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911 Suspension Spotting Guide
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Pelican Technical Article:

911 Suspension Spotting Guide

Thomas C. Gould, III


1 hour1 hr





Applicable Models:

Porsche 911 (1965-89)
Porsche 912 (1965-69)
Porsche 930 Turbo (1976-89)

Performance Gain:

Knowing what suspension you have will enable you to improve upon it through customization and installing the best components

Complementary Modification:

Replace your front and rear shocks
Identifying 911 front brakes and strut assemblies:

Front Struts:

   Boge strut housings were standard equipment, and are the most common found on the 911. They are black (sometimes gray) in color, and used a standard hydraulic shock insert. The advantage of a Boge strut is that you can replace the shock insert with either Boge, Koni, Bilstein, KYB, or your favorite brand shock insert.

   Koni strut housings were optional equipment on 911s through 77, and are identified by their red/orange color. Most Koni shock inserts were originally hydraulic, capable of being adjusted firmer or softer by removing the shock and manually adjusting the setting. Newer Koni replacement inserts are gas shocks with adjustment made by turning a knob at the top of the shock (taking only a few seconds to change the firmness).

   Koni struts can only use a Koni shock insert.

   Bilstein strut assemblies were optional equipment on the 911, and standard equipment on the 911 Turbo. They are identified by their green (sometimes yellow) color. Bilstein struts can only use Bilstein shock inserts.

Front Brakes:

   M calipers.Stock, steel calipers for 911's through 75. Caliper mounting bolt spacing on strut is about 3 inches.  Figure 1 and Figure 2 show 'M' calipers installed on a car.

   S calipers.Aluminum, larger calipers used on 911S and 'S' option cars through 77. Mounting bolt spacing on strut is about 3.5 inches. Cannot be put on 'M' caliper front end. Can be used on A caliper front end.

   A calipers.Stock, steel calipers used on 75-83 911. Mounting bolt spacing on strut is about 3.5 inches (same as 'S' caliper).   Carrera calipers were used on 911's from 84-89, and accomodate a brake pad wear sensor.  Figure 3, Figure 4, and Figure 5 show 'A' calipers from a 911SC front suspension.

   All 911s through 89 used the same size front torsion bar (19mm). Note: The 914 torsion bar and the 911 torsion bars are not interchangeable, as the number of splines on the bar are different.

911 Rear Shocks and brakes:

     Can usually be identified by color, although the brand is usually stamped on the lower section of the shock.

     Black or gray: Boge

     Green or yellow: Bilstein

     Red/orange: Koni

     White: KYB

  Rear calipers were the same for 911's from 69-83 ('M' type)

  Rear calipers on 911's 84-89 were Carrera type

914-6 Front Suspension with 'A' Calipers
Figure 1

914-6 Front Suspension with 'A' Calipers

914-6 Front Suspension with 'A' Calipers
Figure 2

914-6 Front Suspension with 'A' Calipers

911SC Front Strut
Figure 3

911SC Front Strut

911SC 'A' Caliper
Figure 4

911SC 'A' Caliper

911SC 'A' Caliper
Figure 5

911SC 'A' Caliper

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Comments and Suggestions:
NJPorscheGuy Comments: If I have a 69' 912 with boge struts from the factory that have stupidly been cut to remove a very rusty ball joint bold. That in mind, I need a new driver's side strut assembly. If I replace the strut assembly and inserts... could I put Koni's on? Also, would I need to change brake calipers as well? Thanks.
October 13, 2016
  Followup from the Pelican Staff: I am not sure if there is a Koni housing available. There are many options for the inserts. You may have buy a housing, then inserts.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
kaphengst Comments: I'm wondering if rear calipers from a '89 C4 will fit on my '73 911T.
August 20, 2016
  Followup from the Pelican Staff: I'm not 100% sure.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
BrakeGeek Comments: Figure 1 and Figure 2 above are stock M-Calipers
May 9, 2015
  Followup from the Pelican Staff: Thanks Eric! Do we need to change something? Or are you clarifying for us? I know, you know your calipers well! - Casey at Pelican Parts  
joshkobrin Comments: Pretty sure I've got Koni shocks but I'm not sure if they're Boge strut housings. Can you help identify?
March 5, 2014
  Followup from the Pelican Staff: hard to say from the photo. Give our parts specialists a call at 1-888-280-7799. They can help you figure it out. - Nick at Pelican Parts  
makalapa61 Comments: THANKS to the Pelican Forum - Pipe wrench solution - GOTER DONE.
Project = shock insert replacement, all going well with new BYB inserts on hand until I came to the Gland nut, channel locks didn't cut it and an internet search for locally available Honolulu shock wrenches made it clear this project was not going to get done any time soon. Since time budgeted for Super Bowl XLVIII wasn't time well spent, I reattached the front end of my 912. A quick internet search took me to Pelican forum and the pipe wrench solution. WIth Pipe Wrench in hand, my frown quickly disappeared, between commercials. Thanks for your forum, it is an outstanding service.

