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Clutch

Updated 07-Sep-2003

 

General Information:

The car is an original automatic car, I had to decide between using the '99 pedal set I got with the LS1 or finding a set of used 70-81 pedals. I was most concerned with the safety of the brake system. After some investigating I decided that I was more comfortable modifying a ‘81 set than chopping and hacking the '99 set. 

After scouring the local junkyards and coming up empty I found a pedal set on eBay.


Details:

I measured the ’99 pedal ratio and the stock ’81 ratio and found that if needed I could relocate the master attachment point in the ’81 pedal closer to the pivot point for more leverage and less travel. I spent quite a bit of time on the bracket to try and get it at the same leverage and travel as in the '99.  I drilled a new hole in the clutch pedal arm that gave me the same ratio as the '99 pedal set this also reduced the travel on the master cylinder since I had way to much to start with.  Other than I will still have to reduce pedal travel I believe I will at least have similar pedal feel and pressure as the original ’99.

· Stock ’99 pedal

o Overall length 12”

o Attach point 2.125” from pivot point, approx .875” travel of attach point

o 5.65 pedal ratio

· Stock ’81 pedal

o Overall length 11.5”

o Attach point 2.5” from pivot point, approx 1.25” travel

o 4.6 pedal ratio

· Modified ’81 pedal

o Overall length 11.5”

o Attach point 2” from pivot point, approx 1” travel

o 5.75 pedal ratio.

 


The template I made from heavy paper cardboard for the clutch master cylinder bracket. I used a mockup firewall from a piece of old junk sheet metal to test the clutch bracket since the firewall on the '81 is almost flat at the booster. I created the bracket out of 14ga steel using the template as a guide. I plan to bolt it between the booster and the firewall and did not want to drastically change the distance between the booster and the brake pedal. A 17degree bend on the bracket was used but after some hindsight I probably should have gone with a 15degree bend. This angle changed depending on how high or low the clutch master cylinder is mounted on the firewall. I will be using two of the steering column bolts to help hold this bracket as well as a few 90degree bends made with my vise as a sheet metal brake.

 

After the initial single piece of sheet metal was cut and formed I found that my fears of needing to space the clutch master cylinder away from my new bracket were true. This was verified with a piece of wood, shown in the side view on the mockup in order to keep weight down I decided to build another 14gauge sheet metal box and weld it to the first piece to create my spacer.

 


A picture of the bracket that clearly shows the extra spacer welded on as well as the two nuts for the steering column at the top left and bottom center. Here it is on the mockup with booster and clutch master cylinder installed.

 


I drilled the spot weld for the clutch pedal position switch (start switch) bracket from the 99 and welded a small bolt into the hole. I am going to bolt this bracket to the 81 since the switch will be virtually impossible to access once installed. The factory 81 brake light switch for both brake lights and the second set of wires for cruise control disengage. Then move the 81 brake cruise disengage switch to the clutch pedal in a fabricated bracket welded to the top of pedal mount over the rubber bumper. I bent the rubber bumper mount in the pedal mount to stop the clutch pedal at the end of clutch master cylinder travel. The final pedal mount right after it was painted. The clutch cruise disengage switch mount can be seen in the picture, also the holes for the clutch position switch can be seen (there are six holes total, 3 mistakes oops and 3 to be used).

 


This is the final clutch pedal, red arrow is the factory 81 attach point, green arrow is new attach point, yellow arrow is small plate welded on for contact with clutch start switch from the 99. The pedals and all underhood steel will be painted with PPG DP90LF a satin black two-part catalyzed epoxy primer.


Final pictures of the assembled pedals on the mockup taken 9-10-2002.


This will be all for the clutch assembly for a few weeks. I still have to work out a limit stop to keep the clutch master cylinder from bottoming out in the bore.   I'll get to that later once I'm ready to install in the car, for now it's back to the motor mounts and subframe.