Bleeding...

After I changed the brake plumbing between the combo valve and the booster, I spent a good deal of time bleeding the brakes, trying to get rid of the  spongy pedal.  No amount of bleeding the brakes seemed to fix the problem.  I began to question my bleeding procedures, my equipment, and then my sanity!

Worse than that, I took the car on a couple of test drives with mushy brakes.  This really wasn't very smart.  The pedal went almost to the floor... thank God I didn't really need to panic stop again!

The mushy brake issue really bothered me for a couple of weeks.  I kept going over every possible cause, and I just didn't get it... the car had a firm pedal with the old booster, and my original configuration with the new booster wasn't this spongy, so what was wrong now?  Logically, it didn't make sense to me that the pedal would be so mushy.  I started thinking that perhaps the master cylinder needed replacement, or the pedal ratio needed to be adjusted... but that didn't make sense either.

Finally, I considered taking the car to Tire Guy to have him go over the system and pressure bleed the brakes.  Sometimes, I just need help.  The idea of getting some professional help made me relax a little... then I had an idea!

It occurred to me that I might have done something dumb in plumbing in the new booster...

Here's the way the C490 came (the big guy on top).  Note the that it is configured to use the upper port on the outlet (green plastic plug), not the side outlet.  This is consistent with the C3400 below it, which uses the top port on the outlet.

When I plumbed the C490, I thought that using the outlet to the side looked  "cleaner" so I changed the configuration!  This was very poor thinking... it left an air pocket in the booster that can't be bled effectively.  Result: mushy pedal that no amount of bleeding would fix!

Replumbing the booster to use the top port, and then rebreeding the brakes (a lot) fixed the problem.  Now,  solid brakes!

I still don't know why pedal felt firmer when I first installed the C490 (between the master cylinder and the combo valve), but when I changed the plumbing around (so that it was between the combo valve and the front brakes) it must have let enough extra air into the booster that it caused this super mushy pedal.  

This has definitely been a learning experience for me.  I could say that the key lesson here is about air pockets in brake systems, but I think it is more sublime than that.  Here are some key thoughts:

1. If what I am doing isn't working after I have given a complete and honest effort (like bleeding the brakes), then doing more of it probably isn't going to help.
2. If I am agitated, upset, or downright mad, I am unlikely to make a good decision.
3. Experience trumps logic.  I can think my way into all kinds of wrong answers.
4. It is OK to ask for help... and sooner is better.  Once I come to that point, I am probably going to calm down and think more clearly

It's funny how I have to learn this lesson over and over again.

Getting a Boost... not done yet.

I've been asked to post  the template I used to make the C490 booster bracket.  Here it is... on the right is the template I got from Ford Guy, which may work well on a '57 bird.  On the left is my revised template that lines up correctly with the stock holes on a '55.  The graph paper under each template is 1/4" quadrille, so you should be able to determine all of the relevant dimensions.

On my first extended drive with the new booster, I unfortunately had to make a panic stop on the freeway... offramp traffic had backed up onto the freeway, and I had little time to react.  The front wheels locked up, but I didn't get the feeling that the back brakes were doing anything!  I started to wonder if my brakes were plumbed correctly.

Gil Bumgarner highly recommends the use of a combo valve when installing disk brake conversions on early birds.  He specifically references mpbrakes.com.  I downloaded the T-bird disk brake conversion installation instructions from mpbrakes, and was interested to see that they use the same exact front brakes/spindles that I am using, AND that the instructions even include a picture of a C490 booster on the page that discusses power assist on the front only!  They must know what they are talking about!   Here is the diagram they include for how to plumb the booster into the front brake circuit:

Front boost only plumbing diagram from mpbrakes: the combo valve sees fully boosted front brake pressure.

This is how I have been running the brakes with the smaller C3400 booster for the last 3 1/2 years.  My only complaint is that it didn't provide enough boost to the front, and pedal pressure was unduly high.  At one point with the old booster I decided to connect the "brake fail" switch on the combo valve to the dash oil pressure light.  I noticed that when I applied the brakes, the light came on... and if I applied them hard, the light would stay on for a while.  After doing some research on how combo valves work, I decided that this is normal behavior for an unbalanced system like this, and I simply disconnected the switch.   

Note that in this configuration, the pressure differential portion of the combo valve senses the differential pressure between the front (boosted) and back (manual) brakes, and the valve spool moves toward the rear brake side of the valve.  This turns on the brake fail light, and starts to limit pressure to the back brakes... which would be good if the back brakes had indeed failed, but they haven't.   The differential pressure valve spool restores itself shortly after the brake pressure is released.

After my freeway panic stop, I started to wonder how changing the booster, with it's higher pressure to the front brakes, had effected this setup.  Clearly there was now even more of an imbalance between the front and rear brake pressure in the valve, and the rear brakes were being even further restricted during panic stops... perhaps that's why I felt like I didn't have any rear brakes.

Since I want to use a combo valve to enhance safety and performance, AND I want to add boost to the front only, the question is I should have plumbed the booster A) in between the master cylinder and the combo valve (as shown in the mpbrakes instructions), or B) between the combo valve and the front brakes... as shown in the modified diagram below:

Moving the booster so that the combo valve sees only master cylinder pressure.

