short turning would be stressful. A tractor that weighed more than 13K would also place the differential under more pressure. I remember a customer who once got one buried in the mud and rocked it back and forth and back and forth while jamming on the brakes side to side. Soon afterwards the differential was toast. What's the history of the tractor ???  I've always looked back to a D-17 or WD-45 and think of the hundreds upon thousands of hours some of those tractors had on a moldboard plow and NEVER had any differential issues.

Edited by DrAllis - 13 Nov 2024 at 6:00am

One last thing that I forgot.......160 HP fuel setting versus 127.75 HP fuel setting also stresses the differential more.

210-220's used the same differential. They had a larger bearing on the ring gear side of the diff where the D-21 was same bearing on both sides. 210-220's were way heavier in the final drive/bull gear and axle size area. The wheelbase was even 4 or 5 inches longer because of the larger diameter bull and bull pinion gears.

I might have confused myself with the 4-pinion's on 190's and 200's. I know they had a bigger bearing on the right side, and for some reason I thought the 210/220 series did too.

You might want to drain the oil out and remove the large plate covering the ring , pinion, and bull gears.  When I did this found the pinion gear with broken teeth and the bull gear starting to flake.  Ended up replacing ring and pinion with one from a 220 and reversing the rear axles.  This tractor had been turned up to 180 hp.  Good luck.

210/220 got one more tooth on the pinion gear (9 teeth to 10 teeth) and the same tooth count on the ring gear. This was for longer service life but sped things up about 10%. The bull gears and bull pinion gears are much wider and larger in diameter and have their ratio geared 10% slower, so all the ground speeds between a D-21 and 210/220 were essentially the same with equal tire diameters and engine RPM.  The multi-turboed D-21 pullers usually had a 210/220 ring and pinion installed to make road gear 10% faster. After the engine HP levels grew some more, then custom made overdrive transmissions were the next thing.

The very best Super Stock Diesels are turning the rear wheels in the 90+ to 100 MPH speed !! Takes some great big cocoanuts under the hood to do that !!

Don't most of the high HP pullers use a truck rear end?  I know my cousin did.