Odd brake pedal issue - this dang truck.

[rcarlisle]

Ok, so here is one that I'm looking into and it is kinda important to me.   Brakes.   When I go to press the pedal, the pedal resists, like it has a "stop" in it at first.   Then the pedal works sorta normal, but doesn't reeturn to top.   And it makes a noise like the linkage is going thru styrofoam or something.   So I looked and it appears there is some sort of something (pipe insulation?) in the sleeve on the interior side of firewall.   I'll have to investigate further, but what the heck is going on here?  The master cylinder looks to be fairly new.   Pedal is slow to return to top and squaeks, again like the linkage is passing thru the pipe insulation that may too tight around it.  

My general understanding has always been a solid link from pedal to cylinder with rods.   Would the pass-through be insulated normally to prevent air leak?  I'm big and old so getting under the dash is not an easy job.  

Someone please tell me what the linkage is SUPPOSED to look like up in there, so I can chase down what has been half done to use a nice term.  Would prefer to NOT have to remove it all.  But got to chase this one down.  Truck lacks confidence in braking.   They seem to work pretty well, just pedal seems to be in pipe insulation or something that is impeding is movements.

 

[rcarlisle]

I think I found the diagram.   ON the clutch page.   Was googling and got referred back to here.

[Gary Lewis]

Glad you found the illustration you need.

But it sound like you have a booster problem.  That's the big round thing behind the master, and what usually happens is that the master leaks brake fluid into the booster, which then breaks down internally.

In the brake section there's a test for the booster.  I think it is in the General tab, but I'm not sure.  Something to do with standing on the brake with the engine off then starting the engine.

[ArdWrknTrk]

Then vacuum builds and the pedal goes (relitively) soft.

You may be hearing air hissing through the diaphragm of the booster.

That sound will come from where the rod enters the booster (at the firewall penetration)

[rcarlisle]

Ok, here's  where we are this evening.   Unbolted the master cylinder, pulled it away, inspected rod from booster.  Very crusty.    Had wife press pedal and cleaned and cleaned.  Some better, but still does the trick of the initial resistance.  But not always.  I looked for the test.  I can't  do the one with the vacuum gauge.  Will check the other tomorrow.

When wife was pressing pedal, I could feel air coming out of engine side of booster.  The noise I'm hearing is the foam in the sleeve.  I'm  thinking it might be worth it to go ahead and replace booster.  I think the mc has been replaced and it doesn't seem to be leaking down at the pedal that ican detect.  Have had that in previous vehicles

Opinions?

Thanks for all the input you guys are offering.   It really is helping.

.  

[Gary Lewis]

Yes, I'd replace the booster.  If you are feeling air then it is bad.

[rcarlisle]

Booster ordered.  Pick up today or tomorrow.   Hopefully we'll get this issue corrected and can get to the other end of the brake lines - down at the wheels.  

Have watched the videos  - looks like this will be fun for someone with big hands...

Thanks for the help folks.

[ArdWrknTrk]

The trouble is, when the old master's rear seal went bad, brake fluid got sucked into the booster.
They didn't replace the booster and the brake fluid ate the rubber diaphragm.

Happens all the time.

[Gary Lewis]

Yep.  A bad master will kill a vacuum booster pretty quickly.

But make sure you do NOT adjust the rod between the master and booster.  There is an adjustment where the ball on the end can be turned in and out, and the adjustment is critical.  In too much gives you slack in the pedal, which isn't bad but reduces the stroke you have.  But out too much will cause the brakes to drag, which causes them to heat, which causes them to drag more, which..... and pretty soon they lock up.  Don't ask.

[rcarlisle]

Yep, that all makes sense.  THe master cyl looks good and newer than the booster.  THe pedal doesn't leak down to floor so I am hoping the master is still good.  

 But yes, if this doesn't fix it, I will spend $30 more for a new master.  I really dislike the bleeding process, especially the bench bleed.  But I do have a vise now which I didn't last time I tried that.  

I saw the diagram with .995" of rod sticking out.   I will confirm that on new one - wish I had seen that yesterday while I was in to the existing one.   But it's pretty crusty so a new one can't hurt.   Good new brake parts are never a bad thing.  

I hope the brakes are in good condition.  I haven't done drums in a long time.   May have to invest in a drum brake tool set - had one - think it was borrowed and never came back.  Just makes it easier than screw drivers and pliers.   No wobbles when I mash brakes so hopefully rotors and pads still good.  

I think I am going to concentrate on getting hte brakes all sorted.  And work on other projects I've ordered parts from.  Get that brake system fixed where I don't have to worry about it anymore.   Then can concentrate on other parts.

[Gary Lewis]

If you do decide to replace the master I'd recommend going with the later model one that has a plastic reservoir.  They don't leak at the cap the way the cast iron ones frequently do and you can see how much fluid you have.

In addition, it is easy to bleed the brakes on them as you can modify a cap and put a few psi of air pressure on the reservoir and then pressure-bleed the brakes.  Open a bleeder valve until you don't get air bubbles and you have clean fluid.

I use a pressure regulator and my shop compressed air, but others have used a garden sprayer to pump up a little bit of pressure.

[rcarlisle]

FIXED!  Booster cured that issue.  Now just feels like it might need pads/shoes soon.  Pedal is lower than I'm used to but it is old, too.   But it definitely has predictable brakes now.  

And that was pretty easy to replace.  Just like all the videos show.  Only difference was the end of booster shaft end up turned down instead.  No way it was going on pedal pin with it turned up.  

Thanks for all the input.  

[Gary Lewis]

Glad it fixed it.