[Tom '68SS]

I have a '68 chevelle, i'm in the process of doing a frame off restoration,my car has pdb on the front, and drum on the rear. All the components are brand new, front to rear. I,m able to get dot 5 fluid to the front with no problem, but am having no luck getting fluid to the back. I've tried gravity bleeding,also with no results. It seems that after bench bleeding the master,and hooking up the lines,the system will not progress any further, meaning I can't even get a flow of fluid when I crack the fitting on the master and have my wife depress the brake pedal. It seems that because all my lines are new, and full of air,I can't initiate a flow of fluid. I also have tried to use a hand held vacume pump on the back cyl. with only marginal success. I will also note that I returned the master, thinking it was defective, and recieved a replacment. As I have noted, all components are brand new, not refurbished. Any ideas would be welcomed.(I'm still able to bench bleed the master,just can't get any further.)

 

[SoCalRat]

Is there a button on the proportioning valve? May have to depress it.

 

[Tom '68SS]

no,there is no reset button

 

[JimB]

Hey , I had the same problem. I drained all f;uid out and blew AIR from the the brake fartherst from master cylinder and then progressed from there. It did the trick. I would try bleed the brakes starting from the farther from the master cylinder first and then what I did. ( I am assuming you have the correct proportioning valve). I didn't and so I ask. I thought I did. The back brakes don't get the same amout of fluid pressure as the fronts it seems.

 

[SoCalRat]

Your rear brake cylinders may be clogged with 38 years of crud. Mine were on my 67. I just replaced them when I converted to front discs.

Is this an original disc brake car. Check to see if you have a rubber hose in the back that may be swollen. And check this link http://www.chevelles.com/forums/showthread.php?t=146394&highlight=bleeding+brakes

 

[Schurkey]

It seems that after bench bleeding the master,and hooking up the lines,the system will not progress any further, meaning I can't even get a flow of fluid when I crack the fitting on the master and have my wife depress the brake pedal.

If you can't get fluid out of the rear-brake port on the master cylinder, either you have a defective master cylinder; or you didn't bench bleed properly.

I'm going with needing to re-bench-bleed the master.

If you have no fluid at the master cylinder port, there's NO point to blaming problems on the wheel cylinders or other "downstream" plumbing. I'm not saying that downstream plumbing is "good", just that you aren't in a position yet to test it. Establish fluid flow at the master first.

This is exactly why I recommend using a REAL pressure bleeder. You connect the pressure bleeder to even a half-ass bench-bled master cylinder and in five seconds you'll know if you have fluid flow to the rear wheels. Gravity bleeding is unlikely to fill the hydraulic system in a timely manner. Vacuum bleeding is a total waste of time as far as I'm concerned. You have so much air coming around the threads of the bleeder screw, and perhaps past the cups in the wheel cylinder that you'll never know if you're done--you always get air bubbles.

Reverse injection bleeding might do you some good--but ONLY if you already know that there's no contaminants hiding in the existing plumbing. If there's any crap anywhere in the system, a reverse injection system just pushes it up to the master cylinder, contaminating the new part. Also, reverse injection pumps fluid in near the top of the wheel cylinder (includes "calipers") but the fluid port is lower. Therefore you may leave an air bubble in the wheel cylinder. Reverse injection MUST be followed by bit of bleeding in the regular direction.

 

[68L79ELCAMINO]

I had a similar problem with my car after all new components. In my case the front bled fine but nothing to the rear. The pedal would get hard like there was pressure building. In fact the pedal got very hard. The aftermarket booster was to blame in my case. It would not release. After a new one all went well.

 

[ktrim]

had the same problem with mine, My brother in law suggested lifting the back of the car on jack stands and running the engine (for the booster work) while bleeding. It did the trick

 

[JimB]

Wow, I haven't heard of some of these tricks. I am very intrested to find out what fixes your problem. If your are getting fluid to your proportioning valve. and it passed that. I can't understand why you are are not getting fluid to the rear wheel cylinders, You said all were new. If you break a line to each unit . There should be fluid unless there is air. Then if you bleed the brakes in normal fashion it should bleed them in a matter of a few (seconds) Minutes.

 

[Pate]

I had the same problem when I converted my 68 using the Master Power disc kit. They told me to take off the rear line from the prop valve and push a small screwdriver in the hole and push forward to center the prop valve. They said that the valve will close off the rear line because of the unequal pressure. I centered mine and it finally bled like normal. I also used a test light to check and see if the pressure switch had closed and it was. You will hear the piston snap back into place when you push it forward. The light should also go off.

 

[NOTHINBUT69s]

I've heard of the rubber brake line swelling up on the inside and closing off flow from sitting for a long time.
I would start at the master cyl and loosen the line, if you have fluid there, loosen the line at the top of the proportioning valve, fluid there? if so keep going down.
Let us know what you come up with.

 

[jloshotz]

If you have access to a vacuum pump (i know mity-vac makes one) it might do the trick for you. It will actually "pull" the fluid to the wheel locations, almost like priming a siphon.

 

[Olle]

Tom,

You can't get any fluid at all from the rear port, even when you remove the fitting, right? I can see two reasons:

1: Bad m/c. Not very likely, as you have tried two new units already.

2: Something is stopping the piston from returning all the way and letting fluid into the rear section of the cylinder. If you did get fluid when bench bleeding, but not when it's on the car, I can almost bet that this is the case. Check the pedal and make sure that it's not pushing on the m/c when it's all the way up. If everything looks ok, loosen the nuts that hold the m/c a few turns and try again. If it works now, you have a pushrod that's too long (the one between the m/c and the booster). This seems to be a very common problem, as I have seen many posts about this, and it also happened to me not too long ago. The remedy is to either shim the m/c or take the pushrod out and shorten it.

I don't buy the "bad bench bleeding" theory. If the m/c is working correctly, you should get fluid flow even if some air is trapped in it.