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BRAKE PROBLEM - Pedal gets hard, tight, locks


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BRAKE PROBLEM - Pedal gets harder, tighter, locks<!-- google_ad_section_end -->

<HR SIZE=1><!-- google_ad_section_start -->1937 Buick with hydraulic brakes. - (also posted in Buick Section)

We completely rebuilt the brake system:

Master cyl kit

4 new wheel cyl kits

all 3 new flex brake hoses (Each front wheel, and from chassis to rear axle).

Drove the car on tour - after several miles, rear brakes and wheels got hot, so we let them cool - rear brakes were locked so I bled a small amount of brake fluid from a rear-wheel cylinder -- fluid squirted out under pressure - then subsided. Car drove OK for several more miles - then same thing.

I thought that the rear flex hose was collapsing internally, acting like a check valve - not letting fluid return, building pressure.

At the conclusion of the tour we replaced the rear hose and both front hoses.

The problem continued, so we replaced all of the steel lines as well as the hoses, rebuilt the master cylinder again, and replaced all 4 wheel cylinders with new. The problem continued as before.

We placed the car on 4 jackstands, and learned that, while we thought it was only the rear brakes, that was because they tended to lock and heat-up quicker. Really all 4 wheels brakes were affected.

Re-examination of the master cylinder suggested that maybe the piston was not returning enough to clear the return passage / internal bleed. I checked with a Buick expert, replaced the internal spring, and added a second spring which I managed to wind concentric with the first to increase return pressure on the piston, hoping to ensure that it cleared the passage.

It still happens, and after driving some distance, when I feel that the brake pedal is very high, tight, solid -- or the car will not rolll slightly at a stop, or notice a drag - it is time to stop at a level location, crawl under the car with a wrench, bleed the residual pressure from the brake system, wipe the dust from my shirt and jeans, and try to make it to the lunch stop.

Honest, guys and gals, I thought I understood these brake systems. Having replaced the flex lines twice, rebuilt / replaced all wheel cylinders and master cylinder twice, replaced the steel lines with the proper diameter lines, replaced all brake hardware and return springs with new parts, improved the return spring in the master cylinder ----

It has me stumped -----

I love driving this essentially original car, but would prefer not to have to

---- "Get out and get under" every 20-35 miles and shoot an ounce or two of brake fluid at the pavement. If the EPA is listening, I catch it in a coffee can for proper disposal.

I would be grateful for your advice, above and beyond what I've learned over the years -- I know I'm missing something.<!-- google_ad_section_end -->

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The problem continued, so we replaced all of the steel lines as well as the hoses, rebuilt the master cylinder again, and replaced all 4 wheel cylinders with new. The problem continued as before.

Re-examination of the master cylinder suggested that maybe the piston was not returning enough to clear the return passage / internal bleed. I checked with a Buick expert, replaced the internal spring, and added a second spring which I managed to wind concentric with the first to increase return pressure on the piston, hoping to ensure that it cleared the passage.

Wow, after paragraph 1, there isn't a lot left to play with.

If it's affecting all 4 wheels it does sound like the master cylinder is not fully letting go.

Did you check the pushrod adjustment to ensure it isn't over adjusted and stopping the piston from fully retracting ??

That internal spring is also there to maintain a little back-pressure in the system. It sits against a check-valve and that sounds like that's where your problem may be. The pressure from the wheel cylinder return springs, if in good condition, should be more than capable of overcoming this back-pressure. It sounds like the springs are OK as you say the fluid comes out easily when you bleed the cylinders. The check-valve may be the culprit and is not releasing and holding excessive pressure in the lines. What did you do when rebuilding the master cylinder ??

Danny

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Although I don't know about a '37, the same thing happened on my '62. The piston in the kit was slightly longer than the original. This would not allow the cup to uncover the bleed hole in the reservoir. Take a fine wire and make sure that passage is not blocked. I had to grind down the length for it to clear.

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Only experience I've had with an older system is a 34 Oldsmobile, first year for hydraulic brakes. I am headed toward the master as well. Dumb question but I'm gonna ask anyway, is it possible to overfill??? Or does this problem continue until the master is about empty.

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The problem is probably in the master cylinder as suggested, but check for heat transfer to the hydraulic system. I had similar problems with a truck that had a custom exhaust system that contacted a brake line when loaded.

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We took a look at adjusting the free play of the rod going to the master cylinder this morning.

It appears that the free play did not adjust -- only lowered the height of the brake pedal in relation to the clutch pedal -- will try more tomorrow.

Master cylinder is not close to heat source, and is not filled too full, although I've never before had any problem with filling a master cylinder to the top.

