I repaired one walker on my 7720 T2 last year and put new blocks in it. What I found out from the main JD combine mechanic from Deere Trail in Mcpherson ks was to shim the walkers. After I ran it a little and heard a noise...it was the blocks squeeling a little. He told me that every time he puts in a new bearing (set of blocks) he cuts a cardboard spacer ( like out of a cereal box) and puts the same number of shims in the front & rear ( same block I'm talking about) untill there is just a little play sideways and up & down. I talked to several other guys that never heard of shimming the blocks before but if I hadn't done this, I would have had big problems so you might want to check that out.