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Old 04-22-2017, 07:03 PM   #1
deanmerc
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Default 2001 L300 power brake booster and locked brakes

Greetings everyone!

I really need and would appreciate everyone's help; so sorry for the long post. This is what I did on my 2001 Saturn L300 V6 with 84K miles:

I've never been happy with the brake pedal "feel" since I bought the car. It always stopped ok, but I always thought the pedal went too far down. I replaced the front rotors and all 4 sets of pads. No improvement. When I brought her in for an oil change at the dealer, the guy who brought me the car back said it felt like the booster was weak (confirming that the pedal didn't "feel" quite right).

So, I checked the booster check valve by unplugging it from the booster, wrapping my lips around it and blowing into it. Air went through it. So then I sucked on it and stuck it to my lower lip. It maintained "air tightness" until I pulled it off my lip (ok, stop laughing). I guess that's one way of testing it.

So I replaced the booster. Now I have a problem: the brakes are locking up.

This is what I did: I removed the master cylinder. No leaks or sign of wear. I unbolted the booster. Went under the dash and removed the pin and fork from the brake pedal. Then I matched up the thread distance before I loosened the double nuts from the old booster stem, and mounted it to the new booster stem. I re-installed everything and bled the brakes. THEN, I noticed that the brake lights would not go out AND it was a little stiff to push the car while in neutral (pads grabbing a little).

SO I removed everything AGAIN and loosened those double nuts and extended the rod a little, thereby raising the brake pedal into the stop light switch so the lights would turn off. It worked! So I drove to the store to check out the system, only to start smelling hot brakes which eventually LOCKED UP. I limped her home after cooling down.

Do I have to loosen those double nuts and shorten or lengthen that rod? It's only got a few threads before it runs out of travel. And once I do that, how do I get the stoplight switch closer to the pedal so the brake lights go out??

Thanks for taking the time to read this. You guys are awesome.

Gabe in South Florida

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Old 04-22-2017, 08:37 PM   #2
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Default Re: 2001 L300 power brake booster and locked brakes

There is a happy medium, just high enough to turn off the lights but not apply the brakes. You can adjust the shaft under the hood without complete disassembly. I went through the same thing with my LW300.

...
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2002 LW300 sold.

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Old 04-22-2017, 09:36 PM   #3
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Default Re: 2001 L300 power brake booster and locked brakes

Thanks for replying! How were you able to adjust the rod without complete disassembly? And am I correct in needing to make the rod longer, which would push the pedal higher and into the switch to turn off the brake lights?

Thanks!

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Old 04-22-2017, 10:03 PM   #4
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Default Re: 2001 L300 power brake booster and locked brakes

The brake stop switch is separate from the brake vacuum boost repairs.
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Old 04-22-2017, 10:13 PM   #5
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Default Re: 2001 L300 power brake booster and locked brakes

Fdryer,

I was hoping to hear from you. THANK YOU so much for the rod adjustment procedure. That's precisely what I needed.

I need to repair this car tomorrow since I need it Monday and it's currently my only means of transportation.

I hope all is well, and I hope I can help others as everyone has helped me.

Gabe

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Old 04-23-2017, 09:05 PM   #6
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Default Re: 2001 L300 power brake booster and locked brakes

UPDATE:

I think I measured the booster stem and pedal rod correctly. I have attached pictures. Please let me know if I did it incorrectly. The length from the base of the booster mounting bracket to the end of the coupler should be 7.26" +/- .01. Am I looking at the correct pieces?

Brakes still locking up. When I loosened the master cylinder from the booster, I noticed a very slight hiss and then the brakes loosened up. I took off the master cylinder, replaced the rubber O-ring, and tightened the bolts to 17 ft/lb (manual says 18 ft/lb). Since it seems to be too tight, I thought I would loosen it a wee bit. It seemed to do better during a test drive and I thought I fixed it... but after a few blocks, they LOCKED up again.

The brake pedal "feel" has improved dramatically versus the old booster. When the brakes lock up, the pedal gets very stiff with very little travel. Once I loosen the master cylinder and relieve the "pressure", the pedal softens up and the brakes unlock. But when I tighten the bolts at the recommended ft/lb, they keep locking up.

