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#896191 - 09/22/11 12:05 AM Brake pedal goes all the way down after being bled
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
Hi guys, Ive been dealing with this issue for some time now. Ever since ive owned this 83 monte the brake pedal will go all the way to the floor. It wont lock the brakes, but will stop the car well. I have replaced the front and rear brakes wheel cylinders, calipers, rubber hoses and all pads/shoes, calipers and drums. Fully gravity bled and pedal bled the system with no positive results. I even put a bolt between the metering valve end and the frame while pedal bleeding the system to prevent it from tripping. But even after that its still spongy. Any ideas? Maybe bad metering valve? I want to make sure before going ahead to buy parts that I might not need.
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83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896192 - 09/22/11 12:12 AM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
PennsyMonteSSGuy Offline
Member

Registered: 05/06/10
Posts: 332
Loc: Doylestown, PA
Sounds like a bad master cylinder to me. All it takes is a tiny internal leak with the seal.
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#896197 - 09/22/11 12:30 AM Re: Brake pedal goes all the way down after being bled [Re: PennsyMonteSSGuy]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
How would I know if it was the proportioning valve VS. the master cylinder?
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83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896223 - 09/22/11 09:12 AM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
Glenn Tjapkes Offline
10+ Year
Member

Registered: 06/07/01
Posts: 1282
Loc: Grand Rapids, MI
If the pedal hits the floor, pressure isn't building up either because the MC is faulty, there's a leak somewhere, there is air in the system, or the drums are out of adjustment.

I would make sure you have the shoes on the rear brakes adjusted outward far enough. On drum equipped vehicles, most pedal feel is determined by the drum brakes. If the shoes are too far in, all pedal movement is going toward pushing the shoes out toward the drum surface. It isn't until the shoes meet the drum surface that hydraulic pressure begins to build in the system and provide stopping power.

Since you say it stops OK, my guess is that the shoes might be meeting the drum somewhere near the end of the pedal travel. It's free to check, so I would definitely do so if you haven't already. I've had good luck with adjusting drums with the drums off, but you might have to adjust them with the drums on via the access hole to the star wheel in the back plate.

Otherwise, if you're sure there's no leaks and no air left in the system, I would suspect the Master Cylinder as well.
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#896243 - 09/22/11 12:07 PM Re: Brake pedal goes all the way down after being bled [Re: Glenn Tjapkes]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
Thanks for the replys, The entire rear drum brake system is actually only a few months old and its adjusted properly. I double checked it before and after bleeding the lines. There are no leaks, And there is no way I should have any air after bleeding it as much as I have... So im looking at buying a master cylinder. Are there any bolt on upgrades that wont put me in the poorhouse?
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896345 - 09/22/11 09:42 PM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
So I bench bled and replaced the master clyinder. Bled all 4 corners and its just the same as before no difference at all.

Proportioning valve?
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896367 - 09/23/11 12:03 AM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
MoreHPplease Offline
Member

Registered: 02/11/10
Posts: 685
Loc: New Jersey
What about the hard lines?

Years ago on my 93' Ford I had a small pin hole leak that was causing a soft pedal.

My brake fluid leak was so small that It would have been virtual impossible to notice any brake fluid loss.

My other thought is a bad brake booster.

I wonder if a bad brake power boost unit can give you low brake pedal issues.



Edited by MoreHPplease (09/23/11 12:13 AM)
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#896387 - 09/23/11 06:53 AM Re: Brake pedal goes all the way down after being bled [Re: MoreHPplease]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
I dont believe I have a leak in the hard lines. I replaced the entire rear brake line from the proportioning valve back to the wheel cylinders about 4 months ago. And I have been driving pretty regularly since without noticing any fluid loss at the resivor. As for the fronts the rubber hoses are new with the stock metal line which is in pretty good condition But, I will double check. If a front line were leaking I would think I would notice it more than a rear line because of the pressure difference.
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896448 - 09/23/11 03:31 PM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
shuend Offline
10+ Year
Member

Registered: 05/01/01
Posts: 289
Loc: Hawaii
When the brake pedal goes to the floor, if you pump the brake pedal, does the pedal stay higher? If it does, most likly is the brake master cylinder. Does the brake pedal have lotta free play? If it does, you might need to check the push pin from the power brake booster to brake master cylinder. It might be out of ajustment.

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#896466 - 09/23/11 05:30 PM Re: Brake pedal goes all the way down after being bled [Re: shuend]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
I just replaced the master cyl yesterday. It made no difference at all. When I push the pedal down it goes about a 1/2" from the floor with ease. When I pump it or hit the brakes hard/fast it is firm at first but eventually goes to the 1/2" from the floor area. The last 1/2" of pedal is also pretty spongy feeling and I can press it all the way down to the floor without alot of force.
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896653 - 09/24/11 11:44 PM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
Anybody know how to check the pin in the proportioning valve? the brass one that comes out twords the front of the car isnt stuck so im kind of lost as to what it could be.
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#896656 - 09/24/11 11:58 PM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
SilverSS Offline
Member

Registered: 08/24/06
Posts: 748
Loc: Ocala, FL
Good luck figuring it out. We replaced everything on my 86 SS through the years since it was new and it would NEVER lock up the brakes from the day we picked it up. It stopped good but wouldn't lock them up. Now I've got Wilwood discs front and rear. They're slightly better lol.
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1986 MCSS 540 BBC, TH400, S-60



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#896863 - 09/26/11 02:26 AM Re: Brake pedal goes all the way down after being bled [Re: montesleeper83]
MADMIKE Offline
Member

Registered: 07/04/10
Posts: 81
Loc: C.V. CA
Originally Posted By: montesleeper83
I just replaced the master cyl yesterday. It made no difference at all. When I push the pedal down it goes about a 1/2" from the floor with ease. When I pump it or hit the brakes hard/fast it is firm at first but eventually goes to the 1/2" from the floor area. The last 1/2" of pedal is also pretty spongy feeling and I can press it all the way down to the floor without alot of force.

