38mm Piston Rear brake Caliper install

Discussion in 'Workshop Forum' started by Rupunzell, Oct 29, 2016.

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  1. lookforjoe

    lookforjoe True Classic

    I still haven't adjusted the pedal stop to drop the pedal slightly - mine just felt odd the first time I used the brake - once I was out & about with it, I think I adjust to the difference in pedal height. Mine don't feel spongy at all, and the brakes lock up if you brake too hard - which was what made me think about adding ABS ;). Of course, I can manually modulate the braking, since that is what I always did in the past, but that doesn't come naturally anymore, having driven most cars with ABS for so many years now.
     
  2. lanciahf

    lanciahf True Classic

    Location:
    New Jersey
    Rob did you fit a hydraulic handbrake? I have Wilwood calipers all around with 11" discs, kit was made by TCE Brakes. Braking is great but I fear sometimes that I do not have a handbrake.

    Thanks,
    Ralph
     
  3. Not yet. I have yet to work to fit this master and figure out how to mount it solidly and attach it to the existing handbrake handle.

    wil-260-6087_w_xl.jpg

    It's a modern day copy of the classical Girling.

    $_57.jpg

    Cheers,

    Rob
     
  4. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    I will keep this in the rear brake up grade part of the post for X1/9 brake upgrade.

    As you know I purchased after market rear brake calipers. The issue was that stock 38MM rears required a huge core charge.
    With the after market calipers installed it became apparent that the brake pedal was spongy and that by pulling up on the hand brake when braking better braking was obtained.

    This led to further investigation and it was found that there was .025" lash in the rear brake caliper adjusters. The lash can be found in several things in the piston adjusters. Different multi start thread and nut. Thrust bearing and bearing plate. Cir clip retainer. This lash is what is causing the increased pedal travel because the rear brake piston will not adjust out the slop between the disk and the brake pad. A temporary solution was to install shims between the pad and the caliper which has firmed up the pedal, but this is only a temporary fix. The solution was to either make new 38MM pistons and use stock X1/9 rear brake adjusters or to sleeve the stock 34MM pistons and use stock X1/9 adjustor hardware. I took the sleeve route but I think it would have been just as easy to remake the pistons.

    The starting point was the finding the diameter of the rear caliper piston as shown here is 1.491" 38MM is actually 1.497".

    IMG_3761.JPG

    Sleeving started with a cold rolled section of 304 Stainless Steel rod 1.500" in diameter (1.502" as purchased) The section of rod was bored to 34MM and external diameter sized to 1.491".

    IMG_3762.JPG



    The sleeves were then cut to length, cleaned and oiled for pressing. Size of sleeve was.001' under size.


    IMG_3763.JPG



    The sleeves were pressed on to the old 34MM pistons. The pistons had sever pitting.


    IMG_3764.JPG



    IMG_3765.JPG


    The sleeves were TIG welded to the pistons.

    IMG_3767.JPG



    The pistons were dressed and polished.

    IMG_3768.JPG



    The self adjusters were assembled into the piston body.

    IMG_3769.JPG


    • Next week Bob Martin will be at my house and we will be working on his Black Dallara. Once done working on his car we will be removing the rear calipers and installing the new sleeved pistons on my Abarth powered X1/9. Will post our progress.


    • TonyK.



    • Grimsby Ontario Canada.
     
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  5. Rupunzell

    Rupunzell Bernice Loui

    Location:
    California
    Check the piston OD after press fit and welding. Very likely the piston OD and out of round is not what it was before due to welding. Heat from welding can easily change the roundness and OD.

    Not that difficult to do, there is a lathe available, mount a four jaw independent chuck on the lathe. Chuck the piston into the four jaw using some thin brass or copper shims to prevent damaging the piston. Apply a dial indicator to the OD of the piston near where the piston is mounted in the chuck then out towards the end of the piston. Adjust the four jaw chuck as needed to center, then use the dial indicator to check for out of round and changes of dimension across the OD of the piston. Adjust by honing, turning or etc as needed. If the dimensions of the piston is not to OEM spec, out of round, tapered or etc, the piston can stick or hang up in the caliper bore or cause un-happy brake seals.


    Bernice
     
  6. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    Thanks Bernice.

    I expected some truing to be required but today I had a few moments and took some measurements. The piston was now .002" larger and has a taper on it as well. It is no longer round either.

    When turning and trying to remove a slight amount of material the finish suffers. Normally I turn the part to +.002" then use a single cut file and sand paper to produce the finish of the part. Currently I have the piston in the 4 jaw and I am using my tool post mounted grinder to bring the piston back into round and true. As this time I would like to say that I should have just remade the pistons from Stainless Steel bar stock as it would have been easier than what I have been doing. That option my present it's self shortly.

    TonyK.

    Grimsby Ontario Canada.
     
  7. fiatfactory

    fiatfactory Steve Cecchele

    Location:
    Western Australia
    I would have thought a tight interference fit between a sleeve and the piston (cool piston and warm sleeve then press together) would have sealed hydraulic pressure, and negated the need for welding and subsequent refinishing...

    SteveC
     
  8. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    Well there is that possibility, but brakes can get hot and then things change rate of expansion of two different metals. I really don't want to add this factor to spirited driving.

    TonyK.
     
  9. PaulD

    PaulD Paul Davock

    Location:
    Kitchener, Ontario
    I am exploring my after market 38mm rear brakes before I install them as I am concerned about the issues that TonyK and Hussein have experienced. I would like to get mine right on the first installation.

