Brake Bleeding Problems

[Dennis Detweiler]

I've tried the self method with the bottle. That's also in the 1939 shop manual. Problem is, every time you release the pedal you suck some air from around the bleeder screw threads. You can buy bleeder screws that have a factory sealant on the threads. I've also read, wrap bleeder screws with Teflon tape to avoid air leaking around the screw when releasing the brake pedal.

One problem I see, which might be where the air is trapped at my front disc caliper, is the bleeder on my caliper is at about 11 o'clock position and my flexible hose is connected at 12 o'clock. So, removing the lower caliper mounting bolt and rotating the caliper up to get the bleeder at 12 o'clock top dead center, then bleed, might be the fix?

[Dennis Detweiler]

I've gotten replies back from a couple of the on-line brake parts dealer techs. Consensus seems to be, the new Wilwood master isn't big enough (1 inch bore) for my system. The original master is single reservoir 1  1/4 inch bore. Looks like I may have to rebuild my original master, which doesn't look to be pitted. I can probably add a "T" to the output fitting of the original master and connect to my new brake lines and the in-line residuals? This has been a pain in the @$$.

[Sam Buchanan]

1 hour ago, Dennis Detweiler said:

I've gotten replies back from a couple of the on-line brake parts dealer techs. Consensus seems to be, the new Wilwood master isn't big enough (1 inch bore) for my system. The original master is single reservoir 1  1/4 inch bore. Looks like I may have to rebuild my original master, which doesn't look to be pitted. I can probably add a "T" to the output fitting of the original master and connect to my new brake lines and the in-line residuals? This has been a pain in the @$$.

 

I attempted to replace the MC on my '48 P15 with a generic "Corvette" dual chamber cylinder and never could get a pedal. I too decided the 1" bore generic cylinder didn't have enough displacement to replace the 1 1/8" stock cylinder. 

 

Yes, brakes can be a pain in several bodily locations......

[YukonJack]

I got the new issue of Street Rodder Magazine today and it has a brake article in it. It states that the smaller the master cylinder bore, the more pressure you get to the calipers and wheel cylinders. It also states that most people feel that the opposite is true "larger bore = more pressure". It also stated that the problem with using a Corvette master cylinder is that most are designed for power brakes and don't work well without the power booster.

[Los_Control]

Early corvettes did not have power brakes.

They had 6 cylinder engines and drum brakes.

 

If you buy a  scarebird front disk conversion. Then you keep stock rear drums, then buy a Wilwood master and proportioning valve. I would totally expect them to know their business and sell you the correct parts.

If the parts are wrong or bad, and they will not back up their product ... I will mark them off my list of buying parts from.

 

I also read that many dodge truck owners do the disk brake conversion up front, then use a jeep cherokee rear axle in the rear with drum brakes. Then use the master cyl & proportioning valve to match the year of the jeeps.

I imagine the proportioning valve from the jeep disk/drum combo would work for the scarebird disk/stock dodge drums combo.

 

Reading your original post, sounds like you did everything right. I could ask stupid questions, did you get the calipers on correct side and the bleeder screws are on top? 

 

My humble opinion, I would move forward, kick Wilwood to the curb, use a known working product.

Rather then go backwards and use original single stage master.

 

Maybe actually research the bore size of master cyl and proportioning valve size, for a early Cherokee with disk/drum combo  and see what they used.

Only because, I have read many used this combo with no complaints.  You may find you just need to change your current valve, or your current master cyl is junk.

Also there is a large crowd around jeeps and makes the info easier to find.

 

[Dodgeb4ya]

Also....   More pedal travel with a small bore MC, less travel with a big bore M-cylinder.

[Sam Buchanan]

1 hour ago, YukonJack said:

<snip> It also stated that the problem with using a Corvette master cylinder is that most are designed for power brakes and don't work well without the power booster.

 

A veteran parts guy looked at my "Corvette" cylinder and said it looked like what was used on '70's Chevy vans.

 

I think the problem was insufficient displacement due to smaller bore and possibly slightly shorter stroke. I would still like to convert to a dual-chamber cylinder since I have  the mount and pushrod fabricated which worked very nicely.

 

 

Edited September 7, 2019 by Sam Buchanan

[YukonJack]

19 minutes ago, Los_Control said:

Early corvettes did not have power brakes.

They had 6 cylinder engines and drum brakes.

 

If you buy a  scarebird front disk conversion. Then you keep stock rear drums, then buy a Wilwood master and proportioning valve. I would totally expect them to know their business and sell you the correct parts.

If the parts are wrong or bad, and they will not back up their product ... I will mark them off my list of buying parts from.