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Back in the 70's I had this problem with my 38 Special. Problem was the compensating port (or internal bleed as some call it) in the master cylinder was blocked with rust, dirt or who knows what even though I had rebuilt it. Shop Manual cautions about using a metal wire to clean the port lest it would cut a burr around its opening to the cylinder bore. Another disassembly and cleaning took care of the problem and paying attention to the piston clearance.

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I had this problem, it was caused by the rubber cups supplied for the master cylinder being slightly wider than the original. There must have been just enough port opening to bleed the brakes but it must have closed the port off completely when it all warmed up after a few klm as the brakes would lock on.

Found a thinner cup and no more problem.

Ken

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Let me throw in my $.02 worth of what might be causing "......the wheels and brakes to get hot.....and lock up....."

I'm assuming that your 1937 brake system is of the self-energizing principle where the primary (front) shoe lining is SHORTER than the secondary (rear) shoe lining. I've heard guys saying that they install the SAME LENGTH linings on both front and rear shoes "to get more surface contact to the drum and better braking" only to find out that the result is hotter wheels and brakes, and in turn, increases the chances of a lockup. Thin (overturned usually more than .060") drums also add to making wheels and brakes to run hot.

Are your linings of the correct length and location on the brake assembly, and are your drums overturned more than the recommended diameter? Just curious.

Al Mack

"500 Miles West of Flint"

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Pulled it apart and checked-

Both passages are clear-

The piston seems correct, and allows for the bleed passage-

The brake shoes and drums do not seem to be the problem-

The problem now comes on within less than a mile of driving-

All flex hoses , and all hard steel lines have been replaced in the last 18 months since the problem started-

We will next take off the flex hose right behind the master cylinder to see if this "new" hose may have a problem, by forcing compressed air backward to see if it will act as a check-valve

Tearing out what is left of my hair

Thanks for all of your responses

Marty

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Wow, I really feel for ya on this one. Using air may not give you the information you need. Hydraulic fluid does not compress, air does. Wish I had something more helpful than my comment.

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We slightly enlarged the bleed passage in the master cylinder -- no improvement !

Briefly under the car -- steel brake lines do not appear exceptionally close to exhaust system - the junction block and brake light switch are 3+ inches above the muffler -- brake line is 2 inches above front edge of muffler. I think this would be enough clearance, but will experiment with insulating material.

Still looking for a dramatic cause....

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OK, here goes...

1. I totally agree with the comments on the compensating port. The lip seal MUST sit just behind this with everything in the rest position. (you checked this on the bench)

2. Once installed in the car, the pedal could establish a new rest position for the m/c piston and lip seal. This, of course, is why you checked for the free play described earlier. Adding free play and having the pedal drop does sound suspicious, and points to the strength of your return spring. All of the added free play should end up at the push rod, if I'm not mistaken.

3. Opening up the diameter of the compensating port may lead to premature seal failure. The port diameter is intentionally minimized, and (at least in modern times) the port was pierced from the inside out, to add a lead-in radius to the inside of the bore. So, be sure you have not left a burr in the bore for the seal to catch on.

4. The function of the check valve at the exit of the m/c is actually to trap about 6 or 8 psig in the system, after each apply. This serves as an offset to the force (pressure) required to move the shoes against their return springs, and improves the pedal "feel" of each brake apply. As the system heats up, the check valve is supposed to lift off of its seat, and allow the excess pressure to be relieved, via the compensation port. So, you don't want the wrong spring holding this guy in place.

So, pedal return spring and pedal adjustment, check valve and the m/c spring between piston and check valve - these would be the items I would double (triple?) check.

Oh, and one more thing - clean your reservoir cap, and find the tiny vent hole. Open it up if plugged. That fluid returning the the master cylinder has to displace (or compress) the air in the reservoir.

(I'll bet the master cylinder says Delco - Made in Dayton Ohio, USA. That's the company I have worked for since 1988. Now under new ownership, but still at it.)

Jeff

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Sunday I will get back to the Buick, and will exercise the brake system without starting the car. I will try to replicate the problem without generating any engine/exhaust heat in an attempt to rule out one factor at a time, and will report back tomorrow on the results.

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The Buick is a running, driving car, but we don't know what problems existed prior to getting it.

It was a parade car for Mayor LaGuardia, and is believed to have served New York City for perhaps a dozen years, kept on long after the manufacturers no-longer produced convertible sedans. The big Buick then spent likely 50 years in a museum and a private collection, not driving any appreciable amount, if at all.

I test-drove the car in January 2009, made an offer to the Law firm handling the estate of the deceased owner, got agreement and the car in July, 2009, and immediately had the brake sysytem and parking brake cable, exhaust, and all fluids replaced. The car was driven short distances of perhaps a few miles by the friend who did the work, and exhibited no problems.

