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72 Cutlass rebuilding brake with drums front and rear. New master cylinder, ft shoes and drums. Needing to replace proportioning valve or distribution valve. A new pro porting valve came with master cylinder. However going under to replace it, the new one does match the old one. The driver side line originally exited the very front of the valve, but on the replacement part it exits out the top at 45 degrees and has a button on the front.
Looking on the internet all pro porting valve say they are good for disk conversions..... Are they also good for drum drum original set up. Or do they sell an original drum drum valve somewhere?
I assume if the exit is at 45degree my original brake line will not be aligned.
How about posting photos of old and new? Once again, a drum/drum system does not have a proportioning valve, only the distribution block. I've never seen an M/C come with a distribution block, so exactly what do you have? And why do you think you need to replace it?
I'm assuming that the valve has failed since neither rear bleed valve had signs of any fluid even taking the bleed port all the way out. I tried cracking open a front bleed valvrpe and trying again but no change.
I had not order the valve it just came with the master cylinder. Guessing it goes with kit if changing to disc brakes. ?????
What you have in your car is a distribution block (Olds called it a "distributor assembly"). The new part is a proportioning valve or combination valve. See the diagrams below, which are from the '72 Chassis Service Manual. The part in your car is shown in Figure 5-7. The new part you have is shown in Figure 5-8. The new part you have won't do you any good. You to find a replacement for the distribution block.
Last edited by jaunty75; October 29th, 2017 at 09:45 PM.
I'm assuming that the valve has failed since neither rear bleed valve had signs of any fluid even taking the bleed port all the way out. I tried cracking open a front bleed valvrpe and trying again but no change.
I had not order the valve it just came with the master cylinder. Guessing it goes with kit if changing to disc brakes. ?????
That is a combo valve for disc brakes. I'm going to assume that you also have an incorrect master cylinder. Why would you not just buy a correct master cylinder from a source like RockAuto?
Thank you, I ordered online a replacement for my 72 power Brake, Drum Drum and assumed they sent me the correct part. Is their a difference between Disc Master Cylinder and a Drum Master Cylinder. From you comment I'm assuming their is? They appeared to replace what I took off as far as Master Cylinder went?
A 1972 a power drum brake M/C looks like this and has a 1" bore:
A 1972 power disc brake M/C looks like this and has a 1.125" bore.
I have never seen a vendor sell a disc brake combo valve with a drum brake M/C. It would make no sense. Having said that, there are a lot of incorrect listings in catalogs. Many vendors show the disc brake M/C as having a 1" bore for these cars, for example.
Here are a couple of picture of the MC I have. Not sure if it is Not sure of it’s bore ?????
And as I said, that's a disc brake M/C. It's a generic aftermarket chrome "Corvette style" M/C. It doesn't have the residual pressure valves in the outlet ports. The bore could be anywhere from 7/8" to 1.25". Again, I'll suggest that you either reinstall the original (which apparently didn't need to be replaced) or get a correct drum brake replacement.
And as I said, that's a disc brake M/C. It's a generic aftermarket chrome "Corvette style" M/C. It doesn't have the residual pressure valves in the outlet ports. The bore could be anywhere from 7/8" to 1.25". Again, I'll suggest that you either reinstall the original (which apparently didn't need to be replaced) or get a correct drum brake replacement.
Thanks Joe make sense....not much else has gone right. Do you think the booster unit will work with a different MC or do I need to start all over.... I still feel my MC had failed, I lost all Brake press and didn't show a leak in any line or wheel.
Ordered replacement Drums and found out that the drum holes fit the lug but aren't big enough to press over knuel to make it a one piece hub drum. If I attempt to press it will warp the drum.... none of our part stores show replacement drums with larger holes or lugs with knuels that don't extent past the hub.
Last edited by richeyb; October 30th, 2017 at 05:15 PM.
Thanks Joe make sense....not much else has gone right. Do you think the booster unit will work with a different MC or do I need to start all over.... I still feel my MC had failed, I lost all Brake press and didn't show a leak in any line or wheel.
Ordered replacement Drums and found out that the drum holes fit the lug but aren't big enough to press over knuel to make it a one piece hub drum. If I attempt to press it will warp the drum.... none of our part stores show replacement drums with larger holes or lugs with knuels that don't extent past the hub.
