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#2601440 - 04/16/12 10:18 PM Help... 1986 Chevy K30 hydroboost / brake problem.
sw99 Offline


Registered: 03/22/06
Posts: 1814
Loc: Colorado
Truck has 79K original miles on it. The brakes were very spongey and the Hydroboost was wet around the accumulator. I bought a re manufactured Hydroboost from Napa. Switched it out and the brakes were not any better (I swapped out the push rod also per the directions also). I also bled the unit with the tires off the ground and side to side to purge the air. I noticed that the old master cylinder had some fluid getting past the lid so I figured I would just install a new one to see if that was part of the problem. I installed a re manufactured unit from Napa. Bench bleed, installed and tried to bleed the brakes. Now I have zero brake pressure. So I pull the new MS and take it back to Napa for a brand new one. I do the same thing and get it installed. Still, zero brake pressure. The brake pedel goes to the floor very easy (and returns slowly) but will not build pressure.

While bleeding the brakes, the rears would pull solid fluid from the vacuum so I know they were bled well. The fronts will just pull a combination of air and fluid. It will never get a solid stream of fluid. I have run a gallon of fluid and it keeps pulling air from the fronts only...

Since the new Hydroboost unit was not better than the original one, I am thinking that perhaps it wasn't a Hydroboost issue to begin with. I also had pressure with the new unit prior to swapping the two master cylinders. The chevy dealer by my house had no idea what it could have been. How am I pulling air from the front brakes. I even tried gravity bleeding with no luck and the old fashion buddy bleed. I am getting no pedel pressure whatsoever.

I do not see any leaks from the wheels or anywhere else for that matter.
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#2601937 - 04/17/12 02:08 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
The feel of Hydroboost brakes is abomonible, to me, but they work well.
I'd keep bleeding the fronts. If air in the lines is not THE problem , it is one that must be addressed and fixed anyways.
Maybe try another technique.

BTW - You may be seeing air that is from around the bleeder screw mixed with the fluid. This is harmless, but does not look right.

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#2602197 - 04/17/12 07:18 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
punisher Offline


Registered: 09/11/04
Posts: 2350
Loc: snowblind in TX
Hydroboost always feel spongy to me. Nature of the beast.

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#2602341 - 04/17/12 09:59 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
sw99 Offline


Registered: 03/22/06
Posts: 1814
Loc: Colorado
Update...

Kept picking apart the problem and narrowed it down to the hydroboost rod not connecting with the new MS. Turns out that they gave me the wrong MS so it was never pushing the piston on the MS = no brake pressure. Got the new one and I know have pressure. Brakes are still marginal but at lease that was the main problem. I'll now start with the lines, calipers and wheel cylinders. Thanks folks!
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#2603148 - 04/18/12 07:08 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
artificialist Offline


Registered: 09/23/07
Posts: 8384
Loc: Florida
My auto teacher said there is a special test procedure for determining hydroboost problems, and it must always be followed because some hydroboost problems feel like a weak master cylinder.
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#2603226 - 04/18/12 08:11 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
Jarlaxle Offline


Registered: 02/02/12
Posts: 7456
Loc: New England
Are you sure the power steering pump is OK? A weak PS pump will make GM's hydroboost do all sorts of weird things.
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#2603328 - 04/18/12 09:26 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
sw99 Offline


Registered: 03/22/06
Posts: 1814
Loc: Colorado
Not positive if it's hydroboost related or not. I bled them again with my vacuum bleeder and I also discovered that the front fitting on the MS was leaking when I applied pressure to the brake pedal. Tighten that up and they are better today. I think there is still so air in the lines so this may be an excuse to buy the phoenix bleed system...

Not sure if the pump is ok or not. The steering is okay and have not noticed any issued from it.
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#2603397 - 04/18/12 10:44 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: sw99]
yonyon Offline


Registered: 03/06/12
Posts: 3492
Loc: NJ, USA
If the fitting was loose enough to leak brake fluid under pressure it was loose enough to leak air under vacuum. By rights there should be some air still in there. Bleed it out again using either a pressure bleeder or "up! up! down! down!" and then check for leaks.

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#2604392 - 04/19/12 09:59 PM Re: Help... 1986 Chevy K30 hydroboost / brake problem. [Re: yonyon]
sw99 Offline


Registered: 03/22/06
Posts: 1814
Loc: Colorado
I was thinking of doing that since they were tightened. I did notice a difference so far but I will plan on another bleed just in case. I also plan on so heavier duty braided steel lines and the disc brake conversion on the rear 14 bolt. Thanks everyone!
_________________________
2016 Nissan Versa S 1.6L
2012 Honda Civic EX 1.8L
2015 Ford F350 CCLB 6.7L
2014 LS G3038
2016 Yamaha Viking

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