Brake Booster & Master Cylinder

[Jon W]

My brakes work but........ have to pump them each time to bring them up - not a good thing. I am thinking I need to replace my master cylinder?? Question: can I just replace the master cylinder or do I need to replace the entire booster/master cylinder, treadle-vac? I looked at Mark II Enterprises parts book and they only sell it as one unit - booster and master cylinder together. Is this part specific to the Mark II or did Lincolns have the same unit? Thanks, Jon

[Nick DeSpirito]

Jon,

For safety's sake, I suggest that you have the entire unit rebuilt. The Mark II only has a single master cylinder and if you lose your brakes, it will be very hard to stop a 5,250lb. car with just the emergency brake. Also, while you're at it, check all of the brakes hoses. I just had to replace the one that goes from the master down to the frame. It hadn't ruptured, but beings it runs close to the driver's side exhaust manifold, it was dried out and had surface cracks. Also while you're at it, check you wheel cylinders for leakage.

[Barry Wolk]

You can never be too careful with brakes. I'll tell you about my experience. I had my booster rebuilt. The early cars had a slide valve booster while the later cars have a poppet-type booster. The slide valve type is smoother but doesn't work as well as the poppet type. The poppet type have a tendency to lock up the tires, as the brakes are either on or off. Very grabby. I have the slide valve and drive accordingly.

I had mine rebuilt by the guy in Florida. If you have your rebuilt it'll be better than getting one off his shelf. It takes longer but you know what you're getting. He does a top notch job. However I got it back and had the same problem. I was really frustrated. I noticed while timing the Mark II after installing the Pertronix, that my brake booster hose was oblong when the engine was running and round when not. I believe that when my car was restored the large vacuum line was replaced with fuel line, which collapses under vacuum. No vacuum, no power brakes. You should also check the integrity of the vacuum chamber built into the frame. They tend to rust from the inside out as there is no place for moisture to go. If the vacuum chamber is breached you will not have power brakes and your car will run poorly.

There's also a valve on the side of the Treadle-Vac that allows the storage of vacuum in the storage tank, in case of engine failure. You'd still have one or two good mashes on the power brakes before you lost engine vacuum. This valve can stick, leaving you with no power brakes if your engine stalls.

The best fix I've found for a mushy pedal is a complete change of brake fluid. Brake fluid is hygroscopic, picking up moisture in the air in our old vented brake system. Moisture accumulates over time in the lowest point of the brake system, usually the brake cylinder. Since moisture is compressible and brake fluid is not, you would get a spongy pedal. This condition could have already done some damage to the cylinder wall as the moisture contains oxygen, which rusts the cylinder wall, pitting it. Brake fluid should be changed every 2-3 years.

Another mechanical failure that's happened to me personally is expanding flexible rubber brake lines. They can swell up like a ballon taking all of your hydraulic pressure away, giving you poor braking, mushy pedal and potential massive failure. That's an easy malady to check for and an easy one to fix.

If you're doing a new brake job find a truck repair that will arc your brake shoes to match your drums. If you don't do that the shoes have to wear in, giving you poor braking due to decreased contact patch and overheating of the brake material, leading to glazing. That's starting off on the wrong foot and brakes are very important on a 5,000# car.

On last thing and I'll get off my brake cart. REPLACE the return springs when you do shoes. When I was young I did the brakes on my mother's car. New shoes, no arcing, turned drums, replaced the rear seal, greased the bearings, but didn't replace the springs. She only got 2,000 mile out of the brakes. The stupid, totally inexpensive, springs had lost their tension and failed to retract the shoes properly from the drum where they ground themselves into the drums, causing them to self destruct.

I learned a very embarrassing and expensive lesson. I hope someone learns from it.

I guess the lesson is to diagnose the actual problem before you start throwing expensive parts at it. There was nothing wrong with my booster, just my hose.

[Jon W]

Nick and Barry thank you for your reply. I can pump the brakes and they do come up and will stop the car but 30 seconds later- no brakes and have to pump them again. I am thinking that my master cylinder is letting brake fluid pass and thus the need to pump the brakes each time they are applied. You guys agree? Could it just be the vacuum? Anyway, I will bleed the lines and look at the vacuum hoses and see what I get. (need to do that anyway)

Barry: do you have the name/phone# of the guy who rebuilt yours. Did he rebuild the master cylinder AND the booster? Mark II Enterprises has the entire unit (cylinder/booster). Is that the best way to go or would you rebuild mine?

Appreciate it guys. Jon

[Barry Wolk]

The guy's name is Ed Strain.

BRAKES, power rebuilt, Moraine 54-61, 48-hour turnaround. Ed Strain, 6555 44th St, Unit #2006, Pinellas Park, FL 33781, PH: 800-266-1623, 727-521-1597.**24-YR**

Upon further reflection of your problem it could simply be that your brakes are way out of adjustment. If there was too big a gap between the shoes and the drums you would have to pump it up for them to make contact. After releasing the pressure the return springs would draw the shoes back to the rest position, accounting for having to pump them up again. You may simply need a shoe adjustment.

I doubt seriously that your master cylinder is pushing fluid past the seal, There would be a ton of fluid in the car and nothing in the reservoir, or being sucked out of the vacuum hose and into the engine. If the MC was bad you would not be able to stop the car or hold a hard pedal after pumping it up.

Seriously, it sounds like a simple brake adjustment. You need to adjust the brakes and change the fluid before you spend any real money.

[Jon W]

Barry: Thanks again. I will pursue your suggestions and let you know what I find. Have a good weekend. Jon

[Barry Wolk]

Great! A brake adjustment and flushing of the system should only cost about $100. If I were you, I'd have them pull the brake drums and inspect the shoes and drums for wear. I'd have them repack the front bearings and replace the grease seals. When they pull the rears off they can inspect for rear axle seal leaks, too. A bit of weeping is normal for brake cylinders. Unless there's a visible drip, don't to let them talk you into redoing your cylinders.

If you want to safely drive your car with confidence, have that all checked.

[Mad Scientist]

Having to pump the brakes to bring the pedal up is an indication that the brakes need adjusting. Note that the brakes on the MKII are not self adjusting thus you must manually readjust them. Typically every 5000 miles.

A leaky/bad master cylinder shows itself when you step firmly on the pedal and it slowly, or not so slowly as the case maybe :D, squishes down to the floor. :eek:

I agree with everyone else now would seem like a good time to pull the drums and check the entire system.:)

The rear brakes, wheel cylinders and grease seals are readily available and reasonable priced. The front brake parts are a bit rare and may take a little searching to find.

[Barry Wolk]

It's not all that expensive to have them sleeved in stainless. A good machine shop should be able to do it for you, if necessary.

[Don Keller]

I'm going to tag onto this old post if allowed. Having read all the posts related to brakes, I haven't found my symptom. I am not familiar with the Mark II booster system and have never experienced this symptom on "regular" cars. The car has been stored for quite some time with little driving. The brake pedal remains firm (with or without the motor running) in the upright position with no give and next to zero stopping power. There is a sign of previous leaking from the the left rear cylinder. The master cylinder shows near full. The previous owner says that they worked for him, but pulled slightly to the left. It is not driveable as they are. Any ideas as to what this symptom would indicate or what to check?

[Mad Scientist]

Sounds like something froze/rusted up in the master cylinder or power booster from lack of use.

New non leaky rear cylinders can be purchased at local parts store for reasonable $$, not so for the front.

[Barry Wolk]

Simply loosen the brake line at the MC and see if fluid gets pushed out. If the pedal goes to the floor the MC is fine. Could be that your wheel cylinders are seized. That happens because old brake fluid has a lot of moisture in it and falls to the lowest point, the brake cylinders.

Could be plugged rubber hoses, too.

You can take off one drum at a time and have someone push the brake pedal to see if the cylinders are activating.

[Hal W May]

I've got fresh shoes and slave cylinders, the brake system has been completely checked out including the master cylinder and booster-and the pedal still travels 3/4 of its potential before engaging the brakes-is it possible that the "rod" from the upper part of the pedal "inside the cabin" to the booster-needs adjusting. There is an adjustment feature there-where it attaches to the pedal?

[Barry Wolk]

Yes, that's possible, but I'd be looking at brake adjustment and air in the lines.

Air is highly compressible and brake fluid is not. How far can you pull your emergency brake before it engages? If just a little, the rear brakes are adjusted fine. If it pulls most of the way out, you need to adjust the brakes further.

Remember, new shoes are the arc of new drums.If your drums are worn the shoe arc will not match the drum arc and your brakes will not be as effective until they wear in and match the drum arc.

The Bendix MC is different than most. The center rod enters a chamber of fluid and displaces it, rather than compressing it as in a conventional MC.

[Hal W May]

Barry: Pumping doesn't do any good (no better pedal) so I'm assuming-no air, but the arc thing is interesting. I didn't replace the drums-just had them turned. The E-brake play is what I would call normal-about 1/3rd of the way out to begin engagement. Thanks for your thoughts.

[Barry Wolk]

You could be right. The push rod could be adjusted so that you don't have enough fluid pushed into the lines. How is your pedal height?

[Hal W May]

If you mean where is it "at rest"-I'd say normal. Maybe I don't understand the question. I'd say when applying the brakes for a normal stop, the pedal will travel 3/4 of the way to the floorboard before beginning to apply-but not much further at all, for full brake effect. Did I answer your question?

[Barry Wolk]

I think you might be on to something. I have my treadle-vac out. I'll look at it tomorrow. I thought the adjustable rod was for pedal height, but I could be wrong.

