1988 Carrera - Brake Light problem
05-07-2008, 11:04 AM
#16
Nice pictures, they clearly show the right side contacts are burned/damaged from arcing. Have you seen this on most older switches?
I'll cut my old ones open after I install the news ones, will let you know what I find.
I'll cut my old ones open after I install the news ones, will let you know what I find.
Yes, indeed my company is producing and selling the Solution for Faulty BLS's but I am trying to follow forum rules and not make this thread a sales pitch. For those whom are interested they can PM me discreetly.
As far as non-OEM or Cheap Overseas After Market BLS's, with our device this can be avoided:
Cross Section of a BLS, Note right side
I too was skeptical that PAG would tolerate such a design flaw and thought maybe it was a cheap BLS the POs may have put in my baby. Well low and behold it was the OEM BLS. I searched like a insane idiot for a Hi-Performance low pressure BLS's but my Engineer pointed out the issue. Enough said I developed our device.
As far as non-OEM or Cheap Overseas After Market BLS's, with our device this can be avoided:
Cross Section of a BLS, Note right side
I too was skeptical that PAG would tolerate such a design flaw and thought maybe it was a cheap BLS the POs may have put in my baby. Well low and behold it was the OEM BLS. I searched like a insane idiot for a Hi-Performance low pressure BLS's but my Engineer pointed out the issue. Enough said I developed our device.
05-14-2008, 04:08 PM
#19
A ban saw was used to disect the pictured damaged BLS. Be safe the BLS is tiny, don't want to lose a finger in the process.
I would not worry about the BLS's inexpensive or OEM, they are not the issue. All BLS's are basic hydraulic pressure design. But once the contact is damaged, it is irreversable.
It was the over engineering design by PAG and other Manfacturers of the amperage that melts the internals of the BLS's. A 5 year run is quite good with an OEM BLS but eventually the arcing will progressively harm the BLS and result in slow brake lights. My hope is for those lucky ones that their baby's Brake Lights continue to work without delay.
However, a final fix is arc suppression. I am a the type that wants to know why a component failed and fix it if possible.
I would not worry about the BLS's inexpensive or OEM, they are not the issue. All BLS's are basic hydraulic pressure design. But once the contact is damaged, it is irreversable.
It was the over engineering design by PAG and other Manfacturers of the amperage that melts the internals of the BLS's. A 5 year run is quite good with an OEM BLS but eventually the arcing will progressively harm the BLS and result in slow brake lights. My hope is for those lucky ones that their baby's Brake Lights continue to work without delay.
However, a final fix is arc suppression. I am a the type that wants to know why a component failed and fix it if possible.
05-14-2008, 05:41 PM
#20
Rennlist Member
Our shop experience was quite different in that the original switches would usually last the life of the master cylinder (between 110K-140K miles), and on the occasional car that we had to put switches in, because of excessive pressure on the pedal needed to light the brake lights, the car was usually somewhere above 80K miles, and always older than 10 years. Even with our very large clientele this repair was not a regular (monthly) event. We did switches often enough to have a pair of three-pole, and a pair of two-pole, switches in stock, but at times 6-months could pass without doing the job. Also, remember that those switches interact with the brake pressure warning light on the dash, and any modification to the switch circuit must be engineered to; (1) not give false warnings, or (2) not work at all in the event of a system failure.
Last edited by Peter Zimmermann; 05-14-2008 at 08:16 PM.
05-15-2008, 04:07 AM
#21
Burning Brakes
Join Date: Nov 2005
Location: CA
Posts: 798
Likes: 0
Received 0 Likes
on
0 Posts
The issue with our hydrolic brake switch is not that it always dead, but the problem is that it comes on slow, too slow after time. The first time I saw the car behind me screeched rubber, I thought some silly driver didn't watch my behind. Seeing several more agressive braking behind me, I took my car to the front of an all glass building to watch my brake light while stepping on the brake. I found that my brake lights came on but only when my pedal is all the way down almost to the floor. Replacing brake switches will fix the problem, but for only several months in most cases.
05-15-2008, 10:00 AM
#22
Summary of what I've learned and heard so far, MANY of us have had issues with the Brake light switches in the Carrera cars. Most seem to agree that changing the switches fixes the issue. But, others claim that replacing the switches often only solves the problem for a short while.
DRACO posted the best insight into this issue I've heard so far: the pictures he posted of the bad switch he replaced clearly shows burned contacts from arcing. I think he is really onto something and may have found the issue. It seems that the current draw through the switch (most likely 5-8amps, but I will measure this soon) causes the switch contacts to arc. One simple solution would be to simply place a relay into the brake light circuit to activate the lights. Then wire the relay coil to the stock switches, thus reducing the current through the switches to 1/2 amp or less. I plan to do this in my car. One down side is the relay introduces a slight delay because it takes 1/10th of a second or so to pick. (But as it is now my lights don't even come on under light braking.)