PS. I broke the check valve this time. I replaced it with a generic one with a slightly bigger OD stem... So I got stiff fuel line that fit the new valve and then pushed the Saturn nylon hose into the other end with a hose clamp. It's air tight and doesn't collapse from vacuum.

Thanks again for everyone's time...

Gabe
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Last edited by deanmerc; 04-23-2017 at 09:13 PM..

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Old 04-23-2017, 10:12 PM   #7
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Default Re: 2001 L300 power brake booster and locked brakes

I've never meddled with the brake boost unit and have a similar issue with possible braking issues. Without any references from others with L300's to compare braking, I'm reluctant to try any adjustments. I too broke the vacuum valve when checking and was forced to use a larger vacuum line for the generic vacuum valve. This didn't change anything as the valve prevents loss of vacuum after the engine is shut down or if the engine dies while driving; the vacuum boost unit and one way check valve retains sufficient vacuum reserve for several pedal applications for power assisted braking before the reserve vacuum is depleted. Once depleted, braking is all leg power against the brake pedal. The brake master cylinder relies on the power assist unit for power braking. Without it all brakes are weak, the result of weight gains for vehicles adding safety improvements over the years. The power assist brake unit supplies more assist than many imagine.

I may not have sufficient experience to advise you of how to proceed if other members cannot help but I know there's always a solution, based on when and how power assist comes into play.

As a general rule, there's a small amount of play between brake pedal home position and application of braking to the brake master cylinder, the slop ensures no hydraulic or power assist is generated. After this slop, further brake pedal travel begins the hydraulic application thru the master cylinder to generate brake pressure to apply to brakes. Somewhere during pedal travel and very soon after the master cylinder is on its travel stroke, the power assist unit is turned on via the linkage to the diaphragm valve inside the power assist unit. Vacuum is applied to the large diaphragm to provide more force against the rod as it presses the dual pistons in the master cylinder -
power assisted braking. Hissing is air being let into the vacuum reserve as vacuum is depleted when the engine is off. During engine running, a constant vacuum supply is ready to refill the vacuum unit. The linkage adjustment is factory adjusted and never adjusted again unless the master cylinder or power assist unit is replaced. Its my estimation that adjustment of the linkage is too long and should be shortened to stop the power assist unit from being activated when the brake pedal is in home position. In effect, the master cylinder isn't pressing on the tandem pistons to create hydraulic pressure while the brake boost unit is off (not applying boost to the linkage and pressing the rod into the master cylinder, creating brake pressure locking brakes). This adjustment requires understanding the interactions between the master cylinder and brake boost unit. The linkage adjustment calibrates when brake boost is needed, after pedal travel begins, not before. Your descriptions seems to be about the brake boost unit applying assisted braking without pedal movement, suggesting the linkage adjustment is incorrect and readjustment needed. My belief is the linkage needs to be adjusted to a slightly shorter length than specified and testing after adjustment. This means the engine running and simply selecting forward or reverse to see if the brakes are still applied or released as they should be without the brake pedal applied (in home position). Patience and a period of trial and error is needed until you restore this setup back to factory conditions.

Last edited by fdryer; 04-23-2017 at 10:17 PM..

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Old 04-23-2017, 10:24 PM   #8
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Default Re: 2001 L300 power brake booster and locked brakes

This car has a very basic single booster. If you loosen the master you have effectively shortened the rod. Of course you have let air into the simple booster. Other cars have relatively sealed boosters, our cars are open to the atmosphere if the master is loose.
I agree your rod is too long. Fix this first then adjust the brake light switch last.

I am a life long professional mechanic and I had to fiddle with my rod and switch to get everything right.

...
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2002 L200 grandson's car now
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Old 04-23-2017, 10:32 PM   #9
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Default Re: 2001 L300 power brake booster and locked brakes

Hi Fdryer,

That is sound advice... I wasn't sure if the rod was either too long or short overall. I will make the rod about an inch shorter and see what happens. Each time adjust it, I have to remove the master cylinder brake lines, remove m/cylinder, remove booster, adjust rods, re-install and then bleed everything... oy!

When I loosened the master cylinder from the booster the locked brakes released, the pedal had some travel, and the car rolled slightly. After adjusting something, I always begin by feeling resistance when pushing the car while it's idling in neutral. The brake pedal usually starts off feeling nice and solid, with normal travel.

