C30 hydro boost help

[low82c10]

Hello I recently got a 81 c30 short bed single cab with hydro boost, my question is why does my pedal go to the floor? Truck does not run, it got towed to my house and while pushing it around I noticed I have to bury the brake pedal. How do I go about trouble shooting or is this normal.thanks

[D13]

Leaks, no fluid, bad M/C, or air in brakes. Nothing to do with the hydroboost.

[hatzie]

You have a leak in the brake hydraulic system or air in it.

Hydroboost assist has the same function as the vacuum assist cannister.
The pedal should be super stiff with no boost just like a vacuum can booster with the engine off... not spongy or the pedal drops to the floor.

[low82c10]

How do I go about on finding this leak?

[86c20]

add fluid pump look. no leak or full bleed report back

[low82c10]

I added fluid the other day pump a bunch of times and didn't see anything I will look again

[donut]

No drums/calipers look wet? No wet spots under the truck along the hard lines? Did the fluid level drop in the master? If not it's likely it's internal and in the master cylinder.

[Corts60]

I wouldn't tear into it too much until you get the engine running and activate the hydroboost with the power steering pump. The problem might throw itself at you.

[hatzie]

If it's extremely low or completely out of brake fluid then you have a leak somewhere in the lines or Drum Brake Wheel Cylinders. The smaller section of the Master Cylinder reservoir feeds the drums the larger is the front discs. Observing which section is/was empty or extremely low, as in mm left in the bottom, will narrow it down to front or rear fluid circuit. They are separate. Chase the leak from there. Keep in mind that being a little low can just indicate worn disc brake pads because the large bores on the calipers fill with fluid as they push out.

Also keep in mind if one reservoir section has been empty for a long time the Master Cylinder could've, and probably has, lost its' prime. And. If one circuit has sat empty for years then the master is probably rusty internally because glycol based brake fluids attract water like desiccant.

Master cylinders usually break down internally and stop pumping brake fluid out the ports. A real leak out the back is unusual but not impossible. There's a weep slot on the tail of the master cylinder between the master and the booster. If the master cylinder is leaking then you'll see fluid dripping there or it'll be obviously wet. Assuming you didn't overfill the reservoir this indicates a leak. Wipe some off and smell it DOT3 & DOT4 have a very distinctive odor. If the brake fluid is just a little low, like the front pads are worn and fluid is now in the calipers, then there are no leaks in the brake lines or wheel cylinders or master cylinder. If the pedal goes to the floor and it was never empty the master cylinder has failed internally... bad cup seals or grooved bores.

[low82c10]

Thank you guys for all the input, I bit the bullet and replaced the hydro boost unit and all the pressure lines. I put a 5.3 motor in the c30 and slowly been getting ready to fire it up.


We'll today was the day I fired it up, back to the hydro boost I noticed once the truck was running my pedal still had no pressure (still went down to the floor). Both fluid levels were good prior to starting. I began to turn the steering wheel side to side and while doing that the brake pedal was bouncing.


I opened my power steering pump res and the fluid was bubbly. Any idea what my problem may be? Thanks!

[86c20]

air!!!!!! you have air in the brakes and the hydroboost. you never fixed the brakes did you? like was said before the peddle will be hard to push with no boost to it it works the same way as vacc does. fix your brakes bleed what ever it needs then if its still messed up we can dig in more. bleed it out if that dont work check what the master is doing. the brakes in these trucks are simple so dont over think it. i have done the brakes on 8 trucks all the same system both vac and hyrdo. for ten years now. problems are simple if you keep it basic

[low82c10]

Originally Posted by Corts60

I wouldn't tear into it too much until you get the engine running and activate the hydroboost with the power steering pump. The problem might throw itself at you.

I am sorry, I just was going off of what was stated here. ^^^^

Tomorrow I plan on bleeding the air out of the brake system at each wheel. And also I just looked at the service manual on how to attempt to get the air out of the power steering system by raising the front of the truck. I will report back with my finding and thanks in advance.

[86c20]

sorry missed that post. but even with it not runing you should be able to build prussere in the lines. fill with fluid pump if you have no leaks and no brakes check the master. may even want to rebleed the master anyway. two plugs and pump. should get rock hard and peddle not move. if that is fine and no leaks bleed all wheels if you get no air it would be then out of adjustment or the prop valve is tripped. now you can do all this in any order that seems right for you. i start at the wheels as you will be there anyway. if i get nothing there i go to master and checl that.and as i sit here and think my k30 is doing the same thing no peddle but no fluid loss. truck is siting so think its a seal in the master

[donut]

Hydroboost and power steering are same system, brakes another.

