One of the great design characteristics of early 911s is their infinite design interchangeability. While the cars have evolved gradually over time on the outside, what’s under the skin remained similar enough so that scavengers, such as myself, can find just the right parts to transform their cars into a more advanced version of what they once had.
The part interchangeability we’ll talk about today is the rear sway bar. Pre-‘89 911s use two different styles of rear sway bar. The Type-1 sway bar was installed on cars from 1965-77. Starting in 1978 with the 911SC, the type-2 sway bar was implemented and used through the end of the 1989 model year on 3.2L Carreras.
The largest optional rear sway bar for a pre-‘74 911 is 15mm. The standard bar for a ‘74-‘77 911 is 18mm and they are of the same type-1 configuration. So for an ultra-simple upgrade, the later 18mm type-1 sway bar can be installed on any early car originally equipped with the smaller 15mm sway bar, without further modifications.
The problem occurs when trying to find one of these 18mm type-1 bars, since they only came on 3 model years of the 911.
You will also run into a snag if you want to fit a bar larger than an 18mm to a pre-’78 car, since these are only available in a type-2 configuration. This does make for a nice option though, because the heavier type-2 sway bar came on all 911s from ’78-’89, and was also available in 3 different sizes: 18,20,and 21mm. This adds significantly to your list of available years and bar sizes.
The type-2 bar will mount directly to the older chassis with no problem. The difficulty comes in when trying to mount the bar to the control arm end of the car. This is because the two types of sway bars have very different ends. The end of the type-1 sway bar curls around to facilitate the mounting shackle, while the type-2 sway bar is straight with a 12mm bolt hole in the end for mounting of a type-2 shackle. (See Figure #1)
Porsche type 1 and type 2 sway bars
Type-1 sway bar on the left and type-2 sway bar on the right.
The end of the type-2 sway bar is straight with a 12mm bolt hole in the end for mounting of a type-2 shackle.
(See Figure #2)
911SC rear sway bar
Figure #2 – Type-2 sway bar (21mm) with stock mounting on a 911SC.
The type-2 shackle cannot be used with the type-1 mounting ball on the earlier control arm. The solution seemed quite simple to me; make the type-2 sway bar mount more like a type-1 sway bar. This is the key to a successful upgrade to the larger type-2 sway bar.
The type-2 sway bar needed one more bend in it, to mimic the curve in the type-1 sway bar. Fortunately, the type-2 bar has that 12mm bolt hole pointing in exactly the right direction, so all we need is a way to attach an extension to the end of the sway bar.
After a little searching, I came up with just the right thing. Oddly enough, it was a silicone-bronze valve guide blank. It had an outside diameter of 19mm, just enough oversize to tighten the stock bushing to zero play. The inside diameter had to be bored out with a 15/32” drill bit. This allows for a perfect fit of the 12mm bolt. The guide then needs to be cut down to 38.5mm in length (the width of the stock sway bar bushing). The original length of the guide blank is 79.5mm; so two bushings can be made out of the single guide blank (as long as no machining mistakes are made within the 2.5mm margin). This leaves us with a silicone-bronze bushing with a 19mm outside diameter, a 12mm inside diameter, and a total length of 38.5mm. (See Figure #3)
911-rear sway bar bushing
Figure #3 Original guide blank on the left. Modified bushing on the right.
When installed on the end of the type-2 sway bar, we have what is for all practical purposes, a type-1 sway bar in three optional sizes; 18, 20 and 21mm. (See Figure #4)
911 rear sway bar conversion
Figure #4 A type-2 sway bar modified with the kit shown in figure #5.
It now can be used as a type-1 sway bar.
The complete kit consists of 7 pieces per side. (See Figure #5)
911 rear sway bar conversion kit
Figure #5 Complete rear sway bar conversion kit (one side).
1-Silicone-bronze bushing
1-12 x 75mm bolt
2-12mm large flat washers
1-12mm flat washer
1-12mm lock washer
1-12mm nut
If an 18mm sway bar is chosen, all four stock rubber bushings can be used (911.333.793.02 @ $25.65 ea.). If a larger bar is used, larger after-market sway bar bushings can be used where the bar mounts to the body. The original 18mm sway bar bushings will still be used in the sway bar shackle (when the type-1 conversion kit is used).
Another sway bar mounting option would be on a car that was never equipped with a factory sway bar of any type. When this is the case, the standard sway bar consoles can be mounted to the chassis of the car. A complete type-2 sway bar (with type-2 mounting shackles) can then be mounted to the rear control arms. Just drill a 12mm hole where the early ball mount piece would go on the early car. Two standard suspension spacers need to be added at the bar and at the control arm to maintain the correct geometry. (See Figure #6)
911 sway bar kit option
Figure #6 911 sway bar kit option for car without original sway bar option.
The additional hardware needed per side for this set-up is as follows:
2- Spacers, Part #911.573.513.01 @ $22 ea.
2- 12 x 75mm bolts
4- 12mm flat washers
2- 12mm lock washers
2- 12mm nuts
The drop links are not at the optimum angle and should be cut, twisted, and re-welded to the correct angle for maximum drop link life. If this is not done, while it will work, it may also shorten the life of the drop links.
When installing one of these later bars on an earlier car, if you cannot find the right size (or if you simply want a new sway bar instead of a used one), you can still breathe easily. Fortunately, these bars are not too terribly expensive.
The sizes, part numbers, and prices are as follows:
18mm/ 911.333.701.07 / $275
20mm/ 930.333.701.25 / $280
21mm/ 911.333.701.11 / $280
Don’t forget the obvious strictly bolt-on update, for 911SCs and early Carreras. The 21 mm bar makes a great addition for someone who wants a little more turn-in on those tight autocross courses.
The whole point of this article is to help you with options when you can find a used sway bar. The rule of thumb is that the price of used parts should be 50-60% of the new parts list price is reasonable. Sixty percent or less is much better than 100% any day. I find that when I am working on a project, the level of satisfaction is greatly increased when perfectly good used parts can be utilized at a fraction of the price of the new ones. Plus, this saves you valuable money that can be spent on your next upgrade.
For comparison a new rear sway bar kit runs about $600 like this kit from Tarett Engineering.
But, this kit is about 3 times the cost of the used parts list you would need and does not look like the stock “Stealth” units.
The Tarett unit is also a race unit with mono ball links and will make noise eventually.
But if you want the pretty red race setup; Tarett is the way to go and is a direct bolt on system.