Hydraulic brake light switch

Anyone having issues with hydraulic brake light switches ? Looking for comments or suggestions I have had two failures so far and am installing my third switch. First was part of frame mount master/booster kit from Speedway and the end blew out of the switch shortly after installation. The second was from Jegs along with a wiring harness, worked great for 3 or 4 thousand miles and now works intermittently. I hate not having dependable brake lights. If this third try fails I'll go to some type of mechanical switch but have been reluctant to do so because this hydraulic installation is so clean.

The one in my wagon is quite flimsy. The little brass female sockets that hold the wires were brittle and broke so that they won't hold the wires, which are now held in place by alligator clips and electrical tape. I ordered a replacement switch from RockAuto.com. It's a Standard Motor Products brand and the brass sockets seem more robust.

A previous switch, I couldn't get to stop leaking around the threads, so I'm reluctant to replace the one in there, even with its bad sockets.

We had the one on the White Beast that was threaded into the end of the proportioning valve work fine for a number of years with no issue. Then one night,... as we were returning home from the Saturday evening car show at about 9:30pm at night that same damned hydraulic brake light switch decided to short out and fail while driving down a semi busy road..!!!! Aw shet..!!! Now what?
Drove the remaining 7 miles home very slowly and carefully with no working brake lights or turn signals. The next morning as we got to examining it it turns out that the switch had failed inside and was allowing brake fluid to seep up and around the two-pronged electrical contacts that the harness plugged into. So after we replaced that switch..... that too failed within the year due to one of the electrical prongs coming loose in the switch. So now we are currently on brake switch number 3 and so far we will see how long that lasts.

Larry

This is the mechanical switch (from Watson's Street Works) that I ended up using. Seems pretty good. Of course, your brake lights come on the instant you touch the pedal.... no pressure needed.

https://watsons-streetworks.com/product/the-best-brake-switch/

I had a problem with switches not lasting. Seems that the dot 5 brake fluid was the problem. After about 15 years I flushed the system and used dot 3 with the old switch and it has worked properly for the last 5 years.

Yup. I can't officially get my truck on the road, due to no brake lights. I was thinking there was something wrong with my master cylinder, but now I'm going to buy switch number 3.

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tnestell said:

..... Seems that the dot 5 brake fluid was the problem........

Click to expand...

Precisely...!! after we got his truck back on the road after several years of storage..doing the usual flush of fliuds...last thing we did was to rebuild the front and rear brake calipers and flush the brake lines ....he decided to use Blue DOT 5 racing fluid ...same stuff he used in his motorcycles..it was on hand and had plenty of it was a bright color making it easy to know when lines were flushed and bled.

every thing worked fine...for bout year and a half...then came that night driving home from car show......had a guy pull up next to us and point to the rear if truck...Huh?....Say you know you dont got no brake lights back there..? What..? pulled over into a parking lot...but too dark to see much anything so drove on home. no brake lights, turn signal or hazards..... kept thinking some joker was going to rear end us despite being in a big White truck.


it appears that DOT 5 fluid has somingthing in it that is not compatible with brake switchs and destroys them internally...once we flushed with DOT 3 everything has worked fine (fluid wise) So no DOT 5 and you will be ok.


Larry

I generally use DOT 4 fluid... My truck still has the OEM switch from 1950 as best I can tell... In any case I've had the truck for 10 years and about 50,000 miles...The
switch just keeps working with zero problems. The OEM speedo, now that was a weak sister...Overhauled twice... It now lives on the shelf...

Brake fluid is one of those substances where trade-offs are taken into consideration. Dot 3 was traditionally specified for regular passenger vehicles because it is more stable and will absorb less water and "wear" better over time, requiring less frequent fluid changes, but it is not as good for high heat situations. The only real benefit of Dot 4 is that it has a higher boiling point, so it is typically specified for higher performance braking systems where heat is more of a concern.

