December 2011 Chevy High Performance Q&A

Kevin McClelland Oct 24, 2011 0 Comment(s)
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The best way is if you have access to a lathe or a machine shop that can whip a sender out for you. If you cannot pull that off, install the sender up in the intake. If all else fails, check out the bell reducer. You should be able to use one of these options. Good luck, and keep a cool head.

Tranny Mate

Q. I have a 4L60E out of an ’07 Silverado that I want to mate to a ’78 Gen I small-block 350. The torque converter bolts don’t align with the holes in the flexplate. I get conflicting info on a solution. One person told me I had to run a 700-R4 converter. Another told me just to elongate the holes and bolt it up. I can’t find any listings for a Gen I two-piece rear main seal flexplate to fit the stock converter. I purchased a TCI Automotive FAST EZ-TCU to control it but need to get the trans coupled first! It’s going in a ’58 International A100 Golden Jubilee pickup and can’t wait for the rpm to be under 3,000 on the highway. Any information on this swap would be appreciated.

Mike Wheeler
Great Bend, KS

A. As we’ve mentioned several times in the past, the Gen I small-blocks and Gen III small-blocks have a different distance between the rear of block face and the crankshaft flange. Usually people are trying to put Gen I transmissions behind Gen III engines. This requires a spacer on the end of the crankshaft for the converter to register into. The crankshaft flange on the Gen III engines is forward 0.400 inch compared with the Gen I engine. Inversely, you’ve installed a Gen III–style transmission behind a Gen I small-block. This puts the crankshaft flange 0.400-inch closer to the torque converter. The ’07 4L60E has a shorter bellhousing than the earlier Gen I 4L60Es. We’re surprised you’ve been able to mount the trans to the back of the early small-block and still turn the torque converter that it’s not buried into the front pump of the trans. If the converter turns freely and you can slide the converter front and back at least 1/8 inch, you should be OK.

If you don’t have any endplay and the converter just turns, you will run into trouble when everything gets hot and the flexplate does its job and flexes! If you don’t have enough clearance, you could purchase a simple 1/8-inch scatter-shield block plant and mount it between the trans and engine. These block plates are used on manual clutch applications to prevent block damage when you have a clutch failure. This will give you the clearance needed to prevent the converter and pump from getting happy with each other. Check out Jeg’s for a Quick Time block plate (PN 698-RM-6011). Simply cut the lower section from the block plate that extends below the block.

Back to your converter bolthole alignment. We recommend elongating the holes in the flexplate with a high-speed grinder. You should have two bolt circle diameters on your Gen I flexplate. Pick the ones closest to your Gen III converter and open up the holes. The 4L60Es used four different diameter converters based on the engine and application. The smallest came in at 245 mm (9.65 inches) for most of the four- and six-cylinder applications. Then we have 280 mm (11.02 inches), 298 mm (11.73 inches), and 300 mm (11.81 inches). Based on the original application of your trans in a Chevy truck, it’s either the 298mm or 300mm variant. These would have the largest bolt circle.

The Gen III transmissions used a different length bellhousing, converter, and input shaft. If you ensure that you have the proper engagement of the torque converter into the transmission, and the proper clearance between the converter and front pump as mentioned above, you should have no problem. Enjoy those low revs during your highway cruising.



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