Brake clarification
Thread Starter
Racer
Joined: Oct 2021
Posts: 436
Likes: 15
From: Maryland
Brake clarification
Hey all, I just realized my 82 master cylinder has lost nearly all brake fluid on the rear (driver facing) bank only. The front bank is still full. Pretty sure it’s a slow leak. questions:
1) does the rear bank feed rear brakes on a 82?
2) other than visual inspection how can I find the slow leak?
3) do I need to bleed all 4 wheels
thanks
1) does the rear bank feed rear brakes on a 82?
2) other than visual inspection how can I find the slow leak?
3) do I need to bleed all 4 wheels
thanks
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
#1 Yes
#2 Has to be a "wet" spot on the inner side of tire, somewhere.
Or.
Slight possibility the rear Rez is peeing inside the booster.
But that would show up as a damp spot also.
#3. No sense bleeding the system until the leak is not only located but repaired.
Then the master MUST come off the car and be bench bled (its easy) because the rez was allowed to run dry.
#2 Has to be a "wet" spot on the inner side of tire, somewhere.
Or.
Slight possibility the rear Rez is peeing inside the booster.
But that would show up as a damp spot also.
#3. No sense bleeding the system until the leak is not only located but repaired.
Then the master MUST come off the car and be bench bled (its easy) because the rez was allowed to run dry.
Last edited by HeadsU.P.; Oct 19, 2024 at 08:39 PM.
Thread Starter
Racer
Joined: Oct 2021
Posts: 436
Likes: 15
From: Maryland
Appreciate it. For my own understanding, could you explain why I need to bleed the master seperate from the rest of the system?
And can I put fluid in without bleeding just to find the leak?
And can I put fluid in without bleeding just to find the leak?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Yes, good idea. Put some DOT3 in just for testing will be fine.
Once the leak is found / repaired, THEN the master gets a bench bleed.
Otherwise, there will without a doubt be a bubble still in the Rez.
The master needs to be tilted up, down and all around to remove bubbles.
Hense the reason it goes in a vise.
Do Not stroke the MC piston in too far. 1- & 3/8-inches max.
<<<<<<<<<<Click on my avatar.
Look for photo albums bench bleeding, for tips.
Once the leak is found / repaired, THEN the master gets a bench bleed.
Otherwise, there will without a doubt be a bubble still in the Rez.
The master needs to be tilted up, down and all around to remove bubbles.
Hense the reason it goes in a vise.
Do Not stroke the MC piston in too far. 1- & 3/8-inches max.
<<<<<<<<<<Click on my avatar.
Look for photo albums bench bleeding, for tips.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,251
Likes: 4,319
From: US-PNW
If the fluid in the master dipped below the port opening in the bottom of the reservoir then it would be best to bleed the entire system from top to bottom.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Nearly empty but not empty, keep it topped up. Much easier to bleed your brakes if you don't let it go dry.
And a visual inspection isn't that hard to perform.
And a visual inspection isn't that hard to perform.
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Race Director
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Be careful bench bleeding a used master. Excellent way to destroy the piston seals on parts of the master bore that have become corroded from moisture absorbed by the brake fluid.
Thread Starter
Racer
Joined: Oct 2021
Posts: 436
Likes: 15
From: Maryland
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,251
Likes: 4,319
From: US-PNW
Raising the front when bleeding the car or the master will only serve to trap any air that may be ahead of the master cylinder's pistons. Frequent forum advice is to raise the rear of the car and master when bleeding. Put a level on the master and raise the rear until the bubble moves all the way to the back of the level. I've done it this way and don't see any detrimental effects of doing this to achieve a good system bleed.
Safety Car
Joined: Nov 2002
Posts: 4,183
Likes: 1,178
From: out of nowhere
My understanding from read threads is that the raising of the rear was due to the relation of the bleed screw vs the possible air bubbles in the calipers. Thinking of the caliper shape and the areas where fluid or air bubbles may be inside, this makes sense. There are great videos on youtube where folks show how to do bleeds without someone as a helper to pump the brakes. I’m not there yet, so I’ve yet to do it, but think it is a worthwhile thing to take a look at. My past brake jobs included my wife as a pedal pumper, but will incorporate what I learned by those vids due to some of the comments on the vids. Things such as “Man, I’ve been a mechanic doing brakes for 50 years, You just saved me a bunch of time/taught me a lot”. Here’s an example:
Master cylinder bench bleed:
Ton’s of other vids on the subject, but I think you can figure it with those two.
Last edited by litevette; Oct 29, 2024 at 08:22 PM.