Recently, I was performing some extremely overdue service to my 911SC (you know what they say about the cobbler’s kids going without shoes). Before finishing up the service, I checked throttle, clutch and emergency brake linkage. When checking the throttle linkage, I noticed that the throttle was only opening about 75-80% of its capacity. Now, this may not seem like a big deal to some, but to me it was like finding a mystery $20 bill in my pocket (after it was fixed that is).
I knew I had full throttle the last time I had serviced the car, so some piece of linkage or a bushing must have worn out. The number one failure on these cars is the bushings that live in the engine and transmission bell cranks. This was the first thing I checked, but I found them to be in perfect condition.
The problem in this case, was not the bell crank bushings, but the bottom transmission bell crank and throttle rod. The main throttle rod from the pedal pulls the bell crank; which in turn pulls the upright throttle rod to the engine. The point where the bell crank pulls on the upper throttle rod gives us the greatest amount of wear, see figure 1 & 2.
911 throttle rod and worn attachment
Figure 1. Worn Throttle Rod & Attachment Piece
Notice how the throttle rod and attachment piece are pulling through each other and about to break.
New 911 throttle rod and pivot bolt
Figure 2-New Throttle Rod & Repair Piece
Notice full thickness of throttle rod and attachment piece.
The repair in theory is simple, just replace the worn out parts. The throttle rod is connected to the top bell crank with a ball socket, and to the bottom bell crank with a hoop and bail arrangement. The throttle rods vary in length and shape from model to model, and most cost between $100-150.
The bell cranks are another story entirely. The various bell cranks usually cost around $125, but can run as much as $150 for a 914-6! You have probably figured out by now that there is no way I would ever spend $75 for a bell crank, let alone $150. You may also have figured out that this article is going to tell you how to repair that pricey bell crank for a substantially lesser amount. While thinking of a way to repair the bell crank it all came to me. The bell cranks on ‘84 and later 911’s have removable (i.e. replaceable) throttle rod attachment pieces. These pieces can be attached to any transmission bell crank for a quick and easy repair. This repair applies to all 356’s, 65-89 911’s, as well as 65-69 912’s and 914-6’s. The best part of this repair is the price. The repair piece 911.423.227.00 costs around $15.00 and the locking nut 900.910.010.09 costs around $7.
The repair process is as follows:
1. Replace the worn throttle rod as necessary
2. Remove the worn out transmission bell crank
3. Drill out back side of original throttle rod attachment piece, see figure 3.
Drilling out bell crank
Figure 3. Drilling out back of bell crank.
4. Drive out remaining attachment piece with a drift pin
5. Drill the existing hole to accommodate the larger 6mm hole of the repair piece
6. Insert the repair piece and tighten down with the supplied locking nut
7. Re-install the bell crank and adjust the linkage as necessary to obtain 99% of throttle opening
Be careful while adjusting the throttle linkage. If the linkage is pulled too tight and binds, you can create a whole new set of problems. These problems can manifest into a bent pedal assembly bell crank, which can cause the throttle to stick wide open (for a real E-Ticket ride!).
The key to getting the maximum life out of this repair is proper lubrication at all of the critical wear points. I like to use Porsche high temperature clutch grease, Part #000.043.024.00. It seems to last the longest, under the most extreme of conditions, but certainly is not the only option. Plain white lithium grease will work fine when reapplied at each service interval.