About to throw in the towel.....

[SCOTI]

My 74 has kicked my arse. I'm done, whooped, beaten.... you name it.

I had a bad wheel cyl out back (pass side) & lost enough fluid to pull air into the system. This happened a few weeks back so I had to 'temp' it & fill it back up w/fluid to get me by until I had enough time to have it down for a day or two. I was off last week for my trip to Ohio so I did some maint:

I replaced the wheel cyl's out back.
Installed new shoes out back.
Cleaned the drums & re-installed them.
I replaced the front pads & turned the rotors.
I replaced the master cyl & pwr booster (only remaining items that weren't replaced/refurbished when I purchased the truck).

We start bleeding the brakes but something isn't right. I'm not getting 'enough' pressure to the rears. The front L bleeder shoots fluid like you would expect a hydraulic system to when pressurized.

NONE OF THE OTHER BLEEDERS HAVE SIMILAR PRESSURE. We think the R front bleeder is compromised because it gets good fluid flow when completely removed. So a bad bleeder makes sense here.....

The rears just don't do much of anything. I can pressurize the pedal & fluid will barely trickle out of the rear bleeder/s. We thought maybe the master didn't bench bleed enough so we did it more. We hooked up a test line to the port & get decent flow when the pedal is pushed. We hooked the rear lines back up & there's no improvement @ the bleeder/s.

We thought the prop valve was the issue. We tried cracking the lines to it.
No improvement.
We tried the whole 'resetting' thing but couldn't get the 'pin' to shift in or out any measureable amount.
No improvement.
I had a new prop valve for my 68 so we decided to use it. Of course, the front lines wouldn't come loose from the original prop valve which required replacing them as well.

New prop valve, new front brake lines.
No improvement.

When you stand on the pedal & open the front bleeders, the pedal will sink.
When you stand on the pedal & open the rear bleeders, the pedal doesn't change.

I'm open to suggestion here . . ........

[jeffspower]

When you crack the rear bleeders, does the pedal sink? If not, the rear axle hose could be collapsed. If this is what is happening, crack the steel line connection going INTO the hose. If the pedal drops & you have good flow there, it's a bad hose.

[SCOTI]

Originally Posted by jeffspower

When you crack the rear bleeders, does the pedal sink?

No, the pedal does not sink.

If not, the rear axle hose could be collapsed. If this is what is happening, crack the steel line connection going INTO the hose. If the pedal drops & you have good flow there, it's a bad hose.

Good idea. I'll inspect the rear lines tomorrow.

I was also talking w/my buddy & he said maybe we should throw the old master back on & see if things change. I had thought of this but we re-bled the master & it appeared ok.

He's now thinking maybe the new master has 'flow', but it's only a low pressure flow & won't flow @ the higher pressure the system needs.

[Kontrol Phreaks]

These are the processes I've always done and worked for me. I'm sure you've done the same but thought the Info might help others. I first thought proportioning valve myself, but you say it's been changed. I still feel confident that it's relate to that valve still myself. Good luck with the issue though.


Bench blead the master cylinder / booster ahead of time.

Start by bleading the farthest wheel from the master cyl., which would be Right Rear. Complete the back before heading to front.

Keep an eye of the brake fluid level as you go so it doesn't run low and suck air.

Work your way forward from each wheel.

You can also gravity blead a system overnight by barely cracking each wheel cylinder. Run a small hose off the bleader to a catch can below the each wheel and let them slowly drip overnight. Sometimes it takes that, or pressure bleading/sucking to get a large pocket of air out.

[cdowns]

in cases like this it is a real asset if you have a manufacturers service manual a bigger asset is reading it
in most service manuals i've seen they tell how to center the pin on the combination valve for proper bleeding of the brake system

[SCOTI]

Originally Posted by Kontrol Phreaks

Bench blead the master cylinder / booster ahead of time.

Start by bleading the farthest wheel from the master cyl., which would be Right Rear. Complete the back before heading to front.

