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Brake light! The fun never stops :)

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Turbo301 View Drop Down
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    Posted: 15-April-2010 at 11:45AM
I've noticed that my brakes are not giving me the kind of braking power I'd normally expect out of a squishy '70s car, and just last night I started to wonder if something was wrong. Well, today I had to jam on the binders pretty hard for a changing traffic light, and sure enough my brake light came on.
 
As I understand it, this means that either the front or rear is getting more pressure than the other. What I don't know is what would cause this pressure differetial. Do the brakes just need to be bled, or could my pressure differential valve be in need of a tune-up? My fluid level is full and looks okay... I think (what should it look/feel like)? The brakes don't squeak or anything.
 
Any help'd be appreciated. I don't want to dive into self-repairs that would be beyond me, but if it's just bleeding then that'd be a fun weekend job :).
 
Thanks for any insight!
1977 Cougar XR7
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Post Options Post Options   Thanks (0) Thanks(0)   Quote occupant Quote  Post ReplyReply Direct Link To This Post Posted: 15-April-2010 at 12:10PM
The first two things I'd check would be if the front pads wore down quite a bit, or if the rear wheel cylinders are leaking. Barring one of those two things, I'd start looking at the lines themselves.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BIGEMUN Quote  Post ReplyReply Direct Link To This Post Posted: 15-April-2010 at 2:26PM

I would  check your lines as stated above, vacuum to your booster, and depending how old your fluid is, switch in some new stuff.

Good Luck-
 
Jeff
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 2:13AM
Thanks for the pointers, guys!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Psquare75 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 2:51AM

Rubber lines

Low brake fluid?

If the pads are down to bare metal, and the reservoir has fluid, it shouldn't set the light. Something failed, IMO (or he's low on fluid).


How does the pedal 'feel'? Mine in my 77 feels like a brick is under it. Nice and firm. I can usually get someones head to hit the dashboard if I do it hard enough, and if said passenger is drunk (tried and tested LOL).



Edited by Psquare75 - 16-April-2010 at 2:52AM
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 2:57AM

My reservoir is full, but I'm not sure what the fluid consistency is supposed to be like: it is quite thin, a hint of brownish colour on my finger when I touch it to the surface of the fluid.

The pedal is ultra soft (basically dead) until right near the end, when it is very firm. It doesn't move much at that end :). It doesn't have the neck-snapping brakes I remember from my mom's old Marquis! It's almost like what I imagine manual brakes must feel like...

I can't see signs of leakage (and again the reservoir is full); what else could fail to cause that kind of response?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Psquare75 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 2:59AM
You sir, need a brake job. The consistency is about right. 

Are the rears in adjustment?

Are the rear cylinders leaking?

What have you changed on this car since you got it?

Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 3:05AM
The front flex lines are new, that's all that's been touched that I know of.
 
I haven't seen any signs of leakage, but I'll take a closer look today.
 
From the lack of braking power I have, I'd almost say it felt like the rears are fine but the fronts are powerless!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Psquare75 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 3:09AM

If the rears were fine and the fronts weren't functioning, the rears would just lock up and you'd slide. The rear brakes control pedal height and feel to a certain extent. A down and dirty method would be a hose clamp over the rear brake hose, then try the brakes while parked.. the pedal should firm up immediately. This can damage the rear hose however, so try at your own risk.


Paul
77 XR7 460/C6/3.00:1 *SOLD*
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 3:12AM
Good to know about the rear brakes, I'll definitely look closely at them tonight.
 
Could the valve controlling fluid pressure/distribution be malfunctioning, or is that not very likely?
 
I'll likely hold off on trying that idea, but good thinking :).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Psquare75 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 3:13AM
Not very likely, they usually go bad from sitting. 
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 12:06PM

Okay, I'm home and checked out the car; here are the findings for the local Cougar MDs:

1.) no signs of leakage at any brake; dry as a bone at the back, especially (up front there's still some wet-ish oil spray gunk)
 
2.) no signs of leakage at the master cylinder or pressure differential valve
 
3.) all lines looked intact and in good shape as far as I could trace them under the car.
 
4.) the big honkin' vacuum line into the master cylinder looked good, right from the "T" and the manifold connection; however, the white cap that holds the line to the cylinder was a bit loose. Is this acceptable, or should it be fully tight?
 
5.) when the car was on but not running, pumping the brakes built up a lot of pressure in the brake pedal (more to where I imagined it should be). Some wheezing/clicking was heard from underhood as they were pumped. As soon as the car started and the brake pedal was depressed, it was like deflating a balloon: the pressure in the pedal dropped back to its previous state. The "BRAKE" light stayed on the whole time.
 
So, does this shed any light on anything? Could it be a vacuum leak? Could the master cylinder be defective? What does the build-up of pressure, and then the drop when the car is running, mean?
 
Thanks for any help, and for your help so far!
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote occupant Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 2:44PM
Originally posted by Turbo301 Turbo301 wrote:

Okay, I'm home and checked out the car; here are the findings for the local Cougar MDs:


5.) when the car was on but not running, pumping the brakes built up a lot of pressure in the brake pedal (more to where I imagined it should be). Some wheezing/clicking was heard from underhood as they were pumped. As soon as the car started and the brake pedal was depressed, it was like deflating a balloon: the pressure in the pedal dropped back to its previous state. The "BRAKE" light stayed on the whole time.

 

So, does this shed any light on anything? Could it be a vacuum leak? Could the master cylinder be defective? What does the build-up of pressure, and then the drop when the car is running, mean?

 

Thanks for any help, and for your help so far!

 


The pedal will get hard if the car is off because you bleed off the vacuum built up in the underhood canister when the engine isn't running. It's only designed to give you a couple of good stops from speed before you lose vacuum assist. So when it starts up, the pedal is going to drop some because the vacuum assist builds back up. If it didn't do that, you'd be looking at a vacuum leak somewhere or a failing booster. So it's fine like it is. The wheezing sound is vacuum releasing, the clicking is probably the brake light switch.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Psquare75 Quote  Post ReplyReply Direct Link To This Post Posted: 16-April-2010 at 4:48PM
I still say bad cylinders. Something is out of balance. If it were me, I'd do my suggestion on each/all hoses, and eliminate an end of the car.
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mcford Quote  Post ReplyReply Direct Link To This Post Posted: 17-April-2010 at 11:08AM
rears out of adjustment and a possible bad master.  sounds like it could have an internal leak.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72sport Quote  Post ReplyReply Direct Link To This Post Posted: 17-April-2010 at 11:46AM
Originally posted by mcford mcford wrote:

possible bad master.  sounds like it could have an internal leak.


+1 Montego did this exact thing when the master went bad.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Turbo301 Quote  Post ReplyReply Direct Link To This Post Posted: 01-May-2010 at 12:30AM
Originally posted by 72sport 72sport wrote:

Originally posted by mcford mcford wrote:

possible bad master.  sounds like it could have an internal leak.


+1 Montego did this exact thing when the master went bad.
 
Good call, it was definitely my gross master cylinder and gross, flaky, brown brake fluid that was hurting me!
 
I'm happy to say that, with my frame bushings, end links and master cylinder in place, the car drives very nicely, and the brakes work beautifully! For some reason my brake light still won't turn off, but the brake feel is just perfect: not too "land yacht sensitive", and not hopelessly mushy like it was before. She hauls down from 75 mph in a jiffy.
 
Is there some way to re-set the "brake" light to see if I still actually have a brake problem or if the sensor piston might just be hung up on goo or something?
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