IIRC, bleeding the hydroboost. Run truck, turn lock to lock, shut off truck, wait for air bubbles to dissipate in the hydroboost resevoir, top fluid, try again. Eventually the air will be worked out of the system, unless you have a leak and loosing fluid or sucking air. There "should" have been bleeding instructions in the new hydroboost unit.

I still stand by my original assessment that the master is bad. (My C-30 had a bad master when I bought it.)

[hatzie]

As I stated in my prior post. Hydroboost isn't some scary different extra part. It serves the same function as the vacuum canister booster on smaller gasoline trucks. Hydroboost is used on 30-60 series and diesels because the assist is instant. The big 1 ton and larger truck brakes need more assistance and Diesels have no manifold vacuum and a much heavier engine over the front wheels.
A failed assist, either vacuum can or hydro boost will make the pedal so stiff you will almost not be able to push it down. Just like pushing the brake pedal with the engine off and the vacuum line off the vacuum booster.

A failed booster will not give you a loose pedal that pushes easily all the way to the floor. Pedal to the floor is ALWAYS in the brake side of the system not on the assist side.

You have one of the following three or a combo... a leak in the steel or flexible brake fluid lines, leaky wheel cylinders, or a failed master cylinder.

Throwing expensive parts at it will empty your wallet and not fix what's broken.

[low82c10]

Originally Posted by donut

Hydroboost and power steering are same system, brakes another.

IIRC, bleeding the hydroboost. Run truck, turn lock to lock, shut off truck, wait for air bubbles to dissipate in the hydroboost resevoir, top fluid, try again. Eventually the air will be worked out of the system, unless you have a leak and loosing fluid or sucking air. There "should" have been bleeding instructions in the new hydroboost unit.

I still stand by my original assessment that the master is bad. (My C-30 had a bad master when I bought it.)

i will attempt to rebleed i am having trouble getting the 5.3 to fire back up. i did "bench bleed" the new master cylinder prior to installing, maybe i will do as someone else said and replug it and try to bleed again on the truck.

[low82c10]

Originally Posted by hatzie

As I stated in my prior post. Hydroboost isn't some scary different extra part. It serves the same function as the vacuum canister booster on smaller gasoline trucks. Hydroboost is used on 30-60 series and diesels because the assist is instant. The big 1 ton and larger truck brakes need more assistance and Diesels have no manifold vacuum and a much heavier engine over the front wheels.
A failed assist, either vacuum can or hydro boost will make the pedal so stiff you will almost not be able to push it down. Just like pushing the brake pedal with the engine off and the vacuum line off the vacuum booster.

A failed booster will not give you a loose pedal that pushes easily all the way to the floor. Pedal to the floor is ALWAYS in the brake side of the system not on the assist side.

You have one of the following three or a combo... a leak in the steel or flexible brake fluid lines, leaky wheel cylinders, or a failed master cylinder.

Throwing expensive parts at it will empty your wallet and not fix what's broken.

thank you! i did not notice any leak on the front brake lines or any hard lines going towards the back. when i pump the pedal a lot i look under the truck and i dont see any thing leaking. the only thing i did notice is, the rear tires look as there was once fluid leaking down the rear plate of the brakes. so looks like i will have to check is the wheel cylinder is leaking

[hatzie]

Is your master a reman or New?
My experience with remanned brake and clutch Master Cylinders is poor at best. A small few are great and work forever... Most, I'd say 85-95%, should never have left the re-builders.
IMHO My time is too precious to screw with returning cheaply reworked parts over and over... Even if they are under warranty. After the first diagnose, remove, and return cycle... I've spent in time and frustration what a new one costs.
The other side to think about is... This is my life and others I'd be gambling with. Bad brakes could cause a fatal accident. I'm not interested in running down a gaggle of Nuns or School Kids or wrapping my truck around a tree because I was too cheap to get decent parts. That's why I buy NEW Master cylinders.

[86c20]

Originally Posted by hatzie

.
IMHO My time is too precious to screw with returning cheaply reworked parts over and over... Even if they are under warranty. After the first diagnose, remove, and return cycle... I've spent in time and frustration what a new one costs.
The other side to think about is... This is my life and others I'd be gambling with. Bad brakes could cause a fatal accident. I'm not interested in running down a gaggle of Nuns or School Kids or wrapping my truck around a tree because I was too cheap to get decent parts. That's why I buy NEW Master cylinders.

^^^^^same here. better to spend the money and do it once and right. and with the dumb crap i use my truck for i need to stop

[mrolds88]

Check your pump pressure. My Suburban has a hydro on it and is due for a pump. It will let the pedal drop low and it "chatters" . When your setting still at idle, its hard to turn the wheel, but when you get a few rpm it picks up enough pressure to assist.