I just received 2 new switches and I'll be replacing mine and adding the relay soon. I also plan to cut open the 2 old switches (just as DRACO did) to see if indeed I have burned contact(s) as well. I will post pictures soon.
The other solution would be to fit the car with a mechanical brake light switch at the pedal but this requires more wiring and mounting of the new switch. I'm going to go the first route and simply try new switches with a relay.
The other issue with the way the stock switches are wired is that they cut the hot side of the circuit rather than the ground side. Switches wired to the ground side result in less arcing than switches wired to the hot side. I recall this from Electrical 101 class but don't recall why this is.
DRACO posted the best insight into this issue I've heard so far: the pictures he posted of the bad switch he replaced clearly shows burned contacts from arcing. I think he is really onto something and may have found the issue. It seems that the current draw through the switch (most likely 5-8amps, but I will measure this soon) causes the switch contacts to arc. One simple solution would be to simply place a relay into the brake light circuit to activate the lights. Then wire the relay coil to the stock switches, thus reducing the current through the switches to 1/2 amp or less. I plan to do this in my car. One down side is the relay introduces a slight delay because it takes 1/10th of a second or so to pick. (But as it is now my lights don't even come on under light braking.)
I just received 2 new switches and I'll be replacing mine and adding the relay soon. I also plan to cut open the 2 old switches (just as DRACO did) to see if indeed I have burned contact(s) as well. I will post pictures soon.
The other solution would be to fit the car with a mechanical brake light switch at the pedal but this requires more wiring and mounting of the new switch. I'm going to go the first route and simply try new switches with a relay.
The other issue with the way the stock switches are wired is that they cut the hot side of the circuit rather than the ground side. Switches wired to the ground side result in less arcing than switches wired to the hot side. I recall this from Electrical 101 class but don't recall why this is.
Last edited by scarceller; 05-15-2008 at 10:31 AM.
05-15-2008, 10:53 AM
#24
Addict
Could it be that air is trapped in the master cylinder just in front of the switches that causes a delayed switch activation. The air is compressing instead of the switch. Air in the system can cause a delay in the pads if it is trapped in the slaves, why not the switches in the master.
BTW there is already a mechanical switch on the pedal cluster.
BTW there is already a mechanical switch on the pedal cluster.
05-15-2008, 11:21 AM
#25
Doug,
I have an 84 and I do not have a mechanical switch on the cluster. The car even has factory Cruise Control. What year is your car and what options might it have?
Also worth noting is that the 84 wiring schematic only shows the switches on the Master Cyl.
I have an 84 and I do not have a mechanical switch on the cluster. The car even has factory Cruise Control. What year is your car and what options might it have?
Also worth noting is that the 84 wiring schematic only shows the switches on the Master Cyl.
Could it be that air is trapped in the master cylinder just in front of the switches that causes a delayed switch activation. The air is compressing instead of the switch. Air in the system can cause a delay in the pads if it is trapped in the slaves, why not the switches in the master.
BTW there is already a mechanical switch on the pedal cluster.
BTW there is already a mechanical switch on the pedal cluster.
05-15-2008, 11:25 AM
#26
Addict
mine is the '88 and has cruise. I believe that switch is the cruise off switch. I went to replace it when I didn't have break lights. For some reason, when I didn't have break lights, I didn't have cruise. It's a crazy mixed up world.
05-15-2008, 11:38 AM
#27
Doug,
I suspected you have Cruise, in 84 even with cruise I have no switch on the cluster. The 84 car uses the same Master Cly switches for the cruise circuit, it clearly shows this in the schematic for 84&85.
I don't have the 88 schematic but it seems they changed the design for the cruise and put a switch on the cluster. If I had your car I would simply use that mechanical switch to pick a relay and activate the Brake lights. I would then just eliminate the 2 switches on the Master Cyl. I would preffer a mechanical switch on the pedal instead of the pressure switches. I bet the pedal switch picks (closes) with the slightest movement of the brake pedal, most likely it picks even before the slack is taken up on the rod that connects the brake pedal to the master cyl. If this is the case you would have the brake lights on way before pressure even builds up in the brake system.
I suspected you have Cruise, in 84 even with cruise I have no switch on the cluster. The 84 car uses the same Master Cly switches for the cruise circuit, it clearly shows this in the schematic for 84&85.
I don't have the 88 schematic but it seems they changed the design for the cruise and put a switch on the cluster. If I had your car I would simply use that mechanical switch to pick a relay and activate the Brake lights. I would then just eliminate the 2 switches on the Master Cyl. I would preffer a mechanical switch on the pedal instead of the pressure switches. I bet the pedal switch picks (closes) with the slightest movement of the brake pedal, most likely it picks even before the slack is taken up on the rod that connects the brake pedal to the master cyl. If this is the case you would have the brake lights on way before pressure even builds up in the brake system.