I retrieved the Buick, trailered it to the start of the 2010 Founders Tour, and after the first thirty miles or so, found that the rear brakes and wheels were hot, but not so the front. Cracking open the bleeder relieved the pressure, so we assumed that the rear hose from the chassis to the differential housing was acting as a check valve. That flex hose was replaced, along with all others, and the entire system was gone through again, including all steel lines which were run just as the originals had been.

All wheels turn freely, and even the breeze can spin them, but when the brake system builds pressure the front, as well as the rear brakes apply, so we have learned not to concentrate only on the rear (as we had first assummed).

The return spring pulls the pedal all the way back, and the pedal is at the top of its travel,. and cannot be lifted any higher when the problem occurs.

When I first get into the car I can depress the brake pedal 2 - 3 inches, but in short order the pedal becomes firm, and then solid at the top of its travel.

I did not get to the car Sunday, but will attempt to get there Monday, and will work the brakes multiple times, not "pumping", but will simulate as if the engine were running and I were driving in moderate traffic - then see if the pedal goes hard. This could be a way of eliminating the "heat" as a possible factor.

Thanks again for all of the advice and concern.

I look forward to your thoughts toward making this a dependable tourer.

Marty

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When I first get into the car I can depress the brake pedal 2 - 3 inches, but in short order the pedal becomes firm, and then solid at the top of its travel.

In my mind you just proved the rod connecting the pedal to the master cylinder is too long. There should be a little travel on the pedal before the rod contacts the piston in the master cylinder. Not much, but a little. And if the pedal is "solid at the top of its travel" then there is no clearance there at all.

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If it was the rears only, I would say that the emergency brake is hanging up. This would cause the rears to heat up and eventually stop the car. This would also explain having to pump the brakes two or three times initially. But this would have nothing to do with the fronts.:)

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When it apeared that the piston in the Master Cylinder might not have been returning, we doubled up on the spring inside.

Now that we have opened and enlarged the relief passage, we will next go back to a single spring.

Parking brake seems to work fine, and its cables were replaced when brake work was done.

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I gotta agree with the majority here, this has to be a master cyl problem. Dad and I had a 34 Olds, first year of hydraulic brakes. At the time I rebuilt the master I took the parts to NAPA and using 2 or 3 kits, was able to find all I needed, maybe the person that rebuilt the master had to do the same thing not realizing something didn't fit right. Everything you describe points to the master. The system requiring pumps to get to pressure, not releasing until its bled, all symptoms of a bad master.

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Not trying to say anything was done incorrectly on purpose. Just trying to help troubleshoot a problem. This car may have come with this problem, if someone along the line put in a piston that was too long, this would cause the pressure issue. Usually when rebuilding alls that is required is checking clearance, maybe honing or a resleeve, and changing rubber components. All I am saying is someplace along the line, because of this car's history, did someone put in an incorrect part that no one else is looking at.

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If this car came into my garage I would do a visual check first and go through all the steps discussed here to create the locking problem for myself.

Once satisfied and in agreement, I would replace the brake line leading from the with a short piece of capped line. The master cylinder should pump and relieve "standing alone". If it doesn't, at this point, I would toss it and put in a replacement. It has been monkeyed with enough.

If I could not get past the master cylinder pumping up alone I would focus on the linkage.

If the master cylinder works initially I would cap off the brake lines to all but the left front wheel. If it pumps up with only the master cylinder and one wheel, I would thoroughly check the wheel assembly.

Working my way around the system using caps to isolate the hydraulics should resolve the problem even if you have to do a little light driveway driving with one wheel braking.

Bernie

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Marty,

No one has mentioned this yet and I doubt that it is the culprit, but on the 37 80C's I believe there is a set of brass junction block that goes through the frame connected to it are the lines routing to all four wheels (the rear via on line down the TT then splitting at the axle). and the stop light switch.

May I suggest confirming all the ports and holes in the two connecting bolts are clear of debris.

Like I said this is probably not it, but no one has mentioned it, so I wanted to throw it out there.

Good luck, I am certainly interested in the eventual solution.

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Brian,

That is a good thought, and I will pursue it after checking out theresult of removing the second spring -- one step at a time, so we can positively identify the cure.

We removed the extra spring. They were wound together, not to extend the length, but to provide more force to return the piston.

Now with the relief passage opened slightly larger, we will try it out around Thanksgiving. I'll be on the road to AL, OH, and PA, and then back home, hopefully with the 1914 Buick.

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  • 2 weeks later...

