Diesel Engine Driven Vacuum Pump life expectancy - Page 3 - PeachParts Mercedes-Benz Forum

sixto · #31 12-08-2013, 10:28 PM

The adventurer in me likes the project but the more cautious side of me wonders if replacing a mechanical pump that's established itself over millions - probably billions - of miles with a more complex system, certainly more parts, is rational. I mean a weak solder joint and freezing temps could knock out the pump. Is that vacuum pump controller certified for an automotive environment?

Sixto
87 300D

mach4 · #32 12-08-2013, 10:51 PM

Quote:

Originally Posted by sixto

The adventurer in me likes the project but the more cautious side of me wonders if replacing a mechanical pump that's established itself over millions - probably billions - of miles with a more complex system, certainly more parts, is rational. I mean a weak solder joint and freezing temps could knock out the pump. Is that vacuum pump controller certified for an automotive environment?

You raise good points. I wonder if the quality could be any worse than many of the MB electronics that are prone to failure - tach amp, cruise amp, climate control, clock, are just some that come to mind.

The failure of an electric vacuum pump and/or controller would result in a hard brake pedal while the failure of the mechanical one would result in the same hard pedal AND could take out an engine. We're dealing with automotive grade vacuum pumps in this scenario, so the weak link is the controller. I suppose it would be pretty easy to add one wire and a switch that would provide limp-home functionality of the vacuum pump if the controller were to fail. As I'm conceiving the installation of the controller, it would be in inside the cabin fairly near the radio. The essential construction of radio electronics would be very similar to the controller electronics therefore I would expect similar reliability...all things being equal.

I'm not arguing for the solution just sharing a bit of my current thinking in contemplating this kind of a project... and looking to generate some discussion on the merits from the group.

(Of course I'm doing this driving around on a timing chain that's probably overdue for replacement... go figure

)

sixto · #33 12-08-2013, 10:59 PM

There's also EMI and EMC to consider but the radio is probably as high as electronic tech gets in our cars

Sixto
87 300D

mach4 · #34 12-08-2013, 11:18 PM

On the pure mechanical end of the spectrum, here's a simple vacuum switch that is reasonably priced and has a decent range and reasonable hysteresis for the application.

According to the web site -

Brake Vacuum Switch

This simple lightweight vacuum switch turns pump on only when needed. Adjustable vacuum setting. Has COM, NC and NO connections. The switch comes from the factory set with a cut off at 18 to 22 inches of mercury. The hysteresis is 15% to 20% of the 20 inches nominal so it's about 3 to 4 in/Hg. IMPORTANT NOTE: Since this relay is rated at 4 amps and the vacuum pump is rated at 8.5 amps you must use a relay.

Wiring: The silver colored male spade connector is "Common", the middle one is "Normally Open", and the one furthest from the silver one is "Normally Closed". These are marked as such on the side of the vacuum switch. If you are my age you may need a magnifying glass to see them.

Contact Ratings: 4 amp @ 15 VDC, 1/2 amp @ 125 VDC

Measures: 2.25"L x 1.5"W x 1.5"H and weighs 0.8 oz.
Price: $35

The Gears · #35 12-09-2013, 03:21 AM

Re the $35.00 vacuum switch. Where from and is that price for new or used.
Thanks

strelnik · #36 12-09-2013, 10:20 AM

Quote:

Originally Posted by mach4

The failure of an electric vacuum pump and/or controller would result in a hard brake pedal while the failure of the mechanical one would result in the same hard pedal AND could take out an engine. )

There used to be bolt-on vacuum pumps with adjustable waste-gate type vacuum controls but that was maybe 20 years ago.

These were used on smaller diesels that went from stationary applications to running vehicles.

Caterpillar 3208 engines used them, when those engines were put in larger Ford and some Chevy trucks, usually the 3/4-1 ton size. The engine was right around 630 cubes. They made some smaller ones, too.

They could power the brakes very well, and so people didn't add expensive air over hydraulic brakes UNLESS the size called for it.

mach4 · #37 12-09-2013, 10:20 AM

Quote:

Originally Posted by The Gears

Re the $35.00 vacuum switch. Where from and is that price for new or used.
Thanks

Brake Vacuum Switch

OM617YOTA · #38 12-09-2013, 12:13 PM

Mach4-

That vacuum switch is AWESOME. Mine is a bit wonky, will probably need to be replaced, and that looks like a good candidate for sure. Thank you!

mach4 · #39 12-09-2013, 08:36 PM

Here's another switch option I found on Amazon.

Can't tell the specs, however.