I started to wonder if anyone else has thought this through.  As it turns out, CASCO sells a combo valve for use with their disk brake conversion kit.  Here is an excerpt from their 2015 catalog:

The master cylinder CASCO use is from Ford (with the rear portion in the front) instead of the corvette unit I used, and they use 4-piston fixed calipers instead of the single piston floating caliper units I (and mpbrakes) used.  The plumbing attached to the combo valve in the picture is particularly illuminating... the bracket that CASCO includes hangs the valve out of sight underneath the battery heat shield, and the short lines attached to it connect directly to the master cylinder.  If there is a front booster, it is definitely between the valve and the front brakes!  They do require specifying power or manual when ordering.  I'll send them a note and ask what the difference is.  I sent a note to mpbrakes about their schematic, but they have not responded.

Here's a summary of the options:

Booster before combo valve:

• unbalanced pressures will trip pressure differential valve, potentially isolating the rear brakes in a panic stop
• Note that moving the differential pressure spool will adversely effect the proportioning valve, see cdx online eTextbook.  The proportioning valve in meant to be disabled all together if the differential spool moves to the front fail position.  I must assume that the proportioning valve will activate too early (limiting the rear brakes) if the spool moves to the rear fail position, which is what happens during a panic stop if the booster is before the combo valve.
• the front metering valve responds to full brake pressure, front metering delay is minimized.  The implication of this is unclear.  The combo valve was not meant for this kind of setup.
• this configuration was recommended by mpbrakes, but they won’t respond to my queries and I don’t really trust them anyhow.  Front-only power brakes are very much a specialty setup, and I’m not sure they followed through very well on this.

Booster after combo valve:

• balanced pressures shouldn’t trip the differential valve, brake warning light should work correctly
• the front metering valve sees un-boosted pressure… there might be slightly more delay in activating the front brakes, but that isn’t necessarily a bad thing for stability… this would ensure that the rears activate first, an the metering valve intends.
• CASCO 2015 catalog, page 11 shows GM style combo valve with short plumbing attached to inputs (top); clearly the valve goes between the MC and the booster on the front circuit.  I trust this more than the MP brakes install manual.

I replumbed the booster so that it is between the combo valve and the front brakes.  I may not have fully bled the air out of the lines yet, because the pedal can go to the floor if the engine isn't running.  They work (although with a low pedal) if the engine is running.  I intend to get some speed bleeders and run a quart of DOT4 through the front circuit before doing anything rash.

Getting a Boost, Part 3

I clearly haven't posted in a long time.  A lot has happened since my last post.  Several friends of mine no longer walk this planet, and I'm sad to say that Ford Guy is one of them.  He checked out rather suddenly in mid-November.  His health hadn't been what you would call 'good' for many years, but he always seemed to pull through.  This time, he didn't make it.  His funeral was a massive affair, and I had no idea that he was so involved with his church!  About half the people in attendance were car folks, and the other half knew him through his church.

Ford Guy must have owned over a hundred cars, but the one he chose to drive the most in his later years was his black '57 Fairline convertible.  It was touching to see it parked on the church patio during his funeral service, next to the pink '57 thunderbird that he just finished restoring for this daughter.

Ford Guy was a big help to me with Nell.  The last thing he did for me was discuss the installation of a larger brake booster for better pedal feel with my front disk brake conversion.  He even provided a template for the bracket I would need to install this new brake booster.  Later that same evening, he presented me with an award for Nell as the best club T-bird at cruise night!

It has been a long time coming, but I finally got the new brake booster installed.  I started by removing the stock booster, and making a cardboard template from the copy that Ford Guy had given me.  His template didn't fit my car exactly... I think it was for a '57, which must have a slightly different layout of holes in the inner fender.  I was not willing to drill new holes in the fender, so I modified the cardboard template to fit.  The new booster mounting holes needed to be placed about an inch further forward than the old bracket.

I fabricated the bracket from a remnant of square  structural steel tubing I got at the local industrial metal supply house.  It was a lot harder than I anticipated, and took quite a number of trials before the booster was properly positioned and straight.  

the booster in place, but not straight... and some interference problems.

finally, I was able to modify the bracket so that the booster is straight and clean.

I had to take the battery box out in order to re-route the booster hardlines.  Beneath the battery box turned out to be a great place to  install the vacuum reservoir I got last summer.   Since the performance cam in the engine limits manifold vacuum at idle, this reservoir should help provide more consistent braking performance.

Vacuum canister underneath the battery box.  The master cylinder is at the top, behind the heat shield.  The booster is on the left, and the brake combo valve (balance and reserve pressure) is on the lower right.

It took a couple of days to pant the bracket and booster with epoxy primer and then black gloss acrylic enamel, but I think they turned out great!  

After bleeding the brakes, it was time for a test drive!  The pedal feel is significantly lighter, and the braking effort is now equivalent to a standard modern car.  The effort I used to use on a regular high speed stop will now lock up the front wheels.  It doesn't have the precise brake pedal feel of a sports car, but then again it never did.  My goal was to increase the overall drivability and potential for everyone to enjoy the car, and I believe I have succeeded.

On a different note, my dear wife gave me a beautiful new chrome grille for Christmas!   I had to disassemble the whole front of the car to replace it, but it was worth it.  I no longer need the V8 emblem on the grille to hide the rust. 

I have had a productive holiday over the past few weeks, and I can feel good about how things turned out.  I'm feeling very blessed and refreshed, and ready to return to my consulting business and volunteer work on Monday.