Aux electric vacuum pump for brake booster? | FerrariChat

Aux electric vacuum pump for brake booster?

Discussion in '308/328' started by AZDoug, Feb 19, 2020.

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  1. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    Doug
    The cams on the new motor don't generate a lot of vacuum at low, stop and go RPM., so there is very hard pedal at low RPM.

    Anybody ever put an elec vac pump on?
    I was thinking about a pressure/vac operated one, with a check valve, in line, or perhaps Tee'd off the main vac line, with a check valve on the engine side of the main vac line to the booster.

    I think i can fit one in behind the brake MC cover. If not, i can certainly put it in front of a heater blower motor.
    Doug
     
  2. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
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    How much vacuum do you have?
     
  3. AZDoug

    AZDoug Formula 3

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    Not enough below 1500-1800 RPM.

    Doug
     
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    I have driven 308s with P3 cams which had a lot of overlap and never had an issue with the brakes. Poor brake boost at low RPM is a classic sign of a bad Bonaldi booster.
     
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  5. AZDoug

    AZDoug Formula 3

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    The brake booster was just rebuilt, along with the MC. Maybe i will look for a vacuum leak on the way to the booster, the hose is new. Brakes work fine once vac is achieved, even after dropping back to low RPM, then after the vac in the booster is used up, pedal is hard until the RPMs go back up.
     
  6. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
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    I understand how they work. I just suspect you have a problem because you are not the first guy to have a lot of overlap in a 308. Never known it to be a problem with a good booster.
     
  7. thorn

    thorn F1 Rookie
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    We're looking for an actual vacuum gauge value.
     
  8. smg2

    smg2 F1 World Champ
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    Nicks GTB has one, the previous engine he had in it did not produce enough vacuum at idle.. ITB's with aggressive cams, 3.5L etc.. it's mounted in the front tire well. Runs at start, then shuts off, booster holds vacuum so it really doesn't run much.
    New engine is a different beast altogether, but we left it in.
     
  9. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    I may have found something to look at.

    Noodled this last night, IF the cams do produce enuf vacuum, then it seems like it would be vacuum leak as I mentioned earlier...

    I eariler had taken the the charcoal canister out for sandblasting and refinishing as it looked like crap, I also connected the hoses that went to it, together with an inline fuel filter i had handy...

    I may be getting a giant vacuum leak through that line that is supposed to go to the canister, sucking air right out of the RH fuel tank.

    I will reinstall the canister, since it is now finished and see what happens.

    Probably have to readjust the idle speed screw stop, also.

    Doug
     
  10. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    With the vac canister back in proper postilion,and properly hooked up, no noticeable difference.

    Now, I did get vacuum reading, at idle of about ~1000 RPM , based on the in-car tach, of 9" Hg at the hose that goes to the vac canister. I assume it is the same at the brake booster, but will check tomorrow.
    The gauge was pretty bouncy as would be expected as you can feel the vac pulses on the open hose, but by kinking the hose, I got a very consistent and repeatable, steady reading of 9".


    Doug
     
  11. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    Research shows 9" of vac isn't enough. I ordered an aux pump with pressure on/off switch.
    Cutting into the vac hose to the booster for a Tee, showed heavy vacuum stored, so the diaphragm and check valve and hose, seems good.
    Doug
     
  12. Russ Gould

    Russ Gould Formula 3
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    Nov 8, 2004
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    Genius no 1 installed an aux vacuum pump in my car (which has a 355 motor ie ITBs) with a vacuum canister and a pressure switch; but upon inspection, he did not install a check valve between the vacuum pump and the booster. So the vac pump runs a lot. What I wonder also is whether the vacuum sensor for the motec is now reading the pump vacuum instead of the inlet manifold vacuum. He did not isolate the vacuum pump from the original vacuum line that comes from the rear of the car.
     
  13. Jonny Law

    Jonny Law F1 Rookie
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    Been looking at installing a failover pump also.
     
  14. mk e

    mk e F1 World Champ

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  15. bitsobrits

    bitsobrits Formula Junior
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    Is that a custom pedal box, a modified original, or ?
     
  16. mk e

    mk e F1 World Champ

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    Modified original....but I really only kept the mounting flange by the time I finished cutting. This was preempted as I was expecting pretty low vacuum but it actually idles around 40kPa so 17-18inHg so the booster would have worked fine...but I did get bias adjust out of the deal which let the F430 calipers/rotors I have work well and the pedal has really good feedback...it firm for sure but not terrible as far as pressure goes.

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    the pedals got a little rework too...a little longer and added a tube for the front/rear bias adjuster
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  17. bitsobrits

    bitsobrits Formula Junior
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    Very nice. I did a similar thing on my E-type, and am contemplating doing similar on the 308, and have a spare pedal box to experiment with. The pedal length change must have increased the leverage ratio. What ratio did you end up with? I think the stock ratio is about 4.5/1
     
  18. Beta Scorpion

    Beta Scorpion Formula 3

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  19. mk e

    mk e F1 World Champ

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    Its almost exactly 6:1 now. I used .75 masters front and back but I may swap those out for something smaller...I haven't driven it enough yet to decide if I like it or want to soften it a bit I was worried about volume with the big calipers but the pedal doesn't move even a full inch so no worries there it turns out....the braided lines help too I guess, I push the pedal, there is 1/2-3/4" travel with a little lash /play in the linkage and the mastercylinders sealing off, the pads touch the rotor in the next 1/4-1/2 inch and that is where the pedal stops with no more perceptible motion no matter how I push on it....I feel the foam in the seat compress and I move back but the pedal doesn't move, the car just stops faster so VERY different feel form the OEM setup.
     
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