H.A.M.B-er's, Once again asking this vast resource of knowledge and wit for some guidance with this dilemma. Back story, friend of mine buys a 1955 Buick Century, that was supposedly redone and a solid driver.. It has brake issues right from the get go or rather (no stop). It is a factory underfloor power boosted brake system with factory drums all around. He goes and replaces all shoes, springs, and wheel cylinders and still not happy with the pedal feel and stopping ability. His next step is to replace the original factory (hydro?) boosted power brake system with a "known" supplier of a modern power brake system which bolts in to replace the underfloor factory system. We get this new system installed per the recommended procedures, and now it comes to the bleeding process. Following what I have done for years we start at right rear and move about the car pumping pedal and opening bleed screw. repeating until no evidence of air bubbles. The result, pedal is mushy and goes to the floor. Can not pump it up period. Must be air strapped) Next visit I bring the Mity Vac from home and we vacuum bleed the system. I am removing most of a cup full of fluid from each bleed position.and see no evidence of air. I open the m/c bleed screw which is at the top of this system and only fluids rushes out. The bleed screw is lower than the fill tube, so gravity is working. Same result albeit the pedal is a bit firmer but with effort can be pushed to the floor. After discussion with the builder of the system ( he has taken a late 60's single port master cylinder from a GM product rotated it 90 degrees added a fill capacity to the side of the m/c and coupled it with a modern style 7" booster. A bell crank system is adapted to allow the under floor pedal to rod arrangement to articulate the push rod thru the booster to activate the m/c piston sending fluid out the rear of the m/c.) The unit was returned to the vendor and tested "No Trouble Found". Any suggestions tips or technics to assist here? It must be something simple but this simpleton can not figure it. I am hoping for a K.I.S.S from the group.( or at least a little wit and critique.) Thank you again, MrPhat40
Did you adjust the brake shoes? Just did a single to two cylinder master on my Dodge and didn't have good pedal until the shoes were properly adjusted.
Rusty Dusty, Thank you for the reply. Yes the shoes were adjusted out until the drum would not turn. The shoes were then backed off 10 or so turns on the adjuster wheel. The drums turn with slight rubbing sound. So I think the wheel cylinders do not need to move the shoes too much before contacting the drums. MrPhat40
I didn't read you bled the master? Extremely important, I did read there's a bleeder, I'm not familiar with your system, I'm sure you know about what I'm talking...
Since it's 4 wheel drums, are there any residual valves plumbed into the front and rear brake circuits? Does the new master cylinder possibly have built-in residual valves?
Dear Clay Mart, There are no residual valves either in the m/c and or the rest of the system. The m/c was not bled. according to the install guide the remote filler system will bleed the m/c via gravity as the reservoir is higher than the m/c. we were told to just crack open the bleed er on the top of the m/c until fluid runs out. The more I think about this system the more I am figuring the issue is some trapped air in the m/c. Getting it to bleed is going to be an issue as this system does not facilitate the usual bench bleeding methods I have used in the past. The system is sealed with fittings on the top of the m/c to connect the fill line. The other fitting is on the back of the m/c to distribute the fluid pressure to the brake wheel cylinders. I will try to find a picture of this m/c to let all see what I am dealing with. Thx MrPhat40
Without residual pressure valves some fluid can make its way back into the master, via gravity (since the master cylinder is below the floor). Hence, it takes a lot more fluid to operate the wheel cylinders and a lot more pedal travel. I had to put those in my shoebox when I rebuilt the whole system. If I remember right, it was 4 lbs for drums and 2 lbs for discs.
Did you stop adjusting the shoes out when the wheel stopped AND the adjuster stopped or just when the wheel wouldn't turn anymore? I typically keep cranking on the adjuster until it stops so you make sure the wheel cylinder is compressed completely. Also I run some drag on the wheel while its spinning. Easy check, tighten all the brakes until the wheels don't turn and check the pedal.
Some new information Finally found an image of this m/c. The large black cap was the old location of the filler. It has been sealed . The brass fitting just to the left of the black cap in the picture is the connected to the fill line from the under hood fluid reservoir . The system installs with this cap now on the side. Out of sight is a bleed screw for the new location of the top of the m/c. The bleed screw pictured with the rubber cap installed is the old bleed screw. It is now installed on the side. Picture the mounting tabs shown in a vertical location attached to a cross member. The fitting at the end is for the fluid to distribute to the system. I am open to any suggestions as to how to bench bleed this thing. Thank you to all of the respondents.
If you disconnect the lines and plug the outlet, do you get a hard pedal? How is the mechanical adjustment of pedal and pushrod going in to the master? You need very little play and very little gap from pushrod to m/c plunger. Sent from my iPad using The H.A.M.B. mobile app
MissysDad Here is a picture of what I am dealing with. The system installs on its side so picture the mounting ears in a vertical plane. A belled screw is on the opposite of the big black cap in the picture. The filling on top of the black cap is for the fill line from the under hood reservoir. Not sure of how to best bench bleed this thing? Suggestion would be appreciated. Loved the Hot Rod Devils movie.
Try bench bleeding the master in the original upright position. The air exits from the tiny holes in the casting and this may not happen with the unit on its side. But...first I'd call the manufacturer and get his suggestions. He designed the thing and should know how to get the air out of it. Good luck!
Thank you to all responders I will apply those suggestions and let all know the outcome Really appreciate the support from this group MrPhat40 Sent from my iPhone using The H.A.M.B. mobile app
I think the problem is in laying the master cylinder on it's side. I have never in 50 years of messing with cars seen that done. In my view, laying the master on it's side prevents the air bubbles that normally come up and out of the ports that you can see when looking down into a normal master. From your picture even the bleeder is on it's side leaving an air pocket to the top when the master is laid on it's side. I think the only way to make it work is to bleed out the master standing upright the way it was designed to work, then install it on it's side. Bad engineering in my opinion. I would re engineer it so the master is upright the way it was designed to work, by people much smarter then us. Good luck and let us know what the fix is when you find it. Brian
H.A.M.B. er’s The problem of the SpongeBob brake pedal has been resolved. Turns out the under floor rod from the pedal to the booster/ m-c was not long enough to fully engage the piston in the m/c As a result the piston was not moving enough to create sufficient pressure. Lengthening the rod solves the issue! Kind of like some men over the age of 50 who have the urge but not the umph! Thanks to all of you who responded MrPhat40 Sent from my iPhone using The H.A.M.B. mobile app
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