Dial Bore Gauge Set 2-6 in for 4L60E Pump Bore Wear

A dial bore gauge is the only way to actually know whether a pump body bore or a bushing is inside spec. On a 4L60E the pump body bore and the stator support bushing wear oval where the gear set thrust-loads them, and an oval bore lets the pump gears cock over, which is what feeds a low line pressure complaint on a freshly rebuilt unit. This Accusize EE20-1006 set reads 2 to 6 inches in 0.0001 in graduations, so you measure that wear instead of guessing at it with a snap gauge.

The head is self-centering. The spring-loaded anvil and the floating guide shoes hold the gauge square in the bore so the needle sweeps and reverses at the true diameter. You zero the gauge against an outside micrometer set to the nominal bore size, then rock the gauge in the bore and read the point of smallest deflection. Take readings at the top, middle and bottom of the bore, rotate 90 degrees and repeat. The spread between those readings is your taper and out-of-round, and that number is what tells you to replace the pump half instead of reusing it.

On a transmission bench the 2 to 6 in range covers pump body and stator support bores, direct and forward drum bushing IDs, the case rear bushing on 4L60E and 4L80E, 700R4 pump bores, and 4L80E center support bushings. The same range works for engine cylinder bores and connecting rod housing bores if the gauge does double duty in your shop. The set ships with an extension holder, a 6 in stem, a chrome plated handle with an insulated grip, and a fitted case. Accusize part number is EE20-1006.

One thing to plan for: a bore gauge is a comparator, not an absolute-reading instrument. It only tells you how far the bore is from whatever size you zeroed it at, so you need an outside micrometer or a setting ring in the same range before it is useful. If there is no 2-6 in micrometer set on the bench yet, buy that at the same time.