Leaking fuel pump

[Largeowner]

Hello All,

I took my 67 230sl out for a tank full of ethanol-free today.  About an hour later I noticed a strong smell of raw fuel in the garage and a puddle under the fuel pump.  The leak seems to be coming from the electrical connectors which has me greatly worried! (new style short pump)

I read in the tech manual that the rebuild kits only have the 3 O-rings for inside the pump.  Can someone tell me where to find the O-rings that seal the electrical connectors?

Also, it would be great if someone had photos and helpful instructions on how to make this repair.

Largeowner

[mdsalemi]

The fuel pumps cool themselves by bathing the electrical parts in the fuel.  Strange but true.

I think your largest problem is you've got a full tank--you'll need to somehow keep the fuel in there.

Contact George Des on this website, he probably has a source for you for the O-rings.  Might also want to check the gang of known restorers such as Gernold at SL Tech; Michael at Black Forest; David at Bud's and a host of others.

[Largeowner]

Thanks Michael,

I phoned Bud's today but did not find a solution.  They DID confirm that the rebuild kits do not have the O-rings I need.  I also thought a phone call to the Classic Center may produce the parts I need. 

The pump is otherwise in good condition and looks like the PO changed it out recently.  Hate to junk it for want of two O-rings!

Largeowner

[Jordan]

Largeowner, can you not clamp off the fuel lines going into and out of the fuel pump so you can remove it temporarily?  Then you can take the pump apart to see what size o rings you need.  I,ve removed my fuel pump several times by just clamping off the lines.  I use cardboard between the clamp and fuel line so I don't cut into the line.  I put an oil pan under the lines just in case they started to leak but they didn't.  I,ve left it vernight like that.  Make sure there is good ventilation.

[wwheeler]

They also sell small hose clamps intended for things such as this. I have some and they work well. Usually less than $15 for two. They won't damage the hose.

[drmb]

This is an easy fix,tools required flat blade screwdriver,7mm ring spanner,fine point soldering iron & solder.
Remove fuel pump,mark outer housings with felt tip pin so can all be aligned on assembly,remove all screws,dismantle housings,
remove circlip from lower end of armature,take note of thrust washer and shims,
remove two 7mm nuts and remove armature housing,unsolder where coil wires are soldered onto brush holder,pull out both brown
and red terminals from housing after removing central screw.Now you will see the two  O rings required as well as the rest, any shop
that sells Viton O rings will be able to match them up for you,Viton is petrol resistant.
Replace all the Orings resolder the coil wire connections, apply a small amount of vaseline  to all the O rings on assembly.
First time around should take 2 hours max.and cost about $20--$30 for Viton O rings.

[mdsalemi]

Viton is the operative word.  Ensure you get Viton O-rings.

Try small parts.com once you get the size, or granger.  Hardware store stuff will be Buna-N and not stand up to gasoline.

[Largeowner]

Thanks everybody!

It looks like I can get the Viton O-rings I need thru the internet once I have the dimensions.  I just need a way to clamp off the fuel lines.  One suggestion was vice grips with sockets on the jaws (to soften the edges).  I would love to see what the purpose-built clamps look like.

Thanks again for the replies!

Largeowner

[66andBlue]

...  I would love to see what the purpose-built clamps look like.

Here you go - pinch clamps are available from Harbor Freight.

For radiator hoses pinch-off-pliers are better and really leak free.

[280SE Guy]

Would somebody place these in the technical manual so as to stop the guessing on the o-ring sizes for the small electric fuel pump at the rear. The following do not include the size of the o-rings at the electrical connections as I have been told they are a square cut o-ring, however a 1.5 MM thickness by 8.5 MM ID o-ring is what I have understood will work if not a 2.0 MM thickness, might have to try both for the electrical connections or use some fuel resistant sealant per George Dees.

Regards,

280SE Guy

[wwheeler]

Buna-N (NBR, Nitrile rubber) IS resistant to gasoline and most petroleum based fuels. It is the standard if you look it up. Viton is typically 5 times more expensive and is more chemically and heat resistant. That being said for a small replacement job such as this, the cost difference amounts to pennies so I would always opt for Viton if available. But don't be afraid to use Buna-N for fuel applications if Viton is not availalbe.

Those clamps that Alfred shows are what I have and they work great. 

[drmb]

Viton O ring sizes,
                          2  x  70mm x 2mm
                          1  x  55mm x 2mm
                          2  x   8mm x 2mm
                          1  x  17mm x 2.5mm
This will be all the O rings to overhaul the later squat type pump.

[Largeowner]

I made a quick trip to Harbour Freight today.  The pinch clamps were a very reasonable $9.99 and I found an assortment of 180 Viton O-rings for......wait for it......$6.99!

Thanks again for all the replies!

Largeowner

[George Des]

Any idea where the DB/ Robert Bosch engineering drawings came from and who was able to get them? The missing oring terminal drawing would make it quite easy to go to one of the many oring suppliers to have them manufactur new rings in either viton or nitrile. Most of these sources indicate they can do this very quickly and very cheaply. I've tried the 8mmx 2mm and it isn't quite right. The tolerances in that terminal "tube' where they sit is very tight and if off even a small amount they will not seal properly. You can custom cut some from some square profile stock or you could reverse engineer them from a good used one if you can extract it w/o damaging it, but it would be nice to be able to order the correct ones according to the original engineering drawings.

George

[280SE Guy]

Any idea where the DB/ Robert Bosch engineering drawings came from and who was able to get them?

George

George,

I got the drawings after asking my local Mercedes Dealer parts guy (a great resource I have) if he could find out the sizes for the various o-rings for the short fuel pump as the o-rings are not included anymore in the repair kit for the pump. A few days later he called me up and said that he was able to obtain the drawings from the Classic Center in California. I drove to the dealer and those drawings are what he had for me. Sadly the electric terminal drawing was not included in the group nor was it called out on the bill of materials. The mystery of the electric terminal o-rings continues.

Regards,

280SE Guy