Well, ---- we went back to a single spring in the Master Cylinder after enlarging the relief port --- drove the car 2 miles and the pedal was getting progressively higher / harder.

Then backed out of driveway - BRAKE LIGHTS ON !!! ---- CAR NOT ROLLING !!!

Time to find another Master Cylinder -- anybody out there have one???

Is a 1937 Buick Century the same cylinder as a Roadmaster ??

I'D like to buy a NOS or properly remanufactured / rebuilt Buick '37 Roadmaster Master Cylinder

Edited by Marty Roth (see edit history)
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CRAZY IDEA ???

WHAT IF ??? what would happen if we took out the check-valve completely??

How would the system work?

I could try this - then test-drive the '37 and see if it makes a diffference, but WHAT EFFECT will it have on the braking system to drive without the check valve?? If it seems to work OK, then did it mean that the existing check valve is defective? Then should I just leave it out? or buy just a kit and replace only the check valve?

Why is the check valve in there in the first place? To slow the return flow from the wheels to the Master Cylinder? , or to slow the flow to the brakes? - or what else?? I know this must sound like a dumb question, but considering what we have been through, I'll try almost anything.

I can get a sleeved cylinder and a new kit from Bob's, and will do that next if need be, but my existing cylinder has not been sleeved, and is absolutely beautiful, likely original, and internally could not be told from new (could even pass for new), and will assure next that it is the correct GM Part # 54-50231 .

I don't mind replacing, but would sure like to know what the problem really was in the first place -- and be able to share that info with all of you who have been so supportive.

Thanks for your continuing thoughts.

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Marty,

As I understand it the idea of the check valve is to maintain a little residual pressure in the lines and wheel cylinders even after the piston in the master cylinder is fully returned. It is a very small amount but sufficient to keep the rubber cups against the walls of the wheel cylinders and that stops leakage and or seepage of break fluid past the cups. This pressure is easily overcome by the tension of the brake shoe return springs. As for removing it and driving the car, I wouldn't try it in my Buick.

Danny

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Marty;try cracking a wheel cylinder open with a hose going into a glass jar,one wheel at a time,see how much comes out,does the pedal still get harder?does it draw fluid back in?Is one putting out more than another?Is the check valve in backwards?Is the piston longer or shorter than the original?Is the piston too tight in the cylinder? Try one pump at a time,releasing back slowly,with bleeder open,see what happens.

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Hi All,

Been tied-up last few days, but:

No, the Buick is not equipped with "NO-ROL" - no "HILL-HOLDER" that I can find.

We do not know if it worked before rebuild, because the car had been in a large collection for many years until the owner's death, and a year later I was able to complete the purchase from the estate. At that time we decided to "go through" all safety-related items: brakes, exhaust, wiring, etc.

I did drive the Buick about 3-4 miles to a friend's location - he is chief mechanic at a luxury-car dealership. I was driving just to get a few miles, and then check the brake drum temperatures, thinking that as drag increased, they would get hot (Also I could prove if the rears got hotter quicker than the fronts).

The big surprise (or not) was that after stopping for a few minutes to chat with the mechanics who had not seen the car, I got in and started it. I had just checked , and found that the brake drums had not heated excessively. Before driving, all were 62 - 65 degrees. After driving est. 3-4 miles, using brakes in 35 - 45 mph traffic, and sitting a few minutes, all were +/- 75 degrees.

We jacked up the left side of the Buick and confirmed that both the front and rear wheels were locked (Brakes were applied) - this will confirm that any blockage exists forward of the junction blockwhich splits the brake fluid to the front / rear wheels. Additionally, brakes were locked, even though brake drums were not excessively hot - this seems to confirm that pressure build-up is not releasing. I don't think engine / exhaust heat is a factor, but will consider that if the "check valve" theory fails.

Our next test will be to re-assemble the Master Cylinder (temporarily) without the check valve, as previously described - test drive, expecting the potential problem of needing a "second-pump" - and determine if the problem persists.

If the "LOCK-UP" disappears, I'll rebuild the existing master cylinder with a new kit, although I was leaning toward just finding a proper check valve:

If anybody has a CHECK VALVE:

WAGNER # FC - 4654

or

GM part # 1074839

I would love to try this independantly.

Yes, I know that a whole kit is the proper way to go, but the existing kit is fresh and undamaged, with no leaks, so just for test purposes, I want to

"SOLVE", one step at a time . Then when all is working properly, re-install with all correct, new parts.

If nothing improves, we'll next look at heat as a contributing source, shielding the exhaust from the brake lines.

Thanks for all the suggestions and PMs.

Edited by Marty Roth (see edit history)
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