Vacuum bleeding hydraulic brakes?

[Steinar]

My guess is that your problem is because your master cylinder piston is too small for the wheel cylinders. Check the diameter. Since you are not running a dual master cylinder why didn't you use the '39 to '48 master cylinder?

Charlie Stephens

I didn't think a lot when ordering new parts, I just sent a picture and a description of what I had, and this was what they come up with. I was thinking this would be an easy fix, since everything were already set up for a mastercylinder looking like this one. The parts supplier also told me this was a very common mc, found on a whole lot of older US built cars, so to me it sounded about right.. I'll go and double check the piston diameter after dinner.

 

[Steinar]

If you get a good firm pedal on the second pump, then you probably have an adjustment problem rather than an air problem. The old Lockheed brakes can be tricky to get adjusted properly.

Joe

They are adjusted, brakelinings are very close to the drum, I can feel and hear they are in touch with the drum.

I have also adjusted them until they locked all the wheels, same thing happens, but pedal doesn't go all the way to the floor then, but still too deep on the first jump after bleeding.

 

[Steinar]

I'll give it an other try, will put things back into place and bleed it like Patrick L / JoeWay suggest. If no air, it might be the mc as Charlie Stephens indicates. I'll be back when I know more. Until then, thanks to all!

 

[Mike]

I had the same problem on a 30 roadster and I bled the rear brakes just as Pat L suggusted, it works

mike

 

[Charlie Stephens]

I didn't think a lot when ordering new parts, I just sent a picture and a description of what I had, and this was what they come up with. I was thinking this would be an easy fix, since everything were already set up for a mastercylinder looking like this one. The parts supplier also told me this was a very common mc, found on a whole lot of older US built cars, so to me it sounded about right.. I'll go and double check the piston diameter after dinner.

The supplier was probably not thinking about the early Fords when he said "older US built cars". Check out the diameter of the early Ford cylinders compared to the "older US built cars" he was talking about.

Charlie Stephens

 

[JoeWay]

They are adjusted, brakelinings are very close to the drum, I can feel and hear they are in touch with the drum.

I have also adjusted them until they locked all the wheels, same thing happens, but pedal doesn't go all the way to the floor then, but still too deep on the first jump after bleeding.

If you haven't been through the full routine, it's still possible that you have the heel or toe adjusted properly but not the other end, on any individual shoe. Below is some information from the 1953 MOTOR'S Repair Manual on the adjustment.

The supplier was probably not thinking about the early Fords when he said "older US built cars". Check out the diameter of the early Ford cylinders compared to the "older US built cars" he was talking about.

Charlie Stephens

By far the most common size master in older US cars is 1" bore. The 1939-48 Ford master is 1-1/6" bore. That's only about 13% difference in diameter, which would result in a slightly low pedal but not NO pedal, assuming the shoes are correctly adjusted.

I see the scanned images I attached have been reduced in resolution to the point they are barely readable. Here are links to the full-resolution scans:

LockheedAdjust1.jpg

LockheedAdjust2.jpg

Joe

 

[Steinar]

Problems don't usually show up alone, do they? When I took brake parts apart at rear axle, I clamped on a special tool on the flexible tube between the mastercylinder and the front/rear connection, to avoid fluid from leaking out while parts were apart. When I had put everything back in place, I forgot to take off this clamp when we started to bleed the system again. Not much fluid come out at the rear wheel even though my helper was stepping on the pedal as hard as she could. I then remembered the clamp, took it off, but since then the pedal is stuck, does hardly move at all, no fluid is coming through the system. I guess the flexible tube got damaged, so I took it out. I could easily blow through it. So, I guess what happened is, something loosened from the inside of this not so new tubing, and found its way down into the system somewhere else, and clogged it. So I have now one more problem I'll have to look into. But tomorrow I have to prepare for my daughters birthdayparty, so probably won't be much more time for the A until end of week.

But one more question: Is it necessary to have a flexible connection between the mastercylinder on the firewall and the rest of the tubings on the chassis, or could I go with steel tubing all the way from the mc to the wheels? Does the frame twist as much under driving that it could cause stress to the brake tubes if all steel?

