vacuum booster woes (or else ?)

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vacuum booster woes (or else ?)

Postby thegermanfan » Mon Sep 20, 2021 12:45 pm

In the process of reactivating my Mark IV after some years of storage, I had the booster replaced. Reason for this was, that before storage and also afterwards, the brake pedal would return only very slowly when released. Of course only with the engine running. With vacuum reserve depleted, the pedal would return normal and the mechanics did not seem to bind. So I suspected the booster was defective and I managed to get another donor in the US from a wrecking yard. This unit was shipped to powerbrakeboosterexchange.com for rebuilding. Then the booster was sent to me and installed by a garage specialized in US cars. Unfortunately things have not improved much. The pedal return is a bit faster, but still hesitant. And to add insult to injury, the booster looses vacuum more quickly than the old. After less than an hour parked, no assist is available anymore. The check valve seems OK. Changing the booster check valve from the old unit to the newly rebuilt one, does nothing to improve the holding capacity of the vacuum booster. The old booster would hold vacuum for at least a day if not more.
I am frustrated. Having spent a considerable amount of money, and achieved nothing... :(
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Re: vacuum booster woes (or else ?)

Postby action » Mon Sep 20, 2021 1:33 pm

The brake pedal return is not a function of the booster.

During braking applications the vacuum from the engine assists the pedal effort.
When the driver removes their foot from the pedal, a valve closes to shut off the vacuum signal. And vacuum left is vented.

The pedal return is based on a number of springs depending on the braking system.

Disc/Drum
The return springs in the rear wheel cylinders and holding the brake shoes
The return springs in the master cylinder
The rubber square cut O rings in the calipers that are against the caliper pistons

Disc/Disc
The return springs in the master cylinder
The rubber square cut O rings in the calipers that are against the caliper pistons

A common issue with vehicles that sit for long periods of time is the caliper is no longer moving as designed.
There are two types of caliper systems. Floating and sliding
The floating type have guide pins
The sliding type have sliders
Both of these types need clean parts to allow the caliper to move back into the rest position.
In addition to all systems is old fluid will attract moisture over long periods of time. This can be an issue for the piston in the caliper or the pistons in the wheel cylinders.

And the master cylinder has pistons as well. Moisture there or broken springs in there can present the situation you have.

I would start with flushing old fluid out IF the fluid is more than 5 years old.
If that does not make a difference, the remove a caliper (leave brake line connected) and push the piston back into the caliper. (This will push fluid into the master cylinder and over flow making a mess) If the piston pushes back easily, go to the other side. If both push back easily - inspect the rear wheel cylinders (if drums) and open the boot. If it is dry, go to the other side. If all of that is good look at the master cylinder as an issue.

Post back on what you find.
Pictures would be even better.

Action
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: vacuum booster woes (or else ?)

Postby action » Mon Sep 20, 2021 1:36 pm

BTW keep the old booster. It is likely still good

Action
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: vacuum booster woes (or else ?)

Postby thegermanfan » Mon Sep 20, 2021 2:56 pm

The rear drum brakes are all new. They exploded on me some years ago and needed a full replacement. At that rear brake failure event the rear backing plates were bent and wheel cylinders broken, luckily nothing more happened. Master cylinder is a replacement part and maybe 6 years old. The front brakes got new friction material some years ago, but the pistons and calipers might be original or at least decades old. I will shop for replacement.
BTW: The proportioning valve and sure track actuator are the other brake related systems still untouched and as old as the whole car.
Of course I will keep the old booster. That one did not loose vacuum so fast. Maybe I will try another booster check valve on the current booster. This might help at least with the leak down issue.
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Re: vacuum booster woes (or else ?)

Postby action » Mon Sep 20, 2021 3:22 pm

The proportioning valve and Sure track are pass through parts. Meaning fluid just passes through unless some adverse event occurs.
If these fail, for the most part the braking system does not work.
Based on your description the system works. Just not the best after a brake cycle.

