C3500 Almost No Brake Pedal.

[Frank Enstein]

Frank's hydroboost leaks quite a bit. He stops o.k. and the HB on the wife's Astro doesn't.

Maybe that's part of the reason Frank stops o.k. and the Astro will fling you through the windshield if you LOOK at the brake pedal...

 

[Pinger]

Quickest way to a diagnosis here I think would be to manually adjust the rear brakes (all the way to just grabbing the drums) and see if that sorts the pedal. If it does, a dive into the drums to see why the adjustment was necessary.
If it doesn't (sufficiently) improve pedal travel then the problem is elsewhere, probably a leak and probably a wheel cylinder. Drums will be coming off anyway I reckon but doing the adjustment first would help know what to focus on when they are removed. Wheel cylinder boots need to be pulled off to find a leak (they hold the fluid like a secret).

 

[1ton-o-fun]

Thanks! Vacation is in 2 weeks, looks like I'm going to be busy. I have a backup camera, big3 kit, hvac blower and other stuff to install. And then there's the 3500 Express van to strip as well.

 

[BBslider001]

I am going through the same symptoms with my Burban. Did all of the above except replace rear wheel cylinders. I do have a leaky axle seal, so I may just farm it out and get it all done. I have zero time and it's 105* daily right now. When I pulled the drums to adjust today, there was no sign of brake fluid leak, but I have been reading that it can hide? That is odd. Seems like it would come out a little bit at least. I'll report back. If I need to start a new thread, I can do that. Thanks !

 

[1ton-o-fun]

I am going through the same symptoms with my Burban. Did all of the above except replace rear wheel cylinders. I do have a leaky axle seal, so I may just farm it out and get it all done. I have zero time and it's 105* daily right now. When I pulled the drums to adjust today, there was no sign of brake fluid leak, but I have been reading that it can hide? That is odd. Seems like it would come out a little bit at least. I'll report back. If I need to start a new thread, I can do that. Thanks !

Totally fine to use this thread. The more the merrier! Going to start on my truck Tomorrow!

 

[HotWheelsBurban]

Yep, good luck and stay hydrated! Work all day Monday and Tuesday for us, but Wednesday and Thursday are looking good for truck days. I wanna get back in the AC.....

 

[Pinger]

When I pulled the drums to adjust today, there was no sign of brake fluid leak, but I have been reading that it can hide? That is odd. Seems like it would come out a little bit at least.

Did you pull the external boots on the cylinders? They retain any leaked fluid.

 

[BBslider001]

I am going through the same symptoms with my Burban. Did all of the above except replace rear wheel cylinders. I do have a leaky axle seal, so I may just farm it out and get it all done. I have zero time and it's 105* daily right now. When I pulled the drums to adjust today, there was no sign of brake fluid leak, but I have been reading that it can hide? That is odd. Seems like it would come out a little bit at least. I'll report back. If I need to start a new thread, I can do that. Thanks !

Much appreciated! Hopefully this will get resolved without a lot of guessing LOL. I HATE the thought of anyone touching my truck and I do my own work, but time is of the essence with this issue. I do have a shop I trust to do rear brakes and an axle seal. I'm always concerned a "mechanic" won't be able to properly diag it because it's an older truck. I'll get it in tomorrow or Wed.

 

[BBslider001]

Did you pull the external boots on the cylinders? They retain any leaked fluid.

I didn't. Wouldn't it leak past those if it was really pushing it out? Also, the fluid level never dropped in the Master Cylinder. Of course I changed out the Master thinking it was a simple issue when I didn't see any leaks. Live and learn I guess. I don't throw parts at problems, but I really thought, based on the symptoms, that the MC was the issue. It's 30 years old with 160k miles and I saw no fluid anywhere.

 

[Pinger]

I didn't. Wouldn't it leak past those if it was really pushing it out?

Probably.
But another thing to consider is that if they can leak outwards (to any extent) they can draw air in when the brakes is released if the shoes are a bit slow in moving back.

Also, the fluid level never dropped in the Master Cylinder. Of course I changed out the Master thinking it was a simple issue when I didn't see any leaks. Live and learn I guess. I don't throw parts at problems, but I really thought, based on the symptoms, that the MC was the issue. It's 30 years old with 160k miles and I saw no fluid anywhere.

I wasn't losing fluid either and didn't think the cylinders were leaking either - until I peeled back the boots and found fluid. Fluid there attracts moisture and at least one of my pistons was corroded/seized - probably because of that.
FWIW, my journey to good brakes began with changing the master cylinder - twice...