Woogeroo
Valued Contributor
Posts: 2861
Reg: 05-26-02
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 11-14-24 08:03 PM - Post#2875601
1969 brake master cylinder, drum/drum
1965 chevy c10 pickup, 1965 style power brake booster
Hi folks.
This has been the setup in my truck since I bought it, I have had to replace a few brake cylinders in that time.
This latest one though does not seem to want to work, so either I am bleeding it wrong or it is bad off of the shelf.
brake cylinder pic
This setup has the external valve thingy, before it goes down to the wheel cylinders.
I did the bench bleed before installation, no more bubbles. I mounted it up. I did the brake bleed, right rear, left rear, front right, front left around again.
Seems like it only has the rear brakes, which is why I was replacing it.
I did the crack all four bleeders at each wheel with a tube on them, submerged in brake fluid and slowly pumped the brakes... then closed them up.
Same deal.
Anyway... anything else to check or try again before I swap it out for another unit?
I am out of ideas at this point.
Thanks.
-Woog
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bobb
Super Senior Member
Posts: 6857
Loc: paradise
Reg: 09-05-03
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11-15-24 07:08 AM - Post#2875609
In response to Woogeroo
pushrod length?
| 70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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Woogeroo
Valued Contributor
Posts: 2861
Reg: 05-26-02
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 11-15-24 03:32 PM - Post#2875615
In response to bobb
I took the proportion valve off and took it apart as much as possible and cleaned it up, gave it a brake clean bath.
Re-assembled everything... went to bleed brakes, saw brake fluid shooting out of the brake line onto the exhaust manifold.
Hmnn, that seems like a problem.
So, new brake line, new brake union fitting in place... will double check it all tomorrow and trying bleeding the brakes again.
-Woogeroo
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YOUNG57
Frequent Contributor
Posts: 1385
Loc: Tennessee
Reg: 12-06-10
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11-15-24 05:19 PM - Post#2875617
In response to Woogeroo
In the first photo, it appears to me, the proportioning/combination valve is installed/plumbed upside down, i.e. the master cylinder lines go in where the wheel cylinder lines should come out.
I really can’t see much of your proportioning/combination valve but the ones I’m familiar with have the 2 MC limes come in each side of the switch on the top and the wheel cylinder lines come out of the ends, 2 for the fronts and on for the rears.
If it is plumbed backward the proportioning valving inside the proportioning/combination valve will not work and will probably shut off fluid to the wheels.
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Woogeroo
Valued Contributor
Posts: 2861
Reg: 05-26-02
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11-18-24 01:30 PM - Post#2875728
In response to YOUNG57
In the first photo, it appears to me, the proportioning/combination valve is installed/plumbed upside down, i.e. the master cylinder lines go in where the wheel cylinder lines should come out.
I really can’t see much of your proportioning/combination valve but the ones I’m familiar with have the 2 MC limes come in each side of the switch on the top and the wheel cylinder lines come out of the ends, 2 for the fronts and on for the rears.
If it is plumbed backward the proportioning valving inside the proportioning/combination valve will not work and will probably shut off fluid to the wheels.
Well, it could very well be backwards and sideways, but this is the way it has been since I bought it in 2003.
From a few searches it looks like it may be from a 67-69 chevelle/skylark.
Found another brake line that was cracked, having a hard time getting it to seal, so either a bad new line or something broken that I can not see inside the valve on that end.
Old trucks are fun.
Thanks for the replies folks.
-Woogeroo
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YOUNG57
Frequent Contributor
Posts: 1385
Loc: Tennessee
Reg: 12-06-10
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11-19-24 12:18 PM - Post#2875788
In response to Woogeroo
This master cylinder and proportioning vale were not original to your truck so someone added them. Not all hot rodders are master mechanics (me included) and not all modifications are installed correctly.
Do your research on power brake and proportioning valve plumbing and compare theirs to yours.
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 Shepherd
Valued Contributor
Posts: 3603
Loc: Lake George, NY
Reg: 11-11-15
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11-19-24 02:06 PM - Post#2875797
In response to YOUNG57
Never saw an actual " proportioning" valve on 4w drum set ups, "distribution " valve yes. With a prop valve the bleeding procedure changes.
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YOUNG57
Frequent Contributor
Posts: 1385
Loc: Tennessee
Reg: 12-06-10
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11-21-24 07:17 AM - Post#2875841
In response to Shepherd
Drum/drum vehicles did not have proportion/combination valves because brake proportioning on was done by having smaller wheel cylinders and narrower shoes on the rears.
Chevrolet began using dual master cylinders on their vehicles around the 1967 model year because of the federal safety mandate.
Your 65 C10 probably did not have a dual master cylinder but that was a very good upgrade and kudos to whoever installed it.
But the proportion /combination valve was not necessary and looks to have been installed backwards/upside down.
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