Hi,I’m new to this forim. Name is stan and i have a 85 jag,xj6,4.2lit.only problem i might have right noe is when coming to stop ,transmission clunks into low gear.what could i look at or is this normal with my jag. Trans is perfect rest of driveing.
Hi at the top right of this page there is a spyglass icon to search the archives, if you search on ‘Transmission adjustment’ there is a write up on adjusting the bands within the transmission. If you are mechanically minded you could try this to see if there is any improvement.
hi robin. thx for the info I’ll look this up tomorrow.maybe thats all it
needs.
Hi Stan
First, what’s your idle speed? If too high you’ll get a clunk. The old BW66 box, not a paragon of velvety-smooth operation, is slightly clunky to begin with. A too-high idle worsens the matter.
Weak/worn/broken trans transmission mounts can likewise amplify the downshift into low.
That said, the throttle valve cable (some called detent cable or downshift cable) can be slightly adjusted t soften the clunk. Technically this adjustment should be made with a pressure gauge attached but nobody outside of a transmission specialist has one so we wing it a bit.
I’m having a brain fade at the moment if the cable is adjusted sorter or longer to soften the clunk…but somewhere here will know. The adjustment is made where the cable is attached to the throttle body. Make tiny adjustments…1/4 turn at a time.
You are actually altering the internal operating pressure of the transmission so if you don’t get any improvement after, let’s say, three or four adjustments (judgement call on that) in any one direction, don’t go further. If you get the adjustment out of range you can actually hurt the transmission.
Cheers
DD
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The idle rpms may be behind it, Stan - as Doug says…so…?
As the car comes to a stop there is a transition stat; the engine wants to run the gearbox, but so do the rear wheels. A one-way clutch in the box prevents the rear wheels form ‘pushing’ the box in first gear. However, this requires the box to shift to first before the confusion takes effect - and idle setting may interfere…
However, the downshift cable is vital to shift points and shift qualities, so pursuing that as Doug suggests is pertinent. Watch the shift points while driving; under light throttle the 1/2 upshift should occur at 8 - 12 mph and 2/3 at 13 - 19 mph - and the shifting should be virtually imperceptible. Wrong shiftpoints and/or harsh shifting implies that cable adjustment is called for. Pertinent in this case; roll-out downshift 2/1 should be at 5 - 10 mph, and again imperceptible…
Shiftpoints moves to higher speeds with increased pedal, the downshift cable is mechanically connected to the throttle pedal - telling the box what the driver is doing, so cable adjustment is critical. cable adjustment is very sensitive so while trial and error as Doug describes is feasible, altering cable length, but as he says, must not be overdone. Adjustments should be tried both ways as the cause of a problem may be either way. Only a proper pressure adjustment, using a pressure gauge, is really precise enough…
However, when the box was last adjusted a small ferule was crimped on the cable at the throttle pedestal end. Check cable there, and if the ferule is present and immobile adjust the clearance between the ferule and the threaded adjuster to 0.01" - then test drive. However, if the gap is very large, it may indicate that the plastic fastener at the gearbox end has come adrift - which should be checked…
If the ‘clunk’ persists after all this - some further thinking is required…
Frank
xj6 85 Sov Europe (UK/NZ)
So had a clunk with my 87 XJ when moving off, not all the time but after stopping quickly e.g. traffic light or accelerating agressively. Had a complete transmission (filter fluid) service at All Jaguar Longwood, Fl and the culprit was a large rubber mount which had rotted away. First transmission service since new in 87 believe it or not.
Mine is doing the same, I assumed it was the u joints.