brake lights diagnostics

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Gypsie
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brake lights diagnostics

Post by Gypsie » Fri May 06, 2011 10:23 am

1980 Vanagon:

I have been having trouble finding out why my brake lights won't come on. I have checked bulbs and fuses and there's no issue there.
Some conditions that may be germane:
-Rear brakes have about 2000 miles on new drums and shoes that worked good after replacement. I ran out of time to R&R front components.
-Bus sat for a year.

Let me throw a couple symptoms at you:
-Braking is 'slippery" it takes quite a bit of pressure to make things really engage to stop the vehicle. Pumping helps a little.

As I push on the brake pedal there is a noticeable point when I can feal something bottoming out but there is still pedal travel.

Q: do both of the master cylinder brake light switches need to engage to illuminate the lights. In other words if I have a faulty circuit (air in the lines or old non sealing plunger cup) would that prevent the brake lights from lighting?

I was planning on doing a full bearing/brakes once over on the front end but am thinking to buy some time I would just bleed out the system to eliminate the air in the line potential.

I am leaning toward replacing the master cylinder but would like to stop the $$$ bleeding.
So it all started when I wanted to get better gas mileage....

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airkooledchris
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Re: brake lights diagnostics

Post by airkooledchris » Fri May 06, 2011 11:23 am

if I remember correctly the brake light switch is right on the back of the master cylinder behind/below the instrument cluster. I think it's easier to see from above with the top off of the cluster with your hands up under the dash.

when my brake lights stopped working, this was the cause. im not sure how to test it, if you can, but I swapped mine out with another and it started working again.

FWIW, good luck.
1979 California Transporter

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Gypsie
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Re: brake lights diagnostics

Post by Gypsie » Fri May 06, 2011 11:28 am

It appears that on the Vanagon there are two switches on the master cylinder. Perhaps I am misunderstanding the diagram or the devices on the MC.

More investigation is needed.

I did go through the electrical connections because I did some deep fuse box area work when I did a recent rebuild and installed a grip of gauges. I thought I may have bumped something. Maybe a ground? Ooh... maybe a ground in the engine bay area.....Ooooh...
So it all started when I wanted to get better gas mileage....

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dingo
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Re: brake lights diagnostics

Post by dingo » Fri May 06, 2011 3:11 pm

just stick your Voltmeter + on the brake light switch....should read 12V...if not, replace switch
'71 Kombi, 1600 dp

';78 Tranzporter 2L

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Re: brake lights diagnostics

Post by dtrumbo » Fri May 06, 2011 4:51 pm

Gypsie wrote:Q: do both of the master cylinder brake light switches need to engage to illuminate the lights.
No. If either of the switches close, the brake lights will illuminate. Further, if only one closes and not the other, the brake warning light on the dash as well as the brake lights on the rear of the van will illuminate.

You might actually have three problems.

1.) Air in the system.

2.) A sticky wheel cylinder. (I had the same symptoms as you with regard to the "bottoming out" and replacing the rear wheel cylinders fixed it).

3.) Bad master cylinder brake switches. (These are notorious for failing for absolutely no reason).

Bleed the brakes, not the wallet.
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

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