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HomeTech Articles > Installing and Adjusting 914 Brake Pads

Pelican Technical Article:

Installing and Adjusting
New 914 Brake Pads

Difficulty Level 3

Difficulty scale:
Adding air to your tires is level one
Rebuilding a 911 Motor is level ten

[Click on Photo]      Changing brake pads is a very routine procedure for many car owners.  Unfortunately, on the 914 there are several interesting steps and specific problems that may leave you scratching your head, wondering "why did they design the car this way?"  Actually, as we all know, that statement can be applied to many things on the 914.  In this case, the brakes, and specifically the rear calipers, are no different.
Figure 1
Figure 1:
Worn Out Brake Pads (Rear)
     The first step in pad replacement is to determine whether or not your pads are worn enough to warrant replacing.   I recommend jacking up the entire car onto four jack stands so that all the wheels can be removed, and the calipers examined.  Start with checking the remaining amount of lining on left on the brake pads.  You should be able to visually see how much is left by looking down from the top of the caliper.  The factory says to change the pads if they are worn down to 2 mm (~.08 in).  If they are close, then they should be replaced.  Figure 1 shows a set of extremely worn pads.  In this case, the pads got so worn that the edges broke off from contact with the brake rotor.  You should always replace pads in axle sets as well, in order to achieve even wear on the pads.  You can change just the front or just the rear, but don't ever change specific pads within an axle without changing them all for that axle.
Figure 1
Figure 2:
New Front Brake Pads

Figure 1
Figure 3:
New Rear Brake Pads

     If any of the pads look pretty close to being about 2 mm, then you should probably go and purchase a set of brake pads for that axle.  Front and rear are not interchangeable.  Pelican Parts has all the brake pads that you need at competitive prices.  Plus, continued support of Pelican insures that technical articles like this one will survive into the future.   You can pull the pads out, check them, and then replace them, but often there might be problems that render your car undriveable.  It is wise to have a spare set of pads on hand (you will require them eventually) just in case you need them.  Figure 2 shows what a set of brand new front pads should look like, and Figure 3 shows a set of rear brake pads.

Replacing Front Pads

     Start with the front brakes.  For the front brakes, we will refer to the parts diagram located in the 914 Parts Diagrams Section.  Specifically, refer to the exploded view of the front caliper in our parts diagrams section. 

     Now, drive out the retaining pins with a small screw driver or a transfer punch.  Make sure that you place these in a safe place along with the spreader spring which keeps the pads spaced apart.  With the retaining pins removed, you can then pull out the pads.  Depending upon their wear, you may need to wiggle them back and forth, or use a screwdriver placed in one of the holes cast into the pad base to pry them out.  Once removed, you should be able to measure the pad's remaining lining with a dial caliper.  Scrap them if the wear looks uneven, or if there is less than 2 mm left on the pad (.08").  If you are going to use the pads again, make sure that you mark them to make sure that you put them back in the same exact configuration as you had removed them.

     Now, using a plastic handle, or a piece of wood, push both the front pistons back into their housings.  Note:  When pushing on the pistons, the fluid level in the brake fluid reservoir may rise and overflow.   Guard against this by siphoning out some fluid (use an old turkey baster) before you push back the pistons.

Figure
Figure 4:
Front Caliper Piston Retaining Clip
     Pry out the piston anti-rotation lock or piston retaining plate.  Clean the inside of the caliper with some compressed air and isopropyl alcohol.  Don't use anything else, as it may damage the rubber seals that are used in the caliper.  Now, replace the piston retaining plate.  The ring section of the plate should be pushed way down firmly onto the head of the piston.  If the retaining clip is rusted or corroded, it should be replaced.   Figure 4 shows a brand new retaining clip.

