Brake failure light

Okay I need help from all you who no way way more than I. I just got back from a spirited nightime drive in the Dino. Running fabulous all the way to redline, no stumbling at all. Brakes work fine but it does seem the pedal goes down too far before the brakes take affect. But the big problem is when I really stood on the brakes the BRAKE FAILURE light came on. I recently bled the brakes, had it on the lift and checked for any leaks, there were none. HELP, whats wrong.
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I believe that light is triggered by the quad junction at the front of the vehicle. The switch is mounted atop the junction and triggers when the bias between the two sides is not equal. I would check that first followed by the master cylinder seals. The master has front and rear seals which push each of the two brake lines which in turn go to that little quad junction. I suspect if one of the seals in the master were torn that the pressure applied to the junction would be different causing the brake failure light to illuminate.

 

I concur. This happened to me last year. The seals in the master are going and this gives rise to what was explained above. I ordered a new one from GT Car Parts but found, on my 1974 GTS, that there the manufacture was different and this caused the brakes to lock up and seize once the car got hot. We solved the problem by making a 0.060" brass shim to fit between the master and the booster and all is good now.

 

Jon, I concur with John and Shross. The only other thing to consider would be air in the system, which might explain pedal travel and asymmetric pressure in the front /aft systems. Nice to know that the alert system works, however.

Jim S.

 

It is a brand new master cyclinder, so I will report back.

 

Jeez that's a pain with a brand new cylinder like that :/ sorry to hear it

 

Here is a photo of the junction block on USA cars. It isn't easy to get to but I'd attach an ohmmeter to each lead to verify there is a short across them which propgates the failure warning.

Note that the parts book shows that Euro cars have a different block.
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This happened to me and when we replaced the master cylinder, it solved the problem. Not sure if it was the only problem or if a total master cylinder replacement was required, but the original master cylinder was on the car and I felt it was prudent to replace the whole unit.

 

forgot to mention the "new" piece was actually about 1/2" longer that the original piece that was removed. Not certain why, but strange...

 

I bled the brakes again today. Same problem. I took apart the master cylinder cleaned everything and will put it back tomorrow and report back.
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I guess you checked for signs of fluid leaks.

 

All the seals in the master check out ok?

Another thought came to mind. What kind of brake fluid are you using? Might -although I doubt it- be an issue.

 

No leaks. Silicone fluid.

 

any changes in fluid levels?

 

From your original post, it does sound like you are having a pressure differential problem. (When I really stand on the brakes, the failure light comes on)

Does the light go off when you release pressure on the brake pedal? The little piston that is inside the junction block that controls the electrical switch is spring loaded to center, the "OFF" position. If the system is operating correctly, the light should come on when the brake pedal is pressed and go off when the brake pedal is released. This assumes that there is a fault somewhere that is causing the front and rear pressures to be different.

If the light remains on when there is no pressure on the brake pedal, the problem is likely the switch itself. It might also be with piston and springs inside the junction block. The piston inside the junction block has small seals at each end. It might be worth removing the switch and seeing if there is brake fluid leaking into the switch port when the brake pedal is pushed.

 

Excellent point.
I know the electrical switch on the block is in a very difficult location, but it might be prudent to test that electrical switch to see if that is the issue.
Although much easier said than done...still, best of luck in sorting this out, it'll be interesting to see how it gets resolved

 

If you pump the brakes, does pressure come back?
If you get pressure at high pedal and you hold it will the pedal slowly go down or does it keep pressure?

 

I'm having a similar issue. If the junction block is not located where it's shown in the parts book, where will I find it?

 

So I took the master cyclinder apart, cleaned it and put it back together. I then bled the brakes twice. SUCCESS. All is well in Dinoland. Thanks for all the advice and comments.

 

I have the same problem with my 308 GTB i have cleaned the junction switch but my light is still on. Looks like a m/cyl rebuild on the list of things to do.

 

Hey Rizzo308
That's almost a Dino!
I clicked on your avatar, 'cause that's why you put it there, and I see you've got your priorities right

 

This must be the Year of the Brake Failure Light.

I went for a spin Sunday and noticed that the brake failure light came on, I'm not sure at what point. The brakes seem all right. I have not checked for leaks or the fluid level (seemed low when I peeked without a flashlight) and am hopeful that topping up the reservoir will put the light out. The only thing I did different this trip was put on the handbrake at a gasoline stop harder than usual because of an incline.

The brake seals will need renewing, as I haven't touched them since new. If that proves necessary now, I will change the flexible brake lines as well (should I shift to metal-braided lines?) and shfit to silicone brake fluid.

There, I feel better knowing I am not alone (misery loves company).

Andy

 

I would not not use silicone brake fluid Andy. Just change it every two years, use DOT 4 or racing stuff, and for us tropical & humid types, every year. It costs nothing and it is cheap insurance. All the components will last a looong time!
Regards, Alberto

 

I took the Dino out for a spin today, later than usual as I overslept, and the light did not go on. I hope it doesn’t come back! The Dino sounded so good, and flicking that black-knobbed gear lever really feels so period Ferrari. Nice!

Thanks for the advice, Alberto. I will keep that in mind.

 

Along this topic of Brake Failure Light,...my question is, I do not recall seeing this in my Dino Tipo L model. (Maybe there is but never see it go on). Just curious if early models have this warning light also. Thanx in advance for the gurus' wise words. w/ smiles Jimmy