Keep an eye of the brake fluid level as you go so it doesn't run low and suck air.

Work your way forward from each wheel.

You can also gravity blead a system overnight by barely cracking each wheel cylinder. Run a small hose off the bleader to a catch can below the each wheel and let them slowly drip overnight. Sometimes it takes that, or pressure bleading/sucking to get a large pocket of air out.

I follow the same logic & it's worked for years.... on many different vehicles. I don't normally do the 'gravity bleed' thing but we even tried that method to see if would help the cause.

For the record, the 'prop' valve that we installed is 'new' as in never used vs. a newly installed used part. This should eliminate the prop valve as the source of the issue.

I'm going to re-try the original master. If the issue persists, we'll start opening up the rear lines from the master working back to the rear 'T' & see if/when the pedal drops.

[thekid54]

You mentioned you would check the rear lines for collapse or blockage, have you? I would start there before going throught the hassle of changing the master...again. I had a similar problem with my '62. I replaced the rear wheel cylinders and when I went to bleed nothing would come out. Turns out, the rubber line going to the T on the axle was clogged solid. I think the fresh brake fluid caused it to finally break down. I'd check your rear lines first.

[SCOTI]

Originally Posted by thekid54

You mentioned you would check the rear lines for collapse or blockage, have you? I would start there before going throught the hassle of changing the master...again. I had a similar problem with my '62. I replaced the rear wheel cylinders and when I went to bleed nothing would come out. Turns out, the rubber line going to the T on the axle was clogged solid. I think the fresh brake fluid caused it to finally break down. I'd check your rear lines first.

I'll check them tonight. They were ok when I pulled the truck into the driveway so I have my doubts of a collapsed line being the issue.

[SCOTI]

No pinched lines.
No pedal drop even when disconnecting the rear lines @ the master.

I went ahead & installed the old master & bench bled it. When I checked for flow out of my 'bleeding' tube, & it shot out vs. the slow trickle we were seeing.

I started bleeding the brakes. Within 4 or 5 strokes of the pedal I had pressure @ the pass rear wheel cylinder. I decided to just use the old one but after several rounds of bleeding the pedal feels firm...... & then sinks.

Both of them are bad.
It's called 'scot-luck'.

[gringoloco]

Originally Posted by SCOTI

It's called 'scot-luck'.

Dude, you stole my luck... I know you're sitting there the whole time thinking "There's no wayboth MCs are bad!"

[SCOTI]

Originally Posted by gringoloco

Dude, you stole my luck... I know you're sitting there the whole time thinking "There's no wayboth MCs are bad!"

After the wheel cyl puked & I lost all the fluid, I filled it back up to get me by for a week or two. After the second week, the pedal started sinking to the floor so I thought it had lost all the fluid again. When I checked the level, it was full but the pedal was still sinking.

I figured the old master was on it's way out & this was the best time for the swap since I was going to be bleeding the system anyway. The 'new' reman master on the other hand . . . .....

I just returned from exchanging it for a 'new', new Wagner master so I hope to get some color on it & get it installed tomorrow.

[pharcydekm]

There are two parts I refuse to buy remanned that is Water Pumps and Master Cylinders.

Just my .02 but I'm sure your problem will be solved with the new master. Good luck!

[SCOTI]

Originally Posted by pharcydekm

There are two parts I refuse to buy remanned that is Water Pumps and Master Cylinders.

Just my .02 but I'm sure your problem will be solved with the new master. Good luck!

They didn't have a new one @ the time & I needed to get some color on it so I could start the re-assembly process. Compromise sucks sometimes. I asked the guy if they were going to reimburse me for the 2qts of fluid I dumped on the ground trying to bleed the f*cker. He said I prob could get replacement fluid but only the mgr could authorize it...... tomorrow.

