Brakes work better when it's cold and humid (1 Viewer)

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I was hoping to get some input on this strange problem I have been experiencing. My brakes grab noticeably better when the weather is cold and humid (like close to freezing rain kinda weather). It only works for the first 2-3 stops, then the brakes go back to their normal, unremarkable, squishy self (presumably because the system is more warm?). I'd love to have my brakes always work as well as they do on the first couple stops on nasty days. Anyone have any idea why this might be happening? Any ideas on how I could permanently make the system as good as it is when it's cold and humid? Background info. is that I suck all the fluid out of my master cylinder 1-2x a year and top off with a fresh (newly opened) bottle of DOT4, so I don't think there's a moisture problem in the system. Thanks in advance for any input!
 
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Background info. is that I suck all the fluid out of my master cylinder 1-2x a year and top off with a fresh (newly opened) bottle of DOT4, so I don't think there's a moisture problem in the system. Thanks in advance for any input!

Not an answer to your question but there's a lot of fluid in the lines and I wouldn't assume it will "mix" with what's in the reservoir. At least once every few years you should bleed the old fluid out at each brake cylinder so that new fluid gets into the lines.
 

Dave 2000

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A one or a few things.

Water collecting in the system goes directly down to the calipers, bleed the system as changing out what is in the master cylinder simply does not work.

If the car has stood for a couple of days there may well be surface rust on the discs, the pads may grab at this but it is soon rubbed off.

As mentioned earlier the pads may be more suited to cold temperatures, check they are up to snuff.

If you have pistons sticking in calipers then they will heat up the pads and the brakes display an element of fade, left unchecked it will result in warped discs.

regards

Dave
 
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I will bleed the entire system and see how that does. The rear brake shoes are Autozone specials and will be replaced with OEM when they're dead, if not before. The rears are adjusted properly, as is the parking brake. I rebuilt the bellcranks for the parking brake and use the parking brake every time I park since I know operating the parking brake assists in adjusting the rear shoes. I have Powerstop pads and rotors on the front (can't remember which line of pads). They're getting a little low and will need to be replaced soon, but they still have a bit of life left. I had the front calipers off yesterday to diagnose a sound, so I checked out the hardware and general condition of everything, and it appears the pistons and all other parts are moving freely. The sound ended up being a shim that had somehow come off one of the pads and was rubbing on the rotor. I fixed that issue. Also, the front pads and rotors have been upgraded to the larger late-model 80 brakes. The LSPV has been bypassed and removed from the system. I verified on a gravel road that the fronts lock up ever so slightly before the rears. Is OEM going to be the best bet for replacement front pads? I know EBC, Hawk, and Powerstop are all popular options on the forum. I decided the merits of 100 series pad (real or imagined) aren't really worth it. Thank you guys for the input so far.
 
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Not an answer to your question but there's a lot of fluid in the lines and I wouldn't assume it will "mix" with what's in the reservoir. At least once every few years you should bleed the old fluid out at each brake cylinder so that new fluid gets into the lines.

the above,

sucking the fluid out of the master and topping up - you have air in the system unless you bleed the entire system

plus when bleeding you need to do it in the correct order furtherest away from master cyl to closest and do not forget the rear proportioning valve, it gets bled too
 

ppc

M Go Blue
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Once "the brakes go back to their normal, unremarkable, squishy self" what happens if you apply constant pressure on the brake pedal when standing still? Does the pedal slowly sink to the floor?
 
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The brakes have always been unremarkable in this truck (except when cold and humid...). Squishy, but the pedal doesn't slowly drop to the floor. When I upgraded the front brakes to the later model style I also replaced the master cylinder. Bench bled as per instructions. It was a new aftermarket unit (not OEM, unfortunately). I just put together a new 1/2 gallon lawn sprayer with a gauge and cap adapter (poor man's Motive power bleeder) and bought several quarts of DOT4. Gonna try to bleed the system thoroughly tomorrow. Hoping for the best, but experience tells me to expect mediocrity from the system.
 
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Have you changed out the 30 year old soft brake lines with new OEM lines?
Have you rebuilt the 30 year old calipers or the 30 year old rear wheel cylinders using OEM parts?
Are you certain that the 30 year old master and booster have no internal leaks?
Does your handbrake function and get used often along with the internal adjuster mechanism to keep the rear shoes adjusted correctly?
Are you getting proper vacuum to the booster and is the booster check valve functional?
Are you still running 30 year old rotors and drums?
 