    Tony, have you gone further with this project, and did it help the issue? (That was impressive work on the sleeves for the 34mm pistons).

    upload_2017-10-6_12-9-43.png

    Checking the lash on the stock and 38mm adjusters, , it was similar between the two, in the vicinity of 20 thou on each. It is hard to measure,it the screw rotates at all, it changes the measurement.

    I worry that the following description will be gibberish to people who have not taken one of these apart. Somewhere on x web there was a diagram of the adjuster, possibly gone now, The above picture may help.

    In my comparison of the stock and 38mm calipers, I have found a few additional factors that may impact modifications to fix the issue. I wondered why the 38mm units used a different thread diameter and pitch than the stock ones. (8.17 mm X2.5 round cut threads versus 7.96 X2 square cut threads) I noticed that the emergency brake lever has a maximum throw of 1 inch on the stock calipers and .5 inch on the 38mm calipers (it hits the side of the caliper). This could be the reason for the difference in the thread pitch. Less throw requires a greater pitch. (I have not checked the emergency brake lever movement on the car, anyone know what that is?) Perhaps the movement on the 38mm piston is not enough to activate the adjuster?

    Also the disc springs are thicker by .2mm giving 123 lbs of pressure at 25% compression as opposed to 83 lb on the stock ones. This could be to compensate for the change in thread pitch, or to compensate for the increased piston volume. Or because they were available.

    What follows are are just guesses, I need some help here.

    If I hone out the bore for the plunger that holds the disc springs and adjustment mechanism by 2 thou, the stock mechanism will fit into the 38mm caliper with 10 thou lash. I have doubts that this will work to eliminate the play in the system, as the stock caliper had lash as well as the 38mm caliper. Also, the reduced throw on the 38mm caliper emergency brake lever may require the steeper pitch on the adjuster. The stronger disc springs may be necessary for the larger piston volume or may impede the turning of the adjustment mechanism. There is no going back from this modification.

    What might be the source of and correction for the 25 thou lash between the brake pad and disc that Tony and Hussein have experienced? All thoughts will be appreciated.

    Paul Davock
     

    Attached Files:

  10. lookforjoe

    lookforjoe True Classic

    I would have to say mine has settled in. I do not feel extended pedal travel when braking. It's either marginal at this point, or normal tolerance. Either way, I didn't alter anything in the hardware beyond normal cable adjustment for slack.
     
    PaulD likes this.
  11. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Paul, if it were me I'd give them a try as they are first before making permanent alternations...which might not be needed.
     
  12. PaulD

    PaulD Paul Davock

    Location:
    Kitchener, Ontario
    Good thought, particularly in line with what Hussein said. I will see what Tony has found as well.

    It is a good thing I took them apart though, one of the prawls (wedges) was on upside down.

    Paul
     
  13. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Ya, that does not boost a lot of confidence in them. Having reviewed the related posts on this subject I was very disappointed these rear calipers are not working out better, because I was thinking of doing the same thing. Let us know what you learn, there may be hope for them yet.
     
  14. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    I installed shims to take up the slack. I have driven the car about 600 miles and cannot see any difference in brake pedal travel. I think as Hussein has stated the brakes have settled in and the adjusters are working correctly but do not allow for the slack adjustment as quickly when reassembled. Shims are in and I will leave them in. The car does brake better but feels different. The front end does not dive as much under hard braking. The rear brakes do get as hot as the front brakes because they are doing more work than the stock brakes.

    TonyK.

    Grimsby Ontario Canada.
     
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  15. PaulD

    PaulD Paul Davock

    Location:
    Kitchener, Ontario
    Thanks for this. I will put them back together and try them as they are.

    Paul
     
  16. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    Well in a private discussion with Karl Mead he gave me this link that Wilwood that sells residual brake pressure valves that compensate for return piston travel. This may have been a solution and could still be right now for soft pedal or to reduce pedal travel.

    https://www.wilwood.com/MasterCylinders/MasterCylinderValves

    My nephew picked up a used X and when I drove it pushing on the brake pedal was like pushing on a block of wood sitting on the floor. When we got the car back to my place the front calipers were seized. No piston return at all.

    The idea Karl and I were discussing was using two remote brake servos with line regulators to adjust front and rear brake bias. It seems plausible.

    Thanks Karl.

    TonyK.

    Grimsby Ontario Canada.
     
    kmead likes this.
  17. Mark

    Mark FIATFREAK

    Worked for me on my Scorpions. I have larger brakes on them and installed the valve on the front line. Fixed the pedal droop with no Ill side effects.

    Picture 352.jpg

     
    Last edited: Jul 28, 2018
    kmead likes this.
  18. kmead

    kmead Old enough to know better

    Location:
    Michigan
    It appears you used the 2lb retained pressure version? One wouldn’t think this would be much of an issue given the light pressure, but any sense of additional wear on the pads? Or heat from the light dragging?

    Thanks
     
  19. lookforjoe

    lookforjoe True Classic

    So these valves keep a small amount of pressure in whatever circuit you add them to, to offset the pressure drop from addition of the larger (than system was designed to run) calipers? Interesting. How does one ascertain what residual pressure is OK, without causing a pad drag issue?

    (Link doesn't work for me, Safari keeps asking for multiple client ID certificates when trying to load it)
     
  20. Mark

    Mark FIATFREAK

    I didn’t notice any drag on the rotors, additional brake dust (wear) since installing them. Just better pedal feel.

     
    kmead likes this.

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