The message to which you are about to reply is shown first. GO TO REPLY FORM



 VIEW    REPLY TO THIS MESSAGE Replies to this message will be emailed.    PRINT   SAVE 

Working on brake system differential pressure switch (brake failure light) long 200 1984

1984 DL, sunburned ruby red with 325K...



The failure light came on and no amount of stomping would reset it, yet both circuits have no leaks I can see. Against all recommendations I could find I decided to see if I could reset it through the switch hole.

Before loosening the switch (14mm 6pt) I used a continuity tester to verify it was still switched on - in the failure mode. Then, after removing the switch body, spring and pin this was staring at me via bifocals, flashlight and mirror:

Looked like a thing you'd unscrew with a standard screwdriver. But after screwing with it for a while and still seeing the same threads exposed, I decided to stick a hook in and pull it out:

Got all the switch parts out so I could now make out the shaft between the two actuator pistons, I guess are in the ends keeping the brake fluid where it belongs. No threads on that last part, but why it has a slot I have no idea! Cleaned up the switch and used a few Q-tips to clean the opening in the junction box. The probe shown above the switch parts in this photo is how I determined, with my continuity buzzer, the shaft was insulated.

I could see a dimple where the switch contact driven by spring pressure might have dented what looked like shrink sleeve over a steel rod:

Put it all back together, and like the probe predicted, no more brake failure light. Cliff is right -- I spent 10 minutes trying to start those nylon threads back into the junction block -- the spring fights you.

Here's my theory. When I changed a caliper a month ago I upset the balance temporarily. The piston moved, but the switch was dirty inside and took a month to make contact. The spring tension in the switch kept it stuck until I removed the switch, allowing the old piston springs to once again center it.

Either that, or that dimple is worn deeply enough to break through even though I could not with a sharp probe gently applied. Less likely I believe.

Hope I never have to replace this octopus.

--
Art Benstein near Baltimore






USERNAME
Use "claim to be" below if you don't want to log in.
PASSWORD
I don't have an account. Sign me up.
CLAIM TO BE
Use only if you don't want to login (post anonymously).
ENTER CAPTCHA CODE
This is required for posting anonymously.
OPTIONS notify by email
Available only to user accounts.
SUBJECT
MODEL/YEAR
MESSAGE

DICTIONARY
LABEL(S) +
IMAGE URL *
[IMAGE LIBRARY (UPLOAD/SELECT)]

* = Field is optional.

+ = Enter space delimited labels for this post. An example entry: 240 muffler


©Jarrod Stenberg 1997-2022. All material except where indicated.


All participants agree to these terms.

Brickboard.com is not affiliated with nor sponsored by AB Volvo, Volvo Car Corporation, Volvo Cars of North America, Inc. or Ford Motor Company. Brickboard.com is a Volvo owner/enthusiast site, similar to a club, and does not intend to pose as an official Volvo site. The official Volvo site can be found here.