Hello All, our XJ6 was laid up for about 25 years prior to being put back on the road early last year. At about 1990 we had the engine and transmission rebuilt. The engine is great but as I have come to learn, the unmanaged laying up transmissions is not a good idea! I had it serviced only to find that the clutch pack friction material had been compromised by water in the transmission fluid – and was all over the filters. So, another rebuild is in the offing – AUD$2800 for remove, rebuild and refit. I am contemplating a transmission change to a 4 speed auto and understand there a popular conversions for GM 400’s and ZF’s etc. Does anyone have any experience? I would, of course, keep the original transmission for posterity. It gets quite a bit of highway use so dropping the engine revs somewhat would be useful. Paul
A GM TurboHydramatic 400 (3L80) will do nothing as far as dropping the RPM. It is a 3 speed just like the BW model 12. Some have adapted a GM 700-R4 overdrive automatic transmission.
bob
Thanks, my mistake did mean the 700, that’s the one I have been reading about. Paul
I had a GM700R4 in an 84 XJ6 installed with a Johns Cars kit. It’s a very nice setup and I liked it overall. However with the six cylinder and 2.88:1 gears, the car will lug a bit in fourth when driving around town. You can just manually leave it in third to keep it out of overdrive till you get it on the highway. I later parted out that car and put the trans in an 87 XJ12. No problems at all with the V12. There is a ton of aftermarket information on the 700R4(at least here in the states).
John Testrake
St. Louis USA
67Etype2+2, 74XJ12L UK spec, 87XJ12
Thanks! Our '72 has a 3.36 diff - expect it should be about right. Paul