Spongy Brake Problem

[maimu65]

Hello folks
I've got a brake problem that I've not been able to figure out.

The car is a '68 Satellite 2drht. Originally had a 273/at, ps, power 10" drums all around.

I've recently done a brake swap on the front end. I've converted to manual brakes using calipers, hoses, master cylinder from a '76 Dart. I've used the stock brake pedal which I've checked and have a correct 6.4:1 pedal ratio.
I have also added the Wilwood adjustable proportioning valve in the rear brake line after the original distribution block and it is dialed for maximum pressure reduction for the rear drums.

The problem: After bleeding the crap out the system using the pumping pedal method, gravity method, speed bleeder method, and vacuum pump at the caliper/wheel cylinder method I can not get a decent pedal. The bleeding procedures have been done by the book.
The pedal goes down about an inch, then you can feel it start putting pressure into the system. The pedal will go down another 1-1/2" to 2-1/2" and get harder to push but still spongy. My buddies '73 Dodge race truck has a high, hard pedal and stops. That's what I want.

I've done some road testing, the rear drums lock prematurely. I'm not going to drive it on the street again until I solve this issue.

What I've checked so far: I thought it was the M/C which was new, replaced it with a more expensive new M/C, which by the way was bench bled while clamped in my bench vise until nothing but airless fluid was coming out of the bleeder tubes, no change.
Replaced one caliper which was leaking, thought it was drawing air in, no change.
Everythings tight, no leaks.
I've tapped on every component with a plastic mallet, no change.

I could go on but I'll stop to see if anyone has any ideas yet.

Thanks in advance.

[BillyBob]

Are the bleeder screws on the calipers facing up or down?

[bobr]

Originally Posted by BillyBob

Are the bleeder screws on the calipers facing up or down?

I'll bet a quarter down. This gets a lot of guys. I can't think of anything else reasonable. -Bob

[crisser]

Maybe the pedal to m/c pushrod is too short?

[Ray Bell]

Originally posted by crisser
Maybe the pedal to m/c pushrod is too short?

Two reasons this can't be the problem...

1. He's checked the pedal ratio, he's stated that the pedal is making contact with just 1" of travel.

2. The issue is about 'spongy', not 'low pedal'. Spongy brakes comes only from:

a: Air in the system, or:

b: Something not mounted properly, like a master cylinder that's on a firewall that can flex severely.

We know, then, that the only issue is air in the system. It's just a matter of where and how to get it out. Calipers upside down is a likely prospect, but you never know. What makes it seem more likely is that the rears lock, indicating that this system is fine while the fronts aren't doing their job.

[wilks3]

Are the front brake hoses new? If not the hoses can internally collapse and not let fluid flow though, or the other way around, traps pressure and won't let caliper release.
One other thing, are the brake lines hooked up right to the master cylinder?
Sounds almost like there backwards.
Is the Wilwood valve below the master cylinder? I'm pretty sure its supposed to be.

[maimu65]

Bleeders are up. Pushrod has no more than 1/4" freeplay and then contacts the m/c piston. There's minimal firewall flex. New front hoses, calipers are releasing, brake lines are hooked up properly at m/c. The prop valve is installed in the rear line downstream of the distribution block/brake malfunction switch.

[maimu65]

By the way I sure appreciate all the quick responses. This thing has me baffled. I've never had this kind of problem with a brake system.

[bobr]

Incorrect master cylinder? There are different bore sizes that match up to disc or drum. I believe one is 15/16" and one is 1 1/16". I think the smaller one is the one you need but it has been a long time since I dealt with this. Maybe someone else knows for sure. -Bob

[maimu65]

Bob- the m/c I have came from NAPA p/n UP36412. It has a 1-1/32" bore. Everything I have read points to this bore being correct for manual brakes. I found somewhere that mp p/n 5249270 has a 15/16" bore for cars under 2800lbs. and p/n 5249271 has a 1-1/32" bore for cars over 2800lbs. That seems backwards from what you would think i.e. smaller bore = more advantage for a heavier car but with more pedal travel. The bigger bore will give a harder pedal and less pedal travel which I think I want.

