I had a mildly annoying problem; when the car got hot, the throttle would stick a little and the car would idle a bit high.
I sprayed it with stuff and it went away and I forgot all about it.
Well that is until a test and tune day a few weeks ago. The track was wet and I was struggling to stay ahead of a newer M car. It was fun but intense. I nailed the brakes to slow for a left hander and instead of slowing down it felt like my new buddy had hit me from behind. The engine was racing and I was not going to make that corner so I looked for somewhere to ditch. I went off across the grass. Of course, once stopped the car was fine. I limped into the paddock, and a helpful neighbor popped in a stiffer return spring he had in his toolbox and then rode shotgun as we tested the car out. Maybe i had mixed up my feet in the heat of things? Maybe my throttle cable was fraying?
Nope; now I had a witness as we went off across the grass again. This time I opted to limp home.
The stiff bell-crank. The bottom rod going left connects to the accelerator; the top rod heads up through the tin to the throttle linkage at the rear of the engine. You can see the transaxle fill plug above it (just above and right), nearly guaranteeing it will leak when removed.
So what's wrong? The 911 doesn't actually use a throttle cable; it has a series of rods with a bell crank in the middle of it all to change the angle that the throttle linkage acts at. The bell crank is mounted on the side of the transaxle housing. There is a rod screwed into the housing, and the crank rides on greased bushings on that rod. It's all held in by a cotter pin. The bushings are nylon and wear out, which is probably what has happened to me here. When the car gets hot, it sticks from the mix of chewed up plastic, dirt and old grease. That rod may even be rusty from years of exposure.
The one trick to this job is that the rear A-arm blocks the bell crank from sliding off of the support rod. There is almost enough room, but not quite. So what to do? Well when you pop out the cotter pin you will notice the rod has a flat where the cotter pin goes through. It will take an 8mm box wrench and then you can remove the rod with the bell crank together. The other option is to loosen the transaxle mounts and lower the transmission a tiny bit, being careful not to bend the shift rod (no thanks!) On the 915 trans the rod is in a blind hole but on my G50 apparently it goes all the way into the housing and may leak 90W gear oil. Something to look forward to. If you have not had the pleasure, 90W Hypoid oil is probably the smelliest thing on your car. (Dress accordingly)
The smart money says to put some penetrating oil on the the rod/transmission interface maybe a day ahead of time to make sure it's cooperative.
The new support rod, OEM Porsche. The bushes have the right ID, here is hoping the OD is good for the bell crank! You can see the flat we'll use to remove/replace it as well.
I ordered a new rod and new bushings to make sure it will all fit and in case the old rod is rusty. The plan is to pull it all out, clean it up, press the new bushes in, grease, re-assemble and finally put it back on the car. I have a high speed DE day at Lime Rock in August so it will need to be at least a week ahead of that so we have time to make sure we're good to go. Ditching at 30-40mph is not that big a deal. Ditching at a 100+ is.
Ready to lift a wrench! Everything fits perfectly.
Parts
Bell Crank Bushing 914-423-211-00-INT
Support Rod for bell crank 914-301-307-01-OEM
Accelerator lever (with bushings) 911-423-017-01
Transmission Bell Crank Repair Kit NLA-423-020-3M
Bell Crank Pin 911-423-227-00-OEM
Bell Crank Cotter Pin N-012-530-1-OEM
6mm nyloc nut (bell crank pin nut) 900-084-010-02-INT
Follow Up
The new bell crank didn't fit quite right so we just used the new rod and bushes with the original bell crank and the throttle is working properly now. The old rod was bad.
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