1969 Targa, 125000 miles, driven approx 1200 mi/year. Project has included replacement of Michelin's MFR date 207. Shocks/inserts/rebuilt calipers.
February 3, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
GaryH Comments: When installing new inserts in the Boge front strut housings on a 1973 Porsche 911T, I have read that you need to put oil back in the space between the new insert and the old strut housing. I assume this is for heat transfer. Is this needed and if so, what kind of oil and how much?
November 21, 2012
  Followup from the Pelican Staff: A couple of table spoons of engine oil (any type) works fine. If you overfill it will simply ooze out past the new cartridge when you insert that. - Nick at Pelican Parts  
Gary Comments: What does 220/100 valving on the Bilstein RSR struts mean?
November 15, 2011
  Followup from the Pelican Staff: Here is some info on Bilstein valving.

Understanding Bilstein Valve Ratings
Damping forces of Bilstein valvings for Off-Road are measured in Newtons at a velocity of 0.52 meters/seconds (approximately 20 inches/second). The ratings shown correspond to those measurements; rebound force is the first number, followed by compression force (rebound / compression). Conventionally, the ratings are written as one tenth the damping force in Newtons.
EXAMPLE: Valve rating: 275 / 78
Rebound force is 2750 Newtons at 0.52 m/s
Compression force is 780 Newtons at 0.52 m/s
Higher numbers mean higher (firmer) damping forces. For example, 360/80 has more control (is firmer) that 275/78, while 170/60 has less control (is softer) than 275/78.
For valving recommendations please refer to the Valving Guide.
Determining how many shocks to put on a vehicle.
A shock absorber transforms mechanical energy (suspension movement) into kinetic energy (heat). If a shock absorber builds up too much heat, it will not function properly. Shock absorbers exposed to excessive heat will fade (soften) or fail.
If you are experiencing excessive shock failure or fading, it may be time to add another shock.
By adding another shock, you are spreading the work load from one shock to multiple shocks. Increased cooling capability will be achieved from the following factors:
Decreased Friction
Dampening causes friction. When you use a multiple shock set up, lighter valved shocks can be used which will decrease friction.
Increased Oil Capacity
The more oil, the better. Higher oil volumes take longer to heat.
Other methods to consider which will increase oil capacity are to utilize a remote reservoir or to use a larger diameter shock. - Nick at Pelican Parts
bkcarrera Comments: I am replacing front inserts koni on my '86 Carrera - Boge original.
I thought the shaft the top nut goes on would be held with an allen wrench - it appears to be round - how do I loosen the nut????
August 18, 2011
  Followup from the Pelican Staff: You'll want to use a pipe wrench or large channel lock pliers. This is what I do. Just be careful not to damage anything. - Nick at Pelican Parts  
TonyK Comments: My 1975 911 is riding very rough. Seems like the whole car is banging on moderately bumpy roads and I don't recall this behavior from the car years ago. The shocks seem very stiff; maybe too stiff. Do shocks 'lock up'? I've seen other cars bouncing up and down when their shocks fail, but I'm having the opposite problem. Do springs stiffen up this badly? I want my car to ride the way it should. I used to have low profile tires, but the ride was really rough, so now I have the stock tire profile.
June 1, 2011
  Followup from the Pelican Staff: Shock absorbers do lock up: They seize from age and rust. - Nick at Pelican Parts  
John Comments: Thanks again Wayne for the quick advice.
December 14, 2010
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
John Comments: Wayne,
Thanks for the quick over night response to my question regarding 1991 Turbo 911 965.
Alignment is fine, no unusual tire wear or issues. The front suspension does not always REBOUND, on the left side only. This is not a constant problem but an intermittent one. After driving that involves hard, right hand turns and bumps the suspension will return to normal. When the left suspension is loaded up, clearance at the front air dam is only 1.5" and when it Rebounds it is 4" in the normal state. Set up is the original, stock Boge coil over system and the spring appears normal not broken or unseated and the shock is not leaking and offers normal resistance when pushed down.
December 13, 2010
  Followup from the Pelican Staff: Hmm, in that case, I would probably change the springs and the shocks on both sides of the car. I would suspect that maybe the left hand side spring is getting weak and perhaps worn out. - Wayne at Pelican Parts  
John Comments: 1991 Porsche 911 Turbo, 3.3L. 96K miles. Shocks are not leaking and feel firm. Something on drivers side, front suspension is loading up and does not allow L-F wheel to resume normal position. This corrects itself after driving on rough surface. Is this an A-arm issue?
December 12, 2010
  Followup from the Pelican Staff: I typically like to try to solve problems like these with the cheapest solutions first. In this case, I would recommend having the alignment checked, and also take a close look at the tires and/or the tire wear for some unusual patterns. - Wayne at Pelican Parts  
TheGug Comments: Is there any way at all to install KYBs when Konis were ther original equip. ? The price point for the KYBs is much friendlier than the Konis.
July 10, 2010
  Followup from the Pelican Staff: Sure, yes, the KYB shocks are pretty good, cheap alternatives to the OEM units. They probably won't last as long though. - Wayne at Pelican Parts  

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