Check the wheel cylinders, are they installed with the bleeder nipple above the hard line? If upside down you will never get all the air out.I'm fairly sure the WCs are designed to only go on one way, but verify this.
Check the calipers, are the bleeder nipples pointing up? If not you will never get all the air out. Did you use new copper washers on each side of the hose/banjo fitting on the calipers? Two washers per caliper.

Verify there are no leaks around the piston seals. On the rear wheel cylinders remove the dust boots and check that the pistons and seals are free to move. Verify no leakage.
Verify the hoses are not swelling, have damage, or are leaking at the swedge joints. Verify there are no leaks at the hard line connections.

When you replaced the MC which MC did they give you?
On the 78-88 A/Gs there were three different available MCs.
78-81
7/8"([22.5mm].875") for manual brakes
24mm(.944"}for power brakes
82-88
24/36mm(.944/1.417") for power brakes. Quick take up design.

If the MC given is the MB 7/8" design that would explain the long pedal, however the pedal should in no way be spongy. If the pedal slowly drops that is a sign of a leak.

Here's a link to a basic flow chart for brake diagnostics. Download it and print it out.
http://www.michaelsapi.com/data/techpdf/brake%20diag%20flow%20chart.pdf

Here's a link to a very useful tool.
http://www.summitracing.com/parts/SSB-A1704/
I've used this tool quite often. There may be pressure but knowing what pressure there really is very helpful.


Edited by MADMIKE (09/26/11 02:28 AM)
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#898545 - 10/07/11 11:50 AM Re: Brake pedal goes all the way down after being bled [Re: MADMIKE]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
I checked all the lines and connections no wet spots anywhere to be seen. The brake hoses look great I replaced all of them last year. But im not sure what size MC they gave me I just purchased the stock replacment for a 83 monte with the 3.8 V6. I have read that the cast iron metering blocks prop valves tend to stick sometimes. That is the only part of the braking system besides the front hard lines that has not been replaced. But I wouldent know untill I get a pressure reading. It brakes good enough for right now. I will probably just take it to the last show of the year and let it sit in storage and figure it out next spring.
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#898563 - 10/07/11 04:06 PM Re: Brake pedal goes all the way down after being bled [Re: Glenn Tjapkes]
BuzzLOL Offline
Member

Registered: 05/02/06
Posts: 5485
Loc: Toledo, Ohio
Originally Posted By: Glenn Tjapkes
I would make sure you have the shoes on the rear brakes adjusted outward far enough. On drum equipped vehicles, most pedal feel is determined by the drum brakes. If the shoes are too far in, all pedal movement is going toward pushing the shoes out toward the drum surface. It isn't until the shoes meet the drum surface that hydraulic pressure begins to build in the system and provide stopping power.

Since you say it stops OK, my guess is that the shoes might be meeting the drum somewhere near the end of the pedal travel. It's free to check, so I would definitely do so if you haven't already. I've had good luck with adjusting drums with the drums off, but you might have to adjust them with the drums on via the access hole to the star wheel in the back plate.


.. X 2... rear shoes should be adjusted out far enough so that you can barely get the drums to carefully slide back on... the self-adjusters have to be freed up and greased... if you didn't get new ones and grease them...

.. When bench bleeding the MC, the front of the MC should be angled downward to get all the air out... the reason it has to be bench bled is because when mounted on the car, the MC angles slightly upward and so the air stays trapped in the front of the MC... then it has to be carefully re-assembled to the car so no air gets back in... to the extent possible...

.. GM cars are known for a low and slightly soft pedal with some braking control movement, but it sounds like yours are worse than that... the disc brakes usually don't lock instantly at max foot pressure like the old drum brakes, but the disc brakes should be lockable after being applied hard for a second or two at speeds above 40 MPH as they clean off and heat up... you should have to then back off the foot pressure a bit to keep the tires from flatspotting...

.. ALthough they usually say bleed the brakes farthest from the MC first, with a proportioning valve, I've always had best luck bleeding the front brakes first to get the prop valve moved forward in the prop valve body, so it's not shutting off flow to the rear...
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'86 Monte LS (total'd Fall '2013), '87 GTA TransAm TPI350 TH700-R4, '85 Fiero 5-speed, '75 MG Midget Buick Alum.V8 BW 5-speed manual, '77 Pontiac Astre Formula wagon 5-speed posi, '78 F150 4WD 351"M ==> 400" C6, '79 Caddy Seville Olds EFI 350" TH400, 19' Slickcraft 425HP 351W MerCruiser I/O

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#904457 - 11/18/11 06:35 PM Re: Brake pedal goes all the way down after being bled [Re: BuzzLOL]
blue89z24 Offline
Member

Registered: 05/24/11
Posts: 279
Loc: wilmington, DE
i have same issue i was told master cylinder

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