Advice Please: 308 master cylinder/booster problem.. | FerrariChat
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Advice Please: 308 master cylinder/booster problem..

Discussion in 'Technical Q&A' started by greg328, Sep 23, 2006.

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  1. greg328

    greg328 F1 Rookie

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    #1 greg328, Sep 23, 2006
    Well, I finally installed my new 25mm master cylinder (OE is 23mm), all the way from Italy, to accomodate my larger Wilwood calipers. I did this with great hope in reducing brake pedal travel a bit, which became a little long with the new brakes (front and rear).

    Removing the old MC was easy--drain the reservoir, pry off, disconnect brake lines, unbolt the 4 mount nuts and pull out. Installing the new one was a little difficult. It didn't want to seat fully on the booster--I had to knock it in lightly with my rubber hammer. I verified that the booster piston was fully in, and also that the master cylinder rod moved freely in. It did. Not sure why I had to tap it in with the rubber hammer. It fully seated as I tightened the 4 nuts.

    Now, my problem: the brake pedal goes ALL THE WAY DOWN to the floor--I barely have any brakes at all. I ran the engine in my driveway a bit and pumped the pedal a lot. Problem persists. Engine would "pop" each time I fully depressed the brake pedal--must be a vacuum thing? I drove SLOWLY around my block to see if I could build boost--no luck.

    I HAVE NOT bled the brakes yet. I plan to, but frankly, I doubt if much air got in the system. Hardly any fluid came out of the 2 lines as I removed them--maybe they sucked a bunch of air into the lines.

    The big question: Did I possibly damage the brake booster? Sure hope not.. Or, do I simply need to fully flush and bleed all 4 corners? Could air in the system cause the pedal to bottom out, and almost full loss of brakes?

    Any advice much appreciated..

    Regards,
    Greg
    77 308 GTB
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Sep 23, 2006
    The interior volume of the Master Cylinder itself needs to be bled as well (usually done by not tightening the fittings fully so that the air comes out there rather than being forced down the entire line) -- something wrong in the Booster should affect the effort needed, not the pedal distance traveled.

    Why not rebleed well at the calipers? -- with the MC replacement, it gives you a chance to really refresh the whole fluid volume.
     
  3. greg328

    greg328 F1 Rookie

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    #3 greg328, Sep 23, 2006
    Steve, I was hoping you'd reply!

    Not sure how to bleed the MC..my new one doesn't have the little side screw like my OE one. Is this the MC bleed screw?
    If I loosen the MC lines, won't that be a huge brake fluid mess all over the front compartment?

    Seems like a full flush and bleed at all 4 calipers would accomplish the same thing. Is this your recommendation, Steve?

    Pedal effort is normal, it just bottoms out--hopefully this means the booster is OK and I've just got a bunch of air to bleed..


    Thanks,
    Greg
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Sep 23, 2006
    Yes ;) and Yes

    The only good thing about these MC projects/replacements is getting a nice new-looking (non-discolored) reservoir ;)
     
  5. greg328

    greg328 F1 Rookie

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    #5 greg328, Sep 23, 2006
    Actually, my new MC didn't come with a new reservoir. I had to put my old one back on. The new MC had the rubber grommets, however, so it was no prob.

    My old reservoir is surprisingly non-discolored. I took a shop paper towel and a screwdriver and rubbed around the bottom to remove some oily dirt deposits, but it looks great now!

    I'll bleed tomorrow and post results here.

    So glad to have F-Chat!

    Greg
     
  6. jselevan

    jselevan Formula 3

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    #6 jselevan, Sep 23, 2006
    Greg - you've heard the expression "pounding sand?" Well, your pumping air. Can't change a master cylinder without bleeding it. Needs fluid. Nothing more, nothing less. Once you fill the MC with brake fluid, and remove all the air bubbles now traveling down the hard brake lines, you will be okay.

    Word of advice. Once you pressed the brake pedal with air in the master, you have air in the entire system. Have a nice day. (As mentioned by 91tr, this is a good excuse to refresh the fluid in the entire system).

    Jim S.
     
  7. greg328

    greg328 F1 Rookie

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    #7 greg328, Sep 23, 2006
    Thanks Jim...

    Yea, it makes sense now. Obviously, the new MC had air in it, that is now pumped into the lines.

    I'll bleed the system tomorrow. I'm looking forward to improved pedal feel w/ the larger MC..

    Greg
     
  8. PAP 348

    PAP 348 Ten Time F1 World Champ
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    #8 PAP 348, Sep 24, 2006
    A quick test to check if your brake booster is faulty is as follows.