     At this point, you should measure the rotor to make sure that is is not too worn.  Use a micrometer to measure the thickness of the shiny metal section.  If you use a dial caliper from the outside edge, you will probably get a false reading, as the disk is thicker on the edges because it doesn't get worn by the pads there.  The specs on rotor wear are as follows:

914-4 Front Brake Discs
Brake disc thickness 11.0 mm +0.05  -0.15 .433 in + .002 -.005
Min thickness of disc after turning 10 mm .395 in
Wear limit of brake disc (symmetrical wear) 9.5 mm .375 in
Thickness tolerance of brake disc 0.02 mm max .0008 in
Later wobble (deflection) of brake disc installed 0.2 mm max .008 in
914-6 Front Brake Discs
Brake disc thickness 20 -0.2 mm .787 - .008 in
Min thickness of disc after turning 18.6 mm .732 in
Wear limit of brake disc (symmetrical wear) 18.0 mm .709 in
Thickness tolerance of brake disc 0.02 mm max .0008 in
Later wobble (deflection) of brake disc installed 0.2 mm max .008 in

     Therefore, you should check to make sure that your rotor is at least .395" before you reinstall your pads.  If it is less than this, then you need a new rotor.  (see upcoming tech article)

     Now, insert the new pads into the caliper.  Reinstall the retaining pins with the spreading spring separating the pads.  Make sure that you use a hammer to tap in the retaining pins.   Using another tool (like a punch) may damage the front collar on the pins.   Now reinstall the small pin retaining clips.  Stomp on the brake pedal a few times to make sure that the pads seat themselves properly.

     Now, check the front venting clearances.  The venting clearance should be about 0.05-0.20 mm (.002-.008") when operating normally.   Venting clearances larger than 0.20 mm are often caused by the caliper binding up to the rubber o-ring inside.  This can happen especially if the car has been sitting for quite some time.  The remedy for this is to remove the brake pad from one side, and replace it with a piece of wood at least .2" thick.  Then stomp on the pedal several times to (hopefully) free up the piston.  Push the piston back into it's home position and reinstall the pads.  If the caliper doesn't respond to this, and the venting clearance is still too great, then you need to remove and rebuild the caliper. (future technical article)

     You should also make sure that the hydraulic braking system is well bled before determining that you have a problem with either your front or rear brakes.  Details on bleeding the 914 system can be found in the Pelican Technical Article, 914 Brake Bleeding.

Replacing Rear Pads

     The front pad replacement is easy compared to the rears.   The addition of the parking brakes seems like an afterthought with the design of the 914 calipers.  Because of the parking brake and it's action on the rear pad, you need to manually set the clearances of both sides of the 914 rear pads.   Unfortunately, the mechanism for doing this was not very well designed, and in addition, the brake parts often rust out and strip on these older cars.

Figure 1
Figure 5:
914 Rear Caliper

Figure 1
Figure 6:
Close-Up of Caliper and Brake Pads

Figure 1
Figure 7:
914 Rear Caliper

Figure 1
Figure 8:
914 Rear Brake Caliper Piston

Figure 1
Figure 9:
Rear Caliper Inside Piston

     The 914 rear caliper is shown in Figure 5.  Start by checking the wear on the rear pads.  In general, the rear pads will wear less than the front.   Additionally, the inside pad may wear a bit more depending upon if you have the habit of driving with the parking brake on.  Figure 6 shows the side view of the caliper and pads.  Begin by removing the two small retaining clips indicated by the two arrows.  Then, using a small screwdriver or center punch, tap out the two retaining pins that hold the pads and the spreader spring.   At this point, you should be able to pull out the pads by wiggling them, or by prying them out with a screwdriver placed inside on of the holes on the pads.  Figure 7 shows a rear caliper (off the car) with the brake pad retaining pins removed.  Once the pads are removed, you should be able to see inside and clean the pistons with alcohol and compressed air.  Figure 8 and Figure 9 show each side of the rear caliper.

     With the pads removed from the caliper, you should check the disc to make sure that it is still safely usable.  Using a micrometer, measure the thickness of the disc and compare it to the following table:

914-4 Rear Brake Discs
Brake disc thickness 9.5 -.02mm 374 -.008 in
Min thickness of disc after turning 8.9 mm .351 in
Wear limit of brake disc (symmetrical wear) 8.5 mm .335 in
Thickness tolerance of brake disc 0.02 mm .0008
Later wobble (deflection) of brake disc installed 0.2 mm .008
914-6 Rear Brake Discs
Brake disc thickness 10.5-0.2 mm .413 -.088 in
Min thickness of disc after turning 9.5 mm .374 in
Wear limit of brake disc (symmetrical wear) 9.0 mm .354 in
Thickness tolerance of brake disc .02 mm .0008
Later wobble (deflection) of brake disc installed 0.2 mm .008 in
 