Then after driving a few blocks and repeatedly stopping, they begin locking up and then the pedal gets tight - with little or no travel.

I'm going to shorten the overall length of the rod, and then push the stoplight switch closer to the pedal so the lights go out. I will post my progress tomorrow. If I can't get it, I'll have to bring it to a mechanic shop - ugh

Thanks again for helping... I'll update tomorrow.

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Old 04-23-2017, 10:37 PM   #10
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Default Re: 2001 L300 power brake booster and locked brakes

Hi LW300,

That makes sense... I was thinking the same thing - that when I loosened the master cylinder bolts from the booster, the rod moved forward slightly, hence "shortening" it.

It's a nice process to get to the rod... Do you know of a simpler way of adjusting that rod without having to disconnect the brake lines from the master cylinder, removing the master, removing the booster, adjusting rod, then re-attaching and then bleeding the entire system?

I'm getting quite proficient at this though lol...

Gabe

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Old 04-23-2017, 11:12 PM   #11
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Default Re: 2001 L300 power brake booster and locked brakes

As mentioned previously, I never had to remove a master cylinder or power boost unit so I'm out of my comfort zone here. I don't envy your predicament and can only imagine what you're going thru. At the least, since you've already removed things to replace the boost unit, its just a matter of which parts needed to be removed to allow rod adjustment. Its easy in the comfort of my underwear and pc to make replies but I do know and understand your predicament. Patience, time and thinking along with some trial and error should restore this back to where it should be. Service manuals are written for dealer mechanics already familiar with GM autos. The rest of us have to deal with second guessing, reading between the lines..........

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Old 04-24-2017, 10:53 AM   #12
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Default Re: 2001 L300 power brake booster and locked brakes

The booster mount comes apart giving access. Remove the wipers and the black plastic cover. This is the cover over the wiper transmission fender to fender. There is a nut that holds part of the structure to the body. Remove the booster nuts and the mount comes apart. I was able to adjust the shaft without disassembly.

...
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2002 LW300 sold.

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Old 04-24-2017, 11:50 AM   #13
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Default Re: 2001 L300 power brake booster and locked brakes

Howdy,

UPDATE: I loosened the nut all the way until no more threads, which shortened the rod as much as possible. Went thru entire procedure again. Initially, the brakes felt awesome and the car free wheeled ok. I kept testing the brakes and simulated stop-and-go traffic. I managed to drive 4 blocks this time until I began feeling the car "holding back". Then the brake pedal got hard again with little travel, started smelling hot brakes and limped home.

Off to the mechanic she goes... "THANK YOU" to everyone who helped me out. I really do appreciate it. I'm not too familiar with brakes. I assumed (incorrectly) that changing a booster or master cylinder would be plug-and-play. It obviously requires specific knowledge and understanding. I have no formal training, just simple mechanic stuff.

I will update what the mechanic tells me it was in the interest of information sharing.
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Old 04-24-2017, 11:54 AM   #14
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Default Re: 2001 L300 power brake booster and locked brakes





...
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2002 L200 grandson's car now
2002 LW300 sold.

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Old 04-24-2017, 12:30 PM   #15
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Default Re: 2001 L300 power brake booster and locked brakes

Quote:
Originally Posted by deanmerc View Post
Howdy

Off to the mechanic she goes... "THANK YOU" to everyone who helped me out. I really do appreciate it. I'm not too familiar with brakes. I assumed (incorrectly) that changing a booster or master cylinder would be plug-and-play. It obviously requires specific knowledge and understanding. I have no formal training, just simple mechanic stuff.

I will update what the mechanic tells me it was in the interest of information sharing.
Before you do that. There are 2 things to come to mind: Your calipers could be sticky or the front brake flex lines can close up effectively causing what you have experienced.

Brake lines wear from the inside out. (Get loaded up with gunk) This can cause a very slow release of pressure when the pedal is released. The flex lines would be my best guess. If the flex lines are original, new ones would be a small and good investment.

...
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Old 04-24-2017, 12:58 PM   #16
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Default Re: 2001 L300 power brake booster and locked brakes

deanmerc, please update any information how this is corrected. It's unfortunate that you found this not as easy a task as you thought and the reason I'm reluctant to try adjusting factory settings that haven't been touched.

