Brake lites stay on when hot.

[Wild and Free]

Have had the issue of my brake lites staying on when the engine was hot in warm weather. Has been going on for about 3 years or more and I always thought it was due to a misadjusted or sticky switch. I even had intermittent cruise control kicking out on its own so I thought this was the problem. Tried to adjust switch @ brake pedal but there is really no adjustment on a 3rd gen other than maybe bend the bracket which is really thick.

 

Long story short I always had to pull upon the brake pedal when I shut the pickup off to get the lites to go out just became a habit but when my wife and I go to the water she does the trailering and I am on the boat and have to holler at her to make sure brake lites are off.

 

Got tired of that so decided to look into it. I had noticed from my steering gear swap and just normal checks that the power steering pump always had an abnormal amount of pressure when cracking open the lid even when cold so I am thinking this had something to do with it. There is a breather built into the cap and the dipstick is integral to it as the breather passages go through it.

Popped the dipstick out of the cap and found there is a rubber check valve in between the cap and dipstick which looked good. cleaned everything up and nothing was dirty or plugged so figured the rubber must have swelled and was putting too much pressure on the breather hole.

The cap itself has a couple of tabs that act as spacers molded into it that the rubber check sits against they were maybe 1/16" high so I ground them off flush and put it all back together and so far it has taken care of my issue the last couple time I have driven it. today will be the bigger test going to be hot and pulling the pontoon to the water so if it works today I know I found the fix.

[Mopar1973Man]

Following... I'm curious.

[dripley]

Same here.

[Wild and Free]

How I wound up with the idea of it being the power steering pump breather cap was last weekend I had gotten home and noticed the brake lites were still on so I popped the hood and popped the cap off the pump for kicks and giggles and there was a lot of pressure in the reservoir, after popping the cap off I noticed that the brake lites went out which put me into the mode of whats wrong with the breather in the cap.

 

Like I said it has solved the issue the last couple time I have driven it but it was cooler and short trips since doing it but today will be the true test.

Edited July 31, 2016 by Wild and Free

[Wild and Free]

Brake Lights did not stay on once today, looks like my little tweaking on the cap did the trick.

Went out and popped the cap just a few minutes ago and there was a very slight positive pressure which would be normal now but nothing excess like before it would about launch the cap out of my hand if I didn't have a good grip when loosening it.

Edited July 31, 2016 by Wild and Free

[dripley]

Thats one for the memory banks there. Glad you found the problem. You need to get that in a trouble shooting guide somewhere.

[Wild and Free]

I should have taken pics but didn't think about it until after I was done. Hardest part was prying the plastic dipstick part out of the plastic cap without breaking anything, you know how plastic can be.

Edited July 31, 2016 by Wild and Free

[dripley]

I would have thought the hard part was figuring out the power steering vent cap was causing the brake lights to stay on.

[AH64ID]

Very interesting. 

 

The power steering box pump pressure is a known/common issue on 3rd gens but I've never heard of it effecting the brake light. I'm not even sure how it's possible based on sensors and such. 

[Haggar]

AH and Drip,

 

I agree I don't think I would have made the connection.  Great job Wild!

 

AH, I guess it didn't really "keep the brake light on."  That was a symptom of the pedal not returning fully.  With the reservoir holding back pressure on the drain from the spool valve, it could not travel fully to return.  The return springs could not force it fully back. This was not enough "residual" pressure to apply the brakes, but the spool could not fully return.  (though it eventually could have gotten to that point.... a plugged return line on the hydroboost will eventually fully engage the brakes.)

 

Since there was some air in the system at the top of the reservoir, it could work for awhile cold, but the volumetric expansion of the fluid as it heated reduced the air volume and increased the back pressure. 

 

Glad you found it.

[AH64ID]

still very interesting since these PS pumps are known to build pressure. 

[Wild and Free]

1 hour ago, Haggar said:

AH and Drip,

 

I agree I don't think I would have made the connection.  Great job Wild!

 

AH, I guess it didn't really "keep the brake light on."  That was a symptom of the pedal not returning fully.  With the reservoir holding back pressure on the drain from the spool valve, it could not travel fully to return.  The return springs could not force it fully back. This was not enough "residual" pressure to apply the brakes, but the spool could not fully return.  (though it eventually could have gotten to that point.... a plugged return line on the hydroboost will eventually fully engage the brakes.)

 

Since there was some air in the system at the top of the reservoir, it could work for awhile cold, but the volumetric expansion of the fluid as it heated reduced the air volume and increased the back pressure. 

 

Glad you found it.

 

Yep this is exactly what was going on.