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TR power brakes

Discussion in 'Technical Q&A' started by jratcliff, Nov 7, 2007.

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  1. jratcliff

    jratcliff Formula 3

    Sep 7, 2004
    1,024
    Texas
    #1 jratcliff, Nov 7, 2007
    I am experiencing a problem with the power brakes. When I first got my 91 TR I noticed what I thought were poor brakes. No problem, I rebuilt the front and rear calipers, re-surfaced the rotors, and bleed the brakes. The front brakes had been modded with the larger Brembo calipers.
    The poor brake performance exists. It acts like the power assist is not functioning. I checked the booster and was able to pull and hold a 15" vacuum. I took off the vacuum hose from the booster and started the car and it seem to have an ok vacuum (I need to measure). My concern now would be with the auxiliary pump. Does anyone have any thoughts on this?
    John
     
  2. WILLIAM H

    WILLIAM H Three Time F1 World Champ

    Nov 1, 2003
    35,532
    Victory Circle
    Full Name:
    HUBBSTER
    #2 WILLIAM H, Nov 7, 2007
    dont know about the pump but you should upgrade to porterfield brake rotors & pads, that should help considerably
     
  3. jratcliff

    jratcliff Formula 3

    Sep 7, 2004
    1,024
    Texas
    #3 jratcliff, Nov 7, 2007
    I don't think this is about the pads or rotors. The pads are new and the rotors turned. The front calipers and rotors are big bembos.
    John
     
  4. james patterson

    james patterson Formula Junior
    Professional Ferrari Technician

    Dec 8, 2003
    417
    Dallas Texas
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    James Patterson
    #4 james patterson, Nov 8, 2007
    What does the pedal feel like, if you think it is the booster it must be getting a hard pedal at/near the top of the stroke. With the booster working there will be a pretty long stroke before the pedal firms up. There is a problem with the pumps, the shafts shear at the splines and stops turning. This causes no mechanical damage other than the pump and is not extremely noticeable while driving but is noticable in certain driving situations. If the complaint is overall poor stopping power with a hard pedal that does not travel very far then you are on the right track with the power assist. Also keep in mind that with the Brembo fronts and factory rears we have had calls about poor brake performance, this is due to a balance problem with the increase in front caliper volume without changing the balance in the master cylinder. This is not an issue when you do the Brembo's on all four wheels but there are some pedal 'feel' issues with that setup as well.

    I don't have any first hand knowledge of sorting out brake issues with the fronts only setup but if the booster power assist checks ok I would temp paint the rotors and make sure the fronts are doing most of the work, or static check the line pressures.
     
  5. tomberlin

    tomberlin Formula Junior
    Silver Subscribed

    Apr 9, 2005
    854
    Bethesda
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    tom berlin
    #5 tomberlin, Nov 8, 2007
    With the engine off, pump the pedal until it feels firm at the top- 8-10 strokes maybe. This will deplete residual vacuum. While continuing to apply pressure, start the motor. It the booster is working it will suck your foot down a noticeable amount.
    Tom
     
  6. jratcliff

    jratcliff Formula 3

    Sep 7, 2004
    1,024
    Texas
    #6 jratcliff, Nov 9, 2007
    Well I checked the booster by taking my handheld vacuum pump and pumping to about 15" and no leak. I then checked the line coming from the engine and got nearly 32-35 inches (that sounds good to me). There is a proportioning valve in the lower engine bay area. So here is where I'm going next. I noticed the rear pads were very worn when I replaced them and the fronts looked great. Someone might have changed the setting on the valve so that the rears worked harder. Other thought when they installed the Brembos they might have used a racing compound for the pads. They might need to heat up to be more useful. Any thoughts on something I might have missed.
    John
     
  7. Jeff Pintler

    Jeff Pintler Formula Junior

    Jul 20, 2005
    537
    Richland
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    Jeff Pintler
    #7 Jeff Pintler, Nov 10, 2007
    The thread 105840 (I think from June2006) discussed the vacuum pump. An owner that replaced a broken pump mentioned something about pedal effort. The pump is easy to remove and then verify the shaft isn't broken or body crack or broken vane. The master cylinder is a two circuit design so maybe the seals have failed/leak. My thinking is that the proportioning valve should just limit pressure to rear circuit since the bore on the master is the same (same pressure both circuits). Another thought is if someone used Dot5 fluid it could turn the rubber hoses to jello and limitflow to the front calipers. Brake hoses need to be replaced after 7 years (or pick a number) and most don't do that. Let us know what you find.

    Jeff Pintler
    89 348tb, 86tr
     
  8. jratcliff

    jratcliff Formula 3

    Sep 7, 2004
    1,024
    Texas
    #8 jratcliff, Nov 10, 2007
    The Brembo kit comes with new brake hoses, so no problems there. Can't be the pump since it is pulling 32-35 inches at the booster. Booster checked out ok. I took it for a spend and now considering what James at Norwoods had to say is probably what is happening. I think either the guy before changed the pads to a track formula that needs plenty of heat to start hooking up or the differences between the Brembo front and Ferrari rear calipers are contributing to this condition. I guess I could buy some street pads for the Brembos and try that, but all tests to the brake system have proved the system is working (power boost).
    John
     
  9. EDoug

    EDoug Formula Junior

    Apr 19, 2005
    277
    Southern Florida
    #9 EDoug, Nov 13, 2007
    Sugar Land, for what it is worth, on my 86 TR, I do have a similar brake feel that you describe. In my case, I do know that the check valve between the booster and the manifold seems not to flow freely as I would expect in the flow direction when I have taken it out. It seals fine in the check direction. I have replaced same and the new one (Allied Signal Bendix is Ferrari source for this check valve) acted just the same. I have always suspected that a more free flowing valve in the flow direction could help. Maybe someone else out there has some experience with this valve. Just a thought. EDoug
     

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