There are two members presently engaged in battle with their ac system repairs - so far ac is winning (no ac) with many incorrect guesses. You're​ not alone in learning about certain car problems that are not considered casual diy repairs despite many presuming they are.

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Old 04-24-2017, 02:36 PM   #17
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Default Re: 2001 L300 power brake booster and locked brakes

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Originally Posted by deanmerc View Post
I've never been happy with the brake pedal "feel" since I bought the car. It always stopped ok, but I always thought the pedal went too far down. I replaced the front rotors and all 4 sets of pads. No improvement. When I brought her in for an oil change at the dealer, the guy who brought me the car back said it felt like the booster was weak (confirming that the pedal didn't "feel" quite right).
I'm wondering about your original concern with the brake pedal "feel". Did the brake pedal free play seem excessive?
Was it because there was too much pedal travel before the brakes would "bite down?" Did the stopping distance greater than expected?

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Last edited by pierrot; 04-24-2017 at 02:44 PM..

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Old 04-24-2017, 06:28 PM   #18
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Default Re: 2001 L300 power brake booster and locked brakes

Although not recommended under most circumstances, there may be one test to separate the basic hydraulic brake system from the power assist brake unit operating with vacuum. A fair warning not to perform the following suggestion except in controlled conditions and away from all traffic, preferably in one's own level driveway or closed lot with room for low speed braking; disconnecting and capping the vacuum supply line to disable the power brake unit. WARNING! Disabling the vacuum supply line to the power brake unit removes the ability of power assisted braking and should never be attempted while driving on public roads. Disabling power assisted braking and testing should only be performed at low speed for short distances. The basic hydraulic brake system remains but much more pedal effort is needed to stop a vehicle hence the warning not to drive above low speeds. Low speeds, less than 15 mph. Anyone not familiar without power assisted braking will be in for a surprise as to how much effort is needed to apply braking. This not a joke or to provide entertainment. Disabling the power brake unit can help determine why brakes are locking up as disabling one part of the brake system without endangering anyone may help determine whether or not the basic hydraulics or power brake unit is causing this problem. DO NOT TRY THIS METHOD IF NOT COMPLETELY AWARE OF AN UNSAFE CONDITION.

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Old 04-24-2017, 11:32 PM   #19
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Default Re: 2001 L300 power brake booster and locked brakes

Thank you to everyone contributing to this thread. I am familiar with power brakes without the booster working, as well as no power steering - I've actually practiced stopping and steering a car when turned off and the vacuum boost depleted as part of my driving training. It's good to know what to expect and I also recommend it under controlled and safe conditions.

I just drove the car to the mechanic at 11pm due to less traffic and I didn't have to use the brakes as much. I drove about 1 mile. It felt ok, but brakes began binding when I got to his shop. He will see it parked there in the morning. I'm curious what he will find that we haven't thought of, or I haven't already done. I tightened the master cylinder and booster bolts to the correct ft/lbs, shortened the rod as much as possible, bled brakes, filled reservoir properly, etc etc.

I will let everyone know the outcome.

Thanks again,
Gabe

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Old 04-25-2017, 01:12 PM   #20
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Default Re: 2001 L300 power brake booster and locked brakes

Hi Pierrot,

When I test drove the car prior to purchasing, I noticed that the brake pedal seemed to require a bit more pressure than usual before engaging. Kind of like when you don't drive a car for a while and rust forms on the rotors - in fact, that's why I replaced the front rotors.

It was as if the car didn't want to stop as effectively as it should in proportion to the pedal pressure and travel. The pedal never went to the floor, but the brakes just seemed ineffective and to require more pressure than usual to stop. It always stopped, but I needed to press harder than what I thought was usual. And when the Chevrolet mechanic returned my car after an oil change, he also commented that the booster seemed weak.

Note: The pedal never hissed or made that "swooshy" sound or spongy feel when pressed. And I tested the booster by depleting the vacuum when off, and then starting the car and the pedal went down slightly. But it just never "felt" right. Oh, and I never heard any grinding or unusual noises.

NOTE 2: Also, when I was bleeding the brakes the first time, I did notice that the brake fluid was a bit dark, and it appeared to have some small contaminants. Like very small dark specs in the fluid. Of course hindsight being 20/20, I should have just tried bleeding and replacing the brake fluid before replacing the booster. I wonder....

Gabe

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