I have an early XJ6 with a BW Model 8 gearbox. The kickdown doesn’t work, but the gears change OK with normal acceleration etc. The manual says to check the pressure to work out what adjustment is required to the throttle linkage. The manual shows an illustration of removing a screw from just below the throttle linkage and searches on google show similar pictures, but my model 8 doesn’t have a screw in the place indicated - just smooth metal - it’s not in the car at present, so I can’t be mistaken on that. Does anyone else have a model 8 like this and know how to check the pressure?
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The relevant screw is forward of, and level with, the throttle linkage, Derek…
As an aside; the adjustment of pressure by the ‘kickdown’ rod relates to shift quality - and to some extent shift points. The downshift associated with ‘kickdown’ is the box’s reaction to the pedal position, engine rpms and road speed. Ie, the box downshifts when increased rpms is necessary to increase engine rpms for more power as demanded by the driver’s use of the pedal. There is no specific ‘kickdown’ function on the ‘8’…?
The box will downshift in any relevant situation - with light throttle the engine will quickly upchange to ‘3’ at some 12 mph. At this speed the engine should downshift to ‘1’ if you floor the pedal - and ‘2’ with less pedal action. Beyond some 60 mph the box will not downshift…
Frank
xj6 85 Sov Europe (UK/NZ)
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The plug can be in 2 entirely different places, only one shown in manual.
iirc, the other location is on the opposite side of the box!
look for a small square plug
I made a gauge for this job, thread specs, 1/8-27 tpi BSPT male thread… with 5/16" barb outlet
- Note…almost every BW8 owner (including me) cannot achieve auto kickdown
I have corresponded with 2 only that claim theres does.
The BW8 auto kickdown is controlled only by a cable, in conjunction with internal governor
My BW8 will not auto kickdown thru the complete range of cable or pressure adjustment
I stripped apart a couple, and can see no reason why, as the cable connects directly to the kickdown valve.
mine operates normally in all other respects.
It will kickdown one gear if I engage “L” at any speed
Hi Frank,
My box will only downshift if I decelerate - flooring it at any speed will just leave it in 3rd.
Hi Tony,
Yes I do have that square plug - thanks. It sounds like I may be wasting my time anyway from what you say, not that I was particularly intending to floor the old girl everywhere LOL. As you say, engaging “L” does give a kind of kickdown for those rare occasions when you want a bit more speed.
mine works that way too.
The FSM gives very detailed info on how it is supposed to work, including inside the valve body
I took apart a valve body, and the kickdown valve fully closes when the cable bottoms out.
Apparently, the pressure from other valves and governor interact, but my gearbox also measured correct pressures, and I experimented, nothing worked, it will not kickdown
Its a mystery I would like to solve
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Which certainly means something is wrong, Derek…
Downshifting as the car slows is of course what is expected. Automatics just parallels what a manual driver would do; shifting down as the car slows - or downshifting to get more oomph to accelerate.
I’m a but puzzled by reports that the ‘8’ won’t downshift when ‘prodded’. Admittedly the ‘8’ is a mite crude and designed for American V8s with plenty of torque - hence very robust. However, no automatics are designed to accelerate from low speeds in high gear - they should downshift…
‘Kickdown’ downshift is not related to flooring the pedal, though some boxes have such a feature - the box should downshift whenever rpms are too low for the power the driver wants when pushing the pedal…And upshifts should occur at higher and higher speeds the more pedal is applied. With minimum pedal; the 2/3 upshift should occur at some 1200 rpms, and speeds of around 12 mph - and downshift at that speed when slowing down. At full throttle the upshift should occur at some 60 mph.
