Jump to content

300TDi Vacuum Pump


JB750

Recommended Posts

After finally (I hope!) sorting out my overheating/loss of coolant issue, oil change, new coolant etc. I got the engine back in and started last night. Unfortunately I now have an oil leak from the dreaded Wabco vacuum pump :angry2:

I found the info on re-sealing the front cover and removed the rivets and front cover to find the insides as shown. There was a washer-type piece just loose in the casing! At first I assumed it was from the part without the star clip/washer (the black valve on the left) and that it had somehow come adrift. But the valve that is in there does not seem to be able to come out of the recess so I am assuming the very small lip on the casing stops it coming out. It fits perfectly in the other recess on top of the star clip but will not stay so i am assuming it does not belong there.

My last theory is that it is used to seat the clip in place evenly (I removed the clip and then reseated it and used the washer to tap it in evenly). I wondered if it is possible that it was a 'Friday' build and some wally had left it in the pump? :)

Clutching at straws i guess but I can't think where it goes or how it has come adrift. Any help/advice is most welcome.

BTW, the brakes were fine last time I had the truck on the road.

JB

SANY0349

SANY0348

Link to comment
Share on other sites

Hi JB, The washer has come from the suction valve - RH poppet valve as seen on your photo, it is normally pressed into the casting.

The problem with this Wabco vacuum pump design is the lack of adequate sealing of the piston, its a shoddy design. It has a plain composite nylon/plastic piston, with no rings or seals, consequently oil film in the bore bypasses the piston, which isn't, even when brand new, exactly a close tolerance fit.

Under normal operation when the piston is retracted down the bore by its return spring gas/air is drawn from the brake booster into the cylinder chamber through the inlet poppet valve, the piston is then pushed up the cylinder by the lobe on the camshaft and this gas/air is forced through the exhaust poppet valve and into the engine sump.

However due to the poor fitting piston/cylinder bore tolerance, as I said, oil will bypass the piston, this is in part due to the fact that after a very short time of operation there will be a vacuum in this cylinder head chamber, in short this vacuum sucks the oil past the poor fitting piston. This oil is then eventually pumped through the exhaust poppet valve and as oil will, leak through the external sealing cap and drip all over the engine. In addition some oil will, under pressure force it's way past the rubber "O" ring under the Wabco pop riveted cylinder cover.

After two Wabco vacuum pumps I gave it away and replaced it with an electric vacuum pump. The advantages are, 1.) it has a built-in vacuum switch that turns off the pump motor once a vacuum has been achieved - about 30 seconds run time. 2.) The small electric motor (4 amps) crank operates a rubber diaphragm, no oil and the diaphragm can be easily replaced with a scrap of inner-tube rubber cut to size. Oh, and its QUIET !

Link to comment
Share on other sites

By way of historical explanation I should say that in the 1970's I worked for a UK company, Davies and Metcalfe. I worked on the required brake modifications on the locally built (NSW) British Rail designed High Speed trains, known here as the XPT. Incidentally the eight six car sets built here have now done well over a million kilometres each and that equates to over 25 times (each) around the earth!

Wabco (Westinghouse Brake Company) were D&M's chief competitors for train braking systems so I admit that I have a natural competitive prejudice.

Were I to design (redesign that is) this vacuum pump the piston would have a coiled oil ring and the piston return spring would only be equal to the designed vacuum, so that once that vacuum was achieved in the brake booster the piston would be "held" in the end of the cylinder and the pressure pad would only return to the camshaft lobe once that vacuum was lost. The pop rivets technically are fine, after all, most aircraft external panels are riveted and it's an acceptable method of fixing two components together.

Link to comment
Share on other sites

Is that washer supposed to have a crack in it?

I thought exactly that! I wondered if that was why it had come out.

