1979 308 308 Brake System Warning Light - permanently on, even with the engine off? | FerrariChat
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1979 308 308 Brake System Warning Light - permanently on, even with the engine off?

Discussion in 'Technical Q&A' started by tomoshea, May 15, 2006.

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  1. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    #1 tomoshea, May 15, 2006
    I am re-commissioning a 1979 308gt4 which has been off the road for 12 months following a full engine/ gearbox rebuild.

    I have done a search of the archives with little joy.

    I have the following issue:

    With the ignition in position II (i.e the engine is not switched on, but power to all electrics) the brake warning light is coming on( with the handbrake off)

    The brightness of the warning light is much less than the bright luminous red you get when you pull the hand brake.

    When you pull the hand brake with the engine off the brake warning light works fine and you get a bright luminous red.

    Both rear brake lights are working fine, when you push the brake pedal.

    When you take the hand / emergency brake off and it reverts to a lower / dim red light permanently on.

    When you switch the engine on the same situation happens.

    The car drives fine and the brakes work fine, I do not feel any reduction in braking performance.

    What I cannot recall is if ordinarily when you pull the emergency brake whether it should put on the rear brake lights (this does not happen in my car)

    The manual is close to useless,indicating the light means "braking system failure, braking light"

    As I have never seen this behaviour before from the light in the cockpit I am looking for pointers.

    One other observation, to look at the master cylinder I removed the front "boot" cover and truned the engine on. When I push the brake pedal 5 - 6 times I am getting "whosh, whosh, whosh, whosh, whosh" from the master cylinder, like vacuum being pulled. I am presuming this is normal on an old 308, perhaps someone can comment?, anyway form the electrical diagram I cannot see any switch associated with vacuum/ master cylinder!

    Cheers

    Tom
     
  2. 330gt

    330gt Formula 3

    Nov 12, 2004
    2,108
    Seattle, WA
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    Kerry Chesbro
    #2 330gt, May 15, 2006
    Last edited by a moderator: Sep 7, 2017
    In the wiring diagram in the '76 owner's manual, look at #103. That's the switch that detects air in either the front or rear braking circuit. This is usually somewhere near the master cylinder. If there is unequal pressure in one or the other circuit, the switch flips to that side and grounds, turning on the brake light.

    From your description, either the switch is bad (stuck to one side) or you have a short to ground somewhere in that wire. I would find the switch and pull the wire off. If the light goes out, replace the switch. If not, start tracing the wire to find the short.

    Since the brake light gets brighter when you pull the handbrake, I don't think that the problem is in its wiring. However, a partial short to ground (high resistance) in that wire could explain this too.

    These two wires come together at the connector shown by the arrow. You may have to find that connector and disconnect each wire individually if nothing else is obvious.

    Regards, Kerry
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  3. BigTex

    BigTex Seven Time F1 World Champ
    Owner Rossa Subscribed

    Dec 6, 2002
    79,406
    Houston, Texas
    Full Name:
    Bubba
    #3 BigTex, May 15, 2006
    Tom, in the 308 parts cross ref thread there was a post of the switch and someone crossed it over with a Volvo unit, with some mods...

    The location was by the cylinder in that car and the brake tubing in/out made it pretty obvious, yours must be mounted elsewhere!

    Good Luck!
     
  4. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    THE Birdman
    #4 Birdman, May 15, 2006
    In the Mondial, the brake warning light is basically just a brake fluid level switch. Try topping off the brake fluid.

    Birdman
     
  5. barcheta

    barcheta F1 Rookie

    Nov 15, 2003
    3,738
    Maryland
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    Jim
    #5 barcheta, May 15, 2006
    Ditto I had the same issue a month ago... filling the fluid took care of it
     
  6. 4redude

    4redude Formula Junior

    Jan 13, 2005
    733
    Fungus Corner
    Full Name:
    Brian Keegan
    #6 4redude, May 16, 2006
    I would bet it is part #16 on Tav.27 of the 1979 308gt4 parts book. It looks like a junction block but the description says "signalatore innefficienza freni"
    "brake failure signal" basically. This part is NLA from Ferrari. We have seen a recent spike in the need for these. We may have a used one available from a chassis we are parting out (still sealed brake system).
    Brian
     
  7. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #7 Steve King, May 16, 2006
    It could be the brake switch which is located under the car up front where you remove the bottom panel (8 bolts). Sometimes this gets stuck or shorts to ground. If you unplug the wire at the switch and the light goes out then there is the problem. Also I agree it might be the brake level switch in the brake fluid bottle in the boot . I would think those are the 2 most likely causes. Just remove the wires from there and see if it goes out. My 2 Cents
     
  8. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    #8 tomoshea, May 17, 2006
    Thanks for the replies guys,

    Not the level of fluid, the resevoir is full. Did not see a level switch when I checked it though, perhaps I missed it I will look again

    Might be the switch but I won't be able to check until the weekend.

