Soft brakes.

[Hotrod Steve]

Hello I have a problem with soft brakes on my 83 C-10.
Engine 350 4 bolt main.
Trans 4 speed manual.
I converted from a non power brake setup to power brakes.
I now have soft brakes. Can't tell what they where like before.
Truck had a bad 6 banger. Installed a nice 350.
Things I have done so far.
Rebuilt master brake cylinder, rebuilt brakes all around.
Power booster from a 1/2 ton suburban.
Bleed and flushed brake fluid.

Any one have any ideas what might be causing my problems.
I don't drive the truck much because of this problem.
Would a hydro boost system help me?
How hard to install hydro boost system?

Thank you
Steve

[Lt.Del]

first thought is leaking master cylinder.  Could be a hole in a brake line.  Does the fluid go down afer a while?  Of course that would signify a leak. That would cause a spongy pedal.

Still, reconsider your master cylinder.

[Hotrod Steve]

I have installed two master brake cylinders.
Fluid does not leak down.

Steve

[Lt.Del]

soft brakes

It has to be one or the other for "soft" brake pedal.  If it was hard to push down, or not grabbing enough to slow the truck, I'd say your booster or vacuum check valve.

If there is too much play, i'd say the pedal rod needs adjusting.

If it is "soft", it has to be bad master cylinder or losing pressure somewhere in the line.  You are sure it is not leaking around the caliber pistons or rear drum wheel cylinder?  No leakage around any lines or combo valve?    If no fluid needs to be topped off, it is your master cylinder or air/moisture in the lines.  I'd re bleed all 4 wheels again starting at the right rear, left rear, right front, left front. Bleed them good. Have plenty of fluid to refill. 

[smitty77]

soft brakes

It has to be one or the other for "soft" brake pedal.  If it was hard to push down, or not grabbing enough to slow the truck, I'd say your booster or vacuum check valve.

If there is too much play, i'd say the pedal rod needs adjusting.

If it is "soft", it has to be bad master cylinder or losing pressure somewhere in the line.  You are sure it is not leaking around the caliber pistons or rear drum wheel cylinder?  No leakage around any lines or combo valve?    If no fluid needs to be topped off, it is your master cylinder or air/moisture in the lines.  I'd re bleed all 4 wheels again starting at the right rear, left rear, right front, left front. Bleed them good. Have plenty of fluid to refill. 

SgtDel,
Is there a procedure for bench-bleeding the master cylinder?  IIRC, this is to be done on some master cylinders before bleeding the rest of the system or you'll just be chasing your tail.  But I don't know if it applies to these brakes systems or not.

Just a thought.

[zieg85]

Bench bleeding simply recirculates the brake fluid until all the air is out by pushing the plunger in while the fluid is pushed back into the master.  The kits used to be included as part of a master.  Second best without a power bleeder is to have a second person start from the right rear.  Open bleeder, have another person slowly push the pedal to the floor, close the bleeder and repeat.  You should be able to get the air out that way.  You would need to alternate to the right front as to not lock the proportioning valve one way, if that makes sense.  There may be a textbook step by step out there but that is how it can be done.  Good luck..

[Hotrod Steve]

Update, installed rebuilt front brake calibers, bleed the system no air.
Installed new check valve, new in line filter.
Helped a little.
Brake hoses are fine. Checked them all under pressure.

Next I unbolted the master cylinder to check the rod stroke.
Had my son pushed on the brake pedal, the master cylinder didn't move on the studs till the pedal was half way down.
Is this normal should the rod move the cylinder sooner?

Steve

[zieg85]

When you put power brakes on your truck did you just use the power booster and your existing master?  I am pretty sure there is a difference, at least there is in the older applications.  Just a thought.  You should have instant movement when the pedal is pressed. 

[Hotrod Steve]

Master cylinder is for power brakes.
How do I adjust the rod length.
The brake pedal is for manual brakes would there be a difference in the pin location?
Or the shape of the brake pedal arm.

Steve

[Lt.Del]

The brake pedal is for manual brakes would there be a difference in the pin location?
Or the shape of the brake pedal arm.

I don't think there would be a difference as long as the pedal rod is adjusted correctly.  If memory serves, I think there is a threaded part on the rod and you can extend the rod by turning it out, or shrink it by turning it in.  It's been a while since i put my new booster on so I don't recall exactly. By looking at it, you should see how it adjusts.

[Irish_Alley]

this probably doesn't effect you any but on my k20 when i broke the booster i replaced it with one off a c10 it was a free be it works but its hard as heck to push but it you remove the vacuum its even harder. could it be that your booster was made for jb5 when you have jb3 brakes. the booster is made to push harder due to the bigger brakes, since you have smaller brakes its just over powering the master cylinder?

[Lt.Del]

hard to push down sounds like a bad booster or check valve.  Those little plastic check valves on the booster, on the vacuum line are like $5. 

[Captkaos]

Did you not get the rod from the donor booster?

What are you comparing to for it to be Soft?  Anything new is going to be firmer than a 20 year old vehicle.  Does it ever get pressure or is it soft to the floor?

[Chevalade]

Braided lines will firm up the pedal as well. Especially if your existing lines are older than 5 years.

[Hotrod Steve]

Hello

Took off power booster, adjusted rod out about 3/8 of a inch.
Now have good brakes.
Will replace brake lines next, as it's a 26 year old truck.

Thank you all for your help.
Steve