[wilks3]

You say pushrod has 1/4" play before it hits MC? I crawled under my dash just to double check myself. My rod moves exactly with MC plunger, no play at all. Are you saying there is 1/4" between rod and MC plunger? I don't think thats right. Anybody else??????

[bobr]

Originally Posted by maimu65

Bob- the m/c I have came from NAPA p/n UP36412. It has a 1-1/32" bore. Everything I have read points to this bore being correct for manual brakes. I found somewhere that mp p/n 5249270 has a 15/16" bore for cars under 2800lbs. and p/n 5249271 has a 1-1/32" bore for cars over 2800lbs. That seems backwards from what you would think i.e. smaller bore = more advantage for a heavier car but with more pedal travel. The bigger bore will give a harder pedal and less pedal travel which I think I want.

It's been a while since I had the problem but when I had my race car I could not build up enough front brake pressure to do a burnout without creeping. After almost pulling my hair out in trying to find a problem someone told me that I had the wrong M/C. I believe I had the large bore then went to the small which went against my thinking as well but lo and behold changing the M/C solved my problem. You may or may not have this problem/solution. Are you using rubber flex lines? If you are you may try switching to an Earls type braided teflon line. I also assume you are using stock size hardline. If you are using bigger than stock that could also lead to issues. -Bob

[maimu65]

Wilks
I'd say probably less than a 1/4" I'll check tonight.

It is a m/c for a manual brake car, it has the recess for the little rubber retainer. I've checked that the spring in the m/c pushes the piston to the snap ring and it does.

As far as the m/c to caliper ratio is concerned, with the caliper being 2-3/4"dia., and going from a 15/16" m/c at 8.6/1 and a 1-1/32" m/c at 7.11/1, I can't see that as being associated with the problem I'm having much less a problem at all. Essentially if I want 1500psi at the brake pad it's a 5 pound difference in effort at the brake pedal. 28lbs for the 15/16", 33lbs for the 1-1/32". I've read that 1000-1200psi is all that's needed to lock up the brakes. Most of the info I'm getting is coming off Baer Brakes and Wilwoods website.

I think my major malfunction is air somewhere, just haven't figured out where it is.

I appreciate all the thoughts about this

[wilks3]

Did you bleed the rear brakes with the Wilwood valve open, no restriction?
Have you re-checked distribution valve to make sure no junk inside?
I've heard of having to change rear wheel cylinders, to bigger I.D., they would take more fluid to allow front calipers to catch up.
I used the kind of MC with plastic reservoir on top with two twist off caps.
I found the NAPA part#s.....MC line code SS, #47-39034.....plastic reservoir line code UP, #23804. I'm pretty sure MC is from mid 70s to mid 80s Volare.
Hope any of this helps.

[bobr]

"I think my major malfunction is air somewhere, just haven't figured out where it is."


I tend to agree but there really isn't too many places for it to hide. Did you try to pressure bleed? I have an AC Cobra replica with dual master cylinders and I kind of have the same problem. I bled and bled and bled some more. Then I adjusted the prop bar between the 2 M/C's. I never could get the hard peddle I was looking for. I brought it to a brake expert and he bled and adjusted some more but it never got better. Are you disc pads riding close to the caliper? Some M/C's have a valve to keep slight pressure on the pads. You can also get one of these from Wilwood if you determine that's the problem. How's the adjustment on the back brakes? -Bob

[darktone]

I usually gravity bleed on older cars with really good results.

