Confirmation on bleeding brakes

Hey all, I just want to make sure I'm bleeding the brakes correctly on my Defender 90 as I am somewhat confident that there is air in there somewhere. However, if bleeding brakes does not fix the issue, I may need to replace the master cylinder, but wanted to check the box on air possibility first. I know there's PLENTY of conversation about what sequence to follow, but I want to make sure I'm doing the proper setup too.

Steps I'm following:
  1. Using gravity method: fill gravity jar with DOT4 fluid and top off master cylinder fluid to line
  2. Open breather half a turn to allow for fluid to start draining (on a LHD so RR LR RF LF)
  3. Let fluid drain at each cylinder and continue to top off resevoir
  4. Repeat on each cyliner in aforementioned sequence
My question is: what is the point of filling the gravity jar? Does the fluid displace as the air goes through? BTW filling the jar based on steps via manual for bleeding brakes.

Hopefully this isn't a no brainer question, but even if it is, I'll take any answers I can get.
 

Napalm00

Technical Excellence Contributor
If you want to make it easy on yourself just put speed bleeders in each caliper open one caliper a time for this from the master and pump them. It's literally brainless and will guarantee you 100% bleed. This gravity bleeding shit is shade tree stuff from 1950 there's so many better options now
 
If you want to make it easy on yourself just put speed bleeders in each caliper open one caliper a time for this from the master and pump them. It's literally brainless and will guarantee you 100% bleed. This gravity bleeding shit is shade tree stuff from 1950 there's so many better options now
Is there a specific part number I should look for or will any normal speed bleeder work?

My assumption for the bleeder is that I should pump the brakes like I normally would and just have the fluid topped off?
 

Francois1

Member
Here's the procedure from the maintenance manual if you don't have it.
 

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Thanks guys!

@Francois1 that's what I was going off of. Was just wondering why the tube needs to go into a jar filled with DOT4? Also, just being sure, but sounds like this is a two-person job?
 
Referencing the last step when tightening the bleed screw while pedal is depressed. Could probably get away with using a brick or something though...
 

Napalm00

Technical Excellence Contributor
if you have never bled brakes you need to watch some YT videos. The tube is put into the fluid if you DONT have speed bleeders so that the brakes dont pull air back up the hose.

Without speed bleed screws its 100% a two person job, using a brick or a broomstick is silly and dangerous

Speed bleeders:

remove old bleeder screw and insert new speed bleeder finger tight
proceed to bleed that caliper by pumping pedal until there are no bubbles or old fluid coming out
tighten it back up
next caliper
 

Francois1

Member
Thanks guys!

@Francois1 that's what I was going off of. Was just wondering why the tube needs to go into a jar filled with DOT4? Also, just being sure, but sounds like this is a two-person job?
It's definitely easier as a two-person job,

I do this a little differently and just use a bucket to catch the fluid during the bleeding process.

-fill the master cylinder,
-have someone pump the brakes until they feel tight and hold down pressure on the pedal,
-open and close the caliper bleed nipple briefly (the brake pedal will drop some). You should see and hear some air come out.
-check fluid level in master cylinder again (top off if required)
-repeat sequence until no air comes out, working your way around the vehicle, front brakes then rear. I always go around the vehicle twice to make sure I have a good purge.

I think the jar filled with fluid keeps things a bit cleaner, and helps prevent sucking air back in the system if somehow the brake pedal gets released before the bleed nipple is fully closed.
If your brakes still feel spongy and not other leaks are visible, you may have an internal leak in you master cylinder as you already suspect.
I hope you are successful.
 
Thank you both! Will spend some time on YouTube, but makes sense that the jar would keep air and other contaminants from entering the caliper.

Will update on progress.
 
I confirmed threading using those speed bleeders but was only able to confirm them on the front brakes.

The back brake bleeders were completely seized and, out of concern of completely destroying a rusted bleeder, I took it in to a shop to get removed. Bleeding definitely seems to be the main fix at the moment as the shop has confirmed nothing wrong with the MC.
 
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