Modified Accelerator Cable

Started by tmsmini, May 01, 2020, 09:06:41 AM

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tmsmini

My swap to a 45mm SC throttle body continues to annoy me. This is not really an injection issue as even some HIF carbs need some special treatment for throttle cabling.

I have made a number of other changes along the way just to complicate things, but it all did work previously. I was trying to fix things that were marginally "broken."

This issue really has nothing to do with the throttle body as far as I can tell. It is an accelerator cable issue, maybe a cable alignment issue.

SC originally suggested using the MPi cable as they thought because I was using an MPi engine I must have an MPi. It is totally inappropriate and I abandoned it before we went to Oregon two years ago, too long, hits the bonnet and both ends of the cable are terminated.

I am using one of their cables which is supplied by the people who make their throttle bodies, AT Power(https://www.atpower.com/). It worked fine for the 50 MM TB.

I have to be making a simple mistake. I never liked having the adjustable ferrule on the pedal end of the cable, but that is what they supply. I added a couple of Venhill(thanks for the tip) cable ends to make the curves as smooth as possible. I trimmed the cable as short as possible, making sure not to hit the bonnet and still have a smooth radius. I have tried several cable lengths. I added some shrink tubing to the cut cable ends to make sure they centered properly in the metal cable ends.

In this movie you can see that the mechanism sticks, yet the cable is not sticky and falls from the weight of the pedal when free. With no cable, the throttle returns to 0 all the time.

https://www.youtube.com/playlist?list=PLNWUxao2Iq7HsRWOL_yeIzjEL5G-26Bpo

The problem seems to be worse on the road. In the driveway, it will not stick all the time. On a drive, it will stick at the first stop sign. Give it a rev and it returns to 0 most of the time. Sometimes one or two strong revs are required to get it back to 0. I thought it was heat related, but I cannot confirm that.

A friend suggested I shorten the threaded portion of the Venhill cable end on the TB bracket to give the cable a longer untethered run to the throttle quadrant., which I have done. It seems to have improved things a bit.

But any other ideas are welcome.
It seems the slight dimensional changes of the inlet manifold and the throttle body have had some consequences I did not foresee...

LarryLebel

Is there a throttle position sensor that is sticking?

tmsmini

I thought that might be the case. I swapped sensors with no change and this is a new throttle body with a new TPS and the issue remains.

MiniDave

Add an additional throttle return spring? Not heavy, but just enough to overcome whatever is causing the hangup? Could it be simple friction inside that radius tube?
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

tmsmini

I am looking at an extra spring. The later cars had one on the pedal. I am looking to see if the MK I pedal box will make this easy.

The cable slips easily when loose from the quadrant and falls from the weight of the pedal. I think I tweaked the cable bracket on the 50 mm TB to make a smoother transition, but with the position of the fuel rail and the revised filter location, there is no room to change anything.

MiniDave

I guess a spring pulling back on the acc pedal where the cable attaches could work - easy enough to try it
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MPlayle

It looks to me like the turn radius of the throttle quadrant puts the cable at an angle going into the sleeve - causing possible rubbing.

My first inclination was to also suggest a mild return spring, but attached to the throttle quadrant to pull it back to zero.

If the cable angle into the sleeve at the TB is the issue, having the return spring on the pedal will leave the slack at the pedal and the cable may slip out of the slot in the pedal instead of fully returning the throttle to zero.

The other possibility would be stronger spring tension for the throttle quadrant itself is needed or the quadrant too tight on its shaft - not able to rotate freely enough for its spring to overcome the additional drag of the cable?


tmsmini

I adjusted the cable end at the bracket and it had helped.
There is a threaded hole in the quadrant that could be used for a spring, if it is at the right angle

LarryLebel

The end of the outer cable needs to be all the way into hole on the firewall. You should be able to see the end of the cable looking from inside the cabin. The throttle pedal pulls the cable down as well as out, so it helps to have a chamfer on the hole in the outer cable.

MPlayle

Looking at your last picture, you can see the bare cable makes a slight bend toward the air filter between the end of the sleeve and the top of the throttle quadrant.  As the cable pulls up, that bend will increase slightly and is likely the cause of the binding.

Having the end of the sleeve angle towards the air filter just a tiny bit would likely fix the problem; however, looking at some of the other pictures for how the cable has to route in there and is essentially touching the hard fuel connections, I don't think you have room to adjust the end of the bracket holding the end of the cable sleeve.  A small return spring is likely best at this point.

