daveo90s4

My accelerator pedal is particularly hard to push (1990 S4 auto RHD). It was like that when I bought the car 15 years ago. About 7 years ago when I did the complete engine out and top end refresh I replaced the cable between quadrant and throttle body, plus the plastic wheel the cable runs on. No improvement.

Time to fix it.

Have disconnected all cables from throttle quadrant one by one to test which cable is problematic. The problem is at the throttle body. The plastic pulley this cable runs on moves smoothly and is not the cause. Pulling this cable by hand from the quadrant end shows that it moves nice and smoothly, but with in my view very excessive spring tension. No sign of this cable binding on anything en route.

The cable between foot pedal and quadrant is not the problem - moves easily back and forth (as does the foot pedal).

Anyone else experienced these symptoms? Anyone got any ideas for reducing spring tension under the inlet manifold at the throttle body? Seems like it is inlet manifold off again time?

Thanks in advance

DaveO
1990 S4 auto

Ramp

I have a similiar complaint with my S3 and found a few threads describing removing one of the 2 heavy springs on the throttle body. In the end, I decided not to do it at that time but have been thinking of going back and disconnecting one spring.

Look here starting at post 8

https://rennlist.com/forums/928-foru...y-springs.html

daveo90s4

Hi Ramp,

Thanks for your reply. Seems like the removal of one of the two springs might be what is needed.

Removing the inlet manifold to do that seems like a lot of work - plus risk of inlet manifold air leaks, etc, to remove a spring.

I'm wondering if there is some precision tool I can use to get in there (with MAF removed) to cut through one coil on the outer spring to render that spring ineffective? Even a hand held hacksaw blade - as long as I can make one clean cut.

Anyone know if what I'm thinking is doable?

Cheers

DaveO

Ramp

In hindsight I should have done it when I was doing my intake refresh. I don't know if you can get access on the S4 but even if you could, I would be a bit concerned that leaving a cut spring could somehow get jammed with an open throttle but perhaps not if cut at the right spot.

daveo90s4

Agreed about risk of cut spring binding on something - I thought releasing all tension on the outer spring would be a better option than relieving tension on the inner spring, for that reason. I'll have a better look in the morning - it may be that two springs are needed to provide a balanced force on the T piece that both springs lever off.

Two weaker springs may be the best answer - in which case inlet manifold removal is I think necessary.

Thanks again

DaveO

davek9

I wouldn't recommend changing the stock springs, make sure all is lubed up and not binding, the Auto's have a heavy peddle, dual disk clutch cars have a heavy clutch and gas peddle, deal w/ it its not a VW
Go to the gym.

hacker-pschorr

Have you driven other similar year 928's? My 87 has a heavier pedal than my 16V cars, but it's similar to every other 87+ car I've driven.

There's a lot going on when you push the pedal on a 32V 928.

.....or am I misunderstanding and you are acknowledging this is normal you just want to lighten it up?

dr bob

Can I relate a story?...

Only a few decades ago, I had the engine out of my then-current project for some refreshment. A neighbor had purchased a late-60's Mustang as a project, and in parallel it was getting an engine transplant. So we "shared" an engine lift rental for a day. We put his engine in first, and he went to work getting everything hooked up. I moved over to my project and got to work. By mid-afternoon the next day he was ready to test his new engine, a refreshed 351C. I had my project ready to put the hood back on and was in the middle of it when he started cranking the Mustang. It coughed a couple times then went directly to full song and more. I couldn't get to his house fast enough, probably a good thing because of the well-lubricated shrapnel in the immediate blast zone. Seems he'd connected a couple return springs to the wrong side of the linkage, so they held the throttle wide open instead of against the idle screw. I'd given him the concentric return springs, and sort of trusted that they'd be installed correctly. From the driver's seat he couldn't get out to even see the problem. In his surprise he didn't have the sense to turn the key off either.

How does this relate to the 928? There are two concentric throttle springs on the throttle body. Sometimes, especially as part of an intake refresh exercise, those springs get removed for throttle shaft bearing and seal replacement. Sometimes they aren't reinstalled perfectly. Sometimes we are tempted to leave one out, or reduce the tension on one or both of them to soften the pedal. None of those things are good except the bearing and seal replacement.

