Bolt size confusion and stuck master cylinder

[R8rPhan]

Okay, so it's not the push rod length.. I took the mounting nuts off the master cylinder, and when I push on the pedal, I can feel it being pushed off of the booster (and hear it drag on the studs) within about a quarter inch of pedal travel... So that's eliminated...

I don't think it's the rears, but not sure.. I think there is an issue with the fronts... either application (mismatch of what the MC puts out and the calipers need), or the proportional valve (a distinct possibility), or one of the calipers (since it pulled to the right before this all started and still does, that wins the 'most likely' award right now)...

As far as the proportional valve goes, there is a quarter inch line that goes from the front side of the MC to the valve, and an eighth inch line from the rear port of the MC to the valve, then a quarter inch line that goes out of the valve to the rear brakes and two eighth inch lines that go to the fronts (one to the left and one to the right)...

I'll bleed everything again and check that left caliper/pads before I play with the P valve.. I also need to figure out why it's so hard to push fluid to the rears when bleeding.. Think I'll pull the lines off of the wheel cylinders (and go ahead and replace the other back one) and try pushing fluid through it then.. (maybe a blockage???)..

That P Valve looks like a beotch to replace, so I hope I don't have to go there.. Was hard just to get my hand in there to push the reset button...

So anyway, next break in the weather is Monday.. I better start working on getting a ride into town to take care of what business I need to do this week, and I'll keep researching and learning..

But... I got the new thermostat in, and redid the temp sensor, and now the temp gauge works and the truck warms up nice and quick and isn't running cold anymore.. Should be easier on the engine and improve mileage some..

Figured out a mounting place for the intermittent wiper module I bought, removed the circuit board mounted pot from it and extended it with some ethernet cable so that the module can be mounted under the dash near the ashtray and the pot can be mounted right next to the stock wiper control... Made up a little harness with a couple turn signal indicator LEDs because the ones in that digital dash I bought stopped working (and I don't want to mess with having the assembly replaced right now), so I can install them in the dash gauge cluster bezel, and I won't be driving around with my turn indicators on anymore... I can put the LEDs and the wiper control in over the next couple days...

I'll get the brakes fixed before long, if I have to replace every damn part in the system to do it (including the booster/MC I just put in)..

But as soon as weather allows, I'm gonna pull the wheels off again and get to the bottom of all this, one way or the other... In the mean time, I'm gonna try to research/compare caliper piston sizes, wheel cylinder sizes, and master cylinder piston/stroke to try and eliminate a mismatch issue... I kinda doubt that's the issue though, as I would expect it to do 'something'... I barely have brakes at all.. eBrakes work great though..

 

[R8rPhan]

I give up... I took the master cylinder off and bench bled it, and the back port pumped out fluid real good, but hardly any came out of the front port (larger line - rear brakes?), and when it did it was only about every third push of the piston..

Put it back on the truck and tried bleeding the brakes again, and same deal, push like 50 times and the brake fluid only moves up the clear tube I had on the bleed zerk at the rear far side wheel cylinder, about 9 inches or so...

So I called the auto parts store where I got this rebuilt master cylinder and I'm having them bring up a complete rebuilt MC/Booster/push rod assy from another store for a 79 C10, which as far as I can figure out is what this truck really is (mostly)... They didn't have a brand new one in stock at any of their stores or I would have ordered that instead..

So, hopefully this gets my brakes fixed and I can get back on the road.. Sheesh! What a freakin' ordeal!

Oh, and the intermittent wiper module isn't gonna work with this old chevy truck either, as no matter where I try to insert the relay in the low speed circuit, the thing won't park the wipers properly.. So that's a huge fail too! After all that work, I just had to put it all back like it was... I'll have to look into other options... May have to create something custom...

I'm wore out and sick of fighting this thing and losing every battle... Was 'trying' to be smart and not just throw money at an old truck.. That's the reason I got it in the first place, so I didn't have to deal with commie smog laws, could work on it myself, and didn't have to constantly just 'throw money at it'

 

[Big Chip]

I recently found out I have a newer style pulse board in mine but it mostly works, just weird on the intermittent part so I have no idea why. There’s wiring diagrams available on this forum if you need to figure out what’s going on.

Good luck with it all.

 

[R8rPhan]

I recently found out I have a newer style pulse board in mine but it mostly works, just weird on the intermittent part so I have no idea why. There’s wiring diagrams available on this forum if you need to figure out what’s going on.

Good luck with it all.

Yeah, I still have the diagrams and color legends from when I rewired the truck... I've tried inserting the relay in three different places on the low speed circuit, and this little board just isn't gonna work with the older GM switch/motor... That I can figure out anyway..

The aftermarket one offered for these old trucks is an easy install, but it's expensive, and 'inelegant' in operation to say the least.. So I tried this TIMER BOARD because in the notes, they included how somebody got it to work with GM, but now I'm thinking it must have been for a different year range or something..

In fact, rereading the notes it was a 67-72 range of chevy's that the guy got it to work on (maybe I should go look at the wiring diagrams for those years to see how they're different)

When I get the brake issue handled, I'm gonna start a thread on it in the appropriate forum area before I completely give up...