    I note no one has commented on the sound I mentioned eminating from the master cylinder when I press the brake pedal?, I take it this is normal then on a 308?, sound like either vacuum being pulled or a small leak of air breaking the vacuum?
     
  9. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Phil Hughes
    #9 ferrarifixer, May 17, 2006
    It'll be the brake failure warning from the junction block as described.

    It's hard to get to... up behind the steering rack.

    A double pink wire I think.

    Try re-bleeding the brakes, to trip the internal shuttle the other way or back to centre.

    Curiously, I've seen this many times, yet braking is never affected. Never dismantled one, so can't really comment further.
     
  10. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
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    Tom O'Shea
    #10 tomoshea, May 17, 2006
    Phil,

    Any comment on the nosie from the mater cylinder area when I pump the brakes, is this normal or is there any chance I have very small leak in the area?
     
  11. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Phil Hughes
    #11 ferrarifixer, May 17, 2006
    Move your keyboard closer to the noise... I'll have a better listen!

    Sorry, can't say. Yes, some noise is normal, but how much is hard to communicate here....
     
  12. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
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    Gerrit
    #12 gerritv, May 17, 2006
    Last edited by a moderator: Sep 7, 2017
    Hi Tom
    Yes, the whoosing is normal, at least I hear it on my GT4 as well when pressing the brakes.
    The junction block is indeed conveniently located by the steering rack. Mine developed a leak at the sensor switch so I replaced it with a Volvo unit. See http://www.ferrarichat.com/forum/showpost.php?p=135732869&postcount=57. It can be reset by rebleeding the brakes. http://www.swedishbricks.net/700900FAQ/Brakes1.html has the procedure quite a ways down the page (Look for Brake Light "On" After Bleeding). Lastly here is a picture of what is inside:
    The original Ferrari junction block is similar but you 'must' remove (just pry it up) the sensor switch before removing the internals. The switch dangles inside a groove so if you open the unit up with the switch in pace you will destroy the lower part of the switch.
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  13. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
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    Tom O'Shea
    #13 tomoshea, May 18, 2006
    Very funny Phil, thanks Gerrit, great information, I will sort it out on Saturday hopefully.

    Thanks


    Tom
     
  14. Mark 328

    Mark 328 Formula Junior

    Nov 6, 2003
    510
    Orange, Ca
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    Mark Foley
    #14 Mark 328, May 18, 2006
    Does your car have sensors on the brake pads? If so, that cisrcuit may be the cause.
     
  15. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
    79,406
    Houston, Texas
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    Bubba
    #15 BigTex, May 18, 2006
    1979....we don't have much, in the way of electronics! LOL!

    I'd put money on the differential pressure switch, that Volvo modification is great info!

    Good luck, tomoshea!
     
  16. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
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    Tom O'Shea
    #16 tomoshea, May 21, 2006
    OK, I took the unit out over the weekend, and the problem was that over 26 years the switch in the unit had become covered in crud, it had been shorting but with high reisitance which was why there was only a dim brake warning light coming on.

    I used a fine pointed plyers and solvent to clean out the hole into which the switch sits and compressed air to dry out the unit afterwards. I connected the switch back up before re connecting the brake lines to see if the problem had been solved. When I switched the light power on the brake light was no longer coming on, so it was a false alarm, but definitely better safe than sorry with the barking system.

    Only way to do this job is to remove the junction box. And you need a hoist to get access to the junction box from under the car.

    While bleeding the braking system after de cruding the system the light was coming on full strength as air compressed in one or other side of the system, so it is working properly.

    When the system was fully bled ther light went out as pressure was balanced between both sides of the unit, so it does work!!

    This is not a difficult job took about about 2 hours all in to complete, but you need the right tools.

    Anyway thanks to all for your suggestions help.

    By the way Gerrit the internals of my original Ferrari unit was different than yours I think, much simpler no springs, no pins just a floating metal spike connected to the piston, the spike sits between the gap of the 2 conducting terminals on the switch you insert into the top of the unit
     
  17. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
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    Gerrit
    #17 gerritv, May 21, 2006
    Hi Tom
    Glad it worked out without buying parts. That is often the most rewarding solution.
    The picture in my post above is the internals of the Volvo unit, I never took the Ferrari one a part except to see what the switch looks like. When I run out of things to restore :) I might rebuild it with new O rings etc and put the original one back in.

    Gerrit
     
  18. tomoshea

    tomoshea Formula Junior

    Dec 29, 2003
    541
    Ireland
    Full Name:
    Tom O'Shea
    #18 tomoshea, May 22, 2006
    Gerrit,

    best of luck rebuilding it if you get the time!!!, think replacement is definitely the cheaper option and less time consuming.
     

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