Jerky shifting, or delayed upshift under light throttle, sure warrants a pressure check. But lack of forced downshifting with pedal use is abnormal - if you apply pedal with force from 12 mph and the box stays in ‘3’ throughout; the box is not doing what automatic boxes should…
Frank
xj6 85 Sov Europe (UK/NZ)
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almost, but not quite…see it wont be in 3rd at 12mph, as it will have downshifted upon
de-acceleration…just like an auto should…what it wont do is downshift “on command” to a lower gear, if the speed is too high…ie 30mph. (even though the FSM says it should)
The most obvious time this arises is during overtaking…at say 45mph, it certainly will not kickdown from 3rd to 2nd, even though the manual says its should (~2700 to ~4000RPM)
nor will flooring the throttle induce kickdown from 2nd to 1st under any circs
both these functions can be achieved shifting the lever from D1 (or D2) to L…at any speed (FSM does not make this clear)
It seems the valve body functions to prevent down-shifting if the RPM is too high, although I have been a bit cautious in my experiments
D2 is a fairly useless “gear” as all it does is cause the trans to start in 2nd!
be interesting to hear from any BW8 equipped S1 XJ6 owners
bw8 also fitted in 420, MKX, 420G, E-type
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From start it should upshift to ‘3’ at light throttle, Tony - on slowing down there is no pedal input to affect shifting.
In D2 it should start in ‘1’, then upshift at 6 to 7 mph - ‘D2’ just prevents 2/3 upshifts. The lack of ‘kickdown’ downshifting within specs means something is amiss. But if the box otherwise shift smoothly and at spec shiftpoints, it’s somewhat difficult to know what to do about it. It may be something specific to the ‘8’…
Without the downshift the xk would be sluggish indeed - and while manual downshift is one solution; I would not be satisfied…
Frank
xj6 85 Sov Europe (UK/NZ)
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not sure on the XJ version, but here is an excerpt from the MKX manual…D2 = starts in 2nd
so the gearbox behaves as it should as per FSM, except no kickdown
very mysterious, I ask each owner, most say no, or they dont know, 2 said yes…(but maybe they have BW12)
I will post an excerpt from the FSM that describes the valve body function
however, I studied a couple, and obviously, it should kickdown when the kickdown valve is fully closed…but it does not…there are several other valves & springs mentioned that act in concert, so weaker (or stronger) internal springs may work, but it would be guesswork.
I note the BW8 had at least 3 different valve bodies in the MKX-420G
I am far from satisfied 
here is the relevant section for your erudition…states combination of hydraulic and **spring ** pressure is responsible for 3-2 kickdown, hence my thought a 3-2 spring change may be the (only) possible change that can be made
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Thank you for the necessary feedback, Tony…
Altering valve body spring rates is standard procedure to tune the box to suit engine characteristics - allowing the box to be more effective over a wider engine range of vehicles. Usually done by having several variants of valve bodies rather than tuning each valve body individually. Which does not prevent anyone from some personalised tuning…
Like a manual driver using the lower gear for maximum acceleration, upshifting when engine rpms nears maximum power/torque - the auto box delays upshifts the same way. In other situations the box basically upshifts quicker for economy - while still ready to provide power when the driver calls for it by pedal action…
Obviously the logic behind the ‘8’ differs from later practice - as described in ‘Driving instructions’. Maybe derived from common practice at the time with manual boxes, and still is a slippery ‘manual’ trick. However, the torque converter allows for very gradual power application - the auto box is much better for starting on slippery slopes. Adding that driving off in high gear at the time of unsynchronised gears was not uncommon - saved a lot of grinding teeth…
I wonder; as the pressure is adjusted with the downshift cable/rod and the kickdown is activated by ‘excessive’ pedal travel. Is it possible that the problem is a cable/rod adjustment problem…?
The ‘8’ is admittedly crude and it may not downshift unless pedal is fully depressed - but it certainly should then…
Frank
xj6 85 Sov Europe (UK/NZ)
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it would appear not.
I have tested the gearbox extensively with a pressure gauge permanently attached
During that time, I made sure to adjust the cable across its full range of motion, and have established the throttle/kickdown valve is fully depressed at WOT
Adjusting the cable beyond the suitable range only resulted in higher running pressure (but still no kickdown). If the pressure is too high it affects driveability, even whining
So unless the governor is an issue, (and I see no reason it should be, as other functions are on spec), that only leaves the 2 mentioned springs, as the only item that can be altered
I have had apart my valve body (and another one) for cleaning and examination.
There was no apparent faults
a gent on the E-type forum went on a long quest over this issue, having his BW8 rebuilt, to no avail, and then switching to MOD
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The purpose of the pressure adjustment is to synchronise the box and the engine, Tony - a jerky shifting is a sign that pressure adjustement is called for. Going outside the specs the box will certainly misbehave…
I still wonder; in the description of box operation, does it state that it will downshift other than floored…?
