Fuel Pump Maintenance

[mdsalemi]

Hi Folks,

With all this talk about filters, screens, etc. I'd like to offer some sage advice: Don't Forget the Wiring!!

With all my recent issues the fuel pump has been suspect for some of them.  As luck would have it (it pays to know people at Bosch) a new one showed up on my doorstep without an invoice.  But that's another story...anyway, I began the process of swapping out the old pump for the new...AFTER disconnecting the battery:

1)  Have a tray to catch the fuel that will pour out of the intake line until you can fit the hose on the new pump fitting and clamp it down, and wear gloves!

2)  Unless you changed them recently, get a set of 3 new rubber mounting studs.  One they seize themselves on, you might need to break them to get them off.  Part # 126.988.00.11  List $4.20 each.  Only one of mine survived.  Have these BEFORE you start!

3)  Check the wiring!  As my old pump was dangling there by the hoses after removing the mounting hardware, one of the leads simply came out of one of those blasted $#@%^&* crimp connectors.  Apparently at some point during the restoration or subsequent service, somebody cut the wires under the car, butt-crimped new pigtails on them, and then connected to the pump.  This is bad, very bad.  Butt crimp connectors should never be used outside, exposed to the weather!  The crimp didn't hold and I'm sure this was the cause of some intermittant problems.

4)  The repair was easy: I took new cable BACK to the wiring harness in the trunk.  Now there are no crimps outside the car.  the ring connectors I used were crimped AND soldered.  Hopefully this is better and will last a while.

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[waqas]

Regarding fuel spillage while swapping the pumps, I've found hose clamps to be invaluable (locking pliers may also be used, but you may want to put some padding in the jaws so the hose is not damaged). And its always nice to have new hoses on hand, as one might find an old cracking hose waiting to fall apart on contact.

One thing you left out in your list: new rubber boots for the fuel pump connecting nuts, if they need to be replaced. These are pretty good at keeping out dust and moisture, while keeping the connections electrically isolated. SLS lists them for a couple Euros each.

WAQAS in Austin, Texas

[George Des]

Ben,

I'm assuming from the age of your car that we are talking about the early large style pump. If so, make sure you read some of the earlier posts dealing with how to rebuild these. That lower bearing removal requires a complete disassembly of the pump and there are some definite disassembly details to be aware of regarding removal of the main shaft seal.

George Des

[Ben]

Guys thanks for the advice, the hoses are new and I have sets of pipe clamps and a catch tray !

Actually the connectors were indeed previously doctored and one of the connections, a crimp type, was poor !

Still I dont think that would cause a high current situation. I have the pump off and it is the later, small type pump. So far it appears clean but I havent opened the electrical end yet..............any links to this would be appreciated as I have read about the larger pump and seent he photos but nothing on the smaller one !

Anyone ?? (I plan to do this later today ! )

Regards,
Ben in Ireland.
'64 230SL 4sp.

[George Des]

Ben,

The smaller pump is actually less complicated to deal with, but there are some details to be aware of as you will read in some of the past posts. There are no grooved ball bearings, so you can rule that out immediately. The motor portion of this pump is a "wet" motor--the armature runs in fuel-so it tends to be self cleaning as far as brush dust goes--this also cools and lubricates the brushes and armature. However, as with the larger pump, the smaller pump is still susceptible to crud binding the vane or the shims between the shaft and pump body corroding. Best bet though at this point is to pull pump off and get a read on how many amps it is drawing under load before pulling apart. It should be approximately the same draw as the larger pump.

George Des

[Ben]

Yeah since I couldnt put my hand to the ammeter I pulled it apart anyway, as I want to know what its like and fit new brushes anyway !

I didn't manage to removew the "can" yet though...........any photos/how to steps would be appreciated since I dont want to ruin anything !!

Regards,
Ben in Ireland.
'64 230SL 4sp.

[George Des]

Ben,

Let me get back with you this evening. I may be able to get you some phots. Also, brush replacement on these pumps can be very difficult if you don't have the brushes with a recess cut into it to allow the shunt wire to fit under the brush holder. Interestingly enough, some of the brush kits supplied by MB do not have this recess cut into it making brush replacrment all but impossible. There is a way aroud that and being an electrical guy, I'm sure you can figure it out right away.

George Des

[Ben]

Thanks George, I'm going to take a look at what I have right now, maybe take some photos myself !

I would welcome any photos either way !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[Ben]

Okay so I've stripped it and the brushes still look fine ! The new ones DO have the groove but I decided against replacement since the existing ones have about 80-85% material left on there !

No point in exchanging these !

I cleaned up the comm and I hadn't realised that the bearings are really only bushes so having cleaned up whatever I could and fitted new seals I examined the windings and they look very dark !

