'76 280SE

[chrismsullivan]

Finally pulled the pump apart this afternoon. Man, it's a bitch trying to get the bit in the middle out! I think I prefered messing around with the odometer!

I couldn't see that coupling part you mentioned above though Oscar??

[oscar]

Damn.  It's not the first time I've heard of the coupling missing.  The good news is the tangs on the engine side can line up against the tangs on the pump so it'll still work.  However, I've got two pumps still attached to wrecks and there's hopefully a good chance one of them at least has this coupling.  If so I'll PM you for an address and send it down to you.

[chrismsullivan]

That's really kind of you Oscar. Much appreciated!

[oscar]

Talk about learning something new everyday - I've mislead you on the coupling so far as the m110 coupling is different than the V8's.   
The drive side's tangs are located further outwards which makes me think your pump shouldn't be working without a coupling unless the tangs only just touch but I doubt they can.  I dunno, they must do otherwise you wouldn't have that SLS leak when the engine's running.   
Both the 75 280S and 77 280se had this coupling so I would assume a d-jet 280 is supposed to have this one too, I hope.
Just double check the engine side Chris and see what you got or what shape you reckon the coupling should be.  I haven't got a spare of the V8 type, just the type below. 

[chrismsullivan]

Thanks for that Oscar.

I can confirm that I have the coupling that you've pictured.

Can you confirm whether there is any other coupling missing or if it's looking like it's all complete.

Cheers,
Chris

[oscar]

Cool!  That's all it is, just that lump of metal.

[chrismsullivan]

Great! That's good news. All I need to do now is pull my finger out and order the seal kit from MBSpares...

[koan]

Great! That's good news. All I need to do now is pull my finger out and order the seal kit from MBSpares...

Do you know if the MBSpares seal kit has the two high pressure oil rings? The kit from M-B dealers doesn't.

They are not your bog standard hardware store O-rings but high pressure NBR-90 material O-rings.

A tip to get the piston block back in (and out but too late for that) is to heat alloy case in boiling water to expand it a bit. Also note that the pins that hold the reaction valve on need to be positioned away from the the outlet hole.

koan

[chrismsullivan]

Koan, not sure mate. I'm going to try to ring them today, so will ask and let you know.

Yep, I used the boiling water trick to get the piston out.. It was a little tight still, but eventually popped out after much wiggling around.

Pins? Reaction Valve? I have probably already done this, but don't know the specific names for these things..

Cheers,
Chris

[oscar]

Do you know if the MBSpares seal kit has the two high pressure oil rings? The kit from M-B dealers doesn't.

A few years back they did.  I mistakenly put the second ring in the front cover because I didn't know where it went . Still worked though.  Next time I tried to order a kit they didn't have any but could make a kit up from individual bits.  I later bought another kit from autohaus under a w126 suspension section but it didn't have that big rear O ring.  It's just a 3 piece kit - rear seal, gasket and one large o-ring for under $20AUD

[koan]

Pins? Reaction Valve? I have probably already done this, but don't know the specific names for these things..

Probably should have called it reaction band, the band that wraps round the piston block covering the holes in the ends of the bores forming a valve. Two pins hold the band to the block.

koan

[chrismsullivan]

Righto. I know what you're talking about. I've not taken the band off. Yet. Do I need to?

[koan]

Righto. I know what you're talking about. I've not taken the band off. Yet. Do I need to?

No, nor do you need to remove the pistons but if you do (accidentally or otherwise) try and get them back in the bores that came out of.

koan

[chrismsullivan]

Koan, I had a closer look at the piston and the reaction band, then had a look at your photo below:


It would seem that my piston block thing doesn't have any pins holding the band in place. I'd say that someone has tried to service it in the past but forgotten to reinsert the pins.
Should I find a replacement set of pins or will it operate without the retaining pins?

Also, the 4 pistons with the springs attached fell out. I have no idea which bore they are supposed to go back into... Woops.

[koan]

Not sure about the pins, suppose the danger is the band creeping round till the gap is over a delivery hole. Doubt you will find new pins but they wouldn't be too hard to fabricate. Very similar in appearance to a flat head nail, pick a diameter that is a good but free fit in the hole and trim the head down with a file.

In one of suspension pump pics there's a shot of the block, band and pins apart.

I think the pistons are selected for a best fit in the bores so we will see if it matters...

koan