Why your Vacuum pump may have failed.

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Originally Posted by kawaden

if the tdi pumps are a weak point could you replace it with an electric unit?

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Yeah, sure can. For several years now, our '97 300Tdi Discovery has had an electric vacuum pump.

When the mechanical pump failed and was removed, I found the pump cam was quite pitted and decided it wasn't a good idea to run a new pump against it.

The pump I'm using is from a Volvo 740 Turbo. It includes a vacuum switch and starts at about 15" Hg and stops at 20-21" Hg. However, these don't last forever either - I'm on my second one since 2008.

My local mechanic who's qualified to issue Modification Plates in Qld looked up his book and couldn't find any need for certification of a vacuum pump change (unlike, say, changing from drums to discs etc.)

You will need to make a blanking plate to cover the hole in the block.

Pics below.

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Originally Posted by workingonit

Roverlord, who put together the quote in your original post?

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It was passed on to me from a associate at Rovacraft.

Thanks Rovercraft - just noticed the same text appears on your website. Can only guess it is an in-house analysis based on being a (frustrated :( ) re-seller of these terrible pieces of equipment.

I've replaced about 3 of these on my vehicles and partially rebuilt another 3-4. OEM and alternate manufacturer have all proved problematic. Have pulled one to pieces and rebuilt it to get an idea of how it works and try to stop it leaking. The following are my observations and experiences and happy to be corrected by anyone who designs these systems.

The pump is lubricated by engine oil. When the pump pulls a vacuum then engine oil vapour is pulled from the engine block, making its way past the piston seal and piston shaft guide. The lubricating oil and air mixes, the mix is expelled back into the engine block to control pollution and stop your engine bay being covered in oil. We do get this oil all over our engine bay when some parts fail - the oil will leak past the cap seal, past the expulsion side welch plug on the cap, and past the expulsion side welch plug located on the side of the piston. The welch plug on the vacuum side, in the cap, generally doesn't leak oil, but may, when valves fail.

Have experienced:

- failed welch plugs. Welch plugs are often thin mild steel without the strength to maintain wall contact. Have had new pumps, even before installation, where the plugs can be moved with the little finger. Suspect manufacturers rely on enamel paint to help seal the welch plugs. Have pulled the welch plugs, threaded the holes and replaced with bolts and teflon tape.

- caps working loose. Well documented issue. Some manufacturers use rivets, others tap screws to hold the cap on. Have found rivets stretch and screws unwind. 5mm bolts with lock nuts keep the head down, but may still leak past the 'o' ring. I leave the 'o' ring in place but also overlay a paper gasket all glued down with hymolar.

- failed retaining nut. It holds the piston head to the piston shaft. The small retaining nut came through the cap like a bullet. No cure, write off.

- migrating grub screws. The piston shaft moves through a guide. The guide is held in place by two grub screws. The grub screws normally reside deep in their holes. They can be accessed by taking the pump off the engine block. The symptom is a very noisy clattering pump, but no signs of vacuum failure. The noise is the guide starting to move back and forth in its housing as the grubs unwind. Simply screw the grubs back down.

Haven't had lubrication failure yet. I feel that the pump is designed to do two things when creating a vacuum - the first is to pull air from the brake booster, but to also pull engine oil vapour from the engine for lubrication. I feel lubrication failure will occur when insufficient vacuum is formed, either because of a leaking brake booster or a failure of the one way valve controlling evacuation and/or failure of the one way valve controlling expulsion.

I feel that the spring is more than capable of pushing back atmospheric pressure or 'overcoming vacuum suck' and is designed to keep the shaft on the cam at all times.

I've tried the recommendation of using two seals between the block and the pump, and while I continue doing so I really don't think it makes much difference, after all we are only reducing vacuum volume (system stress?) by the thickness of the extra seal, a mill or two at best, and similar effect on spring force on the cam. In the extreme, reduced spring force will result in bounce.

I feel while ever the vacuum in the brake booster remains (no braking action) then the pump is only having to deal with any air-oil mix that gets past the piston seal or piston shaft seal.

Recently viewed a Defender Tdi300 with view to purchase (didn't, even though only asking $4,500). A previous owner had blanked off the engine block and installed a belt driven vacuum pump instead. Downside was he had to ditch the aircon pump so he could get a location for the brake vacuum pump.

Leo109, any photos of your electric pump, a thread somewhere?

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Originally Posted by workingonit

I've replaced about 3 of these on my vehicles and partially rebuilt another 3-4. OEM and alternate manufacturer have all proved problematic.

