Kickdown/throttle linkage P5b/SD1/BW35 confusion

[Jem]

Hello all. I know this is a common theme regarding the kickdown cable and throttle linkages it as I have just bought a P5B only to discover that it has an SD1 engine, I cannot rely on any of the information given on this forum, as it is all for original cars I am assuming

I have made a short YouTube video describing the problem, which may be better than writing it down.

If anybody would care to watch it and then let me have any suggestions. I would be most grateful as this is not my natural game.

youtu.be/WxdTK8MRYFE

[lagain]

It all looks fairly standard to me. The rear of the rod that operates the kickdown should be in a rubber bush, which lifts the rod a little. I think that there are different lengths of kickdown cable, so you may have the wrong one. If the engine does not idle correctly it has not been set up correctly. The procedure is shown in the handbook.
When you refit the gearbox sump use a rubber gasket, available on ebay and do not over tighten it. I found 6 lb ft is plenty.

[enigmas]

Jem I have pasted this directly across from the RoverP5 Facebook page where you have posted your query.

* Note:
I own a modified P5 MK3 Coupe (32 years...daily driver for 20 years) and run a heavily modified original Factory Rover MK3 case BW35 (incorporating later model BW40/51 components) transmission hooked up to a P76 4.4 litre V8.




Check the Following:

If you remove the trans pan the throttle/kickdown cam on the side of the valve body is clearly visible. Some of these Throttle Valve Cam assemblies are adjustable fore and aft whilst others are fixed. Later model BW35/40/51s (same case) usually have an adjustable throttle cam fitted. Check yours. The Cam should "just touch" the throttle valve at rest. If it's correctly positioned have an assistant press the throttle pedal down until it touches the kickdown stop under the throttle pedal (it looks like a small foot operated dipswitch), usually at 3/4 throttle position. At this throttle position the Throttle Valve Cam (TVC) will/should have rotated around to the kickdown position. This can be noted where the radius of the cam increases in diameter markedly. If the TVC is positioned correctly and this has not occurred then the lever that pulls on the cable is either not long enough or some other adjustment that acts on the cable is incorrect.

A viable option if other existing adjustments don't remediate the geometry.
If you can weld or have access to a competent welder, lengthen the lever. If you remove the lever and mechanism from the manifold (add 1" or 25mm) and drill appropriately sized cable holes every 1/8" or so. You can then select an appropriate cable position to increase the cable movement. This movement can be confirmed by viewing the rotation of the TVC. There's nothing complex in this simple modification. Any competent mechanic who can fabricate and has a working knowledge of the BW35 trans should be able to sort this.

Here is some tech diagrams and info that may assist you.


If you look directly at the picture above note the large radius at the top of the throttle cam.
The cam rotates to that radius at 3/4 throttle (when the kickdown stop can be felt under the accelerator pedal.) Kickdown occurs at this rotational position.
(Note: It's just a pressure button indicator for your throttle foot, it doesn't actually physically engage anything with the transmission.)

Note the adjustable Throttle Valve Cam at the top of this valve block
This valve block is for reference only yours will not have the rear pump filter screen and will most likely not have an adjustable throttle valve.
This valve block also has a reverse boost mechanism just below the adjustable cam...simply ignore it.


Another view of the Valve block Cam assembly but from the side.


Here are 2 throttle cam assemblies.
Note that one is adjustable and the other fixed.
Note also that the cams have varying profiles dependent upon which valve body and front servo is used. There are several. Best to stick with the Factory version for the particular car and engine/trans combo if unsure of what you are doing.


Generally later model iterations of the BW35 (BW40 & BW51) had steeper profile cams and are more throttle responsive with part throttle downshifts to both 2nd and 1st gear.

[enigmas]

Is a good Samaritan available.

A call out to a Club Member with some mechanical skills.

I'm guessing that there are P5 and P5B owners across the UK that post to this board. I also assume that a reasonable percentage given the long term affection for these stately cars that they have a modicum of mechanical skill.

It's infortunate that I'm literally on the other side of the planet otherwise I'd offer Jem at the bare minimum an evaluation of what I believe is probably limited to some basic screwups in the geometry of his throttle and kickdown mechanism on his P5B.

Is there no-one reasonably close to Jem's locale that has a smattering of mechanical knowledge who could at least look at the setup that I'm referring to above and point him in the right direction?

[lagain]

His location is not shown, where is he?

[enigmas]

Hi George, I sent him a PM and referred him back here so hopefully he'll pickup on it and post his location/region in the UK on this forum.
Here's the link to his dilemma on facebook.

www.facebook.com/groups/194353942478722/user/626368652

It would be charitable if someone relatively close could assist him and clarify unambiguously where the issue resides. Currently we have too many cooks adding to the confusion with an issue that is in all probability a matter of correctly adjusting some linkages.

I believe he is located somewhere around Sunbury-on-Thames from his Facebook profile...but he will obviously have to post a definitive location in his profile here if anyone is to offer assistance.

[Jem]

Hey

I am in Teddington, west London

I understand that there is a geometry issue but I am being warned by many auto box people not to mess with that per se.

I am taking it to one auto box old timer tomorrow evening to take him for a spin so he can diagnose it from its behaviour. I also have instructions from the wonderful Andy of Morgan’s transmissions on how to measure the cable and its actuation points which I will do with this guy on Thursday too.

That is that issue. The other is that the throttle linkage is somehow not right and that is the sticking point. If it was just the box I could sort it but I can’t find anyone who will deal with getting them both right at the same time! Literally nobody around me is interested!

Thanks for all your help. I can replace things and fix many things but this is beyond my skills and I really appreciate all your input.

[lagain]

Some way from you but you could try Hardyengineering.co.uk at Leatherhead

[enigmas]

For anyone wondering...the issue with the BW35 transmission cable linkage on Jem's P5B was resolved. 😎 👍