The studs are supposed to be pressed out of the hubs entirely, the hub and new drum supported properly on a press plate, and then the stud pressed into both hub and drum simultaneously. The original studs are swaged into place - the ends are slightly mushroomed where they pass through the drum -which is why the holes in the new drum appear to be too small.
Unfortunately, this process is not described in detail in the Chassis Service Manual because it was assumed to be a standard process. Older versions of the CSM do describe it.
Joe the new holes appear significantly smaller than the old holes once the studs are removed. Does the knuel stretch the hole while the plate keeping it from bulging? Just doesn't look like that will happen.
Joe the new holes appear significantly smaller than the old holes once the studs are removed. Does the knuel stretch the hole while the plate keeping it from bulging? Just doesn't look like that will happen.
The whole point of the knurl is that it is forcibly pressed into a smaller hole so that it is retained. Exactly how much smaller is the hole?
In any case, get new lugs. The original GM part number is 3980406. Dorman claims that their P/N 98030 is a replacement for that. 1.5" long, 0.472" knurl diameter.
Thanks Joe, I ordered new set of studs today and will ordering a new MC. Which means I'll have an aftermarket Corvette style MC and booster for sale. Don't think it can be return after bench bleeding a couple times.
Any thoughts on where I can order a new distribution block?
Joe you had mentioned I might even put my old MC back on since I dint really need anew one.
Was my diagnoses of my brake failure in error. I had absolutely no brakes, there was no appart fluid leak of the brake lines or at the wheels, fluid in the MC, but no pressure at all. I figured it was a faulty master cylinder so I searched internet and found the chrome one that said it match a 72 Cutlass(obviously an error). That would start a dress up under the hood and solve my brake problem... but apparently not solving my problem.
Joe you had mentioned I might even put my old MC back on since I dint really need anew one.
Was my diagnoses of my brake failure in error. I had absolutely no brakes, there was no appart fluid leak of the brake lines or at the wheels, fluid in the MC, but no pressure at all. I figured it was a faulty master cylinder so I searched internet and found the chrome one that said it match a 72 Cutlass(obviously an error). That would start a dress up under the hood and solve my brake problem... but apparently not solving my problem.
Sorry, I was under the impression you replaced it because you couldn't bleed the back brakes.
A 1972 a power drum brake M/C looks like this and has a 1" bore:
A 1972 power disc brake M/C looks like this and has a 1.125" bore.
I have never seen a vendor sell a disc brake combo valve with a drum brake M/C. It would make no sense. Having said that, there are a lot of incorrect listings in catalogs. Many vendors show the disc brake M/C as having a 1" bore for these cars, for example.
Joe, is the single bale or double bale master cylinder cap technically correct for '70 CS? Is a '70 CS front power disc/rear drum also a 1.125" cylinder bore? Thanks!
Joe, is the single bale or double bale master cylinder cap technically correct for '70 CS? Is a '70 CS front power disc/rear drum also a 1.125" cylinder bore? Thanks!
1970 with power disc brakes would have used this style M/C (and yes, this is an aftermarket version without bleeder screws). First design used P/N 5470664, second design used 5471802. Both were 1.125" bore.
FYI, you will also see these dual-bale versions. This is actually what was used on the full size cars with disc brakes.
And for completeness, this is what was used on the 67-69 A-body cars with factory disc brakes.
The whole point of the knurl is that it is forcibly pressed into a smaller hole so that it is retained. Exactly how much smaller is the hole?
In any case, get new lugs. The original GM part number is 3980406. Dorman claims that their P/N 98030 is a replacement for that. 1.5" long, 0.472" knurl diameter.
Joe, I ordered new Dorman studs and still have a big problem. The serration drops right through the hub definitely not a match.
The hub holes measure approx .540, the old studs serration measured .554 and pressed into hub and drum.
However the new drum hole measures .449 significantly smaller than the hub.
Don't think original studs size will work to press the stud into both hub and drum?..
The drums are ACDelco 18B469 advertised to be for my car.
Any thoughts after seeing numbers? Thanks..
Last edited by richeyb; November 8th, 2017 at 07:08 PM.
