Saturday, July 19, 2008

Finishing the Firewall Rack Base

Of all the battery racks, the firewall rack is the most complex with the most interferences. I'm going to try and capture all the problems I ran into today while trying to get the firewall rack base installed.

I re-installed the transmission while ago to make sure that I would get the proper spacing with the firewall rack. Since the mounts for the transmission are rubber, they flex, so I needed to use a floor jack to raise the transmission back to its working height to get the proper spacing. As shown in a prior post, the proper height is correct when the bottom of the transmission is level with the bottom of the front bumper, at least in my case.

Initially I had two 2" pieces of angle iron (1/8" thick) for the left and right supports, but I found out that they were too big and interfered with a bunch of brake lines. I reverted back to 1.5" angle iron. In order to properly bolt into the 8mm holes at the rear of the engine compartment, I needed to take off 1.5" of vertical wall from the ends to allow the bolt head to fit.

The piece on the left is 15" long and fits on the driver side. The piece on the right is 24" long and fits on the passenger side. The ends with the 1.5" missing vertical wall goes towards the rear end of the car.

To prepare for mounting, I drilled a 21/64" hole (just over 8mm) 1" in from the rear end and 3/8" in from the edge where the vertical wall was removed. I also drilled two 3/8" holes (center-punch, pilot hole, final drill) 5 3/8" and 10 3/8" in from the rear end up on the vertical walls to bolt into the shock-tower bars.

This is a picture after all the drilling has been done and the 3/8" bolts have been installed.

The vertical bars attached to the shock towers have 6mm holes drilled in them and I used 6mmx20mm bolts with lock washers to hold them in. The vertical bars are 1.25" wide and 6" long. The bottom holes in the vertical bars will be drilled after aligning the left and right support bars of the battery rack.

The rear end of each support bar is 2 3/4" above the chassis and is currently supported by 8mm all-thread with nuts that fits nicely into the 8mm hole. I'm going to replace this in the short-term future by adding a 8mm by 90mm bolt that goes through the hole in the support bar, through a 2 3/4" pipe and screws directly into the 8mm threaded hole in the chassis.

With the rear end of the bar at the right height, the front end of the bar needs to be raised so the bar is level. I used small clamps to attach the side bars to the vertical straps on the shock towers so I could verify placement before drilling any holes.

Here's a look at the right support bar holding up the rear support bar. I had to cut out a triangle of metal to prevent any of these bars from rubbing against the brake lines.

With the rear ends of the left and right support bars in place. We clamp them to the vertical straps on the shock towers after raising the front end so its level with the rear end. Remember the 3/8" holes we drilled in the vertical walls of the left/right support bars? These should line up with the vertical straps on the shock towers, so we can draw a circle on the vertical bars for later drilling.

The front and rear support bars (1.5" angle iron, 1/8" thick) are 31.25" long and have 3/8" holes drilled in them 1/2" from each end. The front-most face of the front support bar needs to be 15" from the rear end of the left/right support bars. After placing the front support bar, the rear support bar should be placed so that there is 31 1/8" of inside distance between them to support the group-31 batteries. With the two bars placed properly, you can draw circles on the left/right support bars through the 3/8" holes for later drilling.

Getting the firewall rack right is difficult due to the tight clearance between the top of the transmission and the underside of the hood. With the rear of the rack 2.75" above the 8mm threaded holes in the chassis, the front support bar should just barely clear the top edge of the transmission. I've used a piece of wood here to make sure the rack is level before marking any holes for drilling.

Alas, even with very little clearance above the transmission, the group-31 foam-core battery interferes with the underside of the hood. If you click on this picture to zoom in, you'll see that I've marked a section on this diagonal support on the underside of the hood that needs to be removed in order to let the hood close without battery interference. I'll have more pictures of that later.

With all the holes drilled and 3/8"-16 by 3/4" long bolts installed in all the holes, the base of the firewall rack is mostly done. I can stand on this and shake quite violently and nothing seems to move. It better not, since it has to hold 280 pounds of batteries.

Since the clearance with the underside of the hood is so tight, I'm going to have to replace the 3/8"-16 x 3/4" bolts on the left support with countersunk bolts so I don't raise the batteries any further. There's simply no room left. Ugh.

Next up: trying to get the power steering reservoir in place...


Ohmaar said...

Since you're looking at cutting into the structural support of your hood, have you considered a lightweight hood replacement (fiberglass or carbon fiber)? You'd eliminate a potential electrical short path (metal hood), save yourself some precious weight and they may even clear your batteries without further modification.

TimK said...

Thanks for the comment. A few people have suggested this. The kit is targeted for a budget-minded conversion, so I'd like to see if I can modify the hood to work. A carbon fiber hood is at least $400, so that makes things a bit pricey. If I run into major problems, I'll probably go with it. Cheers, Tim