And, yes, I measured the mc, they're both one inch diameter.

 

[Steinar]

If you haven't been through the full routine, it's still possible that you have the heel or toe adjusted properly but not the other end, on any individual shoe. Below is some information from the 1953 MOTOR'S Repair Manual on the adjustment.


Joe

Thanks for good info, but does this apply to my brakes? They are fixed at the opposite end of the cylinders, so I cannot see how I can do any adjustment else from turning the two adjustment bolts on the back side of the shields?

 

[Charlie Stephens]

By far the most common size master in older US cars is 1" bore. The 1939-48 Ford master is 1-1/6" bore. That's only about 13% difference in diameter, which would result in a slightly low pedal but not NO pedal, assuming the shoes are correctly adjusted.

Joe

I am surprised the diameter is 1 1/6. I would have expected 1 1/8 and assume you made a typo since you say 13% difference on the diameter. The volume is a function of the area (times the distance pushed) which is about a 27% difference. I can't definitely say this is your entire problem but I feel it combined with leverage of your pedal design would be a good place to start looking.

Charlie Stephens

 

[JoeWay]

I am surprised the diameter is 1 1/6. I would have expected 1 1/8 and assume you made a typo since you say 13% difference on the diameter. The volume is a function of the area (times the distance pushed) which is about a 27% difference. I can't definitely say this is your entire problem but I feel it combined with leverage of your pedal design would be a good place to start looking.

Charlie Stephens

Charlie,

You have a good feel for this, obviously, and about 27% would be correct for 1-1/8" vs. 1", but the '39-'48 Ford car and light truck master is indeed 1-1/16". I've put brass sleeves in several hundred of them.

Depending on whether you calculate up or down, the difference between 1" and 1-1/16" is about 11% or 13%. Depending on the pedal ratio, that would probably be about 1" to 1-1/2"of pedal travel--more travel for the smaller cylinder, as you say.

I'd have to check my books before I said for sure, but off the top of my head the first 1-1/8" Ford cylinder was used in mid-'50s cars with power brakes.

Joe

 

[JoeWay]

Thanks for good info, but does this apply to my brakes? They are fixed at the opposite end of the cylinders, so I cannot see how I can do any adjustment else from turning the two adjustment bolts on the back side of the shields?

Sorry--you said your setup was the same as Vince's in reply #2. He shows the earlier style brakes, to which the MOTOR'S Manual refers as "Lockheed [1]". This setup has two eccentric anchors, one for each shoe.

You must have the later brakes, called in MOTOR'S "Lockheed [3]", with a single eccentric anchor at the bottom (or for you, the top since your backing plates are upside down). Here are scans of the adjustment procedure. The main difference is that the single eccentric anchor is adjusted for the front shoe only (again, as shown in Vince's photo the rear shoe).

If the heel of the forward shoe is not adjusted correctly, you will lose considerable pedal travel as the wheel cylinder tries to push the shoe into contact with the drum--even if the toes of the shoes, controlled by the cams at the sides of the backing plate, seem to be properly adjusted.

Joe

LockheedAdjust3.jpg

LockheedAdjust4.jpg

 

[John Kuhnast]

Just went through the same problem as you. I switched the cylinders so that bleader is on top. cylinder still on bottom of backing plate. This requires grindint the hole so that the bolts line up with the cilinder. I ground the big hole so that the bolt holes lined up this left a quarter moon shaped hole on the bottom which has not been a problem. I used a master cylinder from a 1967 mustang. We removed the rear line and pluged the master. We then were able tobleed the front brakes. Keep bleeding even when you think you got all the air.WE then hooked up the rear and bleed them. When you bleed rear be very gental when you pump so as not to upsead the front. We then adjusted the brakes. After about 100 miles we bled the front and back with disconecting anything but be very gentle when you pump so as not pumpair from frotn to back and vice versa.We know have very good brakes.Much better than expeced. John

 

[1931 flamingo]

Steinar: On post #31 you mention that M/Cyl is on firewall. If so what kind? Are you utilizing "hanging" pedals? As I read your post I assumed (I know....) that you had a 39-48 M/Cyl mounted under the floor. Not that this has any real thing to do with your bleeding problem, but I think you could get away w/out a "rubber" connection to the frame at this point. When I did my 32 with chev dual resivoir m/cyl (hyd brakes and clutch) I only used a pre-formed tube for the clutch connection, not the brakes.
Paul in CT

 

[Charlie Stephens]

Charlie,

You have a good feel for this, obviously, and about 27% would be correct for 1-1/8" vs. 1", but the '39-'48 Ford car and light truck master is indeed 1-1/16". I've put brass sleeves in several hundred of them.