Talked with local brake folks and parts house and the final recommendation I think is to drill out the drum sufficient to allow it to be pressed on the stud with the hub.
Joe I ordered a new distribution block from Right Stuff Detailing and started restoring my brake system. new shoes, new drums, new front brake lines, new distributing block. New Master cylinder All going great until I start connecting the various lines into the distribution block. Major problem--- the back brake line male fitting is larger than the hole. Cross checked and the new distribution block have the same size holes for the front left brake(front of block) and the back brake line (back hole). Not true on old block, back is larger......
Have they sent wrong block or made it wrong?
Taking off and will check sizes tomorrow of both blocks to know what I'm talking about....
J Cross checked and the new distribution block have the same size holes for the front left brake(front of block) and the back brake line (back hole). Not true on old block, back is larger......
Well, that's a crappy repro.
The factory used different size fittings to prevent cross-connetions on the assembly line. Also, the front brake lines are 3/16" and the line to the rear brakes is 1/4". The fittings are supposed to be different sizes.
The factory used different size fittings to prevent cross-connetions on the assembly line. Also, the front brake lines are 3/16" and the line to the rear brakes is 1/4". The fittings are supposed to be different sizes.
Thank you Joe! Working in the dark under the car with a shop light, it took me an hour plus of frustrating installing and uninstalling to finally figure out they were the same. I was afraid I had crossthreaded it to start with and ruined the threads, so I tried the front fitting in the back hole and it screwed right in. That's when I finally looked at the old distribution box and saw different sizes. Design wise different sizes made total since.
I finally got a response from my vendor for the Master cylinder. He said that their Master Cylinders were listed for my vehicle because they are equal reservoir, meaning they use them for disc/drum, drum/drum and disc/disc
I finally got a response from my vendor for the Master cylinder. He said that their Master Cylinders were listed for my vehicle because they are equal reservoir, meaning they use them for disc/drum, drum/drum and disc/disc
That sound you hear is the BS alarm going off.
First warning sign is that GM doesn't waste the money to design and warehouse two different parts if one would do. Second is that this vendor apparently has no clue about the presence of and need for a residual pressure valve for drum brakes. I guess if all you have is a hammer, everything looks like a nail.
I have gotten brakes all put back together including bench bleeding the Master Cylinder and putting in a new distribution block, but still have no fluid bleeding back brakes. Bench bleeding the MC it took two sessions over two days to have air not come through bleeding tube. However, I would continue to get air bubbles come through base of back bowl. It appears to be making air. This is a rebuilt MC. Could it have a leaky seal? Any thoughts??
I haven't started at MC checking for fluid yet to check for flow, but will next. It did have fluid come out of the MC bleed port.
Or just go swap MC at store and start over??
Disconnect the line from the rear port on the M/C where it goes into the distro block. Do you get fluid? Now reattach and disconnect the outlet line from the distro block to the back brakes? Get fluid? Reattach and now disconnect the hard line from the hose that goes to the rear axle. Etc, etc.
Where the fluid stops is where you have something plugged.
Thanks Joe, that's my next step when I get to the barn. I'm having to use the stick trick to hold the brake pressure as I run around and check the connections... I'll post results once I've found where the stoppage starts.
Ran through the trouble shooting step starting at MC and had flow all the way back to the rear wheels. When I loosened the brake tube running to each wheel I had a steady gravity drip from each rear brake line. However I still had no flow from either bleed port . I have to assume that both back wheel brake cylinders are clogged and need replacing. I'll get to that after a up coming trip. ��
Just to finish up post. Replace the rear brake cylinders and flushed the lines and then finally bleed the brakes. Finished it that part of my winter brake project. Thanks for the help.
Update... new set of wheel cylinders and master cylinder, ran 21/2 cans of fluid through until clear. Bleed, until got all air out, stopped showing.... went for a ride with booster brakes seemed to worked ok, but had hardly any brake pressure? Push peddle to floor and stopped. Not sure what that means??
Also it appears front fluid is going into back bowl. Assume it is shoot over top? But after short ride front bowl down and back bowl over flowing when I opened top.
Any thought on my 2 issues. Pedal pressure and fluid levels?.
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Re posted from More Brake Bleeding Issues
October 29th, 2017 | 12:59 PM