The throttle linkage consists of at least two cables, with an intermediate bellcrank arrangement that ties in cruise control and auto trans TV/kickdown cables. I know that the S4+ cars also include low-friction plastic linings in the throttle-body cable, plus a roller to make the pull angle better at the throttle lever. On the pedal side, the cable casing is a lot heavier, and includes a compression spring to reduce the chance of over-pulling on the bellcrank and ultimately the roller and throttle. The cruise servo connects to the bellcrank with a plastic-lined cable, and the auto gearbox has a similar low-friction cable that runs back along the torque tube to the throttle valve on the transmission itself. The bellcrank itself is a nested pair of levers that ride on ball bearings to reduce friction, and it also includes soft return springs. When you push on the pedal, you are overcoming the friction in all those pieces except the cruise control cable and servo. You are also pulling against all those return springs. "All those return springs" need to be stiff enough to overcome any/all friction in the whole system, including the cruise servo.

The throttle shaft springs are redundant, so that when one fails, the other still has enough available torque to overcome all the friction in the whole system. Should one decide to remove one of those springs, one would need to ask oneself if they are feeling lucky. Is the one that's being removed the one that was going to fail first? If one decides to reduce the tension on the system by backing one of the springs off by a turn, will it still have enough tension to close the throttle with the broken spring pieces wedged in the surviving coils? How about if something else wears and adds more friction?

We are all excellent drivers, way above average. Our ears are tuned to hear the slightest abnormality in the sweet engine song. Our delicate and sensitive feet will feel a single throttle spring weaken long before it fails. No worries at all that you'll have to diagnose the symptom, swerve to avoid hitting another car or that pedestrian, while you stab at the brake pedal and finally reach for the key to turn off the engine.... and lock the steering. I'm just not that lucky, or that fast or that good.

----

Engineering is the science of not making the same mistake again. Engineers who decided on two throttle shaft springs did so for a reason. They could have saved weight and money, assembly time and complexity. I can speculate on their reasoning. I also know the mistake they were very anxious to avoid.

nosnow

My 89 had a really stiff pedal that would cause my ankle to hurt on long drives. I decided to go through and replace everything and found the wheel on the throttle cable in the valley was very hard to turn, that helped but what really fixed the problem was replacing the throttle cable on the accelerator.

FredR

As other listers have said the 928 S4 and later have a relatively heavy throttle cable action with double springs [for a reason] and a cam action that accelerates the throttle action from about mid range to top end and of course the spring reaction gets heavier the more pedal one applies. If the components outboard of the throttle plate have an easy action then chances are you are simply reacting to what appears heavy relative to other vehicles that you drive and more so if they have an unusually light throttle action..

In my opinion it is something of a mind trick that one just has to get used to. Just as a teaser, when you are driving along a clear road with no other traffic in sight try a little experiment. Driving along at 60 mph in a straight line try braking with your left foot instead of your right foot and advise any reaction you had.

daveo90s4

Thanks for the input Gents. All good salient points raised and noted.

Ive driven a few late model Auto S4’s and GTS’ and my accelerator pedal is markedly harder to push. I need to use my quads to do so. This cannot be correct. All of these cars are RHD with a convoluted pedal cable that snakes though angles from firewall to behind cam covers to throttle quadrant. And that can’t help things. But that being said, all of my inner cables run freely within their outers. The prime cause of my issue is the tension on the return springs. A pair of weaker springs, each of which in its own is capable of closing the throttle, would clearly be the ideal solution.

And that is definitely an inlet manifold off job. Bugger!

Cheers all

DaveO

daveo90s4

Problem fixed. No throttle body springs were injured in this process!!

With airbox out, MAF still in, holding tongue just so, I was able to shine a small torch into the valley and from above se the throttle body springs by peering down between cam cover and inlet manifold.

With a a long thin nozzle I then liberally sprayed the throttle body mechanism and springs with a dry lubricant. While working quadrant back and forth.

This is has made a very significant improvement and is as good as any 928 I’ve driven (manual 16 and 32v models included).

Very pleased with with the results.

Best wishes all

DaveO

merchauser

good work; congrats!

Bedfordman

Hi Aus., & Fellow RHD 928.

Your solution noted for reference, thanks.

I don't have a big prob with this but:
I found that the angle the pedal to quadrant cable goes into the quadrant made a modest improvement.

Consider route the cable as shown in photo. 2 mins to try it & free !

drnick

Dave, I always thought it was just a problem with the rhd cars due to the throttle cable going across the engine bay. Both my 86 S2 and the GTS engine were stiff and nothing much improved them until I junked the Porsche manifold and put BMW parts in there instead