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Dont know if it is still possible to buy the the non return valves for a CAV mechanical fuel pump as fitted to 2 1/4 litre LandRover engines. but I once used a pair of those to replace the Wabco valves that had fallen to bits.Quote:
Originally Posted by Bushie
Wagoo.
I could have tacked this onto any one of quite a large number of 300Tdi vacuum pump threads. :p
Mine didn't leak any oil. It just stopped sucking. The first thing I noticed was a very hard brake pedal. Fortunately I had been trained by 23 years of driving a Series III LWB with no power assistance, so I managed to get home without any dramas.
After reading several threads here, I had the notion that I would order a new pump and dismantle the old one to see if I could fit new valves, bolt the cover back on and keep it as a spare.
However, it looks as if repairing the old pump is out of the question.
This is what was left of one of the valves. (Plus a little bent bit of wire that used to be a spring.)
http://www.fileden.com/files/2008/7/...444/Valve2.JPG
One of the valves was still intact in the cover.
http://www.fileden.com/files/2008/7/...5444/Cover.JPG
What makes me think that it would be a waste of time to attempt a repair is those scores in the bore.
http://www.fileden.com/files/2008/7/...444/Piston.JPG
I assume they are not made with those grooves in the bore.
http://www.fileden.com/files/2008/7/...444/Scores.JPG
My guess is that what would happen if it was repaired is that a copious amount of oil would find its way past the piston and that once in that chamber, the increased pressure would pop one of those welch plugs out.
Anyone care to confirm my suspicions?
I too have had ongoing 300tdi vac pump grief with a series of pumps lasting from less than 100 km to only a couple of thousand km. I got tired of this and have fitted an electric pump (an old Thomas i had lying around) c/w small vac tank and pressure switch in the box below the drivers seat. Had a ally plate made to blank-off the original mech pump engine take-off. Anyhow, when all done the electric pump ran continuosly on my first test drive with the pressure switch not activating in response to expected vacuum build-up. There was some vacuum in terms of brake response but clearly also a leak somewhere. Following a tip on this site, I removed the servo and, sure enough, there was a hairline fracture (hard to spot without close examination) around a lower master cylinder stud. New servo installed - and my brakes are better than they have been in ages with electric pump cutting in now periodically only and related to amount of braking done.
I suspect that similar problems might contribute to the Wabco issues - they just wear themselves out from overwork if there is even a small servo leak. I also noticed that the old servo was quite dusty on both sdes and it looked like some of that dust was making it's way to the Wabco which could not have aided it's longevity.
Anyhow, if there is a moral it is to check the servo before laying all blame at the foot of Wabco (which nevertheless do seem to have issues).
All Four x 4 Spares seems to agree with you about the reason for pump failures.
Their online store includes this warning:
This is a quality Original Equipment part. Often the seal splits on the brake booster, so the brake booster must be vacuum tested to avoid warranty problems. On a Defender the brake booster often has a hairline crack where it is bolted onto the booster (on the LH side as you are looking at it) - this is the main reason why the vacuum pump fails.
Brake Vaccuum Pump suit Land Rover Discovery & Defender 300TDI - 4WD Spare Parts | Toyota | Nissan | Land Rover | Landcruiser | Patrol | Prado | Land Cruiser All 4x4
On the recommendation of a few earlier posts on this subject, I did check the servo and the plastic hose. My plastic hose is rubbed halfway through, but isn't leaking.
Can you post a link?Quote:
Originally Posted by Bauke
Your thinking of a different design motor or you have confused the power steering pump for the vacuum pump.Quote:
then make the old pump an idler or get a shorter belt if that works
.
It might be interesting to know how many of the people with pump failures, especially multiple failures, had subsequently found servo leaks such as those hairline cracks near the studs.Quote:
Originally Posted by dham
I actualy have a small source of 12v electric vacume pumps and have wondered how to hook these up so they cut in and out when vacume is low or close to low , What switch did you use and what size vacume tank is required im willing to give this ago and share the results and maybe a pump or 2 :cool:Quote:
Originally Posted by dham
Sorry, but I'm skeptical. Can anyone explain the science behind this theory ? My understanding is that the mechanical pump runs continuously off a cam lobe. It doesn't cut in and out based on the pressure.Quote:
Originally Posted by vnx205
I've had pumps fail prior to a hairline crack in the booster and post a new booster.
It is a mechanical pump and the piston does operate continuously, but maybe the valves don'tQuote:
Originally Posted by isuzu110
EDIT:I forgot that the piston is pushed out by the cam lobe but is returned by a spring, so I guess what bee utey says a couple of posts down about the reduced piston travel would be right. I still think what I said about the valves might be right.
I'm only guessing, but perhaps there is some truth in it because it is the plastic one way valves that fail. At least that is what failed on mine and I believe on some others too.
If vacuum has been established and the brakes are not used, then wouldn't it be the case that while the piston was moving up and down, the valves would not need to move or would only move a tiny amount.
If the valves are moving through their full range of movement repeatedly, then they would be subjected to a lot more stress than if they just moved a little bit occasionally.
That is just speculation. Someone with qualifications must know the answer.
Well i can tell you for a fact that if you hook up a 12v vac pump to constant power it will suck the booster inside out this is why it needs to be switched on and off some how when vacuum is near low :eek: Maybe the mechanicle pumps run some sort of by pass vacuum valve only a guess :cool:Quote:
Originally Posted by isuzu110