There never sems to be a shortage of junk R4 compressors laying around. In my opinion, based on many years working on GM and MBZ cars with the R4, I believe the most common cause of failure are leaks that depleat the compressor's oil supply and failure of the low pressure switch to deactivate the clutch when the refrigerant level is too low.

Some of the older MBZ's used the GM A6, which has an oil sump and an oil pump for lubrication. The R4 is more like a two-stroke engine in that it is lubricated only by virtue of the oil that travels along with the refrigerant charge. I always reseal them (both body 'O' tings and a new front seal) every time I install one. I have had a few of them leak and it just isn't worth the hassle when the seals are so easy to replace, especially with the rising costs of R-12.

The front seal will come with a white plastic cone that serves as a seal protector during assembly. Again, I just remove the 4 bolt front hub and change the seal on the workbench, so there is no chance of gouging the sealing surface with a sharp instrument.

NOTE: There is a cone-shaped washer (its called a Bellville washer IIRC) under the front housing. Pay attention to which direction the cone faces on disassembly.

I once worked for a BMW/MBZ shop who threatened me for giving customers DIY advice.

The shop owner was obsessed with profiteering at any cost.

The shop owner once re-installed a USED oil filter on a customer's 5 series BMW, with the customer standing under the car with him, to keep from buying one from a local competitor, and then joked with his staff about his 'slight of hands' expertise.

This is the same shop that also sold a woman a used differential on a 325i in 2004 when the tech told the shop owner, repeatedly, that the noise was a bad axle bearing. After replacing the differential, the owner called the customer and told her that "now that the rear end is quiet, we can hear a abd axle bearing that we couldn't hear before."

She authorized the reapir and the onwer asked me to mark the differential that came out of her car 'good' so it could be sold to another, unsuspecting customer.

I fought with this fellow quite a bit over his unethical practices.

In 2003, while he was away at the coast, I was put in charge of managing the shop.

During this period, we put a new radiator, thermostat and belts in a chiropractor's 750iL. At that time, we bought our parts from IMC and SSF. We got a Continetal belt that was marked incorrectly and the technician didn't catch it. It allowed the tensioner to travel past center. The car threw the belt a few miles from the shop, destroying the fan and radiator in the process. The customer called understandably upset.

I arranged for a tow truck to pick up the car, gave them a loaner 540i off the lot and ordered replacement parts.

I repaired the car at no charge, that included the towing fees, all the parts and the labor. The customer was quite pleased.

When the owner returned, he chastised me for wasting so much of the shop's money on the reapirs. He felt as though we could "blame the failure on something else and made money fixing it."

I protested citing that ethical business practices dictated otherwise.

I was 'laid off for lack of work' a few days later...Robert

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership