retracting piston for brake pad replacement | FerrariChat

retracting piston for brake pad replacement

Discussion in 'Technical Q&A' started by rickjaffe, Jul 19, 2005.

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  1. rickjaffe

    rickjaffe Formula Junior

    Mar 6, 2005
    363
    houston
    Full Name:
    richard jaffe
    #1 rickjaffe, Jul 19, 2005
    Last edited by a moderator: Sep 7, 2017
    I could use some quick help on how to retract the pistons for replacing the rear pads on a 308 gt4. I changed the front w/o problem. the write ups say the pistons have to be retracted. but they don't show what to do.

    carl's tips implies that there is a separate screw or pin which retracts the pistons ("the procedure is identical for the rear except you must first retract the pistons with the 6mm allen key."
    brother garvin's write up on this site talks about a 13 mm nut on one side and a 4 mm hex on the other.
    the service manual is worthless on this point, other than saying that they have to be retracted.

    I don't see any thing like that on my car:
    what I've got are 4 pins, the first one is just above the bleed screw/valve the second is just under it and the other two are on the bottom. (see below); these pins are loosened by an 11 mm wrench and a 4mm hex. I've tried to loosen those 4 pins and the piston doesn't retract. tried to move it with a screwdriver and no go.

    1. am I looking at the right thing? if so what's the secret?

    if not, where is the piston retraction screw?
    thanks
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  2. nizam

    nizam Formula 3
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    Jul 9, 2004
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    Ni Zam
    #2 nizam, Jul 19, 2005
    Last edited by a moderator: Sep 7, 2017
    RickJaffe -

    Don't undo those four pins!! Those hold your caliper together!

    The way to retract the pads is to put a box-end wrench on the hex locknut in the picture below (looks like a 17mm to me), and then put an allen key in the threaded "stud" (looks like a 6mm from here). While holding the allen key stationary, break the locknut free. If this hasn't been done in awhile, spray on some WD40 and try it again. If you can't get enough leverage on the allen key with just your hands, hold the allen key with a vice grip. It will break loose.

    Once the locknut has been loosened, rotating the threaded "stud" will either retract or extend the piston. My guess is you will have to rotate it clockwise to retract it. From the looks of it, you may have a different mechanism on the inboard side of the brake caliper to retract the other piston (where that cable is connected to the lever/arm attached to the caliper).
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  3. spang308

    spang308 Formula Junior

    Jul 17, 2004
    893
    York, PA
    The pic above shows the correct way to adjust the outboard piston. It's a 13 mm nut by the way. Loosen that and turn the allen screw to retract.

    On the inboard side, there is a small metal cap directly opposed to the one in the pic. It is hard to see from the outside of the car and harder to get off. Use an allen wrench to loosen the cap and there is a gear inside with an allen head. Once the cap is off, turn the gear to retract the piston.

    If you can't get the inner cap off, you may have to remove the caliper and knock it off by tapping counter clockwise with a chisel and hammer. Been there, done that as I'm sure others have. You may get lucky and get the inner cap off with an allen wrench. Try spraying penetrating oil on it and letting it sit. Also, take a pick or something similar and dig any and all crud out of the allen head on the cap. Once clean, try tapping the allen socket or wrench into the cap to make sure it is seated well.

    Good luck,
    John
     
  4. rickjaffe

    rickjaffe Formula Junior

    Mar 6, 2005
    363
    houston
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    richard jaffe
    thanks, going to tighten the calliper screws back and will proceed with your instructions.

    looks like it takes a 4mm allen wrench and 13mm box wrench.
     
  5. nizam

    nizam Formula 3
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    Ni Zam
    John - thanks for correcting me.

    Good luck RickJaffe. Tell us how it goes.
     
  6. rickjaffe

    rickjaffe Formula Junior

    Mar 6, 2005
    363
    houston
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    richard jaffe
    I'm working in the inner one first, since if I can't get that one, I'm not going to foll with the outer which looks straightforward. that inner one is tough; can't seem to get enough leverage on the allen wrench. looks like the inside might have been stripped as well.

    just so I'm on the same page, what I have looks like a nut but without the squared edges with a 4mm hex hole. that's the cap. or maybe is it the actual gear which is adjusted. looks pretty similar to the out except for the lack of square sides.

    put some super duper penetrating oil on ; I'll try to pick out some of the grime. guess I'll let it sit overnight and try again tomorrow afternoon.
    much obliged.
     
