[928uk] 3 speed gear change rpm

[todd at oxfordeye.co.uk]

Just to wrap this up (for anyone with similar issues)

I adjusted the bowen tensioning bolt (side of gearbox) and the gear change raised to 4500. I increase pressure module one complete turn (clockwise) and gear change raised to 5000rpm. Im happy there. At some point I will try Smithy's suggestions below, but for now Im happy. 

I must say, for a 45yr old car that has sat dormant for 16 or so years, then rebuilt by a novice like me - it does accelerate pretty well. Its not rocket, but it certainly respectable. And the thrashing its been getting recently has only made it happier.

Thanks all

Todd.
(had to resend for various stupid reasons 😊 )

-----Original Message-----
From: todd at oxfordeye.co.uk <todd at oxfordeye.co.uk> 
Sent: Saturday, June 8, 2024 11:19 PM
To: smiffypr at gmail.com; 928uk at lists.928.org.uk
Cc: todd at oxfordeye.co.uk
Subject: RE: [928uk] 3 speed gear change rpm

Solid suggestion... I'll give it a go tomorrow 

I have 100% confirmed the kickdown now works, that at least that 😊

Thanks 😊

-----Original Message-----
From: 928uk <928uk-bounces at lists.928.org.uk> On Behalf Of Paul R Smith via 928uk
Sent: Saturday, June 8, 2024 11:15 PM
To: 928uk at lists.928.org.uk
Subject: Re: [928uk] 3 speed gear change rpm

Bear in mind that I know nothing about autos, so I am just talking theory.
If you want the box to think you have WoT, it will have no vacuum, so disconnect the vacuum line to the box and block the engine side of the line.
You want the cable to tell the box that the throttle pedal is on the floor, so cable tie the lever to imitate that.
You want the kickdown solenoid powered, so run 12v to that.

If it still won't go to higher revs, you then know that the problem is inside the box.

Smiffy

On 08/06/2024 23:05, todd via 928uk wrote:
> Just to update :
>
>   
>
> I adjusted the Bowden cable and lock nut(side of gearbox where Bowden
> connects) and it's definitely tight enough (I can even tighten it 
> enough to stop throttle opening fully. I've wound it back a bit now).
>
>   
>
> But, the car changes at 4500rpm max throttle.
>
>   
>
> As I understand it, the gear change is based on pressure. On one side 
> you have the vacuum of the engine and on the other you have the 
> throttle position (communicated to gearbox via Bowden cable). Once 
> vacuum pressure exceeded throttle pressure the gearbox changes gear.
> (Shout if that is
> incorrect)
>
>   
>
> So, my new question is : what else could be wrong? Low gear change 
> tells me the vacuum pressure is too high for the throttle pressure 
> (but I know the throttle is max). Is there an o-ring or something I 
> need to change to increase throttle pressure? Or a way to reduce vacuum pressure ?
>
>   
>
> Perhaps increasing pressure modulator?
>
>   
>
> Any help appreciated
>
>   
>
> Todd
>
>   
>