Pretty sure based on your description the calipers are the issue.
But it may only be the caliper mounting (Pins or sliders) needs to be cleaned and lubricated.
With the wheel cylinder and MC replacement, much if not all of the fluid was replaced.
Which makes the pistons in the calipers not high on the suspect list. Unless the dust boot is ripped.

Caliper repair -
Calipers are heavy and range in price from $40 USD to $100 USD each plus shipping. Shipping may cost more than the part.
Caliper boots and O rings are likely $20 or a little more for both sides and are light in weight. For the person that is a little skilled in brake work it is not difficult to replace the rubber pieces in a caliper. There is a good write up in the shop manual. The exception to this would be if the piston(s) is scored. However that tends to create a leak. You have not mentioned a leak. Only disassembly will find this. And partial disassembly is needed to clean and lube the pins or sliders.

Good luck.

Action
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: vacuum booster woes (or else ?)

Postby TonyC » Tue Sep 21, 2021 3:30 am

I think Action's advice may be as sound as anything. I don't have a whole lot of experience with the sliding-caliper designs (Frankenstein has fixed calipers with hydraulic pistons on both sides), but it's quite plausible that you may have scaly rust or brake dust or other debris seizing up the sliding components. Many times people who replace the pads don't think about cleaning off and re-lubricating the sliders, such as the rails or slide pins or such; that may have been overlooked the last time the pads were changed.

Cleaning the calipers should not be all that difficult. Find some brake-clean spray (two aerosol cans should be enough) and some brake-component lubricant in the nearest parts store, then crack open a shop manual and dust off your tools; or have a shop do that job. It's a job you should be able to do yourself if you have jacks to hold the wheels up off the ground. A proper shop can also do that job with ease, but they will cost, and you'll be dependent on their schedule (something I don't care for myself).

---Tony
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Re: vacuum booster woes (or else ?)

Postby thegermanfan » Tue Sep 28, 2021 1:05 pm

Found after further test driving, that the driver side wheels were a little bit hotter than passenger side. Disassembled the drivers side caliper. Lots of sludge! :o
IMG_0163s.jpg

IMG_0160s.jpg

This is how the caliper and piston look after some cleaning:
IMG_0167s.jpg
cleaned caliper and piston

Would you reuse this caliper? It was not leaking. All seals were in top notch shape. But as suspected maybe the Ford Originals from 1974. I have new pistons and seals at hand, but the piston seems OK to me. The caliper is questionable, but so are the remanufactured ones :?:
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Re: vacuum booster woes (or else ?)

Postby action » Tue Sep 28, 2021 2:09 pm

Reuse caliper? Absolutely!!!

With an exception. IS the groove that the square cut O ring is in the caliper clean and free of pits?
Is the inside of the caliper free of any loose debris.
If that answer is yes, then the caliper is re-useable.

Think about it, the piston rides on the O ring. It is the seal between the piston and O ring that makes all of the stopping power happen. The rest of the inside of the caliper to the piston is just close clearance NOT A SEAL! Any pitting inside the caliper (NOT where O ring is) means nothing as nothing really significant is there.

BTW the cause of all of that mess?
Humidity and not flushing the brake fluid every 5 to 10 years.
Every time the master cylinder is opened the brake fluid get exposed to outside air. Over long periods of time and repeated exposure the moisture is the air is pulled out by the brake fluid.

Action
Last edited by action on Tue Sep 28, 2021 2:12 pm, edited 1 time in total.
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: vacuum booster woes (or else ?)

Postby action » Tue Sep 28, 2021 2:11 pm

As a post script based on the pic I might reuse the piston

Action
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: vacuum booster woes (or else ?)

