300tdi Vacuum Pump - Defender Source
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  #1  
Old June 27th, 2011, 09:23 PM
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Neill Thornton
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300tdi Vacuum Pump

OK gents, today's problem...

I have had really crappy brakes on the 90 for about a month, maybe a little more. The pedal goes to the floor without much effort, and very little braking happens. First I thought it was air in the lines, but the entire system has been flushed twice now with a Power Bleeder. So I think I can rule that out.

Today I decided to check the vacuum pump. I hooked up the vacuum gauge and it's reading very strange. It bounces between zero and five inches of mercury. It's not steady, it clearly shoots up when the pump hits the "stroke" and then immediately returns to zero. This is while connected directly to the pump... so there is no hoses involved.

My question is this: should the pump hold steady and increasing vacuum, or should it do as described and drop to zero immediately?

If I am not being clear in what I am saying I can take a short video and post it.
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Old June 27th, 2011, 11:21 PM
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Doug Crowther
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the pump only pumps when the cam lobe comes around. Inside the end cap of the pump is a check valve that is supposed to hold the vacuum achieved. When the pumps fail its often because the end plate that contains the check valve looses its seal to the body of the rest of the pump. There are a couple of write ups out there that show how to fix the pump by drilling out the rivets and resealing the leak and reclosing with small bolts. Are you sure your master cylinder isn't the culprit ?
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Old June 27th, 2011, 11:44 PM
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Neill Thornton
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Thanks for the info Doug. I am gonna find the rebuild stuff out there. I can easily crack it and rebuild which is easier than shelling out 600 bucks for a genuine or wait for backordered knock-offs. I have a huge trip to be on in about 2 weeks so no time to waste.

I already have the rebuild kit for the master cylinder... it's tomorrow's job. But since the vacuum check is so quick I wanted to get it out of the way.

Edit: I also left out a crucial piece of information. When I hooked up the vacuum gauge, after the test there was engine oil in the tube to the gauge (!). That would seem to confirm a blown check valve.
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Old June 28th, 2011, 06:08 AM
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If you leave it alone long the check valve can come apart and ruin the pump housing.
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Old June 28th, 2011, 08:06 AM
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Quote:
I have had really crappy brakes on the 90 for about a month, maybe a little more. The pedal goes to the floor without much effort, and very little braking happens. First I thought it was air in the lines, but the entire system has been flushed twice now with a Power Bleeder. So I think I can rule that out.
I may not know much about Tdis, but from my limited knowledge, isn't the vacuum pump merely a booster for the brakes? I would think that the brakes shouldn't bottom out even with no vacuum boost, but I may be wrong.
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  #6  
Old June 28th, 2011, 08:41 AM
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Just lost the vacuum pump on my powerstroke last week. You are left with manual brakes, but they work. The pedal shouldn't go to the floor with little effort, it should be the opposite, takes a lot of effort to depress.
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Old June 28th, 2011, 10:27 PM
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Well, besides the vacuum pump being completely stuffed, I pulled apart the master cylinder and found a horror show of corrosion, some kind of beige slime, and rotted cylinder wall. Funny thing is the piston seals were pretty new looking, so I wonder if the PO had an issue and rebuilt it trying to fix it.

The master cylinder is clearly shot, so now I am trying to get both from Island 4x4 in the UK. Master Cylinders for an '84 command a ridiculous price here in the states.
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Old June 29th, 2011, 06:43 PM
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fwiw if you get in a time bind I have a new in the box vacuum pump-its aftermarket britpart not oe wabco
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Old June 30th, 2011, 05:04 AM
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Quote:
Originally Posted by kevkon View Post
Just lost the vacuum pump on my powerstroke last week. You are left with manual brakes, but they work. The pedal shouldn't go to the floor with little effort, it should be the opposite, takes a lot of effort to depress.
That's what happens if you exhaust the vacuum by pumping the brakes with the engine not running.
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Old June 30th, 2011, 08:11 AM
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Quote:
Originally Posted by navydevildoc View Post
Well, besides the vacuum pump being completely stuffed, I pulled apart the master cylinder and found a horror show of corrosion, some kind of beige slime, and rotted cylinder wall. Funny thing is the piston seals were pretty new looking, so I wonder if the PO had an issue and rebuilt it trying to fix it.

The master cylinder is clearly shot, so now I am trying to get both from Island 4x4 in the UK. Master Cylinders for an '84 command a ridiculous price here in the states.
The slime comes from the water mixed in after the fluid can no longer absorb it.
Did you try RDS or Trevor for a new one?
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