Brake Failure light on the Dino

First, I'd like to state I searched, then I dug around in the workshop manual for answers. Let me begin at the beginning.

My brake pedal was starting to have a hitch when I released it after braking. Instead of coming right back up, it would come about half way, stop mementarily, then return to the correct position.

An examination of the booster revealed that it was kaput. The rubber grommet, or gasket if you prefer, had shredded, and the innards were a disaster.

I was going to send it out for a rebuild, but was lucky enough to find a new 308 booster that could be substituted. Even better, it had the four bolt pattern to match my 246 master cylinder, not the two bolt pattern that the 308 has and was brand new, not rebuilt.

Ok, all work done new booster in, brakes bled, rear brakes adjusted, all works great. For about 3 hours. I was in a parade on Friday night, an 11 mph "run" through town for about 45 minutes. At the end of the run, I turned off the main street, gunned the car and took off hoping to cool the car a bit. Almost immediately the Brake Failure light came on. I drove carefully home, one hand on the e-brake, my somewhat nervous wife/co-pilot beside me, but without incident. Engine water was at 190, oil a bit over 210.

I did some digging here. Most posts here indicated either a vacuum leak or a bad proportioning valve. I got up Saturday, checked all the hoses (brand new as a result of the recent install) could not find anything amiss. I was going to pull the plug on the proportioning valve, and check that, but figured, ""what the heck" and started up the car. No light, no braking problems, all seems right as rain. Fluid was fine, plenty in the resevoir.

An hour plus drive today shows no symptoms, and no light, so obviously whatever tripped the light, reset itself, right? Or am I missing something? What the heck happened here?

Ok John, here's where you earn your keep!!!

thanks all for any input.

Dave M.

 

Dave,

Can't give you an answer for your particular problem but I finally found a wiring diagram that shows a switch and mentions an indicator. See page 56 and 57 of Wallace's 1976 translation of the Dino Shop Manual. Relay 15 lights the light when you engage the starter solenoid. Switch 70 is part of the pressure balancing valve in the brake system and it will light the light if it thinks pressure balance is off. Like a broken brake line front or rear. There is no tie to the vacuum line that I can see in any of half a dozen wiring diagrams I have. Looks like the indication when you start the engine is a test of the lamp. Any other time the light lights, the wire going to the balancing valve is the controlling one.

Hope this helps,
John

 

John's assessment is spot on. The warning light is controlled by a relay that should illuminate the bulb when starting the car, and when there is an imbalance between the two systems (I believe right front and left rear,,,left front and right rear).

Diagnostics should include:

1) Turn ignition switch on - light should stay off. Turn to start, light should come on while cranking.
2) Check relay 15 to make sure that it is not warm to touch when ignition on (idling or simply switch on not running).
3) Most likely air in the system on one side. I would again bleed the brakes to remove any air. This is most likely the culprit. Pressure on one side of the switch is not equal to the other. If you take the switch apart, you will find two pistons balanced against each other by a spring. The electrical contact is made if these pistons have unequal pressure on them.

In that you recently had the brake lines open, this would be my prime suspicion. Bleed the brakes.

Jim S.

 

Sticky switch mechanism was the culprit.

Internals were a little jammed up.

Couple of good start/stop cycles, which I had done that evening, cleared it up.

Mechanic had done a thorough bleeding of the brakes when he serviced them, and had replaced all the brake fluid lines and vacuum hoses.

He felt the valve switch was stuck, and that a couple of good pops on the brakes would return it to it's rightful position, which it did.

And no further problems. At least so far. (Fingers crossed.)

 

whitch switch?

 

The pressure balancing switch that is hiding under the bottom panel of the car.

 

When replacing the booster, did you recalibrate the adjustable pin between the mastercylinder and the booster? The tolerance should be 0,7mm! I made a misstake with this one on my GT and had problems with my brakes, but after adjusting (difficult to measure) the brakes work good again.

Ciao/ Bjorn

 

I am reviving a 16 year old thread!

So I just went for a drive in 74 246 GTS

And the brake pedal just kept going - so soft like a marshmallow and to its credit the

BRAKE FAILURE light came up - nice and bright

and I thought

that light is correct - the BRAKES have FAILED

it stops - kinda - but it takes many many feet LOL

can the educated here suggest my next move ?

I immediately came home and put the car away

I had not driven the car in maybe 2 months - and I am now remembering that the last time I drove it - the brakes were feeling soft

Now they are clearly soft/gone

the big issue is the guy I would like to do this repair for me has moved a bit further out of town - I could flatbed the car out there

but this is not rocket surgery I don't think

how much am I looking at ?

Any LA based mechanics you guys love ?

 

wait

I may be an idiot

lemme check the fluid

and leaks

 

Does your brake light on dash show on dash when ignitin as position ACC before start ?

 

no - it lights up when I press the brakes

and the brakes are in fact failing

so the gauge / light is working properly !

I need help to identify the brake booster reservoir so I can open it and see if there is no fluid in there

I don't see fluid stains on the floor but I have not played with this car for a bit so it could have leaked and dried ?

 

okay so forgive my fear and ignorance

here goes

I am going to post a picture of the 2 plastic reservoirs that I BELIVE to be the brake fluid and the clutch fluid ?

in this photo the reservoir on the left has fluid

the one on the right is bone dry

before I pour DOT 3 - non synthetic brake fluid in to the bone dry right reservoir ....

can someone tell me if I should do this
?????


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Your 246 has a cable-actuated clutch (not a hydraulic clutch). Both those reservoirs are for the brakes -- so go ahead and add the brake fluid, but it may not be that simple and may require bleeding (however, you almost certainly have a leak somewhere so that need to be looked at, too). Unlike modern cars where the reservoir mounts directly to the master cylinder, your car has hoses from the reservoirs going over to the master cylinder:

https://www.ferrariparts.co.uk/diagram/ferrari/246-dino-gt-coupe-spyder-(from-ch-02132)/025-brake-hydraulic-system

I'd certainly have a look at those hoses (especially #10) before pouring more fluid in, and after pouring some fluid in, before filling it up all the way.

Do you not have a copy of the OM for your car?

 

I bet the reservoir is cracked, often where the brake hose attachment is on the bottom. If you add fluid it will just pour out. Remove the batch board cover and inspect
Cheers
Pietro

 

I'm gonna need to have these brakes bled

I did put fluid in the reservoirs - but one was empty - the other full - seems for sure there is a leak

I need it to stop raining in Los Angeles and then figure out which place I wanna go

will need to flat bed it

ugh - I will report back - thanks for the input