Author Topic: Disc Brake Help!  (Read 4058 times)

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Offline thumper911

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Disc Brake Help!
« on: May 13, 2005, 08:26:37 AM »
I have just done a full disc brake conversion, front and rear, and was wondering if anybody could help me out as to why I'm hardly getting any pressure on the rear brakes. Everything has been bled thoroughly...the fronts grab tremendously well but the rears just don't wanna grab hardly at all. Is there any adjustment on the MC that I am missing or is there an extra piece that I need to add into the system now to adjust pressure from front to rear? Any help would be appreciated. Thanx all!  :D  
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Offline Mike Scott

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« Reply #1 on: May 13, 2005, 03:46:10 PM »
Have you checked the flexible rear hoses to see if they are clogged?  I have never done a 4 wheel disc conversion on a beetle, but Im pretty sure guys that run them just use stock dual circut master cylinders.

When I swapped Integra rear disks on to my old civic I had to pirate the integra master cylinder as well for proportioning (or so I was told).  

Russ

Disc Brake Help!
« Reply #2 on: May 13, 2005, 04:53:19 PM »
i have heard of other using a proportioning valve as well

Offline Bruce

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« Reply #3 on: May 13, 2005, 06:06:38 PM »
Are you using a dual cct master cylinder?
You don't need a proportioning valve.

Offline thumper911

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« Reply #4 on: May 14, 2005, 09:26:03 AM »
Thanx for the input guys. I'm getting plenty of fluid coming through the rear bleeder valves so I don't think that any lines would be clogged.  I'm also using the stock dual circuit master. Its weird 'cause when I bleed the system, the front brakes will do the normal loss of pressure at the brake pedal but when I bleed the rears the pressure remains (no loss of pressure at the brake pedal). I don't think thats normal, is it? I should lose pressure at the brake pedal when bleeding all four corners, am I not correct there? And whats this proportioning valve I've been hearing about? Does it go inline at the master and how does it work? Would I be needing this thing or is my master cylinder possibly shot?? Thanx again for the help!!  :rockon:  
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Offline Scratchy

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Disc Brake Help!
« Reply #5 on: May 14, 2005, 10:41:59 AM »
Hey Thumper, you are correct, your pedal should go soft when bleeding the rear discs.
Sounds like a blockage in the line going back, or possibly a MC problem.
Did you replace/rebuild the MC as well? I had a problem years ago after rebuilding my MC, due to incorrect rebuild parts.

As for portioning valve, this allows you to adjust the pressure between the front & rear for proper brake bias.
The issue of unequal braking pressure can be caused by different sized caliper pistons - front & rear, as well as brake pad size.
You should get what you have working first before you think about a proportioning valve. You may not need one.

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Offline thumper911

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« Reply #6 on: May 14, 2005, 12:31:13 PM »
Alrighty, sounds like a possibility...but it seems weird that if there is a blockage then I shouldn't be getting any fluid through the bleeder screws in the rear on whatever side the blockage may be. When I bleed through either bleeder screw on the rear there seems to be a continuous flow of fluid, not the surge like there is on the fronts. The fluid is clear so it isn't any old stuff stuck in the lines. Its the stock MC thats been in there since I bought the car a looooooong time ago! How hard is it to rebuild a MC? Or would it just make more sense to buy a new one and try that out? Also, how hard is it to adjust the pushrod because there is quite a few inches of play before the pedal engages the front brakes. Is this maybe all part of the MC being fried? Thanx.  
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Offline Scratchy

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« Reply #7 on: May 15, 2005, 07:00:43 PM »
Hey Thumper,

There is a Brake pedal free-play adjustment on the rod that pushes into the MC. There's a thread with a locknut on it to remove the freeplay back down to factory specs. If you've replaced all the wheel cylinders & drums with calipers & discs, then it only makes sense to do everything, including the MC, especially since it's still the old original. No sense taking chances with old parts when everything else is new.
You could even replace the metal brakeline going along side the tunnel to the rear. They usually get rusted out after 25 years or so  :(  

 -= Remember, even at a Mensa convention someone is the dumbest person in the room! =-

Offline thumper911

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« Reply #8 on: May 16, 2005, 07:35:00 AM »
Thanx for the input. I'll have to look for that nut when I change out the MC. I agree that it only makes sense to replace the MC being that everything else in the brake system is brand new so I guess I'm off to do some phone calls!  :D Hopefully the new MC will solve all problems!!  :blush:  
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Offline thumper911

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« Reply #9 on: May 16, 2005, 11:05:41 PM »
Well, picked up a new MC, got it installed and still the same issue.  The pedal stays rock solid when bleeding the rears when it should obviously fall to the floor. The fronts still grab awesome and the e-brake works perfect! But no brake pedal pressure goes to the rear brakes!!!
Help! Anybody??
 :(  :wacko:  
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Offline Bruce

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« Reply #10 on: May 17, 2005, 04:19:22 AM »
Quote
There is a Brake pedal free-play adjustment on the rod that pushes into the MC. There's a thread with a locknut on it to remove the freeplay back down to factory specs.
Do not adjust the brake pedal pushrod.  It is factory set and should never be messed with.  The proper way to adjust brake pedal freeplay is to move the pedal stop bracket on the floor.
It's time to list all your brake components.  

