BXProject

[mat_the_cat]

The Disco has a ZF4HP22 box and I'm not sure it changes gear as it should - at present, if you floor the throttle it won't change into the lowest gear it's capable of - I have to drop it manually at which point it really flies! (This is a source of much amusement when out accelerating people from junctions...) So I checked the kickdown cable adjustment and it was as per the manual (0.25 to 1.25mm) - however the method of adjustment was different so I'm wondering if the manual is for a different version.

Is there any problem with having a cable that is too tight? I was thinking of tightening it a little at a time until it changes as I feel it should. Or is this reluctance to drop down possible indicative of other problems? Fluid is a nice red colour, due for changing next year according to the service history and I plan to change the filter too (inside the gearbox sump). So if I tighten the cable to remove the free play, could this cause more problems or is it hiding the true cause?

Here's hoping Doc or someone else can help...

[Philhod]

Never tried doing that, but all shortening the cable will do will alter the point of throttle depression at which kickdown operates. Whether that will drop it to first I wouldnt know, but I doubt it.
However doing what you suggest shouldn't cause any problems unless you shorten it enough that it snaps
I mainly worked on AP and BW, 3 gear slush boxes. There was a compensating valve on those, operated by manifold depression. The valve assisted change down.
Dunno if ye have one o' they.

[docchevron132]

no no no! the kickdown cable does a lot more than just operate the kickdown!
there's modulation in the box controlled by the kickdown cable. Infact, it's slightly inaccurate to call it a kickdown cable, since in reality it acts as a throttle position sensor.
It effects everything that occurs in the bix, from line pressure to charge loading, which is quite clever. If you're giving it welly the box will increase the pressure behind a valve to speed up upshift and make sure it bites faster, therefore avoiding excess slip on upshift and reducing wear, equally, light throttle upshifts are smoothed by operating at a lower pressure, makng upshifts slower and more refined, in theory at least. It's actually a very clever autobox.
The best and most accurate way to setup the cable is to use a pressure guage capabale of massive PSI and VERY rapid pressure changes, however, short of paying some cunt to it for you, which is always a ballache, you can get it pretty much spot on by setting the cable about right, then making fine adjustments as you go.
What you dont want to do is adjust it to the point where you get "flaring" on upshift, thats real bad shit in all the smaller ZF boxes (Isay smaller because I'm used to ZF transmissions that weigh nearly as much as a BX).
The marked adjustment figure should be between the end of the ouyter cable and a little tab pinched onto the inner cable. I assume it has said little tab? Even if it does, dont always assume the tab is where it should be! When you buy a replacement genuine cable the tab is present, but not crimped, and if the cable is fitted by a bellend then it aint always crimped where it should actually be..
Importantly.. if you depress the throttle pedal to the floor, does it actually operate the kickdown? If you get hold of the kickdown cable and pull it, you'll notice it travels most of it's run, then it should go hard, like it s got a lump in it, before moving some more. IF the throttle action pulls the cable past that point then thats as much downshift as you'll get. the reserve action of the cable past the point of kickdown varies the pressure in the box by next to fuck all. Kickdown position effectively holding the inlet port ot the governor wide open. Hope that makes sense, and is in English..

[docchevron132]

I mainly worked on AP and BW, 3 gear slush boxes. There was a compensating valve on those, operated by manifold depression. The valve assisted change down.
Dunno if ye have one o' they.

The Borg Warner 35 had the fancy shit vacuum compensator valve. My little Borg Warner Model 8 has the old kickdown cable! Which, with fine tuning, can vary the line pressure at idle in gear by over 30PSI!
Fucking lovely autobox though, so sweet in operation, even now, after 40 years! aside from hearing the engine note change, you cant actually feel it shift, even at kickdown!

[mat_the_cat]

Hope that makes sense, and is in English..

Well, one out of two ain't bad...

What you dont want to do is adjust it to the point where you get "flaring" on upshift

Not sure what 'flaring' is?

The marked adjustment figure should be between the end of the ouyter cable and a little tab pinched onto the inner cable. I assume it has said little tab?

I don't remember a tab - basically what the manual said (from memory) is to check and adjust the freeplay from the box end. So I lay on my back in the mud, slide underneath only to find there is no method of adjustment! Open the bonnet, and there's the adjustment, next to the throttle butterfly. I'll have to check and take photos if needed.

Importantly.. if you depress the throttle pedal to the floor, does it actually operate the kickdown? If you get hold of the kickdown cable and pull it, you'll notice it travels most of it's run, then it should go hard, like it s got a lump in it, before moving some more. IF the throttle action pulls the cable past that point then thats as much downshift as you'll get. the reserve action of the cable past the point of kickdown varies the pressure in the box by next to fuck all. Kickdown position effectively holding the inlet port ot the governor wide open.