    1.Stop the engine
    2.Press the foot brake pedal down numerous times allowing the spring to return it to the normal position until the pedal becomes hard to push down.
    3.Press the foot brake pedal down all the way and then start the engine, if the booster diaphragm is working the vaccum from your engine will allow the brake pedal to push towards the floor. If the pedal remains solid and doesn't move your when you started the engine the booster is either knackered or the check valve is also ;)
     
  9. greg328

    greg328 F1 Rookie

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    #9 greg328, Sep 24, 2006
    Thanks Pap, I'll check that out..

    Greg
     
  10. chrismorse

    chrismorse Formula 3

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    #10 chrismorse, Sep 24, 2006
    Greg,

    Looking forward to hearing the outcome.

    Definitely have to bleed the system. Don't forget to clean up all of the brake fluid, then really mash the pedal and recheck for fluid leaks, especially at the mc connections.

    chris
     
  11. greg328

    greg328 F1 Rookie

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    #11 greg328, Sep 24, 2006
    OK, I bled the system today, but I think I still have some air.

    My brake pedal is a bit higher, brakes a bit better, but still way off.

    Lots of air came out of both fronts, similar for the right rear, and NONE from the left rear. I tapped the calipers mildly with a rubber hammer to break loose any air bubbles. I'm using a hand-pump pressure bleeder; it's worked well before for me.

    I believe I didn't bleed the rears enough. I probably need to just go ahead and run ALL the old fluid out and renew. Today I pushed about 1/2 out, and replenished via the pressure bleeder. I'll re-do tomorrow and report back.

    BTW, I tried Pap's booster test--mine's fine. Gotta be trapped air, probably in the rear circuit.

    Bummed out,
    Greg
     
  12. jselevan

    jselevan Formula 3

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    #12 jselevan, Sep 24, 2006
    Greg - if the 3X8 series is similar to the 246, then the rear-mounted proportioning valve likely has air, and will take a bit of effort to get it out. Continue more of the same. You may, ultimately have to crack the thread on the fitting that enters the proportioning valve from the top (bubbles go up).

    Jim S.
     
  13. greg328

    greg328 F1 Rookie

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    #13 greg328, Sep 24, 2006
    Jim, thanks..

    I think I've seen this valve. It sits between the 2 rear calipers, below the engine, on a frame rail, right?

    Just loosen the top fitting to hopefully get those last bubbles out?

    How much air in a system does it take to make a brake pedal bottom out?

    Thanks again for the tip,
    Greg
     
  14. jselevan

    jselevan Formula 3

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    #14 jselevan, Sep 24, 2006
    What little work that I have done on the early 308s suggest that there are many similarities. The proportioning valve on the 246 sits on the driver side, rear frame almost against the luggage compartment firewall, immediately above the lower A-frame suspension bolt where it mounts to the chassis.

    A little bit of air will allow the pedal to completely collapse to the floor.

    It will take quite a few attempts at pumping the pedal and releasing air via the bleed valve of each corner to get the air out. The usual precautions of making sure that the reservoir does not go empy and allow you to suck more air into the system.

    I would first try to bleed the system in the traditional way. Only if this fails to provide a hard-pedal feel would I open the top and/or side fitting to the proportioning valve. If you have not previously opened these fittings, I suggest that you spray them with rust remover or WD-40. Let it sit for a while (overnight). Use the correct claw wrench. It they do not crack easily then don't force them. You should be able to get the air out without opening these fittings, but as a last resort to get air out, you might have to.

    Jim S.
     
  15. greg328

    greg328 F1 Rookie

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    #15 greg328, Sep 24, 2006
    Thanks Jim, I'll check that out..

    Much appreciated..

    Greg
     
  16. PAP 348

    PAP 348 Ten Time F1 World Champ
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    #16 PAP 348, Sep 24, 2006
    ;)

    Keep on it mate, your nearly there by the sounds :)
     
  17. greg328

    greg328 F1 Rookie

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    #17 greg328, Sep 24, 2006
    Thanks Pappy...

    Sorry about Steve Irwin.. the whole world mourns...


    Greg
     
  18. PAP 348

    PAP 348 Ten Time F1 World Champ
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    #18 PAP 348, Sep 24, 2006
    Yeah poor old Steve :( R.I.P

    Steve was a bit of a larakin but was a friend and inspiration too millions.
     
  19. greg328

    greg328 F1 Rookie

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    #19 greg328, Sep 28, 2006
    OK, well, I've bled all 4 corners again. No additional air came out.

    My brake pedal is extremely long, almost bottoms out.

    I didn't totally evacuate the reservoir, but probably 2/3rds of it.

    What am I missing?