Iain, I guess I would like to change it for an electric pump as you suggest, not sure how much they will be here in the UK or what spec I will need (apart from 12V) but as the pump so far seems to be working OK, would I be alright to put it back without the retaining ring temporarily as it was just floating around in their anyhow and was probably the ticking sound I got sometimes when running?

I could try opening it up slightly with heat and re-fitting it which may give it some tension back but not sure.

(BTW, I saw your reply about the electric pump from OZ-drag, but have no idea what I am looking for regards spec hence the question above) I did a quick eBay search but the ones I saw were almost as much, if not more expensive than the Wabco pump!

JB

Link to comment
Share on other sites

The electric vacuum pump I purchased was, I'll admit, more expensive than a new Wabco unit, however it will, in my opinion, have a longer life and as I said, no oil leaks ^_^ and a quieter operation, from the drivers seat with the bonnet down I cannot hear it running.

For selection, any vacuum pump unit designed for a 4-6 cylinder car will be adequate. Mine is wired into the same power supply as the fuel solenoid in the FIP, so it runs as soon as the ignition is on and by the time the 300Tdi is running it's achieved vacuum and has turned off, it's that efficient. If you want I'll go back into my EBay archive and find the local (Australian) distributor so you can see if you have a UK outlet.

There is no need to pipe the pump vent back to the engine sump as I did, just a scrap of an old nylon stocking held in place with a hose clip or cable tie over the pump exhaust nipple to prevent possible egress of dirt into the exhaust poppet valve would be more than adequate.

Link to comment
Share on other sites

I wouldn't try heating it, (the washer) this will only have the effect of making the metal softer, if you can, open up the gap, press it into the casting and then with a sharply pointed punch do several "pops" around the edge of the casting to help secure it in place.

If the retaining washer isn't in place the intake poppet valve could conceivably get "sucked" into the cylinder and that would be a minor disaster.

Link to comment
Share on other sites

I wouldn't try heating it, (the washer) this will only have the effect of making the metal softer, if you can, open up the gap, press it into the casting and then with a sharply pointed punch do several "pops" around the edge of the casting to help secure it in place.

If the retaining washer isn't in place the intake poppet valve could conceivably get "sucked" into the cylinder and that would be a minor disaster.

OK thanks Iain. I did think of peening over the edges slightly to help retain it. Not sure how long the washer has been 'free', but you can see marks where it has been bashed against the cover.

I'll give it a go and start looking for a replacement electric version, maybe second-hand will be OK as I need to spend as little as possible now seeing as how I've spent plenty on everything else! :( As long as I can keep the servo assistance that is the main thing.

Link to comment
Share on other sites

If you open up the gap in the washer, press it in and peen it in it should be okay.

Wabco are not the only manufacturer to use shoddy spring steel, I had a Triumph Spitfire Mk1 many years ago; in the gearbox the main shaft gear cluster was held in place by a similar spring washer, the problem being by the time it had been pushed over the clutch splines and into it's groove to retain the gear cluster it had opened up and would not close up again and was as sloppy as and by result it had a horrid habit of "popping out" under heavy first gear acceleration leaving me with a box full of neutral's :angry2: the only solution was to clamp the washer with a monkey wrench to close up the gap and then silver solder it together.

Link to comment
Share on other sites

Hi Iain,

One last question im afraid !!

Did you leave the old vacuum pump in situ or did you remove it ? I haven't looked at the thing on mine yet but am about to take the inner wings off (its a Disco) and have then finally sprayed as part of my renovation..

Im going to be removing the lift pump and blanking it off ( replacing it with an electric one) and thought whilst I was at it I would do the same for the Vacuum pump.....

Cheers

Andy

Link to comment
Share on other sites

I removed it, hacksawed off the pump section leaving simply the flange, I then cleaned it up, removing all the burrs and sharp edges with a disc grinder and after cleaning it in the dishwasher I filled the hole (normally the piston opening) with liquid alloy, when this was set, I smooth filed the flange face, spray painted it and made up a solid gasket and using high temperature red silicon, bolted the completed flange back on, it doesn't leak and looks just like a OE blanking flange.