[Bob smith]

This is my first time participating on the forum in any way. This is very new to me and I may be breaching protocol and if so I apologize. I'm asking for help and suggestions because my brakes are making a loud air noise when applied.

The car is consistently stopping is a very sure manner with a firm pedal. I find no vacuum leaks in any hoses and feel that the noise is coming from inside the booster. My concern is that on Friday, the car is being transported from So. Cal. to S. Carolina and will the transporter experience a failure with brakes while loading or unloading. If the response fits in the "yes" or "it's anyones guess" category I better scramble for a repair which won't be easy considering my timing. Thanks guy's.

[Barry Wolk]

Hi Bob,

Sounds like a massive vacuum leak in the brake booster. The engine will run for crap, but you'll still have manual brakes, just no boosted power brakes. It should be fine to get it on a transport.

There are two vacuum tubes that run to the booster. One is for the booster and the other branches off and goes to a vacuum storage tank built into the frame. Those rot out from the inside and you get a vacuum leak.

It seems appropriate to jump in here. Please post pictures of your car. We are a visually oriented group.

Welcome to the site.

[Bob smith]

Barry I appreciate your response. I will look forward to more participation on the forum and will seek some guidance in using it. Will give some history on me and provide pics when I get back in S. Carolina.

[Hal W May]

Barry: We live and we learn-I feel like the little boy who cried wolf-Warren and I delved into the brake travel thing last nite and he deems the travel-NORMAL-for drum brakes, gauged by when the brake lights come on during the pedal press (with engine running-of course). I think my mistake came from how drum brakes operate versus how disc brakes operate. Warren thinks the adjustment on the actuating rod would work-but only in a small way-ie-not very much because the danger in using that adjustment is that we'd be running the risk of not letting the master cylinder piston return completely to it's "rest" position and releasing the hydraulic pressure on the system. Btw-break a leg with WCF. Coming from the art world-I'll bet you know what that means.

[Barry Wolk]

Brake lights are controlled by a pressure sensitive switch on the MC. No two are alike, so I don't know if you should use that as a gauge.

Yes, it's very important that the MC piston return to it's stop. There's a little valve in the bottom of the reservoir that keep pressure in the chamber until the rod fully retracts, allowing the chamber pressure to equalize with the reservoir, allowing the brake shoe springs to fully retract. How new are your return springs? If they are slack you could be adjusting the brakes with the pistons partially extended. Did you use a shoe lubricant on the slide pads? Are there any grooves worn in the slide pads?

[Hal W May]

Good points!! We'll check tonite-we're going to attempt an automatic adjuster installation on the rears-then if successful-the fronts. I think I must be a bit paranoid regarding brakes. Thanks for your sympathetic ear and help.

[Barry Wolk]

I just looked at my booster. The threaded rod appears to only adjust pedal height, not plunger depth as the MC must return to its rest.

[Hal W May]

Good to know! Btw when is your interview with Mr. Ford?

[Barry Wolk]

Haven't heard back from his office. Glenn Kramer is joining me, so I'm working around his schedule.

[Doc]

Remember, new shoes are the arc of new drums.If your drums are worn the shoe arc will not match the drum arc and your brakes will not be as effective until they wear in and match the drum arc.



To follow up on Barry's response, the new shoes may actually be slightly over arched to account for some flexing as they wear in--i.e. they may be a little high in the center. If you push hard on the pedal, you may feel as though the brakes grab, then seem to loosen some, allowing you to push even farther. Rather than "pumping up" the MC, you may actually be forcing the shoes to conform across their entire width with the extra pressure. With some driving--300 or 400 miles, that problem will probably be reduced as the shoes wear in. At least that was our experience after replacing our brake shoes.

[Barry Wolk]

They are supposed to be slightly under arced, from what I've been told. Unfortunately new shoes come shaped to fit a new drum. If you have an 1/8" difference new shoes will make very little contact with the drum until they wear into the worn shape. Once that happens you may need to rough up the glazed surface and readjust the brakes.

Automatic adjusters would be nice.

[Hal W May]

Pete and Barry: Thanks for the further follow-up-They do "grab" occassionally, especially when cold. I'll be more patient and do another adjustment a little later. Thanks again!!

[Barry Wolk]

Your brakes should never grab. There is so much mass to the car that the brakes should make the car glide to a stop. You might have a valve problem with your Treadle-vac. The early type used a slide-valve and the later used a poppet-valve that are reportedly more "grabby".

[Cooke]

Since I bought my car the brakes always seemed odd to me. They stop great but with more foot pressure than I would expect. The pedal goes down but feels like a rock it does not really move when you step on it but the car stops fine. Any ideas???

[Barry Wolk]

Disconnect the vacuum line and plug it. If you brakes get worse then the booster is working. Just don't drive very fast.