    Greg
     
  20. FasterIsBetter

    FasterIsBetter F1 Veteran

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    #20 FasterIsBetter, Sep 28, 2006
    Greg,

    Just a thought, but might help. I've sometimes found using the hand-held bleeder that pulls at the calipers that it doesn't suck all the air out of the system. You might want to go back and do it the old fashioned way -- have someone pump the brake pedal while you open/close the bleed valves. Start with the right rear, the farthest caliper from the master cylinder. And be sure to keep the reservoir topped up. You don't want to suck any new air into the system. The other alternative is a bleeder that pressurizes the reservoir, but those are expensive. Much easier and cheaper to just have someone pump the pedal for you. Remember to tell your helper to go nice and slow, down and up, and hold the pedal down until you've said it's okay to go up, so you have time to close the valve. Last pump at each caliper, close the valve as the pedal is going down to assure no air gets back in.

    Hope that helps,
    Steve
     
  21. greg328

    greg328 F1 Rookie

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    #21 greg328, Sep 28, 2006
    Steve,
    Yep, I 'm gonna have to resort to the old-fashioned way!

    BTW, I am using a MOTIVE pressure bleeder, screwed onto the reservoir, @ 10 PSI, full of Castrol brake fluid.

    Just to be clear: Is the proper way to pedal bleed--

    With engine running to provide vacuum, (is this necessary?) have the volunteer press the brake pedal all the way down slowly several times as I open the bleed valve? Do I need to close the valve back as the pedal raises up again? Or, can it stay open for several pumps? For the final pedal release, close the bleed valve on the down stroke to prevent suction at the bleed valve?

    Will this be more effective than 10 PSI at the reservoir, provided by the MOTIVE? Is it OK to use BOTH the pressure bleeder AND human pedal power, or is that too much pressure for the system? Is it even necessary?

    Lastly, using only human foot power, is the reservoir cap left loose, or tight?

    Thanks,
    Greg
     
  22. jselevan

    jselevan Formula 3

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    #22 jselevan, Sep 28, 2006
    Greg -

    Not necessary to have engine running.

    Assistant pumps the pedal slowly three times. When at the bottom of the third pump, they hold it down while you open the bleed screw. DO NOT allow them to raise the pedal while the bleed screw is open. Once air/fluid stops flowing through the bleed screw, you tighten the screw and then tell them to let the pedal up. They then pump three more times, etc.

    I would not use both systems - not necessary.

    Caps do not need to be on the reservoir. However, if the reservoir is filled to the brim, some may spill out while pumping the pedal. Fill 1 cm below top.

    Jim S.
     
  23. tuttebenne

    tuttebenne F1 Rookie

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    #23 tuttebenne, Sep 28, 2006
    Do it the old fashioned way.

    Put a rubber hose on the bleeder (maybe 12 inches of hose or maybe 15). Drop the other end of the hose into a jar with a small amount of brake fluid in it. Make sure the end of the hose is submerged in the fluid at the bottom of the jar. Loosen the bleeder (with the hose on it) and pump the brakes (no assistant needed). Run a full reservoir or two through each caliper. Not only will you be happy to see all that mucky fluid purged from your system but you will get every ounce of air out too. Tighten the bleeder screw, remove the hose and go to the next wheel and repeat the process. Start at the rear and work your way to the front.

    The best part of this is that you can do it yourself. Just make sure you monitor the fluid level in the reservoir because you can push a whale load of fluid through the system with this method. And don't worry about using a lot of brake fluid - its the cheapest part of your car.

    Good luck
     
  24. greg328

    greg328 F1 Rookie

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    #24 greg328, Sep 28, 2006
    Andy and Jim,
    Thanks so much... I'll try these ideas Saturday, and report back..

    Much appreciated..

    Greg
     
  25. greg328

    greg328 F1 Rookie

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    #25 greg328, Sep 30, 2006
    Well, today I pushed a full reservoir's worth of fluid out of each corner.

    The 2 rears and the right front had no bubbles, (never have, really), the front left had MANY bubbles. That corner has been the problem corner since all this began.

    I pushed 2 reservoir's worth of fluid out of that corner tonight. Why would that one corner hold all the bubbles from the master cylinder install? Hmmm...

    BTW, I'm using a MOTIVE bleeder, pushing @ 12-17 PSI. Don't have a helper, and the way I see it, pressure on the system is what I need, no matter how I get it.. :)

    Well, the brake pedal is still going to the floor. I'm beginning to wonder if my new MC is faulty. I don't see how, because I pushed the piston on it on my workbench, felt great.

    One caveat, though. Carelessly, I allowed some air back into the system due to a low reservoir. It wasn't even at the "low" line, but air got in. This was during the front left evacuation. I resumed that corner for 1 more hour and got all the air out finally. Is it possible that some of that new air got into the other 3 lines? I would guess no, because the other lines are sealed full of fluid, right? Can air work its way down full lines?
    I'll do those 3 lines again tomorrow.

    I found that tapping on the MC, proportioning valves and calipers w/ a rubber mallet helped break loose new bubbles.

    Sorry for all the questions, I'm just stumped...

    :(

    Greg
     
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