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Discussion Starter · #1 · (Edited)
544 Brake lights staying on.

I adjusted my brakes a few weeks ago during 70 degree weather. Everything was fine. I took the car out today, 100 degrees, and the brake lights will not go out. The brake pedal is very firm. Could it be the weather? Any Ideas?

Update: The car sat in the garage for two hours (maybe 15 degrees cooler) and now the brake lights are functioning fine. And the pedal feels normal.
 

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Discussion Starter · #3 ·
Looked open last night. I checked again this morning (better light) and used a thin gauge wire to make sure. It's open.

And, with my luck, while I was under the hood I decided to check the water in the radiator. The radiator cap came out in three pieces. I saved the old Stant that was on previously. Threw it on temporarily. Is there such a thing as a "good" radiator cap?

Another hot one today. I need to run the car. I'll see what happens with the lights.
 

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The usual suspects seem to have a variety of brands of caps, recommend one from Iroll, Ipd, VP auto parts or the other Volvo suppliers.
 

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Discussion Starter · #5 ·
The cap that broke was the one Skandix sells. Made in England. It has a plastic center piece and that's what broke.

Update on the brakes. Today, I took it out on the same trip. I'm helping a friend hang Sheetrock. 20 minutes each way. All of it city driving. I was checking the brake light using the reflections off parked cars and storefront windows. It was fine the entire time. I back it up my driveway into the garage and the lights stayed on. Yesterday, I tried rolling the car forward and hitting brakes in an attempt to extinguish the lights. But, it didn't work. Today, I drove the car forward with some speed and hit the brakes hard. Backed it into my garage and the lights were out. Hmm? I also always got a "clunk" sound the first time I hit the brakes after changing direction. i.e. forward to reverse or reverse to forward. Normal?
 

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I'm no big expert (in fact, I've never investigated this on the PV), but I believe that the 544 has a hydraulic brake pressure switch. Either the switch is defective, you have added too much brake fluid or, your master cylinder is on its way out. Perhaps your push rod is too tight. If not the switch, the master likely has an internal bypass valve which is being blocked, resulting in internal pressure buildup.
 

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gb;

Of course your 544 (unless changed to one of my super groovy Pedal Position Sensing Brake Light Switch Kits) has a Hydraulic Pressure Sensing switch, and these are known for having reliability issues, but typically with the symptoms are that they don't close to enable Brake Lights to come ON...

...your opposite symptoms "...BL will not go out...firm pedal, and...temperature related" sound more like a residual or pre-bias pressure is being held by Master Cylinder, and this is holding the pressure sensing BLSw closed!...it sounds to me like this has something to do with the holding-valve (not certain this is correct terminology for this component!) and equalization hole in the MC...this is the valve which holds a little prebias pressure in the system to minimize pedal lost motion/dead travel in drum brake systems (and which must be removed when changing to disc systems), as these do not want this pre-bias pressure, else they would drag...544 experts please chime in and help, and give details here, as my info is strictly what I remember from my readings of the 544 forums!

Also...have you changed to DOT5 silicon brake-fluid which is known for more thermal expansion, and which could therefore be causing this pre-bias?

Cheers
 

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Discussion Starter · #8 ·
Fluid I use is labeled Dot 3 & 4 Synthetic. So, I guess I can rule that out. It's still too hot here to play around with the car. I'm just hoping it is a heat related issue. I never drive when it's this hot. It's just I promised my friend I'd lend a hand and the 544 is my only car. My first course of action, when it cools down, is going to be readjusting the brakes a little "looser" to get more pedal travel.
 

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Discussion Starter · #9 ·
Update. I never did anything to the car. Life and other projects got in the way. Well, I needed to use it today (It's great living where you can walk or bicycle everywhere you need to go). Anyhow, it was raining and 20 degrees cooler. No problem with the lights. I'm calling it heat related. I was a conveyor mechanic for 30 years and learned one thing: "If it ain't broke, don't fix it." Thanks for all the input.
 

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As far as radiator caps are concerned, there are a variety of offerings from Summit Racing, and I would assume, Jeg's. There are some that offer significantly higher pressures than the average, and are also available to allow coolant to flow back into the radiator as the system cools ( assuming you have a coolant recovery container. )
 
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