Postby thegermanfan » Sun Oct 03, 2021 9:29 am

As recommended I reused the calipers and pistons and put on new seals on both front calipers. After assemblywith a small amount of brake fluid for initial lubrication I pressurized the pistons several times with air to make sure they move smoothly. As per shop manual I lubricated the caliper on the V-groove for sliding action only with a very thin layer of copper paste. The pistons do release and the pads just very lightly contact the rotors after pedal release. I would think with that kind of sliding caliper nothing more can be expected.
The rear brakes already are newly assembled with all new hardware. Afterbleeding the brakes, I am still where it all began. The pedal release is sluggish. Especially with the vacuum assist. Pedal travel is probably a litte much, because rear brakes are not fully adjusted yet. Sooo that would mean that two replacement master cylinders were faulty from the start. I would need yet another master cylinder to motivate the brakes to come back quicker.
Please turn off audio for the videos. Audio got destroyed during conversion. Im unable to cure that at the moment.
https://youtu.be/2cOtvG9WaUc
https://youtu.be/C-mOl3tcIeQ
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Re: vacuum booster woes (or else ?)

Postby tomo » Mon Oct 04, 2021 11:07 am

After seeing the sludge in your caliper, I would replace all flexible hoses in the brake system and if the rear brakes were not rebuilt after storage, I would rebuild the rear wheel cylinders as well. The rubber hoses can deteriorate inside and still look good on the outside.
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Re: vacuum booster woes (or else ?)

Postby thegermanfan » Thu Oct 14, 2021 9:52 am

Just for fun I tested the former reman brake booster, which also exhibited a slow pedal return. Without vacuum and nothing attached it is not returning promptly when released.
https://youtu.be/sUqXzxeiYbw
The sure track actuator is capable of up to 4Hz cycle rate. My power brake booster, which is basically also just a vacuum operated servo, does not even 1Hz. It is dead slow. Granted the booster is a bit larger than the sure track actuator, but nevertheless I find the pedal should snap back, when released. Thats what it did, when the 1974 original was still in the car! Unfortunatly at some point it developed a leak and had to be replaced. At the time I lacked storage space and threw away the leaking original. :(
All hoses are new - rear brake hardware including backing plates are new - MC new - booster remanufactured by powerbrakeboosterexchange.com - front calipers new seals and cleaned lubricated.
Lets just for a moment assume I would want to race my black leather couch from a stoplight. It would be quite impossible! Release the brake - wait a second - Go! Hilarious! :( :?
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Re: vacuum booster woes (or else ?)

Postby TonyC » Fri Oct 15, 2021 2:24 am

Then it just doesn't make sense. The pedal should return to rest point pretty quickly after releasing. With the entire system having been operated on at one point in time or another, but all reasonably recently, I just don't know what could cause that step-on-a-plum effect with the pedal, save for one of those new parts being defective.

---Tony
"Don't believe everything you read on the Internet, just because there is a picture with a quote next to it." (Abraham Lincoln, 1866)
"Question Authority!"

1966 Continental Sedan, affectionately known as "Frankenstein" until body restoration is done (to be renamed "General Sherman" on that event)
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Re: vacuum booster woes (or else ?)

Postby tomo » Sat Oct 16, 2021 11:17 am

I would try replacing the vacuum hose and the check valve. It could be that the vacuum is not being restored to the pedal side of the booster fast enough. The booster has a spring to help return the diaphragm to neutral position and the atmospheric pressure vents back through the check valve and vacuum hose.
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Re: vacuum booster woes (or else ?)

Postby thegermanfan » Sat Oct 16, 2021 12:52 pm

tomo wrote:I would try replacing the vacuum hose and the check valve. It could be that the vacuum is not being restored to the pedal side of the booster fast enough. The booster has a spring to help return the diaphragm to neutral position and the atmospheric pressure vents back through the check valve and vacuum hose.

That last video was the booster without anything attached to it (also no check valve). Yes it sounds like breathing through a straw, when released. Which reinforces my thinking the booster is defective. If I attach a vacuum source to the booster, I can press the actual pedal rod and get power assist so I can push the rod further in against the booster return spring. But when released the pedal rod returns as slow or even slower than without vacuum assist. I have mailed a complaint to Booster Steve. Lets see what he says...
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