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Jon, I am a big fan of your cruiser wisdom and input. The entire brake system has been gone through. I am not in a position financially to use all OEM parts at the moment (I know...an old cruiser is NOT a great choice for a poor boy). I have owned this cruiser for about 7 years. It had 135,000 miles on it when I bought it. That said, the master cylinder was a new (not reman) aftermarket that was bench bled according to proper procedure. The soft lines were new aftermarket all the way around. The calipers were reman aftermarket. The pads are Powerstop, as are the rotors. The rear drums were fine, but the shoes were new aftermarket, as are all the hardware and adjusters and wheel cylinders. The LSPV was bypassed and removed (it was frozen up and leaky). The parking brake bell cranks were frozen up from non-use, so I tore them apart, cleaned and painted and lubricated them and put them all back together. I use the parking brake every time I park so the mechanism gets daily exercise to stay moving and clean (and adjust the shoes). Basically, the entire brake system was gone through and replaced ~6 years ago (excluding the booster, hard lines, and drums). I think the reality is what other posters have suggested; there is moisture and/or air still in the lines somewhere.
 
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Flush the brake fluid and report back. I'm a big fan of the "gatorade bottle" method since its easy and works well.

These are handy to extract fluid from the reservoir:

1605810429538.png
 
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Is there a "go to" big brake kit for the 80? I did a search and it doesn't seem like there is. Sorry, not my intention to jack the thread.
 
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Jon, I am a big fan of your cruiser wisdom and input. The entire brake system has been gone through. I am not in a position financially to use all OEM parts at the moment (I know...an old cruiser is NOT a great choice for a poor boy). I have owned this cruiser for about 7 years. It had 135,000 miles on it when I bought it. That said, the master cylinder was a new (not reman) aftermarket that was bench bled according to proper procedure. The soft lines were new aftermarket all the way around. The calipers were reman aftermarket. The pads are Powerstop, as are the rotors. The rear drums were fine, but the shoes were new aftermarket, as are all the hardware and adjusters and wheel cylinders. The LSPV was bypassed and removed (it was frozen up and leaky). The parking brake bell cranks were frozen up from non-use, so I tore them apart, cleaned and painted and lubricated them and put them all back together. I use the parking brake every time I park so the mechanism gets daily exercise to stay moving and clean (and adjust the shoes). Basically, the entire brake system was gone through and replaced ~6 years ago (excluding the booster, hard lines, and drums). I think the reality is what other posters have suggested; there is moisture and/or air still in the lines somewhere.
That is the background info that should have been included in your first post, as opposed to, "Background info. is that I suck all the fluid out of my master cylinder 1-2x a year and top off with a fresh (newly opened) bottle of DOT4."
I'm not trying to bust your chops, but information like this is invaluable when diagnosing stuff across cyberspace.

That said, 6 years is still a long time before looking into the calipers and other brake system items. Brake performance degrades slowly over time.
Doing a full fluid flush is always a good idea as brake fluid is static in the system. It does not "flow" like fluid in other systems. Brake fluid is supposed to be water clear. The darker it is, the more contaminated it is. It should be flushed yearly to keep corrosion inside the lines and calipers at bay.
 
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Right as usual, Jon. I should have included that information in my initial post. Although you come across as a cantankerous old fart, I appreciate the direct approach. I am a cantankerous fart myself, so I appreciate the brusque candor. The update is that my brakes feel just the same as when I started this mess. I used a new lawn sprayer with a air gauge installed so I wouldn't over pressurize the system and a expandable plug to form a tight seal at the master cylinder. I filled the tank with new fluid, pressurized the system to about 10 PSI, and bled the system: RR, LR, RF, LF. No proportioning valve to speak of. I put three quarts of fluid through the system until it was all flowing clean and clear. I never let the reservoir run dry. In the end, I still get the mushy pedal feel and mediocre brakes. I expect them to act just the same in cold, humid temperatures. I am considering replacing the master cylinder with an OEM one, or rebuilding the existing one with all OEM parts (my preference is this, since it's obviously cheaper). There are no obvious leaks along any of the hard lines, junctions, or bleeders. Everything externally is bone dry. Not sure what else to do at this point...
 
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what year model is your 80?
does it have ABS?

mine is a 95 with No ABS, all original calipers, master cyl etc, the only thing ive changed is the brake lines between the body & diffs as its lifted and pedal is as good as the day I bought it in 97

Try bleeding the old fashioned way with a tube and bottle, thats how I do all my cars & bikes

Im surprised your 80 doesnt have a rear proportioning valve? My parents used to have a 91 80 series with the 3f and it had one

have you confirmed your booster is not losing vacuum pressure? run engine and then turn off and listen for a hissing sound around it
 
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My 80 is a '91 with no ABS and rear drums. My 80 had a rear proportioning valve. It was frozen up and not working correctly, so I removed and bypassed it using OEM parts. The front brakes still lock up slightly before the rear brakes (verified on a deserted gravel road) so I see no need to add a proportioning valve to the system. Typically a bad booster will result in a hard pedal and increased stopping force being required. I don't have that problem. My problem is a low pedal and squishy brakes that don't improve when the pedal is repeatedly pressed. Still seems like air in the system or something, but I bled the bejesus out of it earlier today and noticed no appreciable difference, so I am at a loss.
 
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a failed booster can also give a pedal that goes to the floor nearly and hardly any pressure except when nearly depressed all the way yet very little pressure at that point
 

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