[pissonNOS]

dont throw in the towel yet as stupid as it sound you probly got a bad new master cylinder, we get it at work all the time "new" alternators that dont charge starters that dont work, but the most common of them all has to be sh!tty master cylinders. most times we just buy a kit and hone it if we can. man quality is good these days haha

[Kontrol Phreaks]

If you throw anything, just make sure it's not in the direction of the truck. hahahaha

Stand back and take a look at if from a distance and eliminate / resolve different solutions as you go down the list. If the Master keep coming up in each process then you might have to just get yet another one and try it.


Good luck Scott.

[fastbagged68]

When you are bleeding them do not push the pedal all the way down. Pump the brakes 3-5 times and hold the last one about half way. Then crack the bleeder and your pedal should drop a little bit. Do not allow the pedal to drop all the way down. Tighten the bleeder and redo it. I had to bleed my system several times to get it to work right.

[SCOTI]

Originally Posted by fastbagged68

When you are bleeding them do not push the pedal all the way down. Pump the brakes 3-5 times and hold the last one about half way. Then crack the bleeder and your pedal should drop a little bit. Do not allow the pedal to drop all the way down. Tighten the bleeder and redo it. I had to bleed my system several times to get it to work right.

We....
Apply pedal pressure
Crack the bleeder until the pedal starts dropping
Close the bleeder before the pedal is floored.

Repeat @ each bleeder x3 starting from the farthest & working to the closest to the master.

[chevydog66]

Are the rear bleeders plugged with dirt? Mine were on my 72. Try to remove them and clean them out with a paper clip. Blow air thru them.

[tommie]

glad you figured out you had 2 bad master cylinders....

i hate it when you buy new parts that a defective right off of the shelf.

tommie

[SCOTI]

Originally Posted by chevydog66

Are the rear bleeders plugged with dirt? Mine were on my 72. Try to remove them and clean them out with a paper clip. Blow air thru them.

The reason for tearing the system down was to replace the rear wheel cylinders because one failed.... so they were both 'new'.

I got the 'new' Wagner master painted & installed last night. I couldn't do much more w/o assistance so I'm @ a standstill. Hopefully tonight my better half will be able to help me bleed the system again.

Thanks for all the suggestions!

[semperfidoordie]

I'm in a similar boat...going backwards brakes work fine..going forward they hardly work at all...checked the front disc brake pads..they're good...bled the thing probably 10 times...checked the rear drums for brake shoes...they're good...wheel cyls are good...had old gunked up brake fluid in the master cylinder cleaned it...pushed all the badness out and put new brake fluid in...no dice...think it might be booster or the master cyl any suggestions before I go spend a good 100 on it?

[buffle]

had same problem on a 77. if u look on the front crossmember there is a small 3 way block that feed the rear. this , i guess is what make the brake light come on. the light that tells u about brake problems. had a piched line in back when i lowered truck and after replacing line, no fluid to the rear. it worked for me.

[SCOTI]

Originally Posted by buffle

had same problem on a 77. if u look on the front crossmember there is a small 3 way block that feed the rear. this , i guess is what make the brake light come on. the light that tells u about brake problems. had a piched line in back when i lowered truck and after replacing line, no fluid to the rear. it worked for me.

All lines were inspected & in good shape.

I replaced the 'new/rebuilt' master w/a 'new/new' master. The pedal isn't as high as it was before, so I still need to adjust the brake rod. Other than that, the truck is back on the road & the brakes work better than before.

[bigbluthng]

i had the same issue with my 71 camaro. i replace the master cyl, prop valve, rubber brake lines and wouldn't get fluid to the rear. i removed the rear line from the prop valve, disconnected the rear hose and blew air through line. problem solved. all kinds of gunk came shooting out. i later bled the brakes and drove down to the brake shop to have it pressure bled. you might also want to check for kinks in your lines.

[jkade]

Originally Posted by SCOTI

All lines were inspected & in good shape.

I replaced the 'new/rebuilt' master w/a 'new/new' master. The pedal isn't as high as it was before, so I still need to adjust the brake rod. Other than that, the truck is back on the road & the brakes work better than before.

I am glad to hear you got it fixed, damn the luck I am glad mine went as smooth as it did, only took me about 3 minutes.