2/10/2024 0 Comments Gm 700r4 transmission![]() I probably have to change the GM gears as I think the speedo is reading high. I don’t have good numbers yet, but I’m turning about 1600 rpms at about 60mph. ![]() In use, the transmission is very smooth, and with 8:1 initial ratio, gets the big car off the line quickly. I thought of using an XJ6 spin-on, but there is not enough side clearance unless you used a ridiculously short oil filter. To further complicate things, the oil filter canister will barely NOT clear this pan, requiring a 3/8" aluminum shim. I used a series 3 xj6 pan (with the stock Mk10 baffles and xj6 dipstick) which has the return further forward. At issue is the oil return from the filter apparatus which enters the right ear of the pan too far to the rear to allow for the starter motor. The original Mk10 pan will not work, although a 420G pan would (the one I had in my parts bin turned out to badly cracked). The Jaguar rear engine hold-down is not used, unnecessary. The transmission mount is quite simple, a pointed piece of plate steel reinforced by a piece of channel, bolted to the original mount captive nuts, the stock GM rubber mount position adjusted by shims at the bottom and washers at the top. I modified the original BW bracket that sits below the intake manifold at the rear to give the proper cable pull, using engineering specifications posted online by Summit Racing, and shift points were excellent on the first try. It’s absolutely necessary to get this right or you can ruin the transmission. This is really a lot more than a downshift cable, controlling all phases of shifting. The John’s Car shifter bracket works with the stock Jaguar shift mechanism, but creativity is required for the GM downshift cable. I can give more detail about the cuts to the tunnel if anyone wants to do this. Additional access holes with cover plates were needed for the speedo drive and for connecting the lines for the stock transmission fluid cooler. Ridges in the forward left tunnel wall were simply peened down to give a bit of clearance. In addition, the longer tailstock with squared contours requires relief of the top of the tunnel. The GM transmission would fit in the tunnel if it weren’t for the starter motor position, so cutting the right-side tunnel is required. In fact, I pulled the front suspension as well, and dropped the engine out the bottom on my 4-post lift, but you don’t have to do that. This requires some careful shimming to keep things from banging, but the diameter is adequate (barely). The GM transmission is about 7" longer than the BW8 and the required front universal joint is larger diameter, which happens to fall at the narrowest part of the tunnel. So, I have to say, it’s not an easy, no-cutting option, but it can be done without major structural alteration of the car - by that I mean that the main structural cross-member, vital to the strength of the car is essentially untouched. If anyone knows of that, please let me know. John of John’s cars says he sold one for a mK10 some time ago but does not have knowledge of the conversion being completed. To the best of my knowledge, this is the first 700r4 conversion in a Mk10 to be successfully done. Not all the restoration work on the Mk10k, which is ongoing, but the drive-train rebuild including the conversion to GM 700r4.
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