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Discussion Starter #1
I have a Series III 88 dual master brake system. I have run into a problem I hope someone can assist with. When bleeding the brakes I encountered a lot of air in the line in the rear system. I have rebuilt the master, replaced or rebuilt all the wheel cylinders, replaced new all the hard and rubber lines, etc. All the fittings are tight. When I bled the fronts they were fine. When bleeding the rears, especially the drivers rear (farthest from the master) there is a ton of air. I know there is air getting in somewhere but can't figure it out. I thought the bleed screw was letting air in so I removed it and dabbed a touch of grease on it to seal it while bleeding. Still tons of air. Anything I am overlooking? Thanks in advance.
 

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Attach a hose to the LR bleed screw, apply a few pounds of air, and check all your joints for a fluid leak.

Is this a US truck (no proportioning valve) or imported ROW with a proportioning valve?
 

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There are only three ways to get air IN to the system other than putting in new pipes that are full of air.
1) Run out of fluid in the M/C and pump it in.
2) Have a big leak at a connection so that the M/C sucks air in on the back stroke easier and faster than the return springs back off the shoes. If this is the case, you will be leaking piles of fluid when stroking the M/C.
3) Have the pipes in the wrong location on the M/C so you are sucking in air through the air bleed when you crack them. You will find the reservoir is over filling if this is the case.

Fourth way but we won't consider it in this case. Overheat your brakes so the fluid boils.
 

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Discussion Starter #4
Terry: The truck is a US version - no proportioning valve. Probably why the fronts are okay I imagine.

Greg: The master is full, and does go down when I bleed, but I refill before getting to the low mark. I have no fluid leaking from the MC or any coupling or connection. The reservoir is not going up, but holds steady or goes down when actually bleeding.

Would it be more helpful to use Teflon tape around the bleed screw? That's the only way I can see air getting in somehow.
 

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I forgot to mention in my first post that someone, or something has to hold the pedal slightly down to keep the air from blowing right on up through the MC.
88s are so simple to bleed, they practically will bleed themselves by gravity.
Are you certain you haven't gotten the air out of the pipework, and are just drwing it in through the the loosened bleed screw? I only crack them about 1/4 turn.
I use a Handi-Vac, or Mighty Vac, whatever it's called. I've never had a need to get a power bleeder.
 

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Discussion Starter #6
I re-checked the MC connections, and tried to re-bleed (using my Mighty Vac). Still too much air, and not tiny bleed screw bubbles, but fat bubbles. I then had a buddy pump the brakes while I had a bleed screw open (just a 1/3 -1/4 open) and hardly any hydro fluid came out. I think the problem lies with the MC. There may be a blockage preventing enough fluid from flowing. No pressure was building. So, off to investigate. I will post results of that investigation. Thanks so far.
 

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Teflon won't help because they don't seal with the threads, they seal on the tapered end of the screw; it jams in the hole.

It could be the M/C by-passing inside, air getting past a seal. Did you bench bleed it first to get all the air out of the M/C? Have to get that part all full and air out before even putting lines onto the M/C.

Another thing you overlooked. What type of grease did you put on the bleed screw? Any (ANY) sort of petroleum grease will destroy you brake rubber in short order. Man! Do they ever swell.

Your fronts are good from the sounds of it. The rear needs to be bled at the M/C to get all air out, then hook pipe up.
 

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Discussion Starter #8
Okay, figured it out. It was the lack of bench bleeding. Sorry I was so stupid, but I was so anxious to get the brakes bled I forgot to do that part. Wanted to go for a drive I guess. Thanks for the tip Greg, that was the ticket.
 

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I seem to be having the same Problem, and it seems like the rear brakes don't even work. The rover is a Classic 90' that I am going to be buying from a friend. Did it seem like yours did not work at all?
 

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I seem to be having the same Problem, and it seems like the rear brakes don't even work. The rover is a Classic 90' that I am going to be buying from a friend. Did it seem like yours did not work at all?
Completely different animal, post it up in the Range Rover section and you'll get plenty of help.
 
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