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Discussion Starter #1
Hi all,

This is my first post ever and I hope it makes sense.

My brake lights have stopped working when I apply the brake pedal.

I have found a loose wire on one of the vacuum assisted boosters.

It is a black wire, with an open end. See photos.

Can you please advise if this wire is meant to be attached to the brake booster and what the usual way of fastening is?

If this is not the issue, I presume it is a pressure switch either on the brake distributor underneath the drivers seat on the underside of the chassis, or on the distributor next to the booster.

To eliminate the switch as an issue, is it okay just to short circuit the switch with a wire or will this be dangerous?

Thank you so much,

Mann
 

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Discussion Starter #2
Just an update on this.

I short circuited the brake pressure sensor and the lights turned on, as if the pedal was depressed.

So I am sure now that its one of two things.

Either the pressure of the brakes is not reaching adequate pressure.

Or the sensor is faulty.

Does anyone have a link to the sensor in question where I can purchase it?

Thank you so much.

Mann
 

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Richard Jemison
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Wires

From Memory....
There is a sliding piston in there that when fromt & rear perssures "change" alerting to a brake issue.

I assume to "balance" the system in the center, bleeding will be required. I suggest opening all 4 bleeders at the same time and let gravity "bleed the system (keep the reservoir full.) for 1 minute.
Use no petal pressure!

close one sides front & back then the other front & back.
 

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I am confused here - are the RHD versions that different in how the brake lights come on???

"My brake lights have stopped working when I apply the brake pedal." - I assume that's the brake lights on the rear of the car for other drivers, not the brake function warning lamp in the dash!!
The rear brake lights are actuated by a simple switch near the pivot point of the pedal inside the driver's footwell in a LHD 1979 spider - with no under-hood connections.

The pressure switch & fluid level switches under the hood light the dash warning lamp. Nothing to do with the rear tail lamps.
 

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Trained (ex)Professional, , 1953-2018 RIP,
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I am confused here - are the RHD versions that different in how the brake lights come on???
Yes.
While the RHD version has a tandem brake master cylinder, it is floor mounted, activated by floor pedals and has two remote brake boosters. Hence, it uses two hydraulic pressure switches, one switch for the front circuit and one for the rear. It is basically the same system used on the LHD 1969 USA cars except for the location of the brake light switches; one on the bulkhead and the other on the rear brake pressure limiting valve under the car. The LHD versions use a plastic proximity switch activated by the hanging brake pedal.

Welcome to the BB, Mann!
Good diagnosis. By bypassing the brakelight switch for the front brakes and the brakelights coming on, you've proven that the switch is no good (assuming pressure in the system when the brakes are applied). The same would hold true for the second brakelight switch under the car. Touch the two wires together and if the lights come on, this switch is also no good (again, assuming pressure in the system).
If both switches are bad, the most likely scenario is that one of the switches went bad a while ago. There would be no reason to test this because the lights still worked from the second switch. Only when the second switch failed was the problem noticed.

I'll search around for a RHD variant wiring diagram for you but they are extremely hard to come by. What I can say with a fair bit of confidence though is that the loose black wire (an earth perhaps?) does NOT go to a booster.
 

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Yes.
While the RHD version has a tandem brake master cylinder, it is floor mounted, activated by floor pedals and has two remote brake boosters. Hence, it uses two hydraulic pressure switches, one switch for the front circuit and one for the rear. It is basically the same system used on the LHD 1969 USA cars except for the location of the brake light switches; one on the bulkhead and the other on the rear brake pressure limiting valve under the car. ...
I'm in awe.

So it's set up such that a hydraulic failure can be diagnosed by the drivers behind you? :surprise:

I'll just quietly add that fact to my knowledge about Alfas.
 

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I'm in awe.

So it's set up such that a hydraulic failure can be diagnosed by the drivers behind you? :surprise:

I'll just quietly add that fact to my knowledge about Alfas.
Bruce, if it wasn't entirely clear, the LHD cars with hanging pedals like yours and mine are different. The brake lights are controlled by an electrical switch under the brake pedal.
 

