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Username Post: hard pedal but no brakes        (Topic#351935)
fander 
"2nd Year" Silver Supporting Member
Posts: 122
fander
Loc: Hot Springs South Dakota
Reg: 04-28-12
07-08-18 08:02 PM - Post#2739411    

Shop installed dual master cylinder with original drum brakes. Email from shop today. "Good pedal, good fluid stream out of wheel cylinders, no brakes..."

Let me know what other information would be useful. Thanks, Glen

Attachment: 62brakes-3.jpg (78.87 KB) 1 View(s)






 
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japete92 
"4th Year" Silver Supporting Member
Posts: 972
japete92
Loc: No. Virginia
Reg: 01-18-13
07-09-18 08:39 AM - Post#2739447    
    In response to fander

  • fander Said:
Shop installed dual master cylinder with original drum brakes. Email from shop today. "Good pedal, good fluid stream out of wheel cylinders, no brakes..."

Let me know what other information would be useful. Thanks, Glen




If that's a proportioning valve, it serves no purpose on the drum/drum brakes (it would have to be set for equal pressure front/rear; why bother?). Front braking bias on the drums is provided by wider shoes in the front; equal hydraulic pressure thru-out the system. What is needed (if not built into the master cylinder) are residual pressure valves to keep approx 10 lbs of pressure in the lines (does not over come springs and engage brakes, but keep air out of the wheel cylinders).

Plumb front brakes to front 'bowl', rear brakes to rear 'bowl'. A residual pressure valve one each separate system. Make sure you have the proper drum brakes front/rear.

Once the installation is right, if you still do not have 'brakes', if it isn't due to air in the lines, one would need to inspect to find out what's wrong.

Pete



 
junky 
Valued Contributor
Posts: 2544

Loc: Northeast CT
Reg: 06-27-10
07-09-18 10:27 AM - Post#2739460    
    In response to japete92

I had been called into evaluate a similar problem, and it turned out to be wrong brake shoes. I also agree with the above post, about removing the proportioning valve, and making sure that the residual valves are installed in the metal line ports going to the cylinders. I have never seen these port valves sold separately, so I can't help you with sourcing them. They are usually contained in the rebuild kits.
To be honest, I can't see the benefit in a dual master cylinder with all drum brakes, because if your single master cylinder is in "like new" condition, along with the cylinders, lines, and hoses, it is just as safe and reliable. Only neglect causes the need for a dual master on drum brakes. Others are free to disagree, however, I speak from experience.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
japete92 
"4th Year" Silver Supporting Member
Posts: 972
japete92
Loc: No. Virginia
Reg: 01-18-13
07-09-18 11:57 AM - Post#2739465    
    In response to junky

One source of the 10 psi residual pressure valves is Wilwood; sold by Summit and others.

Also, it seems that because many people who switch to dual master cylinders also switch to disc/drum brake combo, some vendors sell only dual master cylinders w/o the residual pressure valves.

This may be helpful:

https://www.mico.com/sites/default/files/d ocument-...

Pete



 
Shepherd 
Frequent Contributor
Posts: 1336

Loc: Lake George, NY
Reg: 11-11-15
07-09-18 12:47 PM - Post#2739469    
    In response to fander

What do they mean no brakes, hard pedal, no stop or good pedal feel no stopping power?Is the booster set up working properly, the shops info is sorely lacking! Is it a drum/drum master?



Edited by Shepherd on 07-09-18 12:52 PM. Reason for edit: No reason given.

 
fander 
"2nd Year" Silver Supporting Member
Posts: 122
fander
Loc: Hot Springs South Dakota
Reg: 04-28-12
07-09-18 05:29 PM - Post#2739494    
    In response to Shepherd

Brake pedal feels normal but no braking action. It is a drum to drum master according to the vendor. I will have to ask about the booster. Thanks



 
fander 
"2nd Year" Silver Supporting Member
Posts: 122
fander
Loc: Hot Springs South Dakota
Reg: 04-28-12
07-09-18 05:32 PM - Post#2739495    
    In response to junky

I will have the shoe size checked. I too was ambivalent about the dual master cylinder as the car has over 200,000 miles with no problems on the single master cylinder. But since I was putting in all new parts I just decided to go with dual master cylinder. Thanks



 
junky 
Valued Contributor
Posts: 2544

Loc: Northeast CT
Reg: 06-27-10
07-09-18 08:36 PM - Post#2739512    
    In response to fander

All "new parts", might be part of the reason for poor braking performance. I have recently learned that some of the brake shoes being shipped today have the same length linings on both primary and secondary shoes. This can prevent the shoes from properly activating inside the drum. You also want the softest brake lining material that you can find. They stop the best, but will need replacing more frequently.
Below is a picture from another website showing a set of shoes, that had to be modified since both primary & secondary shoes were the same.


Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 4256
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
07-09-18 10:09 PM - Post#2739522    
    In response to junky

Hi Fander, Change Brake shops. Drum/Drum don't need combination valves. (The brass unit.)

Combination valves are vehicle specific and usually contain both a proportioning and metering valve which are both about the different line pressures required and the different rates of application of drum brakes V disc brakes.

There is no such thing as a disc or drum master, but you can make a master wrong for discs if it has an internal RLP (Residual Line Pressure valve.) of too high a value. All Chevy underfloor single masters have had an internal RLP since day one of hydraulic brakes.

Underfloor masters must have RLP's if the master is below the wheel cylinders or callipers.

A dual master can only have one internal RLP. The side exit port ones need an external RLP.
So a firewall mount dual master can have an internal RLP in the far end for the drums and none in the side exits for the discs as the weight of the fluid down to the callipers does a similar job.

If you have a firewall mount dual master and Drum/Drum then you need an RLP in both lines. If the master doesn't have an internal, then two externals are required. Same for underfloor.

