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Old 02-13-2022, 04:09 PM   #1
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for the experienced mechanics on here. hydroboost?

i am working on my wifes 04 chevy 3500 with a 6.0 express and after driving it without a trailer much less a loaded trailer.
i dont like the hydro boost brake system.
sure i have researched and know the test of how to check it out.
everything test fine and i know whatever trailer i build or buy will have brake axles because i dont trust the combined hydro boost system.
i have not pulled the pads on front rotors or rear axle drums since i brought it home so that might be the issue.
please educate me before i go down a rabbit hole.
if there is an upgrade my son wants the hydro boost for his diesel swap?
so why does a gas engine even have a hydro boost system.
since the gas engine has vaccume/ why not use it?
i know alot of rambling?
any thoughts?
thoughts
advice
fingers?
tell me i am being stupid?
fine.
i dont like the spongey peddle but i was running 65 when i had to stop in a hurry. and i dont want to burn the trailer tires to stop the bus.

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Old 02-13-2022, 05:56 PM   #2
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Without knowing the condition of your brakes atm it is hard to tell if what your feeling is normal. Check pads and shoes. Bleed the system. Then come back and let us know if it changed. I've had my '99 2500 since new and the brakes are okay but that's about all I'll say about them.
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Old 02-13-2022, 06:31 PM   #3
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ok spaz every one i have talked to experienced have said that a spongey brake is normal.
and your 2500 whatever?
have you or do you tow with it or is it just for show?
do you have the actual hydro boost cause there was a few years like yours that was in between your year model.
not trying to give anyone a hard time. just want first hand mechanic knowledge and not computer you tube stuff.
if nobody has dealt with it then fine.
i can deal with it no more questions asked.
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Old 02-13-2022, 06:48 PM   #4
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I had to replace the hydro booster unit on my van, as it was leaking P/S fluid between the master cyl and booster body.
The pedal feel was hard when applying the brakes and was scary to drive in traffic.
After I changed out to a reman booster, brakes are like new, almost.

GM has used hydro boost in one iteration or another on all of their trucks/vans coming from the factory with dual rear wheels and others, since the early-mid 60's, perhaps longer?

A vacuum assist booster could be adapted, but is not recommended as it is not as robust as the hydro unit.

Spongey pedal could very well be master cyl. or line related...
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Old 02-13-2022, 07:37 PM   #5
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i went to school in the late 80s and early 90s to be a mechanic and joined the marine chorp instead.
i have dealt with many variations of brakes including the lucas girling but i have never seen this one unless its a variation? which feels like it should be but while in the military i didnt mechanic for quite a while ?
which is i am asking for someone experienced to call BS and educate me because i am being stupid.
i know pads, rotors,drums, lines?
always drove old stuff as a kid
only worked on old stuff and built racecar motors after the corps?
worked on my personal stuff when i first got married but never had a hydro boost to work on till now.
haynes owns chiltons now so the manuals suck.
and of course my son i raised to be a mechanic that works for ford told me tonight that my work truck has hydro boost?
aargh?
gotta figure this **** out since my work truck has electric steering for a 2014 truck but a version of hydro boost?
does anyone know the evolution of this brake system that can explain it?
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Old 02-13-2022, 08:37 PM   #6
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guess i knew the system on old tractors and it took my son to explain it to me?
still dont understand why i have it with a gasser?
got research to do?
still dont agree with the technology but hey who am i?
was scared of the power steering fluid effecting the brakes and the brakes effecting the steering.
i still want a better understanding?
my son says its 1970 technology and i remember the idea on some tractors when i was young and learning to work on things and never thought they would relate to each other?
yall can call me stupid on this at anytime or educate me even farther.
i want to understand every aspect of this system and google isnt it so far.
which is why i came here whether you talk **** or not as long as its knowledge i can use i dont care how you present it.
that only reflects on you.
i have had constructive criticism my entire life.
please fire away.
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Old 02-14-2022, 06:44 AM   #7
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There are some youtube videos that may help.



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Old 02-14-2022, 07:45 AM   #8
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check pump pressure and make sure bypass valve is closing when needed i converted a truck from vacuum to hydro and it was way better stopping after i did that.
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Old 02-14-2022, 09:30 AM   #9
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Hydroboost is superior to vacuum IMO.

There are a couple reasons why they used hydro instead of vacuum. Hydroboost is a better booster, but it's typically more expensive then vacuum. It's a lot more powerful of a system, though, and a lot more compact against the firewall. Another reason is to reduce assembly line parts/options, especially if the model truck could have had a diesel engine.

I assume when you say it's spongey, that means it's running when you try it? Is it spongy with the key off and the brake pumped a few times?

If yes, then it's not a booster issue, but air in the fluid, failing abs unit, soft rubber line, or a mechanical issue with the pad/caliper/rotor interface. Even if there is a little air in the brake fluid, adding pressure assist will magnify and give you a really soft pedal.

If it's not spongey at all with the truck off, the spool/sleeve assembly is either worn or sticky and it's not giving you the proper pedal feedback. I've fixed a handful of trucks with this problem. Sometimes they're fixed with a power steering flush, sometimes they're fixed with a new booster unit. Regardless, you start with doing a flush, as you don't want to run contaminated fluid through your new booster. FYI, new boosters are real hit or miss. So if you replace one, the problem persists, and you're certain about the rest of the brake system, don't hesitate to replace it again and send the other back as defective.

