911 front suspension
From The Porsche 914 Wiki
Contents |
Introduction
The front suspension for the 1965-89 911 used a strut type design with a lower A-arm with an integral torsion bar. This article focus on this design vs. the later double wishbone design as the strut design was also the basis for the 914 front suspension.
History
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Components
Struts
The main properties that differentiate one strut from another are ...
- The damping mechanism type and OEM insert type
- The caliper mounting distance
- Spindle size and location
- The balljoint mounting style.
In addition to the different inserts that were used, different calipers were used for different models. These can be broadly broken up into those that use a 3” caliper mounting spacing and those that use a 3 ½” calipers mounting spacing.
Shock/Damper
Over the years, the 911 struts used Boge, Bilstien and Koni inserts. Each strut should be stamped with an identifying mark above or near the spindle. Additionally they typically were a unique color.
Type Color Stamping Boge Black or Gray ? Bilstein Green or yellow ? Koni Red or Orange ? Hydropneumatic
Boge
Struts that used the Boge insert were standard equipment on most 911s over the years. Because most 911s were provided with Boge struts, other strut manufactures created inserts that work with the Boge strut. So you can use Boge, Koni, Bilstein and maybe other inserts in the Boge strut.
Bilstein
Bilstein struts only accept Bilstein inserts
Koni
Koni struts only accept Koni inserts. It should be noted that a Koni insert that is designed to be used in a Koni strut is different from the Koni insert that is designed to be used in a Boge strut. Additionally Koni has different struts for different models and model year cars (as well as for the 914 and 914/6).
Boge
Hydropneumatic
The Hydropnuematic system are unique struts and A-arms that were a main feature of the 911E model. Created by Boge, these combined the functions of springs, shock absorbers, antiroll bars as well as the ability to automatically adjust the height of the front of the car to compensate for a change in ride height in the rear (usually due to extra weight in the car). Ultimatly it was not well received by 911E owners and many eventually converted to the traditional strut and torsion bar setup. When converting, you must swap both the strut and the A-arms as the special Hydropneumatic A-arms do not include the hardware to attach torsion bars.
Caliper mounting
Near the spindle is an ear on the strut that the caliper will bolt to. This ear has two holes and the distance between these is either 3” or 3 ½” center to center.
Spindle size and location
911 hubs will not fit onto the 914 spindles as the 914 spindle uses a smaller bearing. 911 RSR models used a strut with a spindle that was raised up higher on the strut. This effectively helped lower the car. Spindles can be removed from a stock strut and welded in a higher place as a way to replicate the RSR style strut. The spindle on earlier struts uses a smaller and differently threaded locking nut. Early hubs will fit onto a later strut, but the later locking nut that matches with the strut has a diamter that it too larger to fit into the opening of the hub. To use an earlier hub on a later strut, you must machine the hub to enlarge the opening to allow the later style nut to fit.
Ball joint mounting
A ball joint is used to mount the strut to the A-arm. There are three methods for mounting the ball joint to the bottom of the strut. The first method uses three bolts, the second uses a single through bolt and nut that clamps the ball join into place, and the third uses a specially shaped "wedge" bolt and nut that at first glance looks much like the single clam bolt.
The three bolt style was used on very early 911s. The switch from the clamp bolt to the wedge bolt happend in
Caliper
Front calipers generally are sourced from one of three braking systems. The “M”, “S” or “A” systems.
“M” front calipers use the 3” mounting spacing and are made from steel. These are generally from 911s up to 1973.
“S” front calipers are named as they were first used on the 911S models. These use the 3 ½” mounting spacing and are made from aluminum. Due to the smaller production numbers and demand due to their relative rarity, used or NOS examples of these are more expensive than the other two types.
“A” front calipers use the 3 ½” mounting spacing and are made from steel. A Carrera version of these were used on the 911 Carrera and included a brake pad wear sensor. Carrera calipers are also wider than earlier “A” calipers.
Rotor
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Hub
All 911 hubs are designed to utilized a 5 x 130mm mount. It should be noted that 914/4 models used a four lug mount. The 914/6 (and variations) also use a five lug mount like the 911.
Ball joint
A-arm
On one end the a-arm mounts to the car as well as houses the torsion bar. On the other end, the strut mounts to the a-arm via the ball joint. The a-arm is constructed of steel. For models that used the through body style sway bar, a single “U” tab is mounted on the top of each a-arms.
Torsion bar
Instead of using a coil spring, Porsche frequently used a torsion bar to suspend it’s cars. All 911s through 1980 used the same size front torsion bar of 19mm. Torsion bars are mounted to via splines at each end. All 911 torsion bars have the same spline count. But it should be noted that the 914 torsion bar uses a different spline count. This means that 911 and 914 torsion bars are not interchangeable.
Cross member
Between each a-arm there is a cross member in which the steering rack is mounted to. In addition to providing a location for the steering rack, this also helps tie the left and right a-arms together. Earlier models used an all steel cross member. Later models used an aluminum cross member.
Model Year Differences
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914 Relevance
There is nothing inherently wrong with the 914 front suspension. Its entire design is based upon the 911s design. Due to this fact, it does allow for nearly bolt in place swaps between the 911 and 914. Using the 911 components are done for a variety of reasons.
- Ease of conversion to 911 style five lug wheels
- Desire to use 911 components for performance reasons or general “looks”.
Using 911 suspension components on a 914
When you swap in 911 front suspension components into a 914, you can generally use a complete suspension up to a 1989 911. Or you can just do the struts, hubs and calipers. However, you can’t mix and match parts such as the torsion bars and a-arms. This is due to the previously mentioned difference in spline count on the torsion bars.
Misc
The following information may need to be verified and/or integrated into the appropriate area above.
- There are other ways to doing a five lug conversion. For example you can use existing 914/4 hubs and have them modified to accept five lug components.
- Using a complete 911 suspension (including shock inserts that have been optimized (valving) for the 911) may result in handling that is not on par with a well setup stock 914 suspension. The solution is to use a shock insert that matches the dynamics of the car.
- Stock 914 suspension and brakes are more than adequate for the 914. A common misconception is that a 911 suspension (including larger brake calipers) will increase braking capabilities. Generally this is not true. However, if you are using a higher horsepower car (such as for track purposes) then there can be benefits to using the larger brakes from the 911.
- 930 front hubs are 2" wider than normal 911 hubs. For widebody 914s, this means that you can use a larger wheel without resorting to spacers.
- Early hubs used solid rotors. Later hubs used vented rotors and are about 15mm wider.