 

[R8rPhan]

So, I got into town today and bought a brand new master cylinder and booster drum for a 79 C10.. This 'should' be what I need to get the truck back on the road.. if not, there's only about another 100-120 bucks I have to spend before I have replaced 'all' of the hydraulics on this thing except for the lines... Half tempted to do that anyway at this point!

 

[Rusty Nail]

@bucket knows about that wiper thingy .

So you got a hung caliper or what?
The cylinder can get hung up on the bore if it's allowed to wobble.
Maybe you have a soft line collapsing. Sucking itself closed. It's actually very common in this year range.

 

[R8rPhan]

Okay, I have brakes again..

Really took my time bench bleeding the new MC.. Put the new booster in, installed the MC, and bled all the brakes again.. Unfortunately, the dust boot wasn't included with the new booster, so I called down to the auto parts store and had them pull the one that was on the old booster (that I used as a core) and they're holding it for me.. Unfortunately, that means I gotta pull the booster off again, which is the biggest PITA of this whole project (third time's a charm, right?)..

This time it was easier to move fluid to the right rear cylinder, but still took like 250 pumps, and I still had a soft pedal..


So I decided to go ahead and replace the driver side wheel cylinder too, instead of just trying to bleed it.. Just had to get some vice grips on the brake line nut to get it to free up.. Glad I did. because when I took the old one off, the cups on each end were full of fluid (eureka!)..

I hooked the bleeder waste tube directly up to the brake line at the rear wheel and 'now' it was moving fluid.. and as I pumped, I could feel the pedal coming up 'finally!'.. That's what was preventing me from being able to bleed the rears...

So got that replaced, and bled the fronts (I'm gonna go ahead and replace the front calipers in a couple weeks too, then I'll re-bleed everything again).. I have brakes!

Now the issue I'm having is getting the booster to work.. I put a tee in the line going to the heater control vacuum reservoir.. Couldn't tell any difference.. Still felt like no assist... Then I removed that, and disconnected the vacuum line at the front of the throttle body where the PCV is connected, and hooked the booster directly to that.. Still couldn't feel any difference.. No assist..

So I'm not sure what's going on.. That port is full manifold vacuum, right?

So, I'm gonna do a little testing on the new booster tomorrow and see if it's all good, the check valve is good, etc. and I need to get a fitting to hook the thing up at the rear of the carb.. I can't see back there but I can feel the plug, so there should be a threaded port I can screw a fitting into there... I have a vacuum gauge somewhere from my bracket racing days I'll see if I can find.. I think I know where it is, but who knows if it's still any good...

Wish I had a vacuum pump.. would be handy for testing the new booster... would have made bleeding the brakes a lot easier too...

Anyone have any tips on what might be the issue with the booster? Shouldn't I be able to feel a definite difference in how much foot pressure I need to use the brakes?

Anyone know what size threads that plug is so I know what fitting to get? Probably gonna have it sent via amazon prime so I don't have to drive into town for it.. (would be cool if it's the same size as an air compressor air hose, I have tons of those barbed fittings)

Anyways, I have brakes.. They still take a lot of force to push, but I don't have to pump them anymore, nothing leaks, and it isn't pulling hard anymore...

Thanks,
Mark

 

[Rusty Nail]

Pleased that your great brake debacle seems to be nearing it's end.

Yep. Full manifold vacuum from that port at the back of the intake should be good.
You know that is a one way check valve. Are you sure it's facing the right way?

After reading about the wheel cylinder, all bets are off!

Maybe next time it would be more effective to simply pay a shop?

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[Dougnsalem]

I recently found out I have a newer style pulse board in mine but it mostly works, just weird on the intermittent part so I have no idea why.

HA! That's like me saying my truck is mostly rust free.....

 

[Big Chip]

HA! That's like me saying my truck is mostly rust free.....

It isn’t?!!

 

[Dougnsalem]

It isn’t?!!

Lol. Yeah, it's a beauty. Let me know when you want to trade. I'm starting to think mine came from Michigan....

 

[Big Chip]

Lol. Yeah, it's a beauty. Let me know when you want to trade. I'm starting to think mine came from Michigan....

I think you may be right.

 

[Dougnsalem]

I think you may be right.

At least my wipers work.














Mostly.....

 

[R8rPhan]

Maybe next time it would be more effective to simply pay a shop?

You must be registered for see images attach

Would have cost me about 50% more to just have it towed there than what I paid in parts.. and I barely have the money for this as it is..

I don't think the check valve can be put in backwards, but it's not (it came pre installed and there's only barbs for the hose on one end..)

I don't understand your comment about the wheel cylinder or the need for educating me on the meaning of the word 'debacle' (I am in my sixties, and I've even been to some college, so I've heard the word before as well as many others).. You'll have to enlighten me on the meaning and intent of your comments there...

So I take it you don't know what size/thread the port is?

 

[Big Chip]

At least my wipers work.














Mostly.....

Same here amigo.