Taking apart an OVP relay - PeachParts Mercedes-Benz Forum

tinypanzer · #1 04-14-2009, 11:08 PM

Since I replaced mine (probably unnecessarily) I am taking apart my old one to see what makes 'em tick. Pictures coming soon.

It looks like a single contact relay, two diodes, and a resistor. If this is the case, fixing one shouldn't be too hard.

I'll bet that half of the issue is simply burnishing the contacts on the relay.

BTW - the rattling appears to be normal. It's a plastic insulator card that's put in there to keep the circuit board off the aluminum box. The relay itself also rattles a bit, and that is normal for relays.

More soon.... Anyone else who has taken one apart care to share?

babymog · #2 04-14-2009, 11:51 PM

I've got one apart, but didn't bother trying to repair it since I already had a new one.

However, three OVPs on three cars in a year, I should probably start.

It has been my experience that bad relay contacts (and switch contacts) will quickly be bad again, very difficult to clean and lap them properly. If the relay could be replaced, that would be the way to go IMO.

04 Diesel · #3 04-15-2009, 12:11 AM

Yes, pictures please.

Ivanerrol · #4 04-15-2009, 12:59 AM

The Zener diodes go out of spec with age.

They will be just as unreliable if you paly with them.

86560SEL · #5 04-15-2009, 02:10 AM

Tiny... where did you buy a new OVP and how much was it? I dont see them listed here on the site. I hope thats my issue with my car and not that hose you mentioned in the other threads.

Cal Learner · #6 04-15-2009, 08:44 AM

Phil must surely be able to supply you, even if it's not listed on the site.
P/N 201-540-08-45 about $80 (if you're talking about a 1986 560SEL).

ds190 · #7 04-15-2009, 11:28 AM

OVP rebuild?

The "search" feature never stops working.

tinypanzer · #8 04-15-2009, 05:00 PM

Yikes. Yup, those are pictures all right, but that OVP looks like it came from Chernobyl.

I see that he cut it open to get it apart. Not necessary. You just bend back the two tabs at the bottom and pull it out with pliers.

Pics coming....

ds190 · #9 04-15-2009, 05:51 PM

"You just bend back the two tabs".....exactly what the first picture shows......

Kestas · #10 04-15-2009, 05:58 PM

I've noticed that burned relay (and other) contacts seem to be the common denominator on many problems with Mercedes vehicles. They were the root cause of the following problems I repaired recently:

- heated seat module
- seat belt presenter module
- high beam switch

If you can repair electrical contacts, you stand to save a lot of money.

tinypanzer · #11 04-15-2009, 06:26 PM

Man, I need glasses. I could swear I looked at that photo and saw him cutting the thing open. Sorry, ds190..... My bad.

tinypanzer · #12 04-15-2009, 10:22 PM

Pics as promised.....

The second picture shows the insulator card, which rattles around and creates the impression that something is broken.

The third picture shows the circuit board traces. Any cracked or loose solder joints here should be touched up.....

The fourth picture shows the actual relay.....

The fifth picture shows the zener diode as it lives - pressed into the aluminum heatsink/contact. Good luck replacing that part - if you can even find it.

tinypanzer · #13 04-15-2009, 10:23 PM

The first pic here shows the relay itself, and if you look carefully you should see the contacts. Does anybody know if this relay is normally open or closed when the car is running? I don't see much wear on these contacts at all leading me to speculate that the relay only closes when there is a "fault".

The last pic shows the pins. Silver plated!! That's quite a nice touch. For those not in the know, silver is an excellent conductor and even its oxide is more conductive than copper. Silver plating contacts is a premium feature.

tinypanzer · #14 04-15-2009, 11:23 PM

"Tiny... where did you buy a new OVP and how much was it? I dont see them listed here on the site. I hope thats my issue with my car and not that hose you mentioned in the other threads."

I got mine from Phil here on Fastlane. Search under "Overload Relay"

The hose is a much cheaper part than that relay! It's just much harder to install. Really, it's not so bad - just annoying that you have to pull the fuel distributor.

I hate to say it, but with a 19 year old MB, you either need to get familiar with some basic repairs or find a cheap indie mechanic who you trust. These are great cars, and quite reliable, but fixing the age related issues that the previous owner neglected can be time consuming and costly if you have to farm out the repairs........

Good luck!!

86560SEL · #15 04-16-2009, 01:47 AM

Thanks... I was going to check the price of the OVP, but the Fastlane site seems to be on the fritz now (and has been for awhile... I cant get it to load my cars data or even the search).

I wonder if one out of a W116 (late 70s S-Class) would work, or is it strictly a model-by-model part? Reason I ask is a local junkyard has a W116 Mercedes and they also have a early 80s V8 W126.... it would be nice if I could find a used one that is in good shape.

My main concern with the fuel distributor is me screwing something up and ending up with a fuel leak the size of Texas.

True, I wish I was more of a DIY'er and I personally dont know why I buy old Mercedes. I wish I had of kept my old 1984 190D... it was a great car and those dont seem to be plagued with problems that plague the gasser W126 models, such as stalling- seems to be a very common W126 gasser issue and its a safety concern. Frankly, I am suprised a recall was not ever issued since its such a widespread issue. I guess the diesels tend to have less issues such as this? I sold my 190 because it was too small for me. I should have suffered and enjoyed it. I also own a old Lexus, another costly car to maintain only this one is complex.

I know of a couple of local indy MB repair shops I am going to look into on checking the car out... whatever it is its getting worse and it cropped up quickly. I also know of someone that has a business partner that takes her car to a Mercedes mechanic and I am supposed to get more info on that. I think if I could find a good MB service shop with reasonable rates, I will be OK. Too bad I am not related to one. lol.

If this car seems like its going to be a costly repair among the other things it needs, I will probably try to trade it for another car... like a used Camry or a (gulp) new Ford Fusion or some sort of GM car....

Thanks again.

BTW - this is the message I keep getting from Fastlane....

"OOPS!!!!!

There is a slight problem with your request. (See below)

We are sorry, but your request encountered one or more errors and it could not be served. Details about the error, if any, are shown below.

The operation timed out year=1988&make=63&cmd=model_ "

I swear if it was not for bad luck, I would have NONE at ALL!

Quote:

Originally Posted by tinypanzer

"Tiny... where did you buy a new OVP and how much was it? I dont see them listed here on the site. I hope thats my issue with my car and not that hose you mentioned in the other threads."

I got mine from Phil here on Fastlane. Search under "Overload Relay"

The hose is a much cheaper part than that relay! It's just much harder to install. Really, it's not so bad - just annoying that you have to pull the fuel distributor.

I hate to say it, but with a 19 year old MB, you either need to get familiar with some basic repairs or find a cheap indie mechanic who you trust. These are great cars, and quite reliable, but fixing the age related issues that the previous owner neglected can be time consuming and costly if you have to farm out the repairs........

Good luck!!