Wednesday, December 3, 2008

Fixing up the Rear Suspension

Whew! I finally got my internet connection back up at home. This is the first of ten entries that will attempt to show many of the tasks I performed over the four-day Thanksgiving weekend.

First up, we need to beef up the rear suspension to handle the extra 420 pounds of batteries in the trunk. As you may remember, I swapped out the front springs with beefier ones. Since the old front springs were much stronger than the existing rear ones and had the proper taper to them, I opted to take the same route as Rob Connelly and cut them to handle the appropriate rear load.

Rob used six Optima Yellow Top group-31 batteries in his trunk. Since I'm using Concorde Lifeline batteries which are 9 pounds heavier each, I needed to support 54 additional pounds on the rear suspension.

Using Rob's spreadsheet, I was able to calculate the proper spring length from the old front springs that would handle the load. Many thanks to Rob C. for explaining spring physics to me and providing the spreadsheet. You can see a discussion and the spreadsheet in the Google discussion at this link.

After modifying the spreadsheet, I realized that I needed to cut the old front springs to 13.3" long.

Here is one of the old front springs in my cutoff wheel saw. There were quite a bit of sparks, but the wheel did an excellent job of making a nice flat top to the spring coil. Since the cutting process is very hot, I added an extra 1/10" to the cut length just in case the heat softened the top of the spring.

Here are both springs cut off to 13.4" length (13.3" plus the .1" for heat sag).
After cutting the springs, I removed the two rear shock strut assemblies and took them to Les Schwab to swap out the springs with the cut ones above. Several months ago, I had purchased a spring compressor to do this myself, but found it really scary given all the pressure. I found that just having the guys at Les Schwab do it with the proper equipment was $30 well spent.

Here is the spring assembly on the ground with the newly cut spring inserted.

Note: when you replace the springs, make sure you mark the orientation of the shock tower mounting bolts (left end of the assembly in the picture above) and the swing arm mounting bolts. Shock assemblies rotate and if you get the top and bottom bolts back with a different alignment, it's really hard with the spring under tension to rotate the top into the proper orientation.

Here's the spring mounted in position. Follow the instructions in the Helm shop manual to properly remove and install these. You need to raise the rear support with a floor jack to put the car's weight on the spring before tightening all the bolts, otherwise it doesn't sit right.

Since I had all the wheels off, I felt it was a good idea to check the front brake pad thickness. This is a close-up of the passenger side front wheel hub. I still have 9mm of brake pad left, which ought to be plenty for awhile. I will have to watch this since the extra 840 pounds of batteries will put an extra load on the brakes.

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