when did White switch to diff lock rear end

Looking at a 2-155 but the serial number does not appear to match the year. The tractor is equipped with a differential lock and the upper engine speed pto is gone. Can any tell when this change took place year wise. I thought all late 70's still had the old style rearend. Thanks

The 2-135/155's and 2-180 all had the same style rear with diff lock. I'm guessing that would be in 1977 because the last 2255 was produced in 1976 if I remember correctly. Are you talking about the 1000 rpm PTO for the upper engine speed being gone. Some were made with 540/1000 PTO's and you would just have to change the shaft and no switching the shift fork for 540/1000. I'm pretty sure the 2-135 had that option, and think the 2-155 did also. I think I read that the 2-180 only had the 1000 pto and could be the case of the 2-155. Our 2-155 has only the 1000 PTO.

I left the dealership in the fall of 1976 and saw my first 2-135 & 2-155 several weeks later at the Ohio farm Science review.

mkuhns is correct with the diff lock. All the White series that would have the new transmissions with inboard planetary would have had diff lock as standard equipment. This would have been on the 2-135, 2-155, 2-180 and 4-210 series tractors and their replacements that followed. As for the upper engine speed PTO, this was now no longer available on any of these tractors since they all shared a new designed PTO assembly which no longer had an opening for the removal of the live shaft. If I remember correctly, the 540 PTO option did not initially come out with the introduction of the 2-135 and 2-155 tractors and when it did it was only available on the 2-135 tractors. This was due in part to horsepower regulations and I believe the maximum was 150 HP on a 540 PTO; the other problem was that the rear-end casting on a 2-155 (and on up) was heavier in the PTO opening area and a 540/1000 PTO assembly would not fit into it's opening. White did offer a kit to change a 1000 PTO assembly to a 540/1000 PTO and if I remember it involved pretty much keeping only the large cast housing and clutch assembly as all the inner parts were different. And yes, we did put these kits into some 2-155 tractors by removing some of the rear-end housing casting to create an opening large enough for the 540/1000 PTO to fit into. One major difference to tell if you have a dual 540/1000 PTO is that the shafts interchanged by removing the PTO shield bolts and sliding the shaft out, similar to the older Oliver setup; if you have just a 1000 PTO, that shaft cannot be removed unless you take the whole PTO assembly off the back of the tractor. On another note, when a 540/1000 PTO unit was installed, a decal was placed next to the engine tach to warn the operator 540 PTO speed was attained at I believe somewhere around 1800 RPMs. Tractors that came with the dual speed PTO from the factory and a mechanical tach had two PTO speed indicators on it - one for 540 and the other for 1000.