Good afternoon all,

I am hopeful to get some help with this problem so thank you in advance.

I have a 2005 Chevy Express 2500 4.8 v8, and whenever it is below freezing the brakes are uncomfortably spongy. I can pump them a few times and they will firm up. But the difference on a warm day is drastic. The brakes still work but I have to push the petal a lot farther down and ifs often slow to return when I release the pedal. Both the brake fluid and the power steering fluid are new. Any way wondering if anyone has any ideas?

thank you for your time,

Edward

Sounds like this van has hydroboost, right? If so, check the weep hole between the booster and the master cylinder for any sign of leakage.

All of the following assumes that it brakes in a straight line on a smooth, dry, and level surface, that the pads/shoes are all in reasonably new condition, like over half their thickness remaining, and that the brake lines are in good condition with no bulges/cuts/leaks/etc.:

This van has over 120,000 miles on it, right? If so:

If the brake fluid'* life is unknown, I'd flush it all out and see if that helps.

If that doesn't help, I'd replace the master cylinder with a quality unit. Depending on how it was used in its previous live(*), it might be well beaten and/or have sketchy repairs and/or iffy parts hidden, so may as well get it over with.

After that, it may well be the ABS module, but that'* expensive, so that'* why it is last on the list.

Hello,

Yes it is a hydro boost. I changed the master cylinder and calipers and pads about 3 years/40k miles ago, and the seemed to be in good shape when I last looked at them a few weeks ago. It’* not obviously leaking from the seal between the master cylinder and the brake booster, but when I put my finger there I do get a drop of fluid on them. The brake fluid in the reservoir never needs to be topped off.

I’m guessing that there’* a seal there’* that’* a problem.

Edward

Ah, didn't know those had been changed already.

If you used quality parts, and it has been performing well since then up until this started, then it'* probably not that.

What manufacturer of parts did you use?

Were they new or remanufactured?

What kind of fluid is coming out of the weep hole?

When you replaced all this stuff, what process did you use to bleed everything?

I don’t remember what manufacturer, but they were new. Would have been from auto zone or advance auto

I think it’* power steering fluid, though if it is leaking it’* very slow as I haven’t noticed any change in the reservoir. One or more of the seals in the hydro booster?

I haven’t changed the brake lines but I’m guessing one of the last owners did as they are a lot less corroded than everything else underneath this van.

thank you
Esward

forgot to mention bleeding. I did that with a helper, one out pumping the pedal and the other loosening and tightening the bleeder valve.

thanks

I have had (and also seen) less-than-stellar luck with store brand parts like this. Not condemning them, but yeah less-than-stellar. Let'* just say: There'* a good reason for lifetime warranties on a lot of those.

If the drip is power steering fluid, and it is rare, the hydroboost unit is probably okay, just keep an eye on it.

Glad you bed the brakes that way. Takes at least one variable out of the equation.

Assuming all the other stuff that I mentioned (brakes in a straight line, pads/shoes goodish, brake lines are in good condition, etc.) is okay, this is a weird one.

If it were mine, I think I'd try the following next, but first a boilerplate warning: For entertainment purposes only, do not attempt, professional driver on a closed course, individual results may vary, void where prohibited, use as directed, wear all applicable safety equipment, blah, blah, yada, yada.

I'd probably get a little heater like this one:



. . . and I'd rig it up in such a way so that I could turn it on first thing before I drive the van cold in the morning and warm up the master cylinder pretty well without cooking the reservoir or surrounding parts too much. I'd of course supervise it at all times to ensure safety etc. and make sure it didn't get anything too hot, and I'd also remove it completely before starting the engine. Why a little heater like this instead of a heat gun or blowtorch or a nice big hug? Because this little heater likely won't get anything there too hot or have hot spots or cause melting damage like the other two would, and the warming process would be a bit more gradual.

What would this test get you? If you get the temperature of the actual master cylinder to be van-all-warmed-up-and-brakes-happy warm while everything else in the van starts out cold, and then you drive it and the brakes feel van-all-warmed-up-and-brakes-happy normal, then you will have found your culprit. Van-all-warmed-up-and-brakes-happy warm would probably be somewhere in the 180-200 degree (Fahrenheit) range in my mind.

With this recent cold weather here there wasn’t a personal heater anywhere to be found so the best I had was a hairdryer. I have to move the van to get it to an outlet, and in the 30seconds of driving the brakes were normal by the end. I let sit til the brakes soften up, then went at the master cylinder with a hair dryer. I got the metal to about what I’d describe as room temperature, and the brakes were noticeably firmer. It was exactly 32 degrees according to the weather app. So I guess that means master cylinder.


I’m also going to flush the fluid as it’* looking pretty dirty.

Edward

Wow, if a hair dryer will warm it enough to make a difference, that'* pretty scary.

If it wasn't a reputable brand name last time, I suggest ACDelco or some other reputable brand. Whatever the case, make sure it comes with the reservoir.

New master cylinder seems to have done the trick. The brakes are firmer are warmer temps too

thank you,
Edward