Depending on whether you calculate up or down, the difference between 1" and 1-1/16" is about 11% or 13%. Depending on the pedal ratio, that would probably be about 1" to 1-1/2"of pedal travel--more travel for the smaller cylinder, as you say.

I'd have to check my books before I said for sure, but off the top of my head the first 1-1/8" Ford cylinder was used in mid-'50s cars with power brakes.

Joe

Joe,

I think I am going to back out of this discussion since I don't have access to the data I need. Even if I looked up the early Ford (I am sure you are right) I still don't know what the other master cylinder is from.

Charlie Stephens

 

[JoeWay]

Joe,

I think I am going to back out of this discussion since I don't have access to the data I need. Even if I looked up the early Ford (I am sure you are right) I still don't know what the other master cylinder is from.

Charlie Stephens

Charlie, Steinar says both his old and new cylinders are 1" bore. I'm not sure how it matters what the application was for the new one? It's the bore area that determines the hydraulic ratio, as you've said.

If you're wondering about my bona fides, check the URL in my signature.

Joe

P. S. I shouldn't have said I've sleeved "several hundred" of the early Ford cylinders. On reflection, I think probably about 100 is a better number.

 

[Charlie Stephens]

Charlie, Steinar says both his old and new cylinders are 1" bore. I'm not sure how it matters what the application was for the new one? It's the bore area that determines the hydraulic ratio, as you've said.

If you're wondering about my bona fides, check the URL in my signature.

Joe

P. S. I shouldn't have said I've sleeved "several hundred" of the early Ford cylinders. On reflection, I think probably about 100 is a better number.

Sorry I missed the part about the cylinder being a one inch bore. The application is not important, I was just trying to find a trail to the diameter. To change the topic is that a copper line with a compression fitting coming out of the master cylinder? Both are a definite "no no" on brake systems. Still open is the question about leverage in the mechanical linkage.


Charlie Stephens

 

[JoeWay]

Sorry I missed the part about the cylinder being a one inch bore. The application is not important, I was just trying to find a trail to the diameter.

Charlie Stephens

Aha. I understand.

To change the topic is that a copper line with a compression fitting coming out of the master cylinder? Both are a definite "no no" on brake systems. Still open is the question about leverage in the mechanical linkage.

Charlie Stephens

I'm pretty sure you're correct about the copper line. It does not have the greyish tint associated with Cunifer steel-alloyed brake line, and I think this was mentioned back when Steinar first posted his photos. Hardware store compression fittings are typically rated in the 300psi range for the 1/4" size. That's about half the pressure that can be expected in a system like this during a hard application.

I don't recall whether Steinar said his system was functioning acceptably in terms of pedal travel and effort required when he started rebuilding it. If it was, then the mechanical ratio must have been OK.

Joe

 

[V4F]

not to steal the thread , but im having major problems bleeding mine . 1931 ford coupe , 1942 hyd brakes . used a vaccum bleeder , no luck . used the helper old style bleeding ... seems there is no air , but the pedal still goes to the floor . it is firmer than when i started & when pumped it does activate the brakes , but no good pedal . any ideas appreciated . thanks .. steve

 

[miss victoria]

Years ago Dave Wilton (mt products) master brake guy, posted on upside down backing plates as i recall it was not recommended?

 

[Keith True]

One thing you said that stands out at me,the second pump of the pedal is rock hard.Air=sponge.Liquid=rock.Air compresses,liquid does not.If the pedal gets hard,not spongy,I would call it a travel problem too.