 

I also read that many dodge truck owners do the disk brake conversion up front, then use a jeep cherokee rear axle in the rear with drum brakes. Then use the master cyl & proportioning valve to match the year of the jeeps.

I imagine the proportioning valve from the jeep disk/drum combo would work for the scarebird disk/stock dodge drums combo.

 

Reading your original post, sounds like you did everything right. I could ask stupid questions, did you get the calipers on correct side and the bleeder screws are on top? 

 

My humble opinion, I would move forward, kick Wilwood to the curb, use a known working product.

Rather then go backwards and use original single stage master.

 

Maybe actually research the bore size of master cyl and proportioning valve size, for a early Cherokee with disk/drum combo  and see what they used.

Only because, I have read many used this combo with no complaints.  You may find you just need to change your current valve, or your current master cyl is junk.

Also there is a large crowd around jeeps and makes the info easier to find.

 

They are referring to the Corvette dual master cylinders used on a lot of conversions, also mentioned in the previous post. Not 53 6 cylinder Corvettes.

[DJ194950]

Replacement corvette style master cylinders are a very popular one used for many old car/modern disc brake changeovers and have see them available in different bore sizes from the same seller so that may be worth some web search time. Maybe even a big seller like summit racing? Just one example?  https://www.summitracing.com/parts/leb-m-105/overview/

Or,

https://www.ebay.com/itm/Universal-Cast-Iron-Master-Cylinder-1-1-8-Bore-GM-Universa

Many out there.?

 

DJ

Edited September 7, 2019 by DJ194950
add info

[Los_Control]

28 minutes ago, YukonJack said:

They are referring to the Corvette dual master cylinders used on a lot of conversions, also mentioned in the previous post. Not 53 6 cylinder Corvettes.

 

near as I can figure out, whats more important is to match the size of the master cyl bore, with the wheel cylinders, and the cylinder size depends on disk or drum, then match the proportioning valve to fit the parts you have.

 

We can take a pilothouse truck, set it on semi truck axles/brakes, then use a wilwood master cylinder and proportioning valve and make it work.

We just need to know what size bore and valve to use.  There is a science to this formula. (just a stupid example, needs more then this) But you get my point.

 

Something simple like scarebird and stock rear drums, if this is not working, there is something else wrong.

A good example, the builder put the calipers on the wrong side, now the bleeder screws are on the bottom. no way to get the air out of them ... bleeder screws need to be on top.

And if we have no leaks in the system sucking in air ... then they should be able to build hydraulic pressure.

I just have to assume the builder did bench bleed the master

 

Otherwise, either bad or wrong parts?

[Dennis Detweiler]

The original 39 Plymouth master is 1  1/4 bore. The Wilwood that I used is 1 inch bore. Scarebird tech said, the original master is a good match for the disc conversion S-10 calipers and stock rear axle. However, it's a single reservoir. Would the early Vette be a single reservoir? Overall consensus sounds like I need a bigger bore than 1 inch. Anything that I use to replace the Wilwood is going to require a new mounting mod again and a couple of new brake lines. Or, I can go back to the original master more easily. I'll check out the specs on Jeep masters. I've been working on this car for 2 years. Last summer all new wiring and other parts. All of this summer, the brakes with no good results. I appreciate all info.

Edited September 8, 2019 by Dennis Detweiler
more info

[DJ194950]

What Wilwood master do you have. Picture?

Just looked at Wilwood catalog OL and some models of their master are made in different bore sizes bu only up to 1 1/8".

Maybe?

 

DJ

[kencombs]

I think I posted this before but:  Have you confirmed the free play adjustment? Too much free play will result in lack of adequate stroke/fluid displacement also.  and could cause the symptom you mentioned in another post, loss of pedal when either front or rear bleeder is . 

 

As a test, you could reduce free play to zero and see if it changes the symptoms.

 

It seems odd that a company like Wilwood would offer a cylinder no bigger that 1 1/8" if larger is needed.

Edited September 8, 2019 by kencombs

[Dennis Detweiler]

I have the free play at about 1/8 inch.  Wilwood model #260-7563.

[kencombs]

I'd try reducing that to near 0 just to see what impact it has.If it is 1/8" at the piston, it may be too much.  As long as the return port in the master is open when at rest it should be OK with reduced clearance.  Depending on the linkage that may provide an inch .  I see that it only has a 1.1 inch stroke,

 

And assure that the linkage arrangement provides at least a 1.1 inch after the free play is taken up.

[Dennis Detweiler]

Early Vette master cylinder is single reservoir and 1 inch bore.

Jeep Cherokee is dual master and 1  1/8 inch bore.

