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Old 10-16-2009, 11:06 AM   #1
markeb01
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Location: Spokane Valley, WA
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1960-62 GMC to SBC V8 motor & trans mounts

The following shows one method of converting a 60-62 GMC V6 to a 350 Chevy small block engine with a tail shaft mounted transmission. This would apply to a Powerglide or Turbo 350 automatic, or manual 4 speed transmission such as the Borg Warner Super T10, or Muncie M21 or M22. The photos are of my 1960 GMC short stepside. Most of what follows also applies to Chevy trucks for 60-62. The main difference being the GMC motor mounts are welded to the frame and the Chevy mounts are bolted on.

Motor Mounts

Chevys have two styles of engine mounts. A U saddle style on stick shift trucks or multi-piece tower mounts on automatic equipped trucks. The different types of mounts can be seen at the following web link:

http://www.persh.org/pickup/perches.htm

The first two pictures below show the factory GMC V6 engine mounts and manual transmission crossmember.




These must be removed by cutting the welds from the frame and grinding the frame rails smooth. The third pic shows the driver side frame after removing the crossmember and V6 engine mount.



This shot shows the 67-72 style motor mount tower/perch I used, resting loose in position.



To determine correct positioning, the towers were attached to the motor mounts, which were bolted to the engine. The transmission mount was loosely attached to the new crossmember (explained shortly), and the engine was rested in place. The frame on the 60-62 is 1 inch shorter in vertical height compared to the 63-66 frame. To position the tower correctly, I simply added a 1 inch spacer on top of the frame rail.

This photo shows a temporary 1 inch aluminum lowering block used to check the fit.



For the permanent installation, I substituted 2 stacked pieces of Ĺ inch solid steel, drilled to match the bolt holes in the towers. Everything was secured with grade 8 bolts. Sadly I didnít take a picture of the finished install when everything was new and shiny. The next shot shows the steel spacers after 165,000 miles of road grime.



The original 60-62 automatic motor mount towers might work just as well, but they are extremely rare and expensive when found. Also, Iím not sure if new motor mounts are available for these towers. It is also unknown if they will interfere with a power steering pump.

Transmission Crossmember

The type of crossmember (xmbr) I used, came stock on 60-62 trucks with an automatic. There must be at least 2 versions of this xmbr. The type I found is straight across the upper mounting surface. Iíve seen pictures of a different version that has a shallow depression in the center of the span. Apparently, they also come in different lengths, depending presumably on whether the truck is a short or long bed. All 60-62 frames Iíve seen have 3 holes in a crescent pattern to the rear of the bellhousing crossmember, as shown: These holes are for attaching the factory automatic xmbr.



When I searched for this crossmember almost 20 years ago, these trucks were plentiful in wrecking yards. In spite of the volume of trucks available, after looking through roughly 150 trucks, I found only 3 with the bolt in crossmember. One was hacked up and drilled, one was bent and still had an engine and transmission sitting on it, and I bought the third one. Iíve seen 2 on Ebay over the years, so they are as rare as the early motor mount towers. It should be relatively easy to fabricate a similar xmbr from rectangular tubing and steel plate if a person can weld.

Unfortunately, the xmbr I bought must have come out of a long bed (I didnít think to look when I was removing it), because it was too long by several inches. The following shows where I sectioned the excess out of the center. I drilled new slotted trans mount holes, fabricated reinforcements underneath and had a friend weld it back together. The 2nd shot shows the reinforcement many years after it was put together.




This shows what it looked like in position, further back compared to the original stick shift crossmember.



When I first did the swap I installed a Turbo 350 behind a 350 small block Chevy. A few years back I pulled the automatic and swapped in a Super T10 4 speed. The bellhousing to trans mount distance is the same, so no adjustments in the motor or transmission mounts were required.

Everything worked fine with the original torsion bar suspension, and later with a 1975 coil spring front crossmember. There are no doubt other ways to do this installation, but this was relatively simple using stock parts.

Last edited by augie; 04-03-2011 at 10:59 PM.
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