I didn't think this would work until I saw it in a vacuum kit for cars with big cams that don't produce much vacuum to speak of.

mach4 · #40 12-09-2013, 10:57 PM

In researching the option of replacing the mechanical vacuum pump with an electric one, I've compiled a list of possible sources for suitable pumps (my junkyard guide)

2005-09 Audi A8 Quattro [8E0 927 317]
2004-06 VW Touareg [8E0 927 317]
2001-05 VW Passat [8E0 927 317]
1998-01 Audi A4/A6 [8E0 927 317]
1999-05 VW Jetta [1J0612181B and D]
1999-13 Volvo (most) [31317445]
1999-03 Saab 9-5 95 [46 46 220]
1994-99 Saab 9-3 900 9000 93 [46 46 220]
2011-12 Chevy Cruz [13343961] * (Pump appears ok, the problem is with a switch)

* General Motors [GM] will be recalling nearly 293,000 Chevrolet Cruze automobiles, because of problems with the electric vacuum pump that provides supplemental brake assistance. The models being recalled are from 2011 and 2012. These Cruze automobiles were equipped with a 1.4L DOHC gasoline turbo engine, front wheel drive, 6-speed automatic transmission, and equipped with an electric vacuum pump [EVP]. In these affected vehicles, the EVP may not work properly during driving. When the EVP does not activate, extra brake pedal effort would be required in order to stop or slow down the vehicle. As a result, if the driver is unaware of this condition, this will increase the likelihood of a crash occurring.

The problem is a switch in the pipe that goes from the vacuum pump to the booster. This switch can fail and cause a unassisted stop. 27 low speed crashes have been reported.

The problem occurs on a very small number of Cruzes. The vehicles in question have a electric vacuum pump due to the turbo. The switch can fail and prevent the vacuum pump from coming on. The brakes still work and the driver is still able to stop in a reasonable distance.

sixto · #41 12-09-2013, 11:35 PM

Is the OE switch in these cars at the pump or on the booster?

Sixto
87 300D

mach4 · #42 12-09-2013, 11:54 PM

Quote:

Originally Posted by sixto

Is the OE switch in these cars at the pump or on the booster?

I was surprised to find out that there is no switch per se associated with the vacuum pump, but rather it's controlled by the ECU based on various sensors. I went looking for the reference, but I didn't book mark it and Google doesn't seem to like my searches right now. I'll add it here if I find it later.

Here it is - http://www.volkspage.net/technik/ssp/ssp/SSP_257.pdf

A closed loop example.

Functionally very similar to this controller referenced in post #30

By the way, check out the "open loop" configuration that controls the vacuum pump without a pressure sensor. Instead it uses a model that

...calculates the pressure in the brake servo unit from the following input parameters:
- Load
- Engine speed
- Throttle valve position
- Brake light switch

Interesting stuff...

OM617YOTA · #43 12-10-2013, 03:49 PM

Quote:

Originally Posted by mach4

Here's another switch option I found on Amazon.

Can't tell the specs, however.

I didn't think this would work until I saw it in a vacuum kit for cars with big cams that don't produce much vacuum to speak of.

That's the exact vacuum switch I have.

Quote:

Originally Posted by mach4

By the way, check out the "open loop" configuration that controls the vacuum pump without a pressure sensor. Instead it uses a model that

...calculates the pressure in the brake servo unit from the following input parameters:
- Load
- Engine speed
- Throttle valve position
- Brake light switch

Interesting stuff...

Interesting stuff for sure, but that sure seems like a good way to add a lot of complication, expense, and failure points to what is a very simple system.

mach4 · #44 12-10-2013, 04:24 PM

Quote:

Originally Posted by OM617YOTA

Interesting stuff for sure, but that sure seems like a good way to add a lot of complication, expense, and failure points to what is a very simple system.

I don't disagree, save for one fairly compelling factor. If the engine driven vacuum pump gives out it can take out the entire engine. So the trade off is a bit of complexity and a different point of failure vs the opportunity to trash an engine.

These pumps are getting old, expensive to replace, difficult to rebuild and run off the injector pump. The electric ones appear to have provided trouble free service for VW, Audi, Porsche, Saab and Volvo, not to mention GM and large truck diesels.

One more factor I like is that replacing one doesn't require opening up the engine, replacing gaskets and fighting in tight spaces in front of the engine.

I haven't made a firm decision yet, but I'm leaning toward making the switch as an experiment. It's becoming a $50-ish kind of project as the research uncovers suitable options.

OM617YOTA · #45 12-10-2013, 08:18 PM

Quote:

Originally Posted by mach4

I don't disagree, save for one fairly compelling factor. If the engine driven vacuum pump gives out it can take out the entire engine. So the trade off is a bit of complexity and a different point of failure vs the opportunity to trash an engine.

These pumps are getting old, expensive to replace, difficult to rebuild and run off the injector pump. The electric ones appear to have provided trouble free service for VW, Audi, Porsche, Saab and Volvo, not to mention GM and large truck diesels.

One more factor I like is that replacing one doesn't require opening up the engine, replacing gaskets and fighting in tight spaces in front of the engine.

I haven't made a firm decision yet, but I'm leaning toward making the switch as an experiment. It's becoming a $50-ish kind of project as the research uncovers suitable options.

Oh I agree wholeheartedly. I replaced my mechanical VP with an electric Audi/VW VP and I'm thrilled. I look forward to seeing how you quiet yours down, once you make the switch. My comments about complication and expense were in regard to using a bunch of electronics and programming to calculate brake booster vacuum to control the VP vs. just a simple vacuum switch.

That said, I sell electronic components for a living, so game on. The world needs more buttons to push, beepers to beep, and lights to blink.

Edit: I also like that it's a $50 fix if the VP goes bad. And as it won't destroy your motor when it fails, there's much reduced risk in using a junk yard part.