Installed a new M/C, doesn't work at all, what am I missing??
 

Just installed a new master cylinder on my 62 c20 that I got from partsgeek.com last week. I can pump and pump and I get no resistance. What am I missing here?

Pic of the new one on the truck. Old one on the bench.

Thanks. Matt

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Did you bench bleed it before installing it?

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I did not. Is that a must with this cylinder?

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I thought it was a must do situation on all m/c.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Yeah, bench bleeding is a must! I believe you should be able to do it while mounted by screwing in the supplied plugs it came with not 100% sure maybe someone else can chime in.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

You can "bench bleed" with it mounted but it makes a mess. Better just to remove it and do it. You probably need to bleed the clutch side too don't you?

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

May get some negative feedback on this, but it CAN be bled while mounted on firewall just as if in a vise on a bench--but takes 2 people. With pedal properly mounted, and with lines connected, pump pedal 2-3 times & hold to floor. Second person cracks each line to release any pressure(very slight amt. at 1st).

After he re-tightens lines, repeat the process, sometimes several times until all the air seems removed from the lines leading from mc.

Then, go about pumping & cracking lines, starting at farthest wheel cyl from the master, as measured along the line itself.

May then need to do complete process again, beginning with the mc and continuing along the wheel cyls.

Good luck & I hope this procedure works as well for you as it ALWAYS has for me.
Sam

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

And when you do this don't forget to check the resivoir every 5 pumps or so. You don't want to run it dry and have to start all over again.. :lol:

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

you also have to bleed the clutch. same principle as but you bleed the air out at the slave cyl
ron

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Yes it can be 'bench' bled on the truck. Just follow the bench bleeding instructions.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I'm sure this has been resolved, BFWIW, I remember a guy swapping out a fuel pump on a Mercedes work van (like the one on American Pickers) and he couldn't get it started. I asked if he installed in backwards as it had an oblong shape (prob electric). I was kidding. Long and short of it, he removed the fuel pump and found that he did not remove the plastic storage caps at each end of pump.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

This is how I've always done it, but I can't get it to build pressure? Whether the clutch or the brake, I can pump all I want...just doesn't seem like it's doing anything.

Matt

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

bench bleed ... you can do it in the truck but it will take a very long time
be faster to remove it and bench bleed
.
just went through this
spend 4 hrs bleed in truck very flustrating then removed it jigged up in vice
within 10 minutes done 1/2 hr 45 minutes back in truck for full bleed
done moved on

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Buck, try this if u don't wanna remove & 'bench bleed'. Remove the brake line from the mc. Pump several times & while holding pedal to floor, let helper place his thumb over outlet of mc. Let up pedal, THEN remove thumb, & pump several times again, ending with pedal to floor. Thumb over hole again while letting up. etc, etc.

Theory here is that there is NO air available to suck back into mc, as pedal moves back to top. Previous method allows pedal release to draw in air from within the re-tightened lines*. *Keep in mind these re-tightened lines may have a downstream leak directly to atmosphere.

Sam

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I once bench bled a master by using 2 short lengths of brake line that dumped back into the reservoir. The ends of the lines were below the fluid level. As I pumped bubbles would come out thru the fluid, but there was no air to be sucked back in.

Not sure if this way is correct, but it seemed to work...

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

buckroseau, you probably already know that if you get brake fluid on the paint it will remove it. Be sure the wash it off.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

x2 on this... has always worked for me too.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Blown240 has it right. Make up 2 lines that go from outlets and make the lines loop around so they are submerged in the reservoir below the fluid level. Push the cylinder in and out with a screwdriver while you have the master cyl in the bench vice. When the bubbles stop coming out of the lines it is ready to install. Leave the bleed lines on until you are ready to install the brake lines so you don't spill very much when you switch the lines. Also have a piece of cardboard and rags underneath so you don't get any dripping brake fluid on any painted surfaces.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Bleeding the master cylinder makes absolutely no difference whether it is clamped in a vise or bolted to the firewall, as long as you follow the bleeding instructions for the master, and the master only. I find it easier to bleed the master using the pedal to push the piston versus by hand with a screwdriver or similar. The tubes from the ports into the reservoir does work but the current recommended method is to install the plastic plugs into the ports of the master.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I agree, the master cyl can be mounted on the firewall or in a bench vice. The lines looped around and submerged below the fluid level guarantees that all the air bubbles are out, and you can see that all the air is out. What ever method is used, the important thing is you know, and can see, that the bubbles are out before you install it.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Only tidbit I can offer is that when "bench bleeding" on the truck, the master cylinder must be dead level. Jack up the front or back of the truck to make the M/C level. If it is uphill or downhill, air will be trapped in the high end and will never come out.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

I bought a one man bleeding kit at autozone years ago that works great.You can bleed the master cylinder on the bench or in the truck without a problem.It came with all the fittings and hoses.No mess and no need for 2 people.Only problem is I don't now if they sell them anymore.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Is bench bleeding a good idea? Yes. Only because it will make bleeding it on the vehicle go faster, but it's not necessary. I can't count how many times I've bench bled a MC before installing one. ...Because I don't.

You are essentially doing the same thing once it's mounted on the car/truck, it will just take a little longer.

Make sure all your drum pads are adjusted correctly first. Then do long slow pumps of the pedal.

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

Finally getting back to this. I just finished a rear axle swap out of a 97 c3500. Also all new brake hardware and wheel cylinders all the way around. So, I essentially had every brake line in the system opened up.

Bought an pneumatic bleeder yesterday and still getting my ass kicked on this now. I got fluid to start pumping out the rear cylinders with the bleeder, but I can not get anything out the front. I installed a new slave cylinder on the clutch as well and was able to get that bled out and working. But, just can not get fluid to come out the front. This isn't rocket science, at least I didn't think it was?

Matt

Re: Installed a new M/C, doesn't work at all, what am I missing??
 

A poor connection with a tiny leak can cause big problems. Recheck those front connections, wipe them clean and dry then watch for fluid weeping out . That's all I can come up with.