Even though my conversion used lithium batteries, which are 1/3 the weight of lead for the same energy capacity, there is an extra 150kg/330lbs of battery sitting in the trunk. This weight in in conjunction with old springs which were prone to just snapping due to corrosion prompted me to look into suspension upgrades. There were OEM options like the mystical “1BB” and “1BT” heavy duty suspensions which offered higher ride heights and presumably stiffer spring rates. The option on my A4 was the standard “1BA” suspension option.
After a little searching, I found rear springs from Germanautoparts.com which claimed to have a higher spring rate (link here). Presumably these were either for the A4 Avant or they were the springs I was looking for. Upon receiving the springs, there was a dramatic difference in length, almost 3″.
On the left is the original and on the right is the heavier duty spring. The heavier duty spring came in a box from Suplex and was labeled made in Germany, which is all good stuff.
A copy of the Bentley manual or ETKA diagrams are very helpful, but disassembling the rear suspension and extracting the strut was extremely easy. There are 4 bolts securing the strut to the chassis and one bolt on the upper and lower control arms. You will undo the eccentric alignment fasteners in the process of replacing a spring, and you will need an alignment after.
Always be sure to jack up the vehicle safely and use jack stands. Above is a shot of the wheel well with the strut removed. Note that there is some rust residue on the chassis stemming from the top of the strut tower. The rust hadn’t penetrated through Audi’s hot-dip galvanizing and it washed off with some scrubbing. Also note that the brake lines and parking brake cable are not being strained.
It was necessary to compress the spring in order to remove the strut from the car, hence the ratchet straps. I trust nylon braided straps way more than cast metals found in stereotypical spring compressors which can crack or slip. The amount of energy stored in automotive springs is to be treated with great respect. 3 straps were used around the circumference of the spring and once compressed enough for the dampener to be unloaded, one bolt had to be removed to extract the spring.
Installation of the spring is pretty straight forward, it only goes in and sits one way. Even though the spring was longer, I was able to compress it just enough to reinstall.
With the car back on the ground and no batteries, there was excessive wheel gap, but it settled nicely with batteries loaded in and with a few test drives. Now the car site more or less as it did before.