  7. peajay

    peajay Formula Junior

    Apr 17, 2002
    454
    near Paris, France
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    Paul
    So far I have not had to work on the brakes on my 328, but on all other cars I have worked on you can simply push the caliper pistons back in. You need to do it slowly and be sure the resevoir does not overflow, but do Ferraris have something different that does not allow you to push them back ?
     
  8. spang308

    spang308 Formula Junior

    Jul 17, 2004
    893
    York, PA
    Yes. See above.

    John
     
  9. Mr Iceman

    Mr Iceman Karting

    Mar 3, 2004
    101
    Canterbury, England
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    Scott
    #9 Mr Iceman, Jul 20, 2005
    Last edited by a moderator: Sep 7, 2017
    Thats the Cap, its a sort of threaded button cap with a 4mm hex drive (that may well have been rounded off in the past) that protects the 4mm retacting mechanism, the mechanism itself is quite well recessed inside the caliper. I had all sorts of problems removing the cap from the inside of one of my calipers, in the end I had to take a sharp chisel and use a hammer and chisel to drive the cap in an aticlockwise direction to unscrew it. the biggest problem is getting at it with enough dexterity and purchase, I was tying with the car jacked up for over 4 hours before I gave in and reassembled the car and drove it 40 miles to my freindly garage, they put it on a lift, this allowed a much better angle and more force to be used , within 10 seconds the cap was off!!!!

    Once you have the cap off, the mechanism itself is just a splined shaft that is free to slide out, don't be alarmed if when you've finished retracting the pistons the splined shaft will probably come out attached to the end of the allen/hex key, just pop it back in the recess, the cap will hold it in there when you reassemble it back together! I put a little copper grease on the threads of the cap when I put it back on, hopefully this will help prevent too much trouble getting it off next time.

    As an aside the direction of movement to retract the pistons is not very logical and I think is different on the inside of the caliper compared to the outside. just use trial and error, but dont use to much force in the wrong direction, you dont want to strip the splines off of the retract shaft!

    I've included a picture that might help:



    best of luck
    Scotty
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  10. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    Paul (peajay) asked the correct question. Why not simply press the pistons back with a lever (large screwdriver or bar)? The hex screw that everyone is speaking of is to retract or advance the piston for purposes of adjusting the hand brake. There is a specificiation for the distance that the piston must advance when the hand brake is activated, and the hex screw on each side adjusts this. Be careful if you have changed this setting.

    If the pistons will not retract with simple pressure (using either the poor man's tool of a screwdriver or lever or with a tool designed for this purpose) then it may be time for a rebuild of the caliber. Rust or debris may be interfering with free movement of the piston in the bore.

    Jim S.
     
  11. Mr Iceman

    Mr Iceman Karting

    Mar 3, 2004
    101
    Canterbury, England
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    Scott
    I'm not sure why you can't do this on the rear calipers, its what you do with the fronts, but I for one wouldn't do it for risk of breaking something. When I had my problem getting the cap off and I rang my freindly garage for advice, they never suggested just retracting the pistons in a conventional way. I assume it may be possible, BUT you may risk damaging something inside the caliper.


    I've just remembersd this thread from the archives by Dom which certainly helped me: http://70.85.40.84/~ferrari/discus/messages/256120/265911.html

    Cheers
    Scotty
     
  12. tuttebenne

    tuttebenne F1 Rookie

    Mar 26, 2003
    3,189
    Bay Shore, NY
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    Andy
    the second most important aspect of this is to set the correct clearance between the pad and the piston. I think this is covered in the owner's manual.
     
  13. Verell

    Verell F1 Veteran
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    May 5, 2001
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    NO, you can't just push them back in, doing so will ruin a several parts. Because the rear caliper doubles as a parking brake, there's a rod threaded into the back of the piston that's mechanicly actuated by the park brake cable. As the brakes wear, the rod is screwed out of the piston.