Link to comment
Share on other sites

The one I chose is made by a USA company called AMG Racing and their local agent is Rocket Racing Supplies, they are normally used by "big cam" drag cars and such as their engines don't produce sufficient manifold vacuum to operate the serve unit.

Mine set me back AUD $650.00 well over the price of a std OE Wabco pump, but its very quiet, and it doesn't leak oil ^_^

Link to comment
Share on other sites

Okay, try EBay item number 331274995958 that's identical to the one I have, it's brilliant.

I wouldn't advise a system that switches the vacuum pump on with the actuation of the brake peddle, there is bound to be a lag and that you don't want, an automatic system switched by a vacuum switch is far preferable that way the vacuum is already there for when you need it, the pump will only come of with the use of the brakes or to make up any loss of vacuum due to small connection leakages.

Wire the pump up to the same supply as the FIP fuel cut-out solenoid.

Link to comment
Share on other sites

Andy, The more I think about it the more this system scares me.

Say you are traveling down the motorway at 60 MPH, that's 1760 yards a minute or roughly 30 yards a second, given that you have average reactions you see a problem and you hit the brakes, that takes 2 seconds reaction time, in that time you have travelled 60 yards - your braking distance (assuming your brakes are in good order) , is about three times that distance - 180 yards, so from seeing the hazard to pulling up to a stop you have travelled 240 yards --- but if your vacuum pump only operates on peddle pressure and takes 1 second to give you adequate vacuum you have travelled a further 30 yards beyond your minimum braking distance, in other words you have increased you braking distance from 240 to 270 yards !!!!

Andy you must have a system that gives you constant vacuum or a pump that operates on a vacuum switch to maintain a constant vacuum.

Link to comment
Share on other sites

I totally agree !

I did read the bit where you said your system switched on and was at pressure (well vacuum) and a pressure switch turned the pump off. looking again at the pump I found I see that there isn't a reservoir as such, so it's a pump only and pumps on demand....

I will have a look to see if I can find a pump like the one you have posted available in the UK

Andy

Link to comment
Share on other sites

Andy, try EBay and the item number I quoted you, --- 331274995958 --- postage to the UK might be high but the kit comes complete with vacuum hoses, vacuum switch and wiring loom, and the pump itself is quite small and compact. I installed mine on the inner wheel arch just below the brake booster -- the vacuum pipe length between the pump and the booster even with the inline vacuum switch is very minimal, no more than 6" -- and it works well, the pump comes on with ignition (wired to the same circuit as the FIP fuel solenoid) and switches off within 3 seconds and well before the glow plug light has extinguished, once the engine is running I cannot hear it coming on and off even in heavy traffic. I did notice when I installed it that air was being drawn into the brake booster due possibly to the increased vacuum that the electric pump generates, at the rubber pipe connection flange, this was easily remedied with a slick of silicon sealant gasket around the rubber flange. I tested this joint the easy way, a lick of soapy water around the rubber flange and sure enough it was sucked into the booster. The silicon sealant was drawn into the flange in the same way but sealed it perfectly.

Link to comment
Share on other sites

Andy, (& JB) some of these pumps come with an adjustable vacuum cut-out switch, mine did anyway.

To set it correctly (my pump came without instructions :rtfm:) set it at the minimum vacuum, try your brake for feel & operation and then screw the vacuum switch adjustment in to increase the vacuum until your servo is operating correctly, you want the required vacuum and no more.

These pumps will exhaust up to greater than 20" hg -- far more than the standard servo unit is designed for and future damage to the servo diaphragm could result, and in any case why have the pump running for longer than is necessary.

As a guide my pump achieves the required vacuum to operated the brake servo in about 2 seconds once it is powered by turning the ignition on, the slightest depression of the brake peddle brings it back on to maintain the vacuum.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy