2004 6.0 NV4500 Tahoe

[OR VietVet]

You need a Mighty Vac for the one man bleed show. Or some form of that. Yes, brake fluid dark equals needing a flush. That may be the source of the mushy pedal.

"Hydro-boost systems use hydraulic pressure from the power steering pump to amplify brake pedal effort. Pressurized fluid also flows through the hydro-boost to the steering gear to provide power steering. When the brakes and steering are at rest, pressure runs about 150 to 200 psi."

Ok, I gotta ask. How does that P/S fluid stay separate? It is using the HYDRAULIC pressure from the P/S system and that is a flow to and from the brake booster. Is there some sort of check valve I never knew about? If that fluid is cycled to and from is it not the same fluid and therefore if the fluid is old and overheated it can effect both systems? I ask because even at 67 I am very inquisitive.

 

[Dantheman1540]

I guess what I was trying to say is that the power steering fluid and brake fluid never mix. Which you probably already know that and hopefully I don't come off sounding like a jerk because that's not my intention. But I suppose I wasnt thinking that old PS fluid would have an effect on the braking which I suppose it very well could.

I want to say 150-200psi is more online with what a vacuum booster produces where hydro boost is close to 1,000psi. Don't quote me on that until I find a reliable source.

 

[OR VietVet]

I never ever took it the wrong way. I was just confused. I just could not wrap my head around the hydraulic pressure flow being separate from the P/S system. I know that the brake fluid and P/S fluid do not mix. I just know that P/S fluid gets hot under normal usage and over time it breaks down, just like brake fluid because it too gets hot when it absorbs the heat from braking. Like I have said in a couple other threads, I am a firm believer in fluid flushes and changes and I believe that if the manufacturer says change the fluid at a certain mileage, I do it at half that mileage. You know as well as I do that after fluid is changed you can actually FEEL the difference. Seat of my pants feeling is my comfort zone.

 

[iamdub]

You need a Mighty Vac for the one man bleed show. Or some form of that. Yes, brake fluid dark equals needing a flush. That may be the source of the mushy pedal.

"Hydro-boost systems use hydraulic pressure from the power steering pump to amplify brake pedal effort. Pressurized fluid also flows through the hydro-boost to the steering gear to provide power steering. When the brakes and steering are at rest, pressure runs about 150 to 200 psi."

Ok, I gotta ask. How does that P/S fluid stay separate? It is using the HYDRAULIC pressure from the P/S system and that is a flow to and from the brake booster. Is there some sort of check valve I never knew about? If that fluid is cycled to and from is it not the same fluid and therefore if the fluid is old and overheated it can effect both systems? I ask because even at 67 I am very inquisitive.

It's just a booster- It amplifies (boosts) your input from pushing the pedal to push on the rod in the master cylinder with much more force than what you're applying. The hydrabooster doesn't mix power steering (hydraulic) fluid with the brake fluid just like a vacuum booster doesn't mix vacuum with the brake fluid. Ever taken a master cylinder off of a vacuum booster? They're not connected and it's the same with a hydrabooster. For example, I converted my '02 S10 to hydraboost. I unbolted the two nuts on each side of the master cylinder and slid it forward off of the studs coming off of the vacuum booster. I unbolted and removed the vacuum booster from the firewall then slid the hydrabooster in where the vacuum booster was and bolted it up. Slid the master cylinder onto the studs coming off of the hydrabooster and tightened the nuts. Connected the factory lines I got with the hydrabooster in their proper locations, bled the power steering system, and it's been a done deal ever since. Oh, I had already swapped on a power steering pump that had the return nipple on the reservoir.


You're thinking about too hard!

 

[Dantheman1540]

iamdub said it better than I could lol!

But since I did flush the power steering fluid when I got it and not the brake fluid I think that's the main culprit. I won't mighty vac it simply because I don't have one. I'll just bleed and bleed until everything coming out is clean. Probably grab 2 or 3 bottles of whatever is on sale.

 

[OR VietVet]

Maybe it is just the way I said it or responded to a post. I do KNOW that the brake fluid and P/S fluid do not mix. I have always known that. I know it is using the pressure created by the P/S pump to boost brake performance. I know the difference between the vacuum and hydro-boost and known that nothing mixes. I have owned both designs and worked on them. I get it. I promise.


I may be old but I am not so old that I could mix that up but I am old enough that I may not succinctly express it in a post.

 

[iamdub]

Maybe it is just the way I said it or responded to a post. I do KNOW that the brake fluid and P/S fluid do not mix. I have always known that. I know it is using the pressure created by the P/S pump to boost brake performance. I know the difference between the vacuum and hydro-boost and known that nothing mixes. I have owned both designs and worked on them. I get it. I promise.


I may be old but I am not so old that I could mix that up but I am old enough that I may not succinctly express it in a post.

I thought it was a miscommunication cuz that's not something an experienced wrencher would mix up. Looking back at the previous posts, I now see where the misunderstanding happened.

 

[iamdub]

...I won't mighty vac it simply because I don't have one. I'll just bleed and bleed until everything coming out is clean. Probably grab 2 or 3 bottles of whatever is on sale.

I use two quarts of synthetic DOT3 or 4 with the hose in a plastic bottle method. I bleed the right rear until it's just new fluid coming out, then move to the others in the proper order. While bleeding, I'll turn the key to on right after I start to push the pedal, and then I'll make a few strokes, key off, few strokes, key on again with a few strokes, etc. When the key is first turned on, the ABS computer activates the solenoids as a self-check. If the solenoids are activated while the fluid is being pushed downstream, it'll carry old fluid as well as any air out from the ABS module. It's not as convenient as having a bi-directional scan tool to hold the solenoids open, but it's $300-$3,000 cheaper! Oh, if the master cylinder has a lot of miles on it, lay a 2x4 or something behind the brake pedal so it remains within its normal stroke.

 

[Dantheman1540]

I use two quarts of synthetic DOT3 or 4 with the hose in a plastic bottle method. I bleed the right rear until it's just new fluid coming out, then move to the others in the proper order. While bleeding, I'll turn the key to on right after I start to push the pedal, and then I'll make a few strokes, key off, few strokes, key on again with a few strokes, etc. When the key is first turned on, the ABS computer activates the solenoids as a self-check. If the solenoids are activated while the fluid is being pushed downstream, it'll carry old fluid as well as any air out from the ABS module. It's not as convenient as having a bi-directional scan tool to hold the solenoids open, but it's $300-$3,000 cheaper! Oh, if the master cylinder has a lot of miles on it, lay a 2x4 or something behind the brake pedal so it remains within its normal stroke.

Yep same method I usually do with good results. Never thought about the 2x4 though. I need to find a used scan tool for these trucks I've come across a few issues they would have helped diagnose.

 

[iamdub]

Yep same method I usually do with good results. Never thought about the 2x4 though. I need to find a used scan tool for these trucks I've come across a few issues they would have helped diagnose.

I never thought about limiting the pedal stroke, either, and I've never had a problem with not doing so. I learned one night when finishing up a full brake job just days before a trip to Florida. I got to the last corner (front left), and the pedal suddenly went soft and wouldn't firm up for anything. I thought I somehow found and released a big air pocket, so I started the bleeding procedure all over again- no difference. Did some internetting and decided it had to be the MC. O'Reilly had a new one for $10 more than a refurb, so I took my Jeep and hauled ass since they were closing in 20 minutes. Bench bled the new MC and the brake system again and it's been great for 50K+ miles.