My 39 Plymouth master is single reservoir and 1  1/4 bore.

The Wilwood 260-7563 that I currently have in the car is dual reservoir and 1 inch bore.

[Dennis Detweiler]

Currently, the pedal is able to allow the full 1.1 inch stroke of the master. It bottoms out slightly above the floor when a bleeder is open.

[Dennis Detweiler]

76 - 70 Mustang is 1  1/4 bore and made for disc/drum. An option?

[DJ194950]

Buy a single topped master 1 1/8" bore to try out. Most cast master cylinders are of single top with  two separate bowls divided by a internal wall for separate front and rear brakes.

 

Problem is current mc mounts are top and bottom-rare way to mount-almost everything else out there is using the side to side mounts-so??

 

this a example of a conversion top to change over to remote filler. Only  use one reservoir that feeds both sides inside,

https://www.ebay.com/itm/Master-Cylinder-Remote-Fill-Reservoir-Cap-Kit-for-Chevy-Ford-Street-Rods-and-Hot/273817620285?hash=item3fc0cd4f3d:g:8MsAAOSw8X9cuupt

[kencombs]

10 hours ago, Dennis Detweiler said:

Currently, the pedal is able to allow the full 1.1 inch stroke of the master. It bottoms out slightly above the floor when a bleeder is open.

That info makes it sound almost positively a volume issue.  If the master was part of a kit, maybe the seller will swap for the 1 1/8" version.  In any case, that would be my choice as it would require no line or fitting changes.  But, a 1 1/4" would be a safer option.

 

Maybe do some math and determine the volume needed to move the pistons in the calipers and rear brakes then compare that to that displaced by a 1 1/8 bore.  If it is questionable, go for the bigger.

[Dennis Detweiler]

If I go back to the original single reservoir 1  1/4 master, I can keep one of the remote reservoirs that I already have installed on the firewall and remove the screw-in filler on top of the master and adapt the remote line. At least, I think that would work? I used an adapter on it previously to use a pressurized bleeder system to the master cylinder. That was before the front disc brake conversion.  I see no advantage to replacing the original single reservoir 1  1/4 Plymouth master with a Corvette single reservoir 1  1/4 master? I'd like a dual reservoir master, but it would require another modification mount.

Going to a 1  1/8 bore would be a trial run and not worth the expense and time if it doesn't work. I've got a whole summer's worth of time on these brakes as it is and it hasn't been on the road for 2 years when counting the complete new wiring and a few other upgrades.

[YukonJack]

I don't recall anyone recommending a single reservoir Corvette master cylinder. My previous reference and someone else's was to the dual master. Then someone chimed in saying early corvettes were 6 cylinders without power brakes and a single reservoir.  It would serve no purpose to replace a single reservoir master cylinder with another single reservoir master.

[kencombs]

3 hours ago, Dennis Detweiler said:

If I go back to the original single reservoir 1  1/4 master, I can keep one of the remote reservoirs that I already have installed on the firewall and remove the screw-in filler on top of the master and adapt the remote line. At least, I think that would work? I used an adapter on it previously to use a pressurized bleeder system to the master cylinder. That was before the front disc brake conversion.  I see no advantage to replacing the original single reservoir 1  1/4 Plymouth master with a Corvette single reservoir 1  1/4 master? I'd like a dual reservoir master, but it would require another modification mount.

Going to a 1  1/8 bore would be a trial run and not worth the expense and time if it doesn't work. I've got a whole summer's worth of time on these brakes as it is and it hasn't been on the road for 2 years when counting the complete new wiring and a few other upgrades.

That's why I suggested the math first.  If the calculations show it's enough displacement, then it would be worth the work.  It sounds like you just a little short of enough displacement, judging from the recorded symptoms.  1/8 more may do it.

 

It still might be worth a try, IF the kit supplier will swap for you.  not a lot of work to change if fittings and lines fit up ok.  FWIW, I would never use a single piston master.  Single res, serving two circuits is OK but not a single piston.

[Dennis Detweiler]

I've been researching the above suggestions. Wilwood makes another model master that would directly replace the 260-7563 one inch bore. It's the 260-3380 1 1/8 bore. The mounting bolt pattern is the same on both of these (two bolt vertical pattern). However, the rebuild kit looks like a single piston?

I can't get through on the Wilwood tech email. It keeps coming up as an error. I'll have to call them. Scarebird tech has been good about emailing replies to my questions.

[kencombs]

If you have the 260-7563 then this one: 260-14244 looks like a similar fit.  But for some reason it is about 100 bucks more.

 

the one you mentioned above is a single piston unit.

Good luck on your hunt.