[maimu65]

wilks, I did bleed rear brakes with prop. valve open and closed didn't seem to make a difference. I haven't checked the dist. block for crud but didn't really have a reason too either. Kind of a pain to get to with headers, ps in the way but I may look into that. The m/c you mentioned uses 2 bolt mounting, I needed 4 bolt. Also your m/c has 1-1/32" bore, same as the m/c I used which is spec'd for manual brakes.

bobr, I did not try pressure bleeding it. I may get to the point where I pay someone to try that but I'm having a hard time believing it's a problem I can't solve. The pads are pulling away ever so slightly like they are supposed to do. If the pads were pulling too far away or if my rear drums were not adjusted correctly (which I have checked), i.e. too much travel before they hit the drum, then pumping the pedal in quick succession would take up the slack and I'd get a hard pedal.

darktone, yes I will try to gravity bleed again because that seems to me the best way not to introduce more air to the system. If that doesn't work I'll have someone pressure bleed them. And if that doesn't work you'll see an ad for a solid '68 Satellite with no brakes on Craigslist. Ha!

Thanks again

[pishta]

Had a 63(?) 300 manual brake car that had the same problem. problem was the rear drums were totally out of adjustment. They never "self adjusted" if they were ever supposed to. I had to pump them for any brake action. I adjusted until I could freewheel the tire only 1 revolution, then I pumped the brakes to seat the shoe and adjusted again, did this 3 times per rear tire and ended up with a rock hard brake with about 2 inches of travel. Good luck, also Dot 5 fluid never gives a rock hard pedal like dot 3 or 4.

[bobr]

If your problem is air in the lines then pumping should give you a higher pedal. Does this happen? If you can't find anything wrong I would relook at your M/C. -Bob

[darktone]

Originally Posted by bobr

If your problem is air in the lines then pumping should give you a higher pedal. Does this happen? If you can't find anything wrong I would relook at your M/C. -Bob

yeah- do they pump up and get a pedal? I have run a repair shop for a lot of years and it usually ends up being something pretty basic. Like a line not being tight. When you gravity bleed do only one at a time and make sure the m/c cap is off so it can drip. How tight are the drums set? Primary and secondary shoes in the right spots? Wheel cylinders don't have frozen up pistons? On some cars the proportioning valve does not like to recenter it self and this can cause an odd feel to the pedal- usually rapping on the valve while pumpming the brakes clears this up.

[Ray Bell]

Rapid pumping will, but the difference isn't as great as it could be...

I had a clutch problem once in a Peugeot. Simple line, simple system, but the line went up higher than the MC across the scuttle (which it wouldn't do in a LHD car for which it was all designed) and air could get trapped in there.

I even installed a 2-piece line with a bleed nipple in the high point! I never got that clutch right, drove it like that (pumping the clutch like fury) for about a year.

The only thing I didn't do was a pressure bleed. I still have no idea what caused it, but the fact it it was AIR and nothing else that was the problem. Let's forget about adjusting rear shoes (remember, the rears locked up...) and let's assume it's in the fronts because it was the rears that locked.

Can you try a reverse 'bleed'? Here's how:

Working first on the right side caliper, take out the pads, put a tyre lever or something between the piston and the disc, pump the brakes up. It is possible you might push some air through, so do a conventional bleed on this caliper at the point where the lever is trapped by the piston (the sheer flow might actually drive the air down the line).

Then you compress the piston with the lever, all the way in in one move, driving the fluid back up the line and - hopefully - any air trapped in the line with it.

Do the right side caliper first, check the system, then do the left side.

Your levering (it will be a single movement) shouldn't be slow when you do this. Try to have someone observe the reservoir and see if there are bubbles.

If the calipers are mounted at the same angle as they were in the car they were designed for (some mount low, some mount high, that affects the location of the bleed port inside), then they virtually cannot retain air when bled. The nipple should be venting the highest point in the caliper.

There should be plenty of fluid displaced from the caliper to effect the task of clearing the line as long as you move it through quickly enough.

[wilks3]

I bought adaptor for the 2 bolt to 4 bolt mounting, thats the reason I had to get longer brake pedal rod. I didn't know which MC you had exactly.
I even went out and looked the Charger over trying think of something that maybe everybody is missing. You know, can't see the forest, because the trees are in the way.
I like the reverse bleeding idea, might get that #@$!$$%^% bubble out.
Keep going and please let us know what you figure out.

[bobr]

I've actually done the reverse bleed deal before but never knew it had a name. -Bob

[Ray Bell]

Did you do it fast enough?

