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Spongy brakes on '99 suburban

This is a discussion on Spongy brakes on '99 suburban within the Technical / Maintenance forums, part of the General Discussion category; Tonight when I pulled up to a stop light, my brakes suddenly felt really soft/spongy, but a few minutes later ...

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    Spongy brakes on '99 suburban


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    Tonight when I pulled up to a stop light, my brakes suddenly felt really soft/spongy, but a few minutes later they felt fine, then they felt spongy again, repeat until I finally got home. I had to make a stop and I checked my fluid level since I had to add a little fluid the other day, but it was totally full.

    What might cause this? I had changed out the brake booster a few years back, but I don't recall they symptoms at that time, but looking online, it sounds like a faulty brake booster, makes the pedal harder to press, not easier. I did recently have the distributor replaced, so I questioned maybe a loose vacuum line, but the main one going to the booster still appears to be hooked up.

    Any thoughts??

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    Re: Spongy brakes on '99 suburban

    could be the master cylinder
    Selling a front Chevy Dana 60, 5.38s welded, $1000 never run, PM for more
    1992 K2500 6.5 Turbo Diesel/4L80e/4.10s (sas with Dana 60 just sitting around waiting for a rainy day)
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    Re: Spongy brakes on '99 suburban

    Same problem with mine, was also told that its probably the master cylinder.
    1999 GMC Suburban 2500 7.4 Liter 4L80E trans and factory 4.10 rear

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    Re: Spongy brakes on '99 suburban

    Master
    99' GMC Suburban 1500 4X4
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    Re: Spongy brakes on '99 suburban

    Thanks, I'll look into that, I'm guessing besides bleading the brakes, that's probably an easier fix.

    After I posted, my wife had to run somewhere and she didn't think it felt any different, but I was sure it did. Hmmm....

    I did test the Booster, by turning the truck off, pumping the brakes till hard, then turning the truck on again and the pedal dropped like they say it should, so you guys are probably correct, I'll look into the Master. Anything tricks to changing it out or is it pretty straight forward, just have to bleed brakes afterwards?

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    Re: Spongy brakes on '99 suburban

    Ok, well I looked into the Master Cylinder and it seems cheap enough to just replace or rebuild, but I'd likely just replace. Problem is it seems as if one needs a scan tool to bleed the brakes properly, is this true? ....or is there a way to change the Master out without bleeding, I'm guessing not, unless things have changed, since I did it last.

    Also, about how long should it take for a shop to bleed the brakes? I have a shop about 1mile away that would likely do it, but I question if I would even be able to drive the truck to them, if I were to change the cylinder myself and perform a base bleed of all of the cylinders.

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    Re: Spongy brakes on '99 suburban

    bench bleed the MC then install, then bleed the brakes, that easy. usually takes me 30 minutes, if that.
    Selling a front Chevy Dana 60, 5.38s welded, $1000 never run, PM for more
    1992 K2500 6.5 Turbo Diesel/4L80e/4.10s (sas with Dana 60 just sitting around waiting for a rainy day)
    '84 K10, 6" Tuff Country, now 1 ton frame swap and Cummins swap have begun
    Veteran of Afghanistan (Army SGT)

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    Re: Spongy brakes on '99 suburban

    Quote Originally Posted by vic_V8 View Post
    bench bleed the MC then install, then bleed the brakes, that easy. usually takes me 30 minutes, if that.
    So, I don't need a scanner to bleed the system? That would be great, but of course, I can't believe a shop would charge much to do that. I think I'll just plan on replacing the M.C., cost isn't that much and I'm towing my boat to the lake next weekend. Don't really need a failure!!!

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    Re: Spongy brakes on '99 suburban

    Well, I got the new M.C. on that wasn't too bad. I was a bit confused on the rear because it is a split design. One line leading to both sides, splitting off at the rear differential and I had to undo the actual line itself to bleed it as I couldn't find a bleeder valve. I tried to get the front, but the passenger side didn't seem to want to budge and I was running out of time, so I'll either try it later or take it in and have the entire system bled with a scan tool.

    Thanks for the help!

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    Re: Spongy brakes on '99 suburban

    You won't need a scan tool to bleed the brakes. Why would you think you need one? Are you getting your brake light on on the dash? If you are then you still have air in your lines and need to bleed. This is where the bench bleeding process saves you a lot of headache. By that I mean bleeding the MC before you install the lines from the truck back on it. That is what's making your brakes spongy now after your install.

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    Re: Spongy brakes on '99 suburban

    Quote Originally Posted by BluHoe96 View Post
    You won't need a scan tool to bleed the brakes. Why would you think you need one? Are you getting your brake light on on the dash? If you are then you still have air in your lines and need to bleed. This is where the bench bleeding process saves you a lot of headache. By that I mean bleeding the MC before you install the lines from the truck back on it. That is what's making your brakes spongy now after your install.
    No, the light isn't on....does that mean they are ok? I did bench bleed the new Master Cylinder and they don't really feel that bad. I also used a rubber cap I had to cover the brake lines while I made the switch, so maybe I didn't allow any air to get into the system, I just figued it would be good to get them bled, but maybe it isn't necessary. Like I said, I was able to bleed the rear, just didn't get the fronts done as my help needed to go and by the time I had more help, I was finished for the night. I certainly wouldn't say they are spongy/soft at this point, just not sure they are perfect, but from reading stuff online, it seems these trucks are known for somewhat soft feeling brakes.....

    The reason I thought I'd have them bled with a scan tool is that the truck needs to go in on monday for some warranty work on front ball joint and figured if cost wasn't too bad, why not be on the safe side. Maybe I'll ask their opinion as well!

 

 

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