10. Crossmember/Transmssion Mount
10.1. Transmission Bolted to Noncanted Bellhousing
I have read about swaps that use the TH200-4R crossmember (GM 14063883), but using this crossmember requires the driver's side frame extension, which does not exist prior to ca.1984 (depends on model). I wanted to perform a swap that could be performed on any 1978-1988 GM A/G body.
I used a crossmember from a 1979 Malibu equipped with a V6 (1978-1987 A/G body, GM 473725). The crossmember I used can be identified by 473723SR stamped on the bottom of the transmission-mounting pad (Figure 10-1) and large mounting holes on each end. The large mounting holes are for rubber insulators used to mount the crossmember to the frame.
Eliminating the insulators drops the crossmember low enough so that there is no interference with the torque arm mounts on the transmission. The original mounting pad for the V6 transmission is offset towards the right and can be retained (Figure 10-2), though it is cleaner to remove it (Figure 10-3). When I was testing the swap in my 1979 Malibu Wagon, I left the original mounting pad so as not to render the crossmember useless in case the swap was unsuccessful. As the frame mounting holes in the V6 crossmember are larger than the head of a 3/8-inch bolt, modifications are necessary. I have experimented with two techniques for bolting the crossmember to the frame. On my 1979 Malibu Wagon, I made a sandwich out of steel plates (Figure 10-4). On my Monte Carlo, I welded the original holes closed and drilled new ones (Figure 10-5).
I fabricated a mounting pad out of angle iron. To ensure the mounting pad would end up in the correct location on the crossmember, I raised the transmission to the desired height, bolted the fabricated mounting pad to the transmission mount, mounted the crossmember, and then C-clamped the mounting pad to the crossmember. After carefully removing the crossmember, I welded the mounting pad to the crossmember.
I used a solid rubber transmission mount (Figure 10-6). Although the transmission mount is angled, I have not suffered any consequences. After 10 years and countless power shifts, the transmission mount shows negligible distortion (Figure 10-7). I do not recommend using a hollow transmission mount. Figure 10-8 is a picture of the hollow mount I removed from my 1983 Malibu Wagon. I replaced it with a solid rubber mount.
10.2. Transmission Bolted to Canted Bellhousing (1983-1992 F Body)
When using a 1983-1992 F body bellhousing, the bottom of the transmission mount is horizontal. Therefore, a 3-speed automatic or 3-/4-speed manual transmission crossmember can be used. The mounting pad needs to be shortened and the mounting hole needs to be lengthened.
A TH200-4R crossmember can also be used if the transmission mount pad is extended approximately 2 inches, however, this crossmember requires the driver's side frame extension.
Originally Released 11 February 2002
updated 27 August 2007
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