Offline thumper911

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« Reply #11 on: May 17, 2005, 07:38:19 AM »
Yeah I haven't touched the pushrod and now I guess I don't really plan to!!  ^_^  
The parts I have on there:
-all metal brake lines are new within the past few years (very few miles on them)
-all rubber hoses are new within the past few years (very few miles on them)
-brand new master cylinder as of yesterday
-stock/original brake switches
-Nakata brake pads
-CB Performance rotors (front and rear)
-CB Performance calipers (front and rear)
Thats pretty much all I can think of that could possibly affect anything in the system.
What is the stock ratio for pressure approximately....like 60/40 (front/rear), 70/30, 90/10???
I'm baffled now...I have no idea why the rears bleed through the screws but pressure does not decrease on the pedal.  [_[
Hopefully someone can lend a helpful tidbit.  :unsure:
Thanx!
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Offline HeliMike

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« Reply #12 on: May 17, 2005, 11:11:24 AM »
This is just a shot in the dark, but do you have your e-brake engaged when you're bleeding the rear brakes? If you do, disengage it.
I'm not even sure if that would make any difference but at this point I'm sure you're ready to try anything right?
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Offline thumper911

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« Reply #13 on: May 17, 2005, 12:07:12 PM »
Naw, I have the e-brake disengaged 'cause I try to spin the disc with the brakes depressed, and, well they still spin!! :(
keep the ideas coming though, thanx!  :mullet:  
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Offline HeliMike

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« Reply #14 on: May 17, 2005, 02:17:00 PM »
Quote
Naw, I have the e-brake disengaged 'cause I try to spin the disc with the brakes depressed, and, well they still spin!! :(
keep the ideas coming though, thanx!
« Last Edit: May 17, 2005, 02:19:34 PM by Gutterslug »
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Offline thumper911

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« Reply #15 on: May 17, 2005, 03:47:04 PM »
Yeah it seems to be pumping through pretty good. I have a plastic hose plugged over the bleeder screw running into a little container that sits ABOVE the caliper so it definantly needs some force to run uphill. But it seems to be a continuous flow instead of the surge like there is on the fronts.
I hooked the MC back up the way it was on the old one. I didn't put anything on differently (at least to my knowledge!!). I've run a good couple litres through the whole brake system but can't seem to get rid of the problem. I don't know if maybe the original MC was attached incorrectly before I bought the car...  :huh:  Are the switches supposed to be placed on the bottom set of outlet holes on the MC??  And then the brake lines come out of the top outlets, correct?? THat would be gay if all it was the lines/switches plugged in wrong...but I don't think thats it either.

ARGHH!

Boy  I sure do love my VW!! (no really, I honestly do!!  :D )
Cheers!  
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Offline silas

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Disc Brake Help!
« Reply #16 on: May 17, 2005, 03:49:23 PM »
just thinking out loud here.

did you bench bleed the new m/c?

are you maintaining a full brake fluid reservoir at all times when bleeding?

are you bleeding the caliper that is farthest away from the m/c first and working your way forward? (right rear, left rear, right front, left front).

are the bleeders at the top of the caliper? if they are on the bottom, you'll never get the air out of the lines.

Offline Bruce

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« Reply #17 on: May 17, 2005, 04:11:13 PM »
Since we don't know if it is a problem with the MC or the rear caliper, here's a way to
 isolate which one it is.  Take a rear caliper off and plumb it on one of the front hoses.
  You can put the front caliper on the rear to hold pressure.  You will have to either
 place a 9mm shim between the pads, or slide it over the rotor.  Now try to bleed
both calipers.

Hey Scratchy, could you reduce the size of that pic so we don't have to do a bunch of side to side scrolling??????
« Last Edit: May 17, 2005, 04:14:09 PM by Bruce »

Offline Geoff

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« Reply #18 on: May 17, 2005, 04:41:57 PM »
Also have a look at those rear calipers, Some have two bleeders one on top and one on the bottom. I belive the CB calipers only have the one as they are left or right only. Some kits have two as they are universal calipers and people bleed from the bottom thinking thats the correct one but that is a drain and you only bleed from the top bleeder. Just a thought.
G.

Russ

Disc Brake Help!
« Reply #19 on: May 17, 2005, 05:10:12 PM »
Quote

Hey Scratchy, could you reduce the size of that pic so we don't have to do a bunch of side to side scrolling??????
i was gonna post the same thing
 ;)
« Last Edit: May 17, 2005, 05:10:35 PM by Russ »

Offline Scratchy

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« Reply #20 on: May 17, 2005, 07:27:03 PM »
Hey Bruce, I totally forgot about the stop plate on the floor pan - good call!

The other thing to do, would be to crack open the rear brake line at the T fitting and see if you're getting pressure there when you depress the brake pedal. if not then try cracking the flair nut for the rear line right at the MC and having someone depress the pedal.

You've either got a partial blockage in the brake line, or most likely air (lots of it) in both calipers.

(( Sorry 'bout the wide graphic  :blush:  I'm running a 19\" monitor, so I didn't have to scroll... ))
« Last Edit: May 17, 2005, 07:29:23 PM by Scratchy »

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Offline thumper911

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« Reply #21 on: May 18, 2005, 09:35:16 PM »
Thanx for all the input rolling in!
Well, I have not bench bled the MC...I think thats gonna be the next plan of attack. I have kept the resevoir full with fluid and have bled farthest to closest caliper from the MC.  The rears only have one bleeder screw but the fronts have two...I've been bleeding through the top one not really knowing why there was two...now I know the one is a drain (thanx Geoff)!! I also like the idea of swapping a caliper front to back and testing to see whether or not it may be a caliper problem or MC problem. But I've just started my first day back on the work cycle so its gonna be a while til I can get some time to try these new tips out. Hopefully I'll get something sorted out sooner rather than l8r...she's soooo close to getting on the road; its just this brake issue, inspection and then insurance!! woot! :mullet:
« Last Edit: May 18, 2005, 09:35:38 PM by thumper911 »
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