I too considered the governor - and thought the same. However, the downshift valve opens to the 2/3 valve to control pressure and the combined spring and fluid pressure works against the governor pressure to open the 2/3 valve to downshift…?
Which to suggest three alternatives, together or in combination. The control pressure is too low (unlikely, as it was properly set?). The 2/3 spring is too weak or the governor pressure is too high - ie, a faulty governor.
It would better explain the widespread lack of ‘8’ kickdown. If the governor was not checked out in these cases, and no faults were found when examining the valve body - it is more likely that governors fail than a slack spring?
Somewhere there should be spring specs for the ‘8’, and fitting a stronger spring as you consider would likely lead to the same problems as an excessive control pressure…?
I think I would rather consider checking the governor - which should deliver pressure varying with speed. Which would then allow downshifts, including kickdown, over a wide range of initial speeds. The description of the 2/3 valve spring function seems to allow normal upshifts with a constant governor pressure…?
Frank
xj6 85 Sov Europe (UK/NZ)
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thanks for the long consideration.
some further info;
- upshifts occur FSM spec speeds at all throttle openings
- downshifts take place with no throttle input, at FSM spec speeds
- no downshifts take place with any throttle input
The above make me think the govenor is acting normally, as it controls the road speed aspect of shifting
operating pressure is changed only by adjusting the kickdown cable
There is no other thing that can be adjusted to alter operating pressure.
Screwing the cable in makes the trans pressure rise, and yes, makes the change very rough and jerky, eventually it whines @130psi
at pressure below ~50psi the trans slips and changes are slurred.
No setting gave kickdown
The MKX FSM clearly describes how it should kickdown…but they dont
I will check the S1 XJ6 FSM and see what it says!
Wait a minute. If the kickdown cable is disconnected or not doing anything you have both very early up-and downshifts (as in no pedal input) and no kickdown.
I had no kickdown some time ago and it might have been a stuck kickdown valve.-
If the upshifts are to spec, the cable works.
If cable adjustment works, the cable works.
If the governor does it’s road speed information job, it works and
If you can alter pressure over the whole range, the pump and eventual relief valves, filters, regulators should perform well.
Must be a shift valve or something not mentioned before, then, by exclusion? Can the kickdown valve be stuck? Provided there is one. I dismantled the valve body back then and it looked good, but that one valve might have been a little stuck or restricted in travel, can’t remember right now.
I dont think so, my valve body was perfect inside & spent some time examining each spring, and that pistons all slid easily in the bores. I also have a spare valve body that I studied upon.
Not 100% sure from your reply
do you have a BW8, if so did it ever kickdown at WOT?, and does it now ?
One thing to mention is the BW8 only has the cable, unlike the BW12 which has cable, vacuum cannister & microswitch, and FMX, which has cable & vacuum
Tony the lack of kickdown in your transmission is just that . Your transmission has a problem not ALL BW type 8 transmissions.
I think the 70s Jeeps had BW 8 A/T installed. Try to find an older transmission shop familiar with BW 8s and ask them if they can help you. Pete
Hi Pete. I have individually polled quite a few BW8 owners on this forum and others, and emailed at least a dozen personally
Some say they do not know!
At least 6 have the same issue I do
Only 2 have said that theirs does, and that is not proof, as they may have BW12
there is an extensive thread on the E-type forum on this issue
that is why I am asking S1 XJ6 owners with BW8 (only pre 1970)
It so happens I do know of an absolute master in these transmissions , I will give him a call
I previously spoke to the old-time guys in the largest trans shop in our region, even they were pretty clueless on BW8, having rarely if ever worked on them, I had to tell them it was same as FMX
It may be some fault is present, but if no parts are worn or dysfunctional, and pressures are within spec, and no parts can be adjusted, that does make rectifying the fault difficult
No, not an 8. BW66 which is quite different however the basics should apply in both units, which is why I was so vague with the valves, etc. forgot to mention that. But there should be a lot of FMX users to poll, I went on corresponding forums as there is some similarity.