Figure 1
Figure 10:
Cover for Outer Adjusting Screw

Figure 1
Figure 11:
Cover for Outer Adjusting Screw

Figure 1
Figure 12:
Loosening Retaining Screw on Outer Adjuster

Figure 1
Figure 13:
Adjusting Outer Pad Clearance

Figure 1
Figure 14:
Rear Adjustment Screw Cover

Figure 1
Figure 15:
Replacement Inner Covers

Figure 1
Figure 16:
Removing Rear Cover Of Inner Adjusting Screw

Figure 1
Figure 17:
Close-Up of Rear Cover

Figure 1
Figure 18:
Measuring Outer Rear Brake Pad Clearance

     If your brake disc is not in spec, then you need to install a new one (future tech article).  Assuming that your discs are fine, you now need to install the new pads in to the rear calipers.  First, you need to move the pistons back to their 'home' position inside the cylinders.  To do this you need to manually crank back the starting position of the calipers.  Start with the outer piston.  Remove the small black plastic cover shown in Figure 10 and Figure 11.  This cover is not screwed on.   It is simply pressed into the hole.  Simply place a wrench on its end and twist it off.  Dave Darling has noted that some caps in rebuild kits do in fact have threads on them.  After the cap is removed, then loosen up the retaining nut using a 13mm wrench, as shown in Figure 12.  Then, using a 4 mm hex key, turn the adjusting screw clockwise while pushing on the piston with a dull hammer or like object.  Although counter intuitive, this should make the piston return into the housing.  Make sure that you turn it clockwise.  This is shown in Figure 13.   Again, there might be some overflow in the brake fluid reservoir, so be sure to siphon some off with and old turkey baster (don't reuse the baster again in November, even if you forgot to replace it in the kitchen and all the stores are out of them).

     Now you need to do the same for the rear piston.  Note: there is a small cover on the rear of the caliper that is very easily stripped.   To gain access to the adjusting screw, you need to remove this small cover.  Figure 14 shows the cover on a caliper that has been removed from the car.  Figure 15 shows steel replacement covers (the original ones are soft aluminum) that we highly recommend putting on your car.  The small cover needs to be removed using a 4mm hex key with a long extension to reach through the access hole in the trailing arm, as shown in Figure 16.  I often wonder who thought of this design.  The factory manual states that the shock absorber must be removed in order to do this.  Be very careful in removing the cover, as it will very often strip out.  Make sure that you look in-between the caliper and the trailing arm to make sure that you even have the cover on the rear (Figure 17).  There should also be a copper washer/gasket in-between the cover and the caliper.  Remove the cover by turning counter-clockwise.  Make sure that you don't accidentally turn clockwise as you will probably strip the cover.

     If the cover strips, then you need to remove the caliper off of the trailing arm.  The good news is that you don't need to disconnect the brake lines.  Simply remove the two bolts that hold the rear caliper onto the trailing arm (see Tech Article about replacing rear caliper), and the clip that holds the connection point between the rubber brake lines and the steel brake lines.  You then should have enough room to take the caliper and get a set of needle-nose vise-grips on the stripped cap.

     After you get the cap off, use the 4mm hex key to turn the adjusting screw counter clockwise while pressing on the piston.  The piston should move back into it's housing.  Now, you can insert the pads into the caliper.   Make sure that the large holes in the pads line up with the larger pin.  It may take a bit of tapping with a small rubber hammer to get the pads in.  Replace the retaining pins without the separating spring in-between.

     Now adjust the venting clearance for the rear pads.   If you don't do this, you will have extremely spongy brakes.  Using a feeler gauge placed in-between the rotor and the pad, tighten the adjusting screws until the clearance is 0.2mm (.008") on both sides.  This is shown in Figure 18.   For the outer pad, turn the adjusting screw counter clockwise to tighten.  For the inner screw, turn it clockwise to tighten.

     At this time, if you are planning to rebleed your brake system, then you should do it and then readjust the rear caliper venting clearance again.   For more info on bleeding 914 brake systems, please see our Pelican Technical Article, Bleeding 914 Brakes.   After the brakes are bled, then check the adjustment and readjust if necessary.

     After all the adjustments are made, remove the retaining pins and replace the separating spring.  Replace the retaining pins, and secure them with the small clips.  Be sure to tighten down the nut on the outer adjustment screw.   Reattach the two covers over the inner and outer adjustment screws.