    If you try to force the piston back in, you'll either strip the piston or rod's threads, bend the rod, or cock the piston & damage the caliper so it won't seal.

    Minor varients of system are pretty common, MAZDA used it on most of their cars including all the Rx7 models. Ford's Probe used it, Toyota uses it. The Dodge Stealth used it. These similar calipers, you have to fit a tool into indentations in the front of the piston & literally screw it back into the caliper. Then let the auto-adj mechanism actuated by the handbrake do the adjusting. Big problem with these calipers is that, because you can't retract the piston, you have to grind or otherwise remove a portion of the wear lip from the rotor's perimeter to get a caliper off.

    Big difference between the Ferrari rear caliper & the others is that the Ferrari caliper has the retraction/adjustment screw on the back of the caliper. IMHO, this is one that Ferrari got right.
     
  14. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    Verell - I have my calibers apart on the bench, and have rebuilt both front and rear. The hand brake mechanism will impede retraction of the piston, but only beyond the initial position. If the piston retracted enough to allow new pads in the past, then they should retract to the same position now. As I am looking at it, with the set screws snug, there is no "self-adjusting" nature to the adjustment screw. It appears that this must be set when rebuilding the caliber and then left alone. Wear on the pad is accomodated by the hydraulics as the piston moves out.

    I have taken the entire handbrake mechanism apart and cleaned all parts. The apparent confusion on which way to turn the hex allen screw comes from the fact that there is a "transfer" gear effect - what you turn does not turn the screw moving the piston...it turns a small gear which turns the screw. This reverses the clockwise / counterclockwise rotation.

    Before I took my calibers apart I gently spread the pistons without difficulty. They retracted to a position almost flush with the inner caliber face.

    Perhaps I am looking at this wrong. Verell has far more experience. Heed his advice.

    Jim S.
     
  15. Verell

    Verell F1 Veteran
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    May 5, 2001
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    jselvin,

    Haven't had to rebuild a 3x8 caliper, but was working from experience with changing 3x8 pads, the 3x8 FPC, other cars as I mentioned.

    On a a couple of 3x8s, including Steven's I definitely had to back off the adj screw a turn or so in order to remove the old pads, then had to back it a lot to install the new pads, & then finaly readjusted it to set pad clearance.

    I guess it's possible that the screw had been adjusted after the pads had worn down.

    Hmm, unless you know for sure that the adj hasn't been changed since new pads were installed, then it's still best to back it off rathar than risk damaging the mechanism.

    Ah, Yes, Had forgotten about the 'transfer' gear effect, but we did ecounter it, just thought the screw had a LH thread.
     
  16. bert308

    bert308 Formula 3
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    Nov 30, 2002
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    The handbrake only works on the inner piston. If the outer piston had no resistance (if it could be pushed back without to much force) applying the handbrake strong would result in bending the brake disc. Maybe not much, but if left like that for longer time I suppose a vibrating disc could develope.
    I had a brakedisc break (and when it broke it wouldn't brake :)) on my Alfasud because in a hurry for a track day I adjusted the pads wrong. The 'Sud has the same calipers as the 308, but on the front wheels gearbox mounted with front handbrake (it is a cursed car by mechanics, yes). The outer disc portion just snapped from the inner attachment ring and could spin freely, not very visible at first until a fellow Sud driver (10 years ago I wasn't the only one with an Alfasud) told me it was a common problem.
     
  17. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Never adjusted it personally, though the PO could very well have. So no idea either way :(

    FYI: KTR installed new rear pads and did a full readjust. Not a clue what that specifically entailed.
     
  18. wise3

    wise3 Formula Junior

    Oct 10, 2004
    370
    FL
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    Ward Orndoff
    I replaced about 15 sets of rear pads on my last 308 (lots of track time :) ) without any problems, although it did get to the point where I occasionally had to use a screwdriver as a chisel on the outer knurled edge of the inside cap. But some enterprising P**** 914 owner apparently got tired of it, or saw a market opportunity. There is now an inner cap with a standard hex head bolt type stand-up instead of the hole for the allen head wrench. I just ordered a pair from Automotion for $10.95 each, plus shipping. I'm 99% confident this is a common part. For those who want that last 1%, it will probably be a couple weeks before I get the parts and find time to put my new pads in my current car. (or has anyone else already checked this out?)
     
