Mast cylinder residual check valve? Dual MC conversion issue

[Jeff Wilk]

SOS....two years dater our brakes failed and we ended up taking off the entire front clip and suspension to detail and restore all is back together but my brake pedal goes to the floor!!!

Here is what we did:

Rebuilt original power booster
New raybestos dual MC
New wheel cylinders
New brake hoses
New brake lines
New shoes all around
Bench bled MC
Bled whole system
Checked vac to booster
Adjusted treadle rod from booster to MC

Pedal still goes to floor!

Called Brake parts supplier who said we must need a residual check valve for each of the two new lines as this MC has no internal check valve like the original '59 MC. These new calves simply get installed in line,  one on the line ti the two rear wheels and the other on the line to the front two wheels.

I never heard of the original having that yet tonight i see it in the factory shop manual in the exploded views.

Sooooooo..... It sounds like this is the problem but since it was not mentioned originally when i ordered the MC i am just a bit nervous about it being some sort of "fix" for a bad MC or something.

Any ideas or knowledge about this here?

[curly]

Makes sense. The residual check valves hold a very low psi in the brake lines when the brakes are off.  The psi keeps the wheel cylinder cup tight against the cylinder wall so they don't leak.  The psi is very low, something like 2 or 3 psi.
If the M/C you purchased doesn't have them, it must be for a Disc/Disc set up.  Can you post the part number of the M/C?

T Lewis

[Dave Shepherd]

The residual valves will not in themselves correct a no pedal condition, to make sure your m/c does not have them insert a small drill into the m/c ports you should feel a slight spring loaded resistance, if not, no valves. Curly is correct on his description of how they work, usually more critical on under floor masters.  No pedal is almost always air or improperly bench bled m/c.

[russ austin]

Is that the original master cylinder? You could have a short rod on the booster, and a deep cup on the master cylinder. Happened to me on a 68 CDV I bought. Owner couldn't figure out why the brakes went to the floor.   It was the problem described above.  Brakes worked great after a new master cylinder.

[Jeff Wilk]

Upon more research ive learned that the factory original MC for 59 had an internal residual check valve (rcv). Ive also learned that this new Raybestos MC has no rcv built in. We bench bled the MC again, and did need to adjust the rod on the rebuilt original booster just slightly. Still a spongy pedal without holding power.

Two New 10#psi inline residual check valves were shipped yesterday and will hopefully correct the problem..... Found many references to this on The HAMB, and other vintage car club forums for late '50s/'60s cars. Wish i knew sooner or used a MC with the internal rcv

[Dave Shepherd]

Jeff, never saw a drum brake master without residual valves built in,  Are you sure this is the right master for the car?

[Bigfins (Dan Morehouse CLC 16464)]

Jeff,

I did the similar conversion on one of my 59's.. But have the complete opposite problem.

Here is what we did:

Rebuilt original power booster from a 1964
Rebuilt with stainless steel sleeve  dual MC, also from a 64.
New wheel cylinders
New brake hoses
New brake lines
New shoes all around
All Drums turned
Bench bled MC
Bled whole system
Checked vac to booster
Adjusted treadle rod from booster to MC
Loosened up the brake shoes with the adjusters
Adjusted the pedal height so there is more brake pedal travel.

When the car is driven more than about a mile, the rear brakes lock up.  Literally can not move the car an inch.  Front wheels move fine, but the rear wheels are stuck.  I've jacked the car up and it is both wheels.  Could this be a  problem with the residual check valve within the master cylinder?  How would that be checked?  How could it be replaced if that is the problem?  The car will move after about 30 minutes of cool down time.

I've done this conversion on a number of 59's and never had a problem.  I've been using rebuilt 62 to 64 brake booster m/c combinations because of the built in check valve and because the original pedal assembly for the 59 bolts right up. 

Thanks.  Dan

[Dave Shepherd]

If you crack the line at the master for the rear brakes and they release then there is an issue with the master not uncovering the bypass port, this usually is caused by insufficient rod to m/c piston clearance or the power booster is bad, leaking by the control valve and appling the brakes.

[Bigfins (Dan Morehouse CLC 16464)]

Here's some additional info. I called Booster Dewey (great guy great company etc.). He had me go through some checks on the booster and it checked out. At one point I pulled the master away from the booster and the rear brakes held tight.

I have two 60's that aren't running and a trailer blocking the 59 from getting out so I can't do the test of cracking open the rear lines right away. I will have to tighten up the rear brakes since I think they are adjusted to the point they aren't engaging. How would I fix the master?

Appreciate the help. Dan

[Dave Shepherd]

Dan, crack the line to the rear with the master away from the booster, if they release then the master is sticking internally.

[Coupe Deville]

I am doing a dual m/c and new booster to my 59. Do i need one of these check valves? The master says its used for drum brakes. Thanks

Here is the link for the booster and m/c: http://www.summitracing.com/parts/aaz-50-1117

It doesnt look like the picture in the add, just to say.

[Jeff Wilk]

Update- supplier did not send me the inline chexk valves but instead sent me a master with internal valves like the original.  Now i have a brake pedal!!!!! Still a bit soft but still need to rebleed the whole system and adjust......

[Dave Shepherd]

Good news, Jeff.

[Rod Dahlgren #19496]

When ANY car comes to me with these inline residual check valves added, I remove them and install a tested, correct master cylinder. If a brake parts supplier tells me I need to add residual check valves when using his parts, I don't buy his parts.

DAN---- Your master cylinder is NOT returning enough to clear the port...

[Dave Shepherd]

When ANY car comes to me with these inline residual check valves added, I remove them and install a tested, correct master cylinder. If a brake parts supplier tells me I need to add residual check valves when using his parts, I don't buy his parts.

DAN---- Your master cylinder is NOT returning enough to clear the port...

Seconded on all points, I do the same in my shop!!  They are needed on say a disc/drum brake conversion on a car with the m/c below th the floor, if the m/c does not have them built in.