Will try this - currently it will drop a gear or so but not enough if you're trying to overtake someone quickly. There is always another gear available if you drop it manually. If this is a 'normal' feature then it's liveable with but what everything to be right if possible.
So if I try pulling the cable by hand, mark the point in the inner cable when resistance increases, and then if that point isn't reached when flooring the throttle I should adjust the kickdown cable so it just does? (Ignoring the amount of free play present?

[jayw]

Not sure what 'flaring' is?

Something one does with trousers!

[mat_the_cat]

It was his talk of bell ends that worried me!

[docchevron132]

bell ends FTW! wait..
Flaring is the engine revving up between upshifts, like a pause in the upshift that allows the engine to rev before being pulled back down by the clutches engaging fully. Like slipping a clutch on a manual car.

ahh, see it should have a tab! And AFAIK the adjustment is always at the butterfly end, I've never seen adjustment at the gearbox end since the actual business end of things is inside the box.
In essence, when the throttle pedal is about 1/4" off full throttle the kickdown should come in, which you can feel if you pull the cable.
Bear in mind also that the kickdown will be determined per application to put the engine smack in the maximum power band, so it could be that dropping 2 ratio's was deemed unneccessary? That said, if you're bimbling about and floor it, I would expect it to drop a couple of cogs..

[mat_the_cat]

I'll have to double check about the tab, since it was a while ago that I checked it. It's just that I've been doing a spot of heavy towing recently, and it struck me that on some of the hills I *had* to drop a gear or two to actually accelerate. And when overtaking solo, if you don't change manually it's the difference between "Come ONNNNNNNNN!" and "Fuck, that's quite quick" if you nudge it down. If anything it's more reluctant to change at higher road speeds, say about 50mph you can push your foot a fair way down with nothing happening apart from the engine note getting deeper (if you do floor it it'll drop to 3rd). Whereas if you don't quite floor it you can actually go faster keeping the throttle the same and just dropping into 3rd manually.

Don't know if this is a new thing as Lana drives it more, and with me being more used to a manual car I've always tended to drop the cogs manuallly anyway for overtaking.

[mat_the_cat]

Right - managed to download a proper factor manual (all 1000 odd pages of it - that took a while) and the method of adjustment is completely different to Haynes which says to adjust at the box end. This may be pretty standard but the way it works is that it's connected to the throttle arm on the opposite side of the pivot to the throttle cable. Apparently the correct way to adjust it (more on that in a minute) is to position the kickdown cable ferrule a certain number of threads screwed into its bracket, then lock it with locknuts, then adjust the tension of the throttle cable to position a crimped on ring (equivalent to the tab you mentioned) 1mm away from the threaded ferrule.

First thing I did was pull the KD cable as described /\
As I started KD would come into operation *just* before the throttle was fully open, with about 15mm extra travel once the throttle hit the stop. I then tried to adjust it by the (new) book but to get the crimped ring 1mm away from the ferrule meant the throttle cable was pulling the throttle off its closed stop. Not right!

So I tightened the KD cable a bit, so KD occurs earlier. I read about one guy on the net who simple adjusted till there was *just* a bit of extra travel at WOT. I now have about 8mm still to go, so tighter than before. Test driver - more responsive I think but still not dropping as I think it should. I noticed it would upchange under full throttle at just over 4k rpm (can't remember what it was previously). Surely it should rev at least close to the red line? (5k +)

Oh well, see how it goes when Lana takes it out tomorrow...

[Philhod]

It was a smooth box Doc, althought that valve was a bit of an achilles heel on some cars.

Namely the 2600 SD1 I had. I got through 2 before Rover came up with a mod.
The manifold depression used to draw petrol vapour down the tube. This degraded the rubber inserts on the inside of the valve eventually blocking it. What happend next was rather amusing. With the valve blocked it would stay in second and start to suck the ATF out of the box quite rapidly, causing the petrol to be diluted, causing what sounded like an engine death rattle, coupled with a mahoosive smoke plume behind you.
The only upside was the valve was mounted on the outside of the box, at the side of the vacuum tube and took 15 mins to replace.
The mod was to cut a section of the pipe out, up near the manifold and fit the replacement piece which had two loops in it and was attached by two little compression fittings.
Happy days!!! ........well they weren't boring

[docchevron132]

In theory it should almost redline before upshift at FT yes. IF it's changing up that early it would indicate that the cable is too slack at idle..

[docchevron132]

my model 8 is rather un standard as is mate. It had to br to cope with the weight it lugs about!

[Philhod]

Have you put weight on then?????

[docchevron132]

I have a bit yes! just over 11stone now. I was referencing the vehicle to which the model 8 is fitted though!

[Philhod]