300 Tdi electric vacuum pump retrofit

**antvz** · 2015/11/29, 11:09 PM

This thread will eventually become a record of my attempt to retrofit an electric vacuum pump to the Tdi.

**antvz** · 2015/11/29, 11:16 PM

We all know of the reliability issues surrounding the 300 Tdi vacuum pump. After hearing another story from my indy about a brand new unit failing, and experiencing my own vacuum pump beginning to weep after just 3000 km, I'm getting sceptical about keeping this unit long-term.

There is a fix available, which involves replacing the pop-rivets with bolts and adding a thicker Welch plug.

However, if you study the info on the internet about the working principle of this pump, the reason for failure of both the above is actually to do with the poor design of the piston, which causes oil to get into places it shouldn't and then get forced out of the Welch plug because it's got nowhere else to go.

So, fixing this will buy you some time, but it's treating the symptoms and the unit is probably going to fail, eventually, catastrophically.

**antvz** · 2015/11/29, 11:18 PM

A few guys overseas have fitted electric vacuum pumps. It seems that some of the modern cars have them, so you could get one from a scrap yard if you know what to look for.

The solution I like, however, is this one from Ebay:

http://www.ebay.co.uk/itm/3312749959...958%26_rdc%3D1

Apparently it has a variable pressure switch, so you can set the amount of vacuum to the original spec of the system. Important because you don't want to over-do things and destroy your booster.

**antvz** · 2015/11/29, 11:22 PM

One of my thoughts is to make a nice thick metal blanking plate for the existing vacuum pump. Then, by means of rubber shock mounts, attach the electric pump to the blanking plate and connect it up. This way, the vacuum pump still sits in the original location.

The problem is that the pump may require shielding from engine heat. I need to go and measure the temperatures in that part of the engine bay.

Otherwise, mounting on the firewall somewhere, or on one of the inside fenders, is probably the solution.

Another advantage of this pump is that it would make the Tdi a bit quieter, especially at idle.

**biltong** · 2015/11/30, 02:52 AM

Your best bet would be to install a Bosch Alternator that fits without mods, which has a vacuum pump on the back. Then you also solved the alternator problem.

The Marelli is a really good unit, but it is not possible to really recondition it.

**hgbosch** · 2015/11/30, 06:37 AM

Anthony

listen to Biltong's advise. He has got tons of experience with the D1 300Tdi.

The 2.8 Powerstroke motor used such an alternator.

**jelo** · 2015/11/30, 07:13 AM

The old school Nissan diesels also had the same alternator/pump combo unit so finding one with the right pulley and so on shouldn't be hard.

**biltong** · 2015/11/30, 07:20 AM

Originally Posted by hgbosch

The 2.8 Powerstroke motor used such an alternator.

Have you got a part number?

Would be something that deserves to be a sticky.

I also tried to find that Bosch alternator once. Apparently it does exist but I did not had time hunting it down.

**Sam vd Merwe** · 2015/11/30, 07:29 AM

And how to get the revcounter working again. Its running of the alternator. Can it work?

**Byron** · 2015/11/30, 07:36 AM

Originally Posted by Sam vd Merwe

And how to get the revcounter working again. Its running of the alternator. Can it work?

That's strange I thought it came from the gearbox and not the alternator.

**hgbosch** · 2015/11/30, 07:39 AM

Originally Posted by Byron

That's strange I thought it came from the gearbox and not the alternator.

Hi Byron

there are 3 connections on the back of the Magneti Marelli alternator. The rev counter feed is connected to the middle one.

**antvz** · 2015/11/30, 07:48 AM

Some interesting info posted here already. Thanks guys.

I've heard about the alternator mod. It's also attractive to have a Bosch alternator instead of the Marelli.

BUT, the vacuum pump now runs very close to the exhaust manifold, and also on the wrong side of the engine (brake booster on other side, so you would need some more piping). And of course the rev counter issue.

And the new pump would still need an oil feed, so more piping needs to be added and rerouted. Opening another oil path gives one more chance for something critical to go wrong.

Hence the interest in going the electric route...

**hgbosch** · 2015/11/30, 07:53 AM

Hi Anthony

Back in 2010 I had designed a kit for the Vacuum pump, that takes care of the cover coming loose and the bottom welch plug popping out. It contains 6 x 5mm ss bolts with a special metal lock nut, impervious to oil.

It is available from British 4x4. Just ask Allan.

**biltong** · 2015/11/30, 07:59 AM

Originally Posted by antvz

And the new pump would still need an oil feed, so more piping needs to be added and rerouted. Opening another oil path gives one more chance for something critical to go wrong.

Correct. It certainly is a bit of work.

That said, I also looked at an electrical vacuum pump unit and could not find something that made me happy. Very pricey for something of quality.

Hence, I installed a new Wabco back then and kept the old one.

Make no mistake, this is one of those thorny Tdi issues. Regardless of the way you go, you either compromise, pay or work.

Tough one.

If it was me, I would plumb in the oil feed and return from the turbo.

**jelo** · 2015/11/30, 08:14 AM

Originally Posted by biltong

If it was me, I would plumb in the oil feed and return from the turbo.

and make sure the Madman/LBB was watching the oil pressure..........

**Landyluvver** · 2015/11/30, 08:21 AM

there are 2 makes of vacuum pumps available for the 300Tdi - Wabco and Unipump
I have stopped using Wabco as a result of comebacks
fit a new Wabco and 3 weeks later the customer is back
he demands a warranty replacement while the suppliers refuse
guess who takes the knock to keep the customer happy?
not 1 Unipump return is the past 2 years

**hgbosch** · 2015/11/30, 09:09 PM

Hi Landyluvver

I have made the same observation. The 300Tdi Wabco unit is absolute rubbish, the quality control is non-existent.

The Unipump I fitted after going through 3 "new" Wabco units in 2010.

The Unipump was still working perfect after 120'000km when I sold the D1 earlier this year.

**biltong** · 2015/12/01, 09:20 AM

Originally Posted by hgbosch

The Unipump was still working perfect after 120'000km when I sold the D1 earlier this year.

Great to know. Is so, then I would have no reservations going this option next time.

What is the difference in cost?

**Landyluvver** · 2015/12/01, 11:44 AM

Originally Posted by biltong

Great to know. Is so, then I would have no reservations going this option next time.

What is the difference in cost?

the last time I bought, the Unipump was actually a couple of bucks cheaper
I got them from LP4A but think Dover stocks them now as well

**antvz** · 2020/08/08, 12:18 PM

Reviving my old thread as I begin thinking about how to do my electric vacuum pump mod.

I've attached an Audi/VW document I found on the internet, explaining a bit of how their system works.

From this, I think I'm going to do the following:
- look in scrapyards (or at Goldwagen) for a vacuum pump and pressure sensor
- get an inline vacuum reservoir somewhere
- build a circuit to monitor the pressure and toggle the pump as necessary. This should include a warning light/buzzer if the requisite amount of vacuum cannot be maintained