Here's a good tech article on brake fluids: http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

Lookout Ranch said:

Brake fluid is one of those substances where trade-offs are taken into consideration. Dot 3 was traditionally specified for regular passenger vehicles because it is more stable and will absorb less water and "wear" better over time, requiring less frequent fluid changes, but it is not as good for high heat situations. The only real benefit of Dot 4 is that it has a higher boiling point, so it is typically specified for higher performance braking systems where heat is more of a concern.

Here's a good tech article on brake fluids: http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

Click to expand...

When I put the big brakes (11"), new rubber lines and rebuilt the master cylinder on my Willys I went with DOT 5 brake fluid. When I rebuilt my master cylinder it had rust in it, as you know rust comes from water. I went with DOT 5 because my master clyinder is under my Willys where all the water is. I've been using DOT 5 for at least 16 years with no problems other than needing a brake light switch every 6-7 years.

I disagree with your statement about DOT 3 not absorbing water, there are good reasons to use DOT 3 but it's a magnet for water. If you still have the original master cylinder under the floor in your Willys, it will get water in it. From the article you linked...

"Non-silicone-based brake fluid (DOT 3) is strongly hygroscopic, meaning that it naturally absorbs water from the humidity in the air. That is why the shipping container and the brake reservoir have to function as a barrier to the moisture in the air reaching the brake fluid. Modern brake reservoirs are thick enough, and the bellow seals on top function well enough, to provide a long life to the fluid once in use."

Modern brake cylinders is NOT us if you have the stock stuff under your Willys.

From the article...

DOT 3 fluids are usually glycol ether based, but as stated earlier, that is not because they are required to be. The brake fluid industry has determined by consensus that glycol ether fluids are the most economical way to meet the requirements.


DOT 4 fluids are also glycol ether based, but have a measure of borate esters added for improved properties including increased dry and wet boiling points. A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3.
The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption.

The original DOT 5 fluid specification was expected to be fulfilled by silicone based (SSBF) composition. It was designed for use in applications where its resistance to water absorption (and therefore low corrosion) was desired - like in military equipment. It has also found use in antique cars because it does not dissolve paint finishes.

64 Traveler said:

When I put the big brakes (11"), new rubber lines and rebuilt the master cylinder on my Willys I went with DOT 5 brake fluid. When I rebuilt my master cylinder it had rust in it, as you know rust comes from water. I went with DOT 5 because my master clyinder is under my Willys where all the water is. I've been using DOT 5 for at least 16 years with no problems other than needing a brake light switch every 6-7 years.

I disagree with your statement about DOT 3 not absorbing water, there are good reasons to use DOT 3 but it's a magnet for water. If you still have the original master cylinder under the floor in your Willys, it will get water in it. From the article you linked...

"Non-silicone-based brake fluid (DOT 3) is strongly hygroscopic, meaning that it naturally absorbs water from the humidity in the air. That is why the shipping container and the brake reservoir have to function as a barrier to the moisture in the air reaching the brake fluid. Modern brake reservoirs are thick enough, and the bellow seals on top function well enough, to provide a long life to the fluid once in use."

Modern brake cylinders is NOT us if you have the stock stuff under your Willys.

From the article...

DOT 3 fluids are usually glycol ether based, but as stated earlier, that is not because they are required to be. The brake fluid industry has determined by consensus that glycol ether fluids are the most economical way to meet the requirements.


DOT 4 fluids are also glycol ether based, but have a measure of borate esters added for improved properties including increased dry and wet boiling points. A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3.
The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption.

The original DOT 5 fluid specification was expected to be fulfilled by silicone based (SSBF) composition. It was designed for use in applications where its resistance to water absorption (and therefore low corrosion) was desired - like in military equipment. It has also found use in antique cars because it does not dissolve paint finishes.

Click to expand...

As I said, brake fluids involve compromises. Further reading on the topic:
https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5

Lookout Ranch said:

As I said, brake fluids involve compromises. Further reading on the topic:
https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5

Click to expand...

Yup, kind of what I said. My point was DOT 3 is a magnet for water NOT that it's a bad fluid.

I made a decision that works for me and that sure does not include anyone else. Once I move my master cylinder to the firewall and get the disc brakes on the front if not both axles I'll probably run different fluid.