Also, just recently on a truck I found the new shoes the customer installed weren't arched correctly to the drum, which caused the shoe to flex and a spongey pedal. In the old days they had a sanding machine that would sand shoe material to match the curve in the drums, but asbestos eliminated the practice and the machines. I ended up getting a set of shoes from a different manufacturer and they fit correctly.

Not sure what vehicle you're looking to swap on, but a lot of late 80's early 90's ford pickup owners rave after doing a hydroboost upgrade. It'll make a truck that butt puckers coming to a stop throw you through the windshield. Most also used a larger bore master, which pushes more fluid then the old ones. Not sure which change did more good, but it's typically night and day different.

FWIW, I plan on installing a mid 2000's mustang hydroboost brake setup in my torino whenever I get around to it. Reason being is the hydroboost is more compact on the firewall, has better boost performance, and the engine I'm building might be too radical to make enough vacuum for it.
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Old 02-14-2022, 09:32 AM   #10
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A quick check to see if it's a booster/master vs a brake issue is to use plugs in the master cylinder. I'll plug off both ports, bleed the plugs, and then start the truck and test. Theoretically there should be only a smidge of pedal movement. So if you have more then that, either the master has failed or the booster is problematic.
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Old 02-14-2022, 03:03 PM   #11
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thanks everyone for the responses.
i will go through the checks and see i can track it down.
the pedal doesnt feel spongey with the engine off.
i think i need to start with checking the pads rotors and drums but i was putting that off until pulled the tires to get new sneakers and thats still at least 4 months out.
the brakes are not a rush issue until that time frame just before it hits the road.
i have kind of worked on these types before i just had never heard it actually named and i started questioning as being more like the lucas girlig set but with the power steering and the brakes mixing or fighting and i have been wanting to understand it better and couldnt understand why it was in a gasser but i understand the production line thing.
i will get it right
thanks
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Old 02-19-2022, 06:45 PM   #12
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My '74 Grumman box truck (Chevy chassis dually) has hydroboost. Massive ventilated disks up front, huge finned drums in back. Works well. Would never presume to know more than GM's engineers and replace with a vacuum system despite have the mechanical know-how and the shop in which to do it. Compact, strong, reliable, and just works. What's not to like? Spongy pedal? Troubleshoot like you would any spongy brake pedal, e.g. air in the line, hose gone south, leaks somewhere, etc.
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Old 03-22-2024, 04:26 AM   #13
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Did you ever get the brakes lined out? My 2008 I do not like the way it stops either, very different than my 2017 express 3500..??

Mine has almost new pads from before I bought it and I just had the dealer flush the brake fluid and no change
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Old 03-22-2024, 07:49 AM   #14
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If you have drum brakes in the back, make sure they're adjusted properly and the self adjuster works. Most frequent issue that I see with poor braking performance.

Then you can go down the list I created above.

But know that your 17 brakes better because it's a better system. Like most everything else, that's also gotten better in the last 20 years.
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Old 03-22-2024, 12:00 PM   #15
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i have disc all four and think they are two piston, so was wondering about going to a 4 piston upgrade kit like powerstop or something like that
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Old 03-22-2024, 12:02 PM   #16
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someone told me it may be the fleet type pads the school put on it?
does anyone know what is the actual difference between my 2008 vs 2017? more pistons or what?

does anybody have a chevy short bus with good brakes
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Old 03-22-2024, 12:25 PM   #17
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Quote:
Originally Posted by Vin1 View Post
i have disc all four and think they are two piston, so was wondering about going to a 4 piston upgrade kit like powerstop or something like that

you typically cant just swap calipers.. you will need a master cylinder that can move the volume of fluid required to handle 4 piston calipers if you choose to swap them.. also the number of pistons on the caliper arent the only reason for "bad brakes"... do you have good pad contact area t othe rotors? are all of the pistons in all calipers working? "no sticking".


have you verified that the pads and rotors are actually the correct one for that vehicle? ie make sure the part number for your Bus chassis is different than that of a regular cargo van and make sure someone didnt install the wrong stuff at some point..
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Old 03-22-2024, 12:30 PM   #18
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Trucks and vans used the same calipers/master/pads and rotors for a decade or more. Good chance it's the same stuff between the two, you just have something wrong between one bus vs the other.

Cheap pads can create poor braking.

They never said what was poor about them, whether it was a soft pedal travel or poor overall performance. But I agree that there's likely an issue that redesigning the system won't correct.
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Old 03-22-2024, 05:44 PM   #19
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sorry here is the differences between what's going on, the 2017 feels very responsive one or 2 inches of pedal pressure get you a good response, quick modulated braking depending in how hard you stomp on it

The 2008 you have to push it twice as far and it never gets a really good response, yes it stops but they're just not as sensitive or responsive I guess you would say

It's not spongy or soft to push down or hard at all
feels like it's breaking normally just not very responsive and not a super strong immediate braking like the 2017, I guess it could just be pads but I'm guessing that the school bus company knows what pads to put on their buses

I was pretty sure power stop showed an upgrade kit with calipers rotors and pads for this but I thought they were 4 piston but I'll confirm that later
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Old 03-22-2024, 06:54 PM   #20
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how would i find specific brake pads for my bus? i dont just check for an express 3500? does it have a different brake set up than a regular 12,300 rated van?
i do all parts searches off gm parts and vin number
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