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Which aftermarket ones workingonit ?

I'm using a Bearmach one ATM and it's been ok for a few years now.

The original Wabco ones appear to be pretty awful.

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Originally Posted by roverrescue

I find that theory a little stretched
The spring preload in a vac pump is surely far in excess of the vacuum pressure it can create.

I would be amazed if any amount of vacuum could hold that sucker back into the pump can?
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I wonder about that.

If the vacuum was only half of atmospheric pressure that would be about 7 lb/in2 . The piston is about 2.5 in across (I think). That gives an area of almost 5 square inches. So the force on the piston would be 35 lb or about 15 kg. Is the spring stronger than that?

(I hope you will forgive the imperial measurements, but that is what I was taught in science classes in the early 1960s. At least I converted the final figure to a metric unit.)

[QUOTE=workingonit;2486438]Thanks Rovercraft - just noticed the same text appears on your website. /QUOTE]
:wasntme: We are Roverlord , not Rovacraft, we don't have it on our website . Trouble is there are too many Rovers around. I often get invoices for our opposition, Naturaly I don't pay them :p

My apologies Roverlord. I can't even misquote correctly as it was Roverparts and not Rovercraft.

Link

Land Rover Parts - BRAKE VACUUM PUMP - L/ROVER 300 TDI (includes gasket ERR2027)(select aftermarket or WABCO)

Rick130, three of my Disco's (blue, green and grey) have Wabco units on at the moment, all having had the rivets replaced by bolts, but they continue to leak through the welch plugs. The fourth Disco (red) is not home at the moment, and I don't recall the brand, but I do remember it is also leaking through the welch plugs and from memory the cap as well.

The unit that blew the retaining nut through the lid like a bullet is simply branded as 'Rm'. The unit that had the loose welch plugs and as a new unit leaked as soon as it was installed is branded 'Unipump'.

To be fair all the units look much the same inside, other than maybe a variation in the brand of one way valves used, and otherwise look well constructed. The pity is they have all copied into their manufacture the same weaknesses, being the cap clamping and the welch plugs.

The Rm pump was on the red vehicle when I bought it. The Rm pump got to the point where it leaked so much that I decided to replace it. So in went a new Unipump brand. The Unipump leaked straight away and badly from the welch plugs. I swapped in another old unit I had lying around to keep red running (it leaks, but not so bad).

So now I had two units sitting on the work bench, the old Rm and the new Unipump.

Given the age of the Rm I decided to experiment on it. I knocked out the three welch plugs and threaded the three plug holes to take bolts backed up with teflon tape. I also replaced the rivets or screws (can't remember) with 5mm tensile bolts and locknuts. I left the 'o' ring in place but layered over it an oil resistant paper gasket, treated with hymolar. The unit was kept spotless regarding swarf etc.

The 'reconditioned' Rm went back into red. After a week in the vehicle there were no leaks. Considering it a success I gave the new Unipump the same treatment and put it on the shelf as a spare. About two months later the Rm unit blew the retaining nut through the cap. The backup unit went back in. The 'reconditioned' Unipump is still on the shelf until I get time to reconsider options.

Ta.

The original Wabco I had leaked from the welch plug, so I cleaned and epoxied it and it was ok for years.

Can't recall now why I replaced it ?
Probably started gushing oil, and the replacement Beamach dropped its welch plug really quickly, I installed a replacement plug, the importer said there was a bad batch, so I received a new pump and its replacement has been fine for years now.
I could never work out who Bearmach sourced their pumps from, couldn't identify a manufacturer.

I've had a Wabco one in for four years 50,000kms and no issues. Only using one gasket.

ALL4X4 Kotara wouldn't warranty it unless you fitted a new booster as well, which is what I did. The theory that a leaking booster causes the vac pump to work too hard has been around for a few years now.

Steane, no leaks at all? Did you reclamp the lid?

Rick130, I might try your epoxy trick on one of the Wabco.

Found this, bottom of page 13, the discussion seems to say the piston is unlikely to park due to vacuum 'suck' - although the situation may change under very high revs and lead to the push rod chattering on the cam, in which case you might be better with a leaking booster. Makes sense to me that the push rod always follows the cam. Otherwise a push rod being released to find the cam is a bit like throwing a ball at a bat - the one place you might find something like this is under your rocker cover, the tappet gap, but then lash caps are in place to protect the valve stem from the hammering force.

http://www.peachparts.com/shopforum/...uum-pumps.html