[maimu65]

I'm going to double check the rear brakes to make sure they're together right, adjusted correctly and make sure I don't have a cracked drum or something silly like that. That should eliminate the rear brakes as a problem.

Then I'm going to try the various bleeding methods again, first gravity, then Ray's reverse bleed, if that doesn't work I'll have someone pressure bleed it.

[Mecki]

I have been using a big transparent syringe and a plastic hose connected to the bleeding nipple to do the reverse bleed. The transparent hose and syringe makes it possible to avoid pushing air bubbles in the system. The threads on the nipple are leaking and have to be sealed. I have done this by forcing a short piece of tight rubber hose on the threads of the nipple. When you then close the nipple the rubber piece will be forced up to a position where you can open the nipple about ½ a turn and still have a tight seal. This way you won't even make a mess. The syringe can also be refilled anytime by closing the nipple, disconnecting the syringe from the hose without draining the hose and when you reconnect the syringe you just keep it up so that the air bubbles are coming out from the hose.

This is standard procedure on Mercedes car and Scania truck clutches and works every time without any issues. It is completely impossible to remove the air from these systems without doing reverse bleeding. I usually fill a drained system completely from the bleeding nipple and it takes about two 50ml syringes to do it.

Try it out, the idea is exactly as Ray described, but the method is more simple, fast and clean and it has solved similar issues for me.

[charger_dan]

Originally Posted by maimu65

I'm going to double check the rear brakes to make sure they're together right, adjusted correctly and make sure I don't have a cracked drum or something silly like that. That should eliminate the rear brakes as a problem.

I went through this same exact problem when I swapped out my 10" drums
for 11.75" OEM discs. Went through A TON of fresh brake fluid and still had a
spongy pedal—with no air bubbles visible in the clear bleeder line. Finally
went out back and checked my drums, readjusted them. Resulted in a nice
firm pedal

[maimu65]

I rebuilt the rear brakes using new parts. Then I adjusted the shoes out so I could just get the drum over them. The drums look to be in good shape. My faithful helper (my wife) and I tried a little more aggressive pedal bleeding. She would put a lot of pressure on the pedal, then I would open the bleeder and try to close it before the pedal got to the floor. I may have seen some little bubbles as a result. The pedal still didn't feel much different. I then gravity bled the front calipers, while doing this I tried forcing the caliper piston in by hand with the bleeder valve open, the fluid flowed faster but didn't result in any more air bubbles coming out. I also tried Mecki's reverse bleed method which seemed to work good, good flow into the m/c but I didn't see any more air come out. I test drove it and it stops better but still not as good as it should by a long ways. The pedal is a little better now but still spongy. I'm sick of bleeding these brakes. That's where it sits right now.

[Mecki]

You can most probably rule out air as the cause after all the bleeding you have described.

Did you adjust the rear brakes with the drums in place? Press the pedal before final adjustment to center the shoes in the drums. It's a long shot, but you could even lock the brakes by adjusting the shoes tightly against the drums and see if there is any change in the pedal. That way the rear brakes could be ruled out if the problem still exists.

The only reason remaining would then be that something is flexing. You could then narrow the search by using blind plugs to block off different parts of the system and see how it affects the pedal. Pretty desperate though, but I'm out of ideas.

Annoying problem, I feel for you. Let's hope that your inspiration returns and that you find something easy to fix like a flexing hose (I don't know if it could even be possible that a hose caused this, just a desperate thought).

Good luck!

[wilks3]

Found these rear wheel cylinders ( 280227266245 ) on ebay. Sounds exactly what is happening to you. I've bought from this guy before, the brake rod for converted MC. He has alot of "problem solving" stuff for Mopars. I guess I got lucky when I converted mine over, somewhere in the past, somebody had put 11" drum brakes on back of my 69 Charger. I just matched casting numbers on wheel cylinders and got new ones. They had come off a big station wagon (Newport?) that had factory front discs so when I matched them I got cylinders for the disc brake setup, and the MC I used is also for disc brake setup. Makes sense what he describes is happening.