Topic: GM Hydroboost problem (Read 6352 times)

HiProfile · « **on:** August 15, 2015, 04:22:27 PM »

I figured some of you nogs might be able to help, since this shit is used on diesels. The beater Sierra I just bought developed an odd brake problem, and I think it's the booster which uses the P/S system for assist instead of vacuum.

Pedal goes to floor (no assist) but brakes work fine, pedal returns by itself slowly. The only pedal resistance is when I pull it back with my hand faster than it automatically moves. Steering is fine, PS fluid is good & smells okay, no odd noises.

My guess is the P/S line may be blocked? I've read most issues are from a bad P/S pump, which knocks out steering too. I have steering but no brake assist. I've also seen that an internal seal can go, as it's weeping fluid (covered but no drips), but it was a very sudden failure while driving not a long-term degradation.

Any ideas??

highroller54 · « **Reply #1 on:** August 15, 2015, 06:25:47 PM »

What's it feel like with the engine off?

HiProfile · « **Reply #2 on:** August 16, 2015, 02:32:24 AM »

It felt soft, same as I think it felt before. The problem is I've only had it a week, but it did have strong brakes before. Regardless, I think I found the issue...

Today I got home and I noticed a decent puddle on the concrete below (feels/smells like fresh brake fluid), and the reservoir is now empty. Looks like our lovely salty winters ate away at the lines as they loop under the steering shaft. I can also hear the PS pump whine when I really reef on the pedal, so I'm thinking the hydro system is fine but there's just no brake fluid. The two front lines are wet were they dip below the steering shaft, and seem to drip onto the frame & then to that spot on the concrete.

SO now it looks like I have to just do the brake lines & bleed them, but the info I've found says bleeding the modulator is no fun. I do have several gravel lots nearby, so it shouldn't be terrible - I just hate doing brake lines.

highroller54 · « **Reply #3 on:** August 16, 2015, 09:57:58 AM »

That was why I was asking lol. My guess was a brake line. Bleeding the system is fuck all. Usually they go at the back around the gas tank first though

HiProfile · « **Reply #4 on:** August 16, 2015, 12:27:31 PM »

What happened was a friend used it (typical!) for a 10hr round-trip, and apparently it happened in the first hour. They were determined as fuck to get the task done. It was returned at 1am after it had rained, so I didn't get to check everything. I didn't think it would even have stopped with no brake fluid, but I'm guessing with ABS shit's a little different.

My dad knows a place that can bleed the ABS module with a tech1, and as I said there's a gravel lot on the next block. It looks like these trucks used weird lines (5/16" fittings with 1/4" lines), but I think that works for me. Impossible fabrication = full replacement kits. I found you can get a COMPLETE stainless line kit for under $75 shipped for these trucks.

http://www.partsgeek.com/8m2r84k-chevrolet-silverado-2500-brake-line.html?utm_source=pricegrabber&utm_medium=pf&utm_content=mcs&utm_campaign=PartsGeek+Pricegrabber&fp=pp&utm_term=Chevrolet+Brake+Line

HiProfile · « **Reply #5 on:** August 16, 2015, 12:34:30 PM »

Looks like they have a full ACDelco kit in coated steel for $61:

http://www.amazon.com/ACDelco-22933203-Original-Equipment-Hydraulic/dp/B00H91RLFA

highroller54 · « **Reply #6 on:** August 16, 2015, 01:20:39 PM »

You will be stopping in front brakes only right now. You should be able to bleed those brakes without a automated bleed (scan tool).

HiProfile · « **Reply #7 on:** August 16, 2015, 02:44:29 PM »

That sounds right, at least before the reservoir emptied out. I added some fluid to try pinpointing the leak and it was the rear line. The front line is leaking a little, but it just pours out the rear. I think I'll get the stainless lines for $10 more since the acdelco kit doesn't have the line that goes along the axle. I can probably sell it to a clueless local for 2-3x as much when I junk the truck.

Random Hero · « **Reply #8 on:** August 22, 2015, 11:20:34 PM »

Sounds like its got a leaky brake cylinder or line. coming back slowly is a cause of it refilling the master cylinder with brake fluid from the rez. hope its an easy fix!

HiProfile · « **Reply #9 on:** August 28, 2015, 04:26:16 PM »

Just a quick update, everything is working again.

The brake lines were nice but getting them in was the worst part. GM must have designed their routing after everything else in the truck was done. I opted not to raise the cab/bed because of the rusted bolts, but that would have made it MUCH easier.

Bleeding was a pain, as always. I had to bench-bleed the MC (clear pvc tube and the old fittings helped), then do a typical bleed. I used an oil extrator vacuum pump from Northern (tip: slather grease around the bleeder screws to seal them) along with pumping the pedal. Now I just have to do some gravel road stops to cycle the ABS and re-bleed.

Even w/o the last step the pedal is firm and the truck stops quickly. It has the heavy duty JH6 brakes - disc w/dual piston on each corner.

HiProfile · « **Reply #10 on:** August 28, 2015, 10:53:48 PM »

This bitch does some crazy burnouts. It's got an Eaton G80 locker in it, easy as hell to whip out the rear.

92CXyD · « **Reply #11 on:** September 01, 2015, 12:29:55 PM »

Who cares all we want to know when does the turbo(s) get put on?

BTW IdealOne is selling a turbo manifold set and maybe a turbo for cheap on facebook.

ratcityrex · « **Reply #12 on:** September 01, 2015, 03:11:40 PM »

Quote from: 92CXyD on September 01, 2015, 12:29:55 PM

Who cares all we want to know when does the turbo(s) get put on?

BTW IdealOne is selling a turbo manifold set and maybe a turbo for cheap on facebook.

Link?

highroller54 · « **Reply #13 on:** September 01, 2015, 03:28:45 PM »

We need pics of that turbo setup stat!!

turbohf · « **Reply #14 on:** September 01, 2015, 04:01:09 PM »

Quote from: highroller54 on September 01, 2015, 03:28:45 PM

We need pics of that turbo setup stat!!

turbo?

highroller54 · « **Reply #15 on:** September 01, 2015, 04:45:06 PM »

HiProfile · « **Reply #16 on:** September 01, 2015, 08:18:46 PM »

The plan is to use it for familiarizing myself with HP T00nars & refine some GM data for my injectors. After that's don I want to toss this engine into another car, probably be the Firebird.

turbohf · « **Reply #17 on:** September 01, 2015, 08:54:41 PM »

what engine is in yours?

HiProfile · « **Reply #18 on:** September 03, 2015, 01:17:43 PM »

5.3 in the GMC (3% of all 2500's). The Firebird has a Chevy 350, originally a 326. So with the 5.3L it will be back to virtually the original motor size.

danz · « **Reply #19 on:** September 06, 2015, 03:09:04 PM »

More rusted out lines? Jeez

HiProfile · « **Reply #20 on:** September 08, 2015, 01:04:18 PM »

Yeah, me and fucking brake lines...

At least my 2 project Civics were from SC & TX, so there's very little rust.

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Author Topic: GM Hydroboost problem (Read 6352 times)