  19. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,150
    way north california
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    chris morse
    Yes, this is a good parking brake mechanism. Porsche used almost the same caliper on the 1970-1976 914 porsche, The (914-6) used exactly the same caliper. I have not been able, yet, to find a larger piston variant of this ATE, (Alfred Teves), caliper to go with the bigger varities of the 308 brake modifications.

    As others have pointed out, when dealing with cv joints or brakes or steering wheel allen bolts, use a new goood quality allen bolt, CLEAN out the inhex, so the allen wrench has a chance.

    hth,
    chris
     
  20. jon s

    jon s Formula Junior

    Mar 9, 2005
    509
    pocasset ma
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    jon shoukimas MD
    have done several calipers and the inner cap is always bunged - the small hex hole is striped and there are multiple chisel marks. i removed the last set with a chisel and cleaned them up as best as possible. afterwards i cut a slot across the cap with a fine hack saw blade. easy to remove now with an ordinary flat head screw driver blade. rebuilds from t rutlands come with old buged caps so you are on your own. the slot works - good luck. jon s.
    p.s.: worse hand brake mechanism i've ever seen-now i know why the history of disc brakes for all 4 wheels records the ate design as an absolute dead end. note all modern designs have small drums integral with disc for handbrake.
     
  21. rickjaffe

    rickjaffe Formula Junior

    Mar 6, 2005
    363
    houston
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    richard jaffe

    I thought it was just me. because I don't have a lift and am just using the ferrari jack to jack up the car, can't seem to get the right angle to do a chisel approach thing. looks like either the hack saw or the porsche part would solve the problem.
     
  22. Verell

    Verell F1 Veteran
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    May 5, 2001
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    Hmm,
    I think my adjuster caps are in mint condition. If so, then
    I'll make a mold & source them out of fibreglass reinforced polyurethane if there's some interest.
    Probably will be about $30 w/shipping.

    Sorry I can't make them cheaper.
     
  23. John Corbani

    John Corbani Formula 3
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    May 5, 2005
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    John Corbani
    You have gotten mostly great advise. My Dino rear calipers have the same mechanism.

    Pistons WILL NOT go back by pressure alone. Outer adjust is easy. Loosen nut, push on piston and turn Allen screw to let piston back out. When new pad will go in, lock screw.

    Inner piston requires removing cap before being able to get at Allen retract screw. I used Allen wrench on cap first time, then put slot in cap and have had no problen since. Remove old pads, push on piston and turn screw. Once pistons are back far enough to install new pads, stop turning; you are done. Put cap back and snug down. Keep clean. Full oil pressure is inside and cap has to seal.

    When you retract pistons, oil goes back into brake resevoir. Make sure it does not overflow and run out onto things that can get destroyed or stripped of paint. Brake fluid is nasty on lots of surfaces. A rag under the dual resevoir is a good idea.

    Pump brakes and bleed after any re-work. Auto adjust will set up normal clearance and you will be back in business. Re-check brake oil level.

    Fronts are trivial. Remove old pads. Push pistons back, watch oil level during retract. Slip in new pads, pump and bleed. Re-check brake oil level.

    Emergency brake is not affected by anything if pad clearance returns to normal.

    Luck,

    John
     
  24. John Corbani

    John Corbani Formula 3
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    May 5, 2005
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    Full brake oil pressure can be on inside of caps. Metal might be better.

    John
     
  25. Verell

    Verell F1 Veteran
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    May 5, 2001
    7,017
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    I'm pretty sure the inner caps are plastic, that's why the hexes strip so easily. Will find out when i get round to pulling mine tho.

    The inner caps I've pulled in the past have been dry.

    Are you sure about there being full brake pressure on them?

    Could this be a difference between GT4s & newer 3x8 calipers?
     

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