What the RLP's do in practice is prevent the brake return springs collapsing the seals and turning the wheel cylinders, and to a lesser degree the calliper, into a syringe drawing in air as they are forced back each time the pedal is released.
They also keep the seal in shape ready to work so the brakes are primed against the return springs ready to apply quickly.
This gives a comforting pedal feel if the brakes are adjusted correctly.

RLP's range in pressure settings and may be from 5psi to 25 psi for drums. The aftermarket uses the nominal value of 10 psi for drums and 2 psi for discs. Don't mix them up or put them in backwards.


Have you verified that the wheel cylinders are not seized?

The dual master, if it is the same bore diameter as the original master, should give you the same brake pressure as before, the gain will come from the booster ratio. probably about 1.3 to 1.5 which is enough for drums.

Cheers Kiwi



48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 07-09-18 10:15 PM. Reason for edit: No reason given.

 
rrausch 
"14th Year" Silver Supporting Member
Posts: 13842
rrausch
Loc: L.A, Cal. & St. Louis...
Reg: 04-07-03
07-09-18 11:02 PM - Post#2739525    
    In response to junky

  • junky Said:
........... To be honest, I can't see the benefit in a dual master cylinder with all drum brakes, because if your single master cylinder is in "like new" condition, along with the cylinders, lines, and hoses, it is just as safe and reliable. Only neglect causes the need for a dual master on drum brakes........



My experience too. My daily driver all through the 1990's was all drums and a single master cylinder, and I never had a problem. I grew up with these cars, and never had a problem with all drums either--even with the Corvette in my avatar. That was a 327, double hump, cammed engine with a quadrajet. Never had a problem stopping it and I drove it hard at times.

1953 210 Convertible, 261 with dual Carter YF 966S carbs, P.S., Remote Bendix P.B. Booster... shade-tree restoration about done.




 
omarine 
Contributor
Posts: 161

Loc: San Diego
Reg: 06-29-15
07-10-18 05:27 PM - Post#2739612    
    In response to rrausch

I too had single master on my daily driver. I did swap it to dual and ran 3/16" line to the rear as well as the front, drum/drum master. Car stops perfectly.

So if line sizes are correct, did the master bore size change? If it's not 1" bore size, it might be creating this issue.

Did they check PSI at the wheel cylinders?



61 Impala bubbletop, 283, 2bbl Rochester, generator, points and drum brakes- daily driver
'49 Harley Davidson FL - Panhead


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 4256
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
07-11-18 04:17 PM - Post#2739728    
    In response to rrausch

Hi Robert and Junky, I had a total brake failure on my 48PU coming up over a blind hilltop.
It dropped an axle circlip and sent me across the road and into the ditch. No brakes and just the key and handbrake on one wheel.

This caused various physical effects and utterances, which I now call an "instantaneous moment of faith."

I like dual masters for that never gonna happen moment that actually does occasionally.

Changing a 1" bore single master to a 1" bore dual will do nothing to the car's braking except add a margin of safety.
If the original had an RLP which all the Chevy underfloors did then you now need them on the new master. Both lines

Cheers Kiwi

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 07-11-18 04:19 PM. Reason for edit: No reason given.

 
junky 
Valued Contributor
Posts: 2544

Loc: Northeast CT
Reg: 06-27-10
07-12-18 07:38 AM - Post#2739767    
    In response to Bel Air kiwi

I had the front brake line failure on my 1997 Ford Explorer, and it was on a flat road. The rear brakes were just about useless, and had it been on a hill, they would have been useless. I believe that way too many people put way too much faith into dual master cylinders. On my Explorer it was dual disk brakes with the parking brake being a drum brake inside of the rear rotor. If it were not for that parking brake, I would have had a collision with the car in front of me. I was going about 25 MPH in moderate traffic that was slowing to go around a rotary when this happened. My brakes were in good working order, however, the brake line had rusted through where it ran alongside of the frame rail, in a difficult place to see.
I have OEM master cylinders on all my collector cars, and since they are not driven during the winter, there is no rust as a result of salt. I also use silicone brake fluid in them.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
junky 
Valued Contributor
Posts: 2544

Loc: Northeast CT
Reg: 06-27-10
07-12-18 07:40 AM - Post#2739768    
    In response to junky

a "cut and paste" from a post on the www.g741.org forum

  • Quote:

First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, a petroleum fluid. DOT 5 is silicone chemistry.
Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.
The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.
Fluid boiling point DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition . By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.
DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.
With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.
Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.
If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).
Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.
By Steve Wall



Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
omarine 
Contributor
Posts: 161

Loc: San Diego
Reg: 06-29-15
07-12-18 03:37 PM - Post#2739787    
    In response to junky

Thanks for this info junky. So to conclude, dot 3-4 would be the best of both worlds in old brakes?

I think the percieved peace of mind, at least for me is with dual master cyl, the opposite brakes will remain effective rather than lose pressure because of one leak in a a wheel cyl in series.



61 Impala bubbletop, 283, 2bbl Rochester, generator, points and drum brakes- daily driver
'49 Harley Davidson FL - Panhead


 
62chevy427 
"12th Year" Silver Supporting Member
Posts: 2123
62chevy427
Loc: laurens sc
Reg: 04-13-06
07-17-18 04:46 PM - Post#2740337    
    In response to junky

jegs has residual valves

56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
14 camaro (new)


 
62chevy427 
"12th Year" Silver Supporting Member
Posts: 2123
62chevy427
Loc: laurens sc
Reg: 04-13-06
07-17-18 04:53 PM - Post#2740339    
    In response to junky

used to use silicone brakefluid in some of my cars. went to the mountains and had almost no brakes until i came back down. switchec back to dot 3.

56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
14 camaro (new)


 
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