I would see about mounting a small 'L' bracket on the bulkhead cross-member straight below that hole in the throttle quadrant and hook a small return spring between the two.  As the quadrant rotates from the throttle cable pulling up, it will also pull up the return spring.  Releasing the throttle, the spring will pull the quadrant back down.


94touring

Was looking on their website and they offer a 45 and 50mm throttle body.  One for small bore and other for large bore?

tmsmini

For the 50 mm you would need a well worked head and matching exhaust, maybe 1380. The 50 mm has been on the car for about three years, seemed to overfuel no matter what adjustments I made. Hence the reason to try the 45 mm.

I did email SC to see if they had runinto this before.

94touring

Hmm. Well I'm curious to know how that works.  I have a hot 1310.

MPlayle

Can you compare the profiles of the throttle quadrants?

If the quadrant from the 50mm TB is a tighter radius, it would be more in line with the end of the cable sleeve.  If the quadrants could be swapped, that might also fix the problem.


tmsmini

I gave S.C. the specs of my setup at the start of this and they suggested the 50. I do not have a hot engine, mildly tuned head etc.

The original Rover setup is 48 mm, but that apples to oranges

tmsmini

Here is a little history on the evolution of the S.C. throttle body.
Silver version is early, a lot of hand machines parts
Cast grey version is about five years old
Black version is current

No parts except for injectors and TPS are interchangeable

Jimini II

#16
Something else to check would be the alignment of the pedal and cable through the firewall hole, it is a bit fiddly but the pedal assembly has some wiggle room to get them aligned 100%, after removing the cable i check the alignment with a straight piece of wire or an appropriate drill bit.
Also years ago I changed a throttle cable on a Mini that was miss aligned and had worn a groove where it passes through the firewall which made the new throttle cable stick just like yours, I ended up drilling it out the next size and had no more sticking throttle cable issues.

If you add a return spring I would add it to the pedal rather than the throttle shaft. You could use a P clip on the pedal and drill a small hole in the pedal box to mount it.

John Gervais

There are a lot of suggestions above, but I'm curious about the interesting setup you've got at the throttle pedal and why you haven't gone for a known mini cable such as the C-AHT85 with a suitable casting which nestles within the recess of the pedal, and utilizes a NAM6983 retaining clip to hold the cable within the pedal's slotted nest.  I made a very nice HIF cable from a new C-AHT85 by cutting it slightly shorter and fitting an HIF bracket-end to the shortened '85 sheath.

As you know, cable sheaths can be carefully trimmed shorter and cables can be cut and soldered to prevent fraying.  I suspect that your current setup is fouling on the slotted pedal shaft.
- Pave the Bay -

tmsmini

Unfortunately that is the way the S.C. setup is designed. The throttle body quadrant is not machined to take an adjustable ferrule at that end. I have thought of modifying it, but the existing setup has worked fine for about 5000 miles, just not with this throttle body and the the other accommodations that have been made.

I never liked the way they did that, but I guess most modern cables are terminated at both ends with fittings.

tmsmini

I took the car for a drive around the neighborhood and it seems much better.  It did not really stick, but was slow to return to idle at a couple of spots. It seems the longer throw from the quadrant to the Venhill curved/radiused cable end has helped.

The quadrant does have a 5 mm threaded hole which I may be able to use for an aux spring.

As I am stuck with the ferrule at the pedal end I would really like to find a ferrule with the shape in the photo. The narrow end would fit into the pedal bar and the larger section would be used to clamp onto the cable. The firewall passage is clear as the car was stripped when we had it painted a few years ago.

Jimini II

Is it possible to use a longer cable and get rid of the 90 degree bend at the firewall, maybe over the rocker cover similar to a regular Mini set up.

tmsmini

I started long and kept going shorter.
The cable bracket location means the cable points up at the bonnet. I had issues with the bonnet closing changing the shape of the cable loop and causing an idle change.

It was a real problem with the MPi throttle cable as it is much thicker and does not like to bend.

Something like the right hand drive throttle cable support on the valve cover bolt would probably help with a longer cable.

Willie_B

Simple lathe projects are fun. Could not find 3/8 brass rod so used aluminum. I can mail it to you if you want to try it.

tmsmini

#23
I would love to try it!!!!

I sent a personal message, but i cannot tell if it went through.
tmsmith510@gmail

Willie_B

I got it. Will get mailed Monday.

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