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Bruce, if it wasn't entirely clear, the LHD cars like yours and mine are different. The brake lights are controlled by an electrical switch under the brake pedal.
Rich - thanks, yes I have been through the process of debugging my brake lights (brake lights flashed for each pot hole hit - switch adjustment fixed it, which I see would not have occurred for the RHD hydraulic pressure switch :laugh2: )
 

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Trained (ex)Professional, , 1953-2018 RIP,
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I haven't (yet?) found a RHD wiring diagram @Man Mohan (not even sure Alfa published one) but did manage to find a basic RHD brake system component diagram that shows both brakelight switches. Please click below for the diagram.
And for those with 1970 and later LHD cars, your brake component diagram is also linked below.
Both diagrams come from user manual #1552 dated 02/1970.
 

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Discussion Starter #12
Hi everyone, I am very sorry for a late reply. I havent got notifications set up for my email and will get this sorted soon.

Please give me time to review and read.
 

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Discussion Starter #13
I'm going to assume that's a RHD car. First off, contact member @papajam and get a wire diagram from him.

If you're in the UK, any vendor should have that switch. Try Highwood, Alfaholics or Classicalfa.
Thank you, I will get in touch with Papajam for a wiring diagram.

I am in Perth, Western Australia, so I may have to freight it over.

By the way, I will be replying to each post, not sure what the convention is here!
 

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Discussion Starter #14
From Memory....
There is a sliding piston in there that when fromt & rear perssures "change" alerting to a brake issue.

I assume to "balance" the system in the center, bleeding will be required. I suggest opening all 4 bleeders at the same time and let gravity "bleed the system (keep the reservoir full.) for 1 minute.
Use no petal pressure!

close one sides front & back then the other front & back.
Hi, I believe that the car uses a pressure switch. It doesnt look like there is a switch underneath the drivers seat where the brake distributor is. (The thing that the pedal pushes a piston against that lets the brakes get pressure)
 

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Discussion Starter #15
I am confused here - are the RHD versions that different in how the brake lights come on???

"My brake lights have stopped working when I apply the brake pedal." - I assume that's the brake lights on the rear of the car for other drivers, not the brake function warning lamp in the dash!!
The rear brake lights are actuated by a simple switch near the pivot point of the pedal inside the driver's footwell in a LHD 1979 spider - with no under-hood connections.

The pressure switch & fluid level switches under the hood light the dash warning lamp. Nothing to do with the rear tail lamps.
Yes, it is the brake lights to warn other drivers when I depress the pedal.

I cannot see a switch by the pedal? I have looked all around it. And there are no electrical cables going to it.
 

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Yes, it is the brake lights to warn other drivers when I depress the pedal.

I cannot see a switch by the pedal? I have looked all around it. And there are no electrical cables going to it.
papajama pointed out that RHD (and earlier LHD) spiders do not have a switch at the brake pedal, but instead use a pair of pressure switches - as you found.
 

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The first thing you pointed to is the air valve on the booster. No electrical aspect to the booster at all; it's hydraulic and pneumatic.

Did you find your brake light switch? Would be plumbed into a junction, probably right rear of the engine bay.

Andrew
 

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Some posts here are worth subscribing just to satisfy...curiosity. :)
 

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Discussion Starter #19
The first thing you pointed to is the air valve on the booster. No electrical aspect to the booster at all; it's hydraulic and pneumatic.

Did you find your brake light switch? Would be plumbed into a junction, probably right rear of the engine bay.

Andrew
Hi Andrew,

Yes, I found the first brake light pressure switch. I believe it is in the third post I did with a photo.

Im just working out now if I should drain the brake fluid before removing the switch as to not get brake fluid everywhere!
 

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There's no need to drain the system. Just have everything ready, remove the old and install the new. Given that the location of the switch is below the brakefluid reservoir, gravity will make the procedure self bleeding. Have a container of water at the ready to rinse off any fluid that seeps out.

The same test procedure can be used for the second switch; connect the two wires together and see if the stop lamps come on.
 
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