Not what I expected, they do look burned, or else they are varnished !

So I put everything back together and ran the motor without the "pump" end attached and it coggs slightly and got very hot very quickly. I was surprised at this !

Not sure what to do now..........any thoughts or advice ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[George Des]

Ben

Sounds to me like something is binding the armature. Ck the "can" to see if there are any dents that may be causing this. Also look at the very top of the "can" where the shaft fits into it to see if the bushing is burred. If this cks okay go to the bottom part of the shaft and carefully pry out the e-clip, the thrust washer and shims. Ck to see if they are clean and burr free. Also the bushing where the shaft goes through. If this all cks out re-assemble and run the motor again. You need to be very careful when you tighten the two nuts that hold the "can" to the pump body. It is only necessary to tighten these enough to ensure that the rubber o-ring seals the "can". Overtigthening them can also be a source of binding. The armature is wound with varnished wiring--you may want to clean it up with some electric contact cleaner. Could be that it is caked with carbon paste or gasoline varnish causing it to run hot. If all this fails, the armature can be re-wound with a new commutator for about $75.00 U.S. This is still much cheaper than the cost of a new pump. Let me know if you decide to go this route and I'll pass on to you the info where you can get this done here in the U.S.. On another point, we may be talking about two different things on the brushes. There should be a horizontal groove that runs across the shunt end of the brush--this is where the wire brush spring rides. The shunt wire itself should be attached in a recessed portion of the top of the brush so as to allow the brush and shunt wire to slip through the metal brush holder. As I mentioned, some of the repair brushes I've gotten from MB do not have this recessed shunt wire and it makes it virtually impossible to flatten the wire sufficiently to allow fitting it into the brush holder. Good luck

George Des

george Des

[Ben]

Thanks George, I see what you mean about the brush groove, but the new ones are identical.

I will clean out the bearing bushes and the shims. I'll give the windings a shot of cleaner and I'll get an ammeter today, reassemble and check it again !

We do a lot of work with a rewinder here in Dublin so worst case I'll talk to him !

Keep you all posted !



Regards,
Ben in Ireland.
'64 230SL 4sp.

[Ben]

Well having cleaned and checked everything, and reassembled the unit with new seals I ran it and it sounds fine and is drawing 2.5 amps !

Back on the car later for a test, after I replace the wiring terminals with some better quality items !

Thanks again folks !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[Ben]

nope I'm back in the horrors again. The car ran fine for two days then it blew the fuse again. In fact the fuse looked as though it melted a little before blowing, which seems very strange.

I checked it just now whilst the engine was running and it is drawing 11 amps !!

Does this sound like a wring/earthing problem to anyone else ??

I was going to run fresh wires through a fuse direct to the pump and see what happens. I could then measure the draw and if all is okay I will hard wire it in correctly !

Any comments ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[George Des]

Ben,

My guess is that you have a short somewhere in the line. I'd first verify that the pump is the only feed you have off this fuze. Then I would take a close look at the wiring at the pump end to make sure it is not frayed there. The back wiring harness is separate from the front engine harness and you can unplug it from the main. On our cars over here the connection is on the left side right above the hood release mechanism. I would unplug and do a continuity test along with a current test to see what the pump draws from that part of the harness. This will help to isolate where the short or extra draw is coming from. From what you're telling us, it does not sound like a faulty pump--. Hope this helps.

George Des

[Ben]

Okay an update, I have checked the wiring and the plugs and cleaned everything but did not see any issues.

So I ran a fresh earth to the pump and also a new power cable with a built in fuse. It blew immediately !

I removed the pump and tested it again on the bench and it sounds horrible, at one point it peaked to 19a !! I opened it but dont see anything different, it spins freely without power, but the windings are very burned looking.

There must be a breakdown in the motor windings somewhere. I could get it rewound but I think I'll try the option of a newer modern pump now !!

Anyone know the exact flow/pressure rate requirements, I know it 1ltr/15 seconds but what pressure is required ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[George Des]

Ben,

Sorry to hear this, but it sounds like you've found the problem. Based on your earlier current ck , I would have been certain the pump was okay. Were you running fuel through it when you took that reading ? If not that may have been the cause of the low reading. As I said earlier, you can have these armatures re-wound with a new comm for about $75. Let me know and I'll get the info to you if you decide to go that route.

George Des

[Ben]

George the low reading was without fuel, but it was around 5.5a with the car running innitially which I thought would be okay but it obviously intermittantly rose well above that !!

I'm off now to collect a new small pump.............wish me luck, anmd thanks again !

BTW I will upload photos when finished !



Regards,
Ben in Ireland.
'64 230SL 4sp.