05-15-2008, 11:41 AM
#28
Instructor
Join Date: May 2008
Location: Maple Glen, PA
Posts: 141
Likes: 0
Received 0 Likes
on
0 Posts
electrical experience = yes
Porsche experience = NO
scarceller: Ans could be that the voltage drop is lower on the return side, chances of arcs are reduced with lower v (figure small drops across terminals, larger ones across the lamps, and the potential on the return path would be 0 v (only when path completed)- but if there is air in the hot side path (not a positive contact/contamination), you could still get arcing up stream there away from the switched return. Current'd be the same thu-out of course.
Draco: just curious, if you reply, my eyes aren't so good and you obviously did your research (re: pics), but are those deposits (something added) or cavities (removed material), or burns on the RH contact? Do those contacts move/plunge?
Any e-types know why a current limiter wouldn't work if current is the issue?
I dig the electrical side, but as a pcar neophyte, you can ignore me and I'll walk away. (home on Drs orders so your stuck w/me).
cheers,
Dan
Porsche experience = NO
scarceller: Ans could be that the voltage drop is lower on the return side, chances of arcs are reduced with lower v (figure small drops across terminals, larger ones across the lamps, and the potential on the return path would be 0 v (only when path completed)- but if there is air in the hot side path (not a positive contact/contamination), you could still get arcing up stream there away from the switched return. Current'd be the same thu-out of course.
Draco: just curious, if you reply, my eyes aren't so good and you obviously did your research (re: pics), but are those deposits (something added) or cavities (removed material), or burns on the RH contact? Do those contacts move/plunge?
Any e-types know why a current limiter wouldn't work if current is the issue?
I dig the electrical side, but as a pcar neophyte, you can ignore me and I'll walk away. (home on Drs orders so your stuck w/me).
cheers,
Dan
05-15-2008, 12:02 PM
#29
Dan,
I also have lots of electrical experience and education (EE educated more than 20 years ago so some theory a little rusty).
One more reason for arcing is that Incandescent lamps have an initial current draw when they are first turned on that can be 2 times or more the draw of the bulb when lit. This is why switches that turn these bulbs on and off a lot tend to burn and pit.
Putting a current limitter may not be a good idea because it will cause the bulb to take longer to get lit.
I also have lots of electrical experience and education (EE educated more than 20 years ago so some theory a little rusty).
One more reason for arcing is that Incandescent lamps have an initial current draw when they are first turned on that can be 2 times or more the draw of the bulb when lit. This is why switches that turn these bulbs on and off a lot tend to burn and pit.
Putting a current limitter may not be a good idea because it will cause the bulb to take longer to get lit.
electrical experience = yes
Porsche experience = NO
scarceller: Ans could be that the voltage drop is lower on the return side, chances of arcs are reduced with lower v (figure small drops across terminals, larger ones across the lamps, and the potential on the return path would be 0 v (only when path completed)- but if there is air in the hot side path (not a positive contact/contamination), you could still get arcing up stream there away from the switched return. Current'd be the same thu-out of course.
Draco: just curious, if you reply, my eyes aren't so good and you obviously did your research (re: pics), but are those deposits (something added) or cavities (removed material), or burns on the RH contact? Do those contacts move/plunge?
Any e-types know why a current limiter wouldn't work if current is the issue?
I dig the electrical side, but as a pcar neophyte, you can ignore me and I'll walk away. (home on Drs orders so your stuck w/me).
cheers,
Dan
Porsche experience = NO
scarceller: Ans could be that the voltage drop is lower on the return side, chances of arcs are reduced with lower v (figure small drops across terminals, larger ones across the lamps, and the potential on the return path would be 0 v (only when path completed)- but if there is air in the hot side path (not a positive contact/contamination), you could still get arcing up stream there away from the switched return. Current'd be the same thu-out of course.
Draco: just curious, if you reply, my eyes aren't so good and you obviously did your research (re: pics), but are those deposits (something added) or cavities (removed material), or burns on the RH contact? Do those contacts move/plunge?
Any e-types know why a current limiter wouldn't work if current is the issue?
I dig the electrical side, but as a pcar neophyte, you can ignore me and I'll walk away. (home on Drs orders so your stuck w/me).
cheers,
Dan
05-15-2008, 01:52 PM
#30
Instructor
Join Date: May 2008
Location: Maple Glen, PA
Posts: 141
Likes: 0
Received 0 Likes
on
0 Posts
scarceller,
Thanks for the wisdom. Same here on the ed/yrs and rust. Amazing how basic stuff can rust (theory) and go out the window depending on the application too. I see your point regarding the current if the bulbs need to warm up. I always love puzzles tho and couldn't resist 'barging' in.
- I appreciate it,
Dan
Thanks for the wisdom. Same here on the ed/yrs and rust. Amazing how basic stuff can rust (theory) and go out the window depending on the application too. I see your point regarding the current if the bulbs need to warm up. I always love puzzles tho and couldn't resist 'barging' in.
- I appreciate it,
Dan