Installation of 930 rear brakes on a 911

This is meant to be a quick overview of the process for installing a set of '78-'89 930 rear brakes to a normally aspirated 911. The subject car is a 1977 911S. This procedure required moderate mechanical skills, and a normal set of hand tools. You should to be familiar with Porsche brakes, and/or brake systems in general, before attempting this procedure. If in doubt, defer the work to a competent Porsche shop - I wouldn't want Midas to do this job.

You must have the calipers modified before you can attempt to mount them to the 911 trailing arms. This work must be performed by a competent machine shop familiar with Porsche brakes. I won't go into the machining procedure here, but you can go VCI's web site to see how they do it.

Also check out the Front Brake conversion page.

Find a way to push the pedal about 1/3-1/2 the way down and hold it - this keeps the master cylinder from draining while you have the brake lines open.

Raise the car and set it on jackstands, and remove the wheel. Here's what your old brakes will look like once you get the wheel removed.

Remove the upper caliper bolt (19mm wrench)

Remove the upper caliper bolt (19mm wrench) - be patient!

Remove brake line clip (screwdrive and hammer) I found it easier to disconnect the brakes on the inboard connector, rather than at the caliper, and since I was going to have to fab a new brake line anyway...

Remove brake line (17mm and 11mm wrenches)

Remove caliper (watch for dripping brake fluid)

Remove screws holding rotor on (could be either phillips or flat)

Rotor comes straight off - may need some coaxing if it's been on a while. Remember to release parking brake!

This is what it looks like with the rotor removed.

Here's the differences betweent the stock brakes and the 930 brakes.

Your 930 calipers have to be machined to fit on the 911 trailing arms

You'll also need spacers, which the shop that does the calipers can provide. I 'glued' mine to the caliper with Aviation Permatex to so they wouldn't fall off during assembly.

You will now have to cut the backing plate mounts off the trailing arms. Backing plates aren't shown here because I'd already removed them months ago for better cooling. Here's a shot showing the interference between the caliper and trailing arm

So, get your favorite cutting tool and carefully cut the mount off. I used an air-powered body saw, but the trailing arm is aluminum, so it cuts easily.

Then use a grinder to trim the edge up nice and remove the last bit around the corner

And then the bottom mount...

It should look something like this when you're done

Test fit the caliper to make sure you've removed enough material; trim with the saw or a grinder if it still interferes. You should be able to easily get the bolts started into the holes with your fingers when it's right. You don't want any binding!

A closeup of what the caliper to trailing arm interface should look like.

Once the caliper is ready, remove it, and fit the rotor.

Once the rotor is attached, fit the caliper. You'll need bolts that are about 1/2" or so longer than the ones your removed. Be sure to source these ahead of time, as you won't be able to find them at the hardware store!

You will also need to fab a new brake line. The better auto parts stores have metric brake lines. 12" works perfectly.

You must bleed the entire brake system after installing the new brakes!