     Well, that about sums it up.  It's not a real easy job because the calipers are often very old and don't work very well.  It can also be frustrating when plenty of things strip on you.  If you liked this article, and would like to see more of them, then please continue to support Pelican Parts with your business.  You'll find that we have very competitive prices with personal service that can't be beat!  If you have any comments or questions, then please feel free to send us some email.  Thank you for your support.

Comments and Suggestions:
Christo Comments: The Haynes manual must be wrong. It says to turn both sides counter clockwise when pushing the pistons back.
August 12, 2016
  Followup from the Pelican Staff: On what vehicle? - Nick at Pelican Parts  
TJ Comments: Okay, this article helped me out. A lot. Thanks for sharing, appreciate it!
June 25, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Dug Comments: Do you sell th steel replacement inner screw covers? Part # please.
August 11, 2015
  Followup from the Pelican Staff: I am sure we can get them.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Jack B. Comments: Very helpful article, and I would say this is not the hardest job but it is finicky and a little time-consuming, compared to some other cars.

Question: are the inner piston adjusting screw covers fig. 15 available?

Thanks!
February 16, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
babs Comments: Can you use rear calipers from a 1975 914 on a 1976 914?
September 20, 2014
  Followup from the Pelican Staff: If the part numbers are the same. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
PorscheMel Comments: Thanks a bunch ! Would like to see an exploded view photo of the rear caliper as you did with the front so one could tell if there is damage to the adjusting venting gears to the pistons. Thanks again !
March 30, 2013
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Dave Comments: I have a 1975 Porsche 914 when I push down the brake peddle it will not return I have to pull the peddle back with my foot. How can I solve this problem?
September 7, 2012
  Followup from the Pelican Staff: This could be a faulty master cylinder. The master cylinder is likely compressing past the point of return and the helper spring cannot bring it back. - Nick at Pelican Parts  
milo Comments: thank you this article was very helpfull.
September 5, 2012
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Bob L. Comments: It may not need any adjusting or attention but I'm curious about the mass of washers, clips and doodads inside the brake pistons. I assume its has to do with the automatic adjustment of the brakes as the pads wear. I would just like to know how it all works.
Anyone...
September 4, 2011
  Followup from the Pelican Staff: I think you are referring to the parking brake parts in rear brake calipers. These do not require service, usually when the parking brake parts fail the caliper is replaced. - Nick at Pelican Parts  
Keith Comments: Nice Article. I'm having trouble with the parking Brake? I did the adjusting but can't get the parking brake to bind up? The cables & levers are are moving but not to stopping disc from turning by hand? Any suggestions? Thanks.
July 1, 2011
  Followup from the Pelican Staff: Could be the pill is misinstalled? Did you pull the parking brake components apart? Check the assembly order, if correct, you will have to replace the caliper. - Nick at Pelican Parts  
Boer16 Comments: Your article is very, very useful. I just changed the rear brake pads and the rotors, both wheels of course. When inserting the inside pad and doing the venting clearance for the passanger side, the adjusting screw started leaking fluid. when I was done and I tite everything back, it stop leaking. My question is: Is this normal or is there something wrong that I have to take care of?
May 28, 2011
  Followup from the Pelican Staff: I have seen these leak before and I prefer to replace the caliper at this point. With that said, there is an O-ring inside, if you can get the part and tear the caliper down to rebuild it.- Nick at Pelican Parts  
MCAR Comments: Great article! couldnt have done it without pelican!
February 28, 2011
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
porsche913b_sp Comments: Can you elaborate "while turning the adjustment screw, where/how do I push the piston with a dull hammer ?

Thank you
February 21, 2011
  Followup from the Pelican Staff: When you turn the screw, you can use the back end of a wooden hammer handle to push the piston back into place. - Wayne at Pelican Parts  
leashypoo Comments: wow a bit harder than it looks for a first timer. hey let me ask you, the covers over the inner adjustment screws pain in the butthow important are they? like if i forgot to replace one...is that bad? any way i could not have done it without you all thanks.
March 28, 2010
  Followup from the Pelican Staff: I would get a replacement cover as soon as possible. Don't leave any parts, no matter how superficial they seem off your vehicle. - Nick at Pelican Parts  
svsv Comments: lots of to the point info thanx
October 4, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Charlie Comments: Great write up. Very useful. Thanks.
September 8, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Skip Comments: Very helpful, I appreciate it!!
July 7, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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