69 brakes, different problem
Thread Starter
Racer
Joined: Jul 2008
Posts: 353
Likes: 30
From: warwick rhode island
69 brakes, different problem
the car is a 69 convertible with non-power brakes.
while checking the fluids today i pulled the master cylinder cap and noticed the forward reservoir was full to the brim
and the rear was down about a half inch. i always fill to about a quarter inch below the top.
there are no leaks anywhere on the car. the brakes work great. they release fully and there is no drag when turning the wheels by hand.
the dash brake light did come on and stay on yesterday. repeatedly punching the brake pedal and releasing it will not get the
dash brake light to go off with the master cylinder cap on or off. taking the wire off the distribution
block brake switch makes the dash brake light go off.
i used my large syringe and removed some fluid from the forward reservoir and squirted it into the rear reservoir until they were both even.
that left the fluid levels where i usually have them.
the question is where can fluid transfer from the one reservoir to the other? i am thinking the master cylinder, but the brake
light being on makes me wonder if the problem is in the distribution block with the brake light switch in it.
ideas? comments? solutions?
while checking the fluids today i pulled the master cylinder cap and noticed the forward reservoir was full to the brim
and the rear was down about a half inch. i always fill to about a quarter inch below the top.
there are no leaks anywhere on the car. the brakes work great. they release fully and there is no drag when turning the wheels by hand.
the dash brake light did come on and stay on yesterday. repeatedly punching the brake pedal and releasing it will not get the
dash brake light to go off with the master cylinder cap on or off. taking the wire off the distribution
block brake switch makes the dash brake light go off.
i used my large syringe and removed some fluid from the forward reservoir and squirted it into the rear reservoir until they were both even.
that left the fluid levels where i usually have them.
the question is where can fluid transfer from the one reservoir to the other? i am thinking the master cylinder, but the brake
light being on makes me wonder if the problem is in the distribution block with the brake light switch in it.
ideas? comments? solutions?
Race Director
Joined: Jul 2004
Posts: 12,690
Likes: 329
From: Scottsdale Arizona
I'm not sure that a defective block would cause this either, especially if the brakes are working. Really the only way for the fluid to rise is if the pistons in the calipers are being pushed into their bores or if air is being introduced or expanding. If air, that would account for the light coming on but you'd expect a poor pedal.
Certainly justifies some more investigation.
Certainly justifies some more investigation.
Pro
Joined: Apr 2009
Posts: 650
Likes: 1
Hi OldBoat,
IMHO, I think your problems are mutually exclusive. I think your fluid loss in the rear of the MC is due to displacement. Your pads have worn down and have subsequently created move volume for the brake fluid to flow in the system. The light is a mystery to me. If it were me, I would re-bleed the entire system. That way you could guarantee that the system is in good shape initially. Then monitor fluid level and brake performance. If your brakes work great and the fluid stays at the desired level then your problem is most likely the distribution block warning system. Hopefully a full system bleed will correct the distribution block as well. Here's a cool post by Roger about how the distribution block works.
Good luck!
http://forums.corvetteforum.com/c3-t...ck-switch.html
IMHO, I think your problems are mutually exclusive. I think your fluid loss in the rear of the MC is due to displacement. Your pads have worn down and have subsequently created move volume for the brake fluid to flow in the system. The light is a mystery to me. If it were me, I would re-bleed the entire system. That way you could guarantee that the system is in good shape initially. Then monitor fluid level and brake performance. If your brakes work great and the fluid stays at the desired level then your problem is most likely the distribution block warning system. Hopefully a full system bleed will correct the distribution block as well. Here's a cool post by Roger about how the distribution block works.
Good luck!
http://forums.corvetteforum.com/c3-t...ck-switch.html
Thread Starter
Racer
Joined: Jul 2008
Posts: 353
Likes: 30
From: warwick rhode island
interesting ideas.
the brakes have less than a few thousand miles on them so the pads are not worn.
the part that gets me is that there are no leaks, and the front reservoir level is going up while the rear is going down.
next weekend i will be removing the block first and replacing that. if that doesn't fix it i will replace the master cylinder.
the brakes have less than a few thousand miles on them so the pads are not worn.
the part that gets me is that there are no leaks, and the front reservoir level is going up while the rear is going down.
next weekend i will be removing the block first and replacing that. if that doesn't fix it i will replace the master cylinder.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
If the two reservoirs were originally at exactly the same level and now one has risen that other lowered by the same amount, the fluid is transferring via failed piston seal in the M/c or the distribution block. The brake light detects pressure differential in the two systems which pretty much confirms the fluid transfer.
Thread Starter
Racer
Joined: Jul 2008
Posts: 353
Likes: 30
From: warwick rhode island
i agree mike.
the reason i will start by replacing the block is that the block is almost 44 years old and the master cylinder is less than a year old.
we shall see what happens next weekend.
the reason i will start by replacing the block is that the block is almost 44 years old and the master cylinder is less than a year old.
we shall see what happens next weekend.
Advanced
Joined: Jun 2013
Posts: 64
Likes: 1
From: Lambertville Michigan
Please review the link above to Roger's post. I'm confused. It stated that the light would ONLY be on when the brakes are applied. When released the light would go out. Please read the "note" on the attachment. My light is on when I'm NOT depressing the brake. However I can get it to go out sometimes when depressing the peddle.
Does that mean that I have a faulty proportioning valve? Or could it be a bad ground in the circuit?
Does that mean that I have a faulty proportioning valve? Or could it be a bad ground in the circuit?
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Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
oldboat
You have better chances of winning the Powerball than having the differential valve allowing the fluid to transfer to the front reservoir.
You master is starting to fail, secondary cups, not all that uncommon. Age doesn't matter these days. Also causes the distracting lite to come on.
Ely
Ideally, the light should go off with no pedal, but with age and a little crud, it can stay on. Not anything to really be too concerned about. You can clean it internally.
To check the lite, just remove it from the switch and ground it to turn it on.
More importantly, you probably have a pressure leak somewhere.
You have better chances of winning the Powerball than having the differential valve allowing the fluid to transfer to the front reservoir.
You master is starting to fail, secondary cups, not all that uncommon. Age doesn't matter these days. Also causes the distracting lite to come on.
Ely
Ideally, the light should go off with no pedal, but with age and a little crud, it can stay on. Not anything to really be too concerned about. You can clean it internally.
To check the lite, just remove it from the switch and ground it to turn it on.
More importantly, you probably have a pressure leak somewhere.
Thread Starter
Racer
Joined: Jul 2008
Posts: 353
Likes: 30
From: warwick rhode island
update
i pulled the old distribution block out today. the plunger assembly was stuck toward the side of the front outlet. didn't take too much to un-stick it. the o-rings did look old and tired. i will measure them to see what size should be used for replacement.
i didn't see anything that would indicate why the fluid was being pushed from one side of the master to the other.
i put a new distribution block in. a minor victory in that the brake light finally went out.
re-bled the system and have a nice firm pedal.
i will monitor the system to see if the problem reappears, but as of now i still have no idea why it happened.
for those of you who have never taken a distribution block apart the picture below shows what is inside.
[IMG]
[/IMG]
i didn't see anything that would indicate why the fluid was being pushed from one side of the master to the other.
i put a new distribution block in. a minor victory in that the brake light finally went out.
re-bled the system and have a nice firm pedal.
i will monitor the system to see if the problem reappears, but as of now i still have no idea why it happened.
for those of you who have never taken a distribution block apart the picture below shows what is inside.
[IMG]
[/IMG]