97 XK8 transmission bump

Most 5HP24 transmissions built before August 2001 will have had the original 0501 208 317 F-brake piston replaced with the updated one (0501 212 967) due to the original piston seal material wearing badly, allowing it to leak. I wonder if that's the case with your transmission?







Another possibility is that the two phosphor bronze bushes in the sun gear drive sleeve, which act as a seal for the C-clutch circuit, are worn.







When ticking over the pump doesn't produce enough flow to overcome the leakage so the clutch doesn't engage but as soon as the engine revs are lifted the extra flow engages the clutch with a bang. Is the problem worse when hot than cold?

Phil

I would agree, that is likely to be something worn out. Mine was similar between 2nd and 3rd before it failed completely. Though also there is also a rotary microswitch in the J gate that can wear out and stop the gearbox engaging reverse easily/quickly, though it doesn't usually engage with a bump, just sticks in N. Worth checking as cheaper than gearbox, though still lumpy.

I would opt for a refurb of existing, at least you know its history. (A new one is about £7,000 fitted). If you are looking for someone to crack it open, I had mine refurbished by Surrey Jag Centre. They send them out to a place in Croyden they have used for years... They can just refurbish the gearbox for about £1,500 or also the torque converter and all other parts for £2,500 ish in VAT from memory. From my reading around you don't quite get the gold standard refurb offered by a place up in Scotland who completely re-manufacture the box, but its pretty good and probably in keeping with age and value of car and much cheaper.

I had a couple of hitches with mine (my XK8 was always problematic), but as ever SJC sorted me out amicably and I was pleased with it overall - it worked perfectly after for several years.