Author Topic: M129.980 Fuel Pressure Damper Diaphragm Replacement  (Read 3394 times)

austinado16

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M129.980 Fuel Pressure Damper Diaphragm Replacement
« on: September 10, 2022, 05:29:55 »
Replaced the diaphragm in the fuel pressure damper, part # A1270700052 today.  Part readily available through the dealer for $37 plus tax.  In stock, in Los Angeles, and was to my dealer in 2 days.
« Last Edit: September 12, 2022, 18:09:59 by Todd »

Figoulu

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #1 on: September 10, 2022, 06:58:59 »
I need to do mine as well
1965 230 SL
1991 Porsche 911/964 carrera 2
1990 Porsche 911/964 carrera 4 SOLD
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2018 Harley Davidson Street Bob SOLD
2003 Harley Davidson Road King Classic SOLD
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roymil

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #2 on: September 10, 2022, 14:17:10 »
I'm curious if there was a symptom or something you noticed that made you want to change it?
Mark Miller
1968 280SL
Rode in his pagoda's first mile.

wwheeler

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #3 on: September 10, 2022, 14:54:11 »
I did mine as well and there is one thing you want to do when clamping the case(securing the diaphragm). That is to load the diaphragm so that it is roughly in the position it will be during operation. That will ensure the edges of the diaphragm are not buckled. I used a modified bolt to do so. See attached.

I rebuilt it just because I was doing the entire fuel system and was part of it. Seems like I remember the diaphragms were starting to get hard to find. BTW, these are the same as the W113 and so this could be posted in the regular forums.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

austinado16

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #4 on: September 10, 2022, 20:25:40 »
@roymil:  I've owned the Coupe since Apr '92, and have never changed the diaphragm.  On top of that, the car sat "stored"(poorly) for 10yrs from 2009 until Jan. '19.  So along with rebuilding the fuel pump in Jan. '19, this was on the laundry list.  But to answer the other part of your question, no, there were no running issues.  Surprisingly, the old diaphragm was still quite nice.  It was a little stiffer than the new one, but still pretty good.  My hunch is that it was replaced at some point in '90-'92 prior to my purchase, because the car had become undriveable.  It would run for about 30min, shut down, and could not be restarted for hours, or until the next day.  It had been to umpteen shops in the SF Bay Area, and no one could figure out what was wrong with it.  So the owner sold it.

@wwheeler:  I don't want to post my Coupe shenanigan's to the W113 area.  It's nice enough that they even allow a Coupe owner here.  Cool idea to do that long bolt trick.   Was that something shown in the big blue book?  I installed the cover by slowly finger tightening the bolts in a rotating X pattern, hoping to achieve the same thing, and letting that inner metal hub settle down over the fitting inside.  Now you have me wondering if my method was wrong and I wound up clamping down the diaphragm all wavy/wrinkled.  Shoot, I better pop it off and redo it.  Hope I haven't ruined it.

Now if I could just get the radiator back!!!  I'm really looking forward to driving the car, especially with the FI linkage dialed in.  The seatbelts arrived today and the sill mats arrived yesterday, so at least I have a couple fun jobs ahead.
« Last Edit: September 12, 2022, 06:30:30 by Todd »

wwheeler

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #5 on: September 12, 2022, 04:26:51 »
Todd,
The bolt trick was my thought looking at how it went back together. May be overkill but made sense to me at the time. I really don't know if it is necessary. They are easy enough to take apart, so may not hurt to check. 
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

austinado16

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Re: M129.980 Fuel Pressure Regulator Diaphragm Replacement
« Reply #6 on: September 12, 2022, 15:34:33 »
@wwheeler:  Reinstalled the diaphragm, by supporting it.  Thanks for the outstanding tip!

Now it's time for new seatbelts.

wwheeler

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #7 on: September 13, 2022, 00:02:21 »
Good deal. I am not sure exactly what these do and why there are two. So who would know if they are really working and how to diagnose. That is unless they leak externally.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

austinado16

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #8 on: September 13, 2022, 00:15:23 »
I can only guess, but I wonder if it's doing something to buffer volume for the changing amount of fuel being removed from the system in the range from idle to full throttle?  Maybe they help keep the MIP from running out of fuel under high load/full throttle?  Since the electric pump is always running at the same speed and providing the same amount of fuel to the MIP, and the MIP is like a variable fuel leak to the pressure.  So at idle, or lower volume fuel consumption, the diaphragm is pushed more open, because there's less of a fuel leak from the system (what the MIP is using), and as that fuel leak increases, the diaphragm moves more towards closed, keeping more fuel "in" the MIP.  Again, that's just a guess.

wwheeler

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #9 on: September 13, 2022, 18:28:10 »
That’s over my head. You should be a Mercedes engineer!
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

Figoulu

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #10 on: September 17, 2022, 05:32:28 »
Those devices are made to not over pressure the gas system in the injection network.
The gas pump flows the gas under pressure at more than needed to feed the pump and then the injectors. If the pressure becomes too mulch then the diaphragm opens a return path, so the gas goes back to the gas tank

I’m rebuilding the gas and the cooling system on mine. See my progress / story here : https://www.sl113.org/forums/index.php?topic=33638.0

I have to do so as well.
Did already the gas and the pump refurbishment , as well as the gas hoses that runs underneath the car. There are 2 hoses : one to feed the fip, and its twin brother to flow back the gas in excess back in the tank.

I’m not an engineer so forgive my approximate explanation, and anybody is welcomed to correct / modify / precise my own understanding but basically this is it !
« Last Edit: September 17, 2022, 05:38:21 by Figoulu »
1965 230 SL
1991 Porsche 911/964 carrera 2
1990 Porsche 911/964 carrera 4 SOLD
2020 Harley Davidson Fatboy
2018 Harley Davidson Street Bob SOLD
2003 Harley Davidson Road King Classic SOLD
2017 Harley Davidson softail Slim SOLD
2008 Harley Davidson Softail Fatboy SOLD

My youtube channel #lfgdf

Figoulu

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #11 on: September 17, 2022, 05:41:35 »
By the way here is a very interesting video from Mark Habel a distinguished member of this forum 👍👍👍

https://youtu.be/yKm0Gx0rNXg
1965 230 SL
1991 Porsche 911/964 carrera 2
1990 Porsche 911/964 carrera 4 SOLD
2020 Harley Davidson Fatboy
2018 Harley Davidson Street Bob SOLD
2003 Harley Davidson Road King Classic SOLD
2017 Harley Davidson softail Slim SOLD
2008 Harley Davidson Softail Fatboy SOLD

My youtube channel #lfgdf

roymil

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #12 on: September 17, 2022, 14:17:47 »
I'm laughing because I just went and looked in our own wonderful tech manual.   I need to go back and re-read the whole thing.

https://www.sl113.org/wiki/Fuel/Damper
Mark Miller
1968 280SL
Rode in his pagoda's first mile.

austinado16

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #13 on: September 18, 2022, 01:00:29 »
The damper never actually closes.  It's always allowing fuel to be cycled back to the fuel tank.

wwheeler

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #14 on: September 18, 2022, 02:06:36 »
I had heard something about the diaphragm absorbing pulses in the fuel system. Not sure why there are two. It wouldn't be the first time Mercedes over engineered. These are installed on my '60 220SE Ponton injection system which is the first generation port injection. In the You tube video, he did not support the diaphragm like it was shown in the Tech manual. Seems like an iffy proposition if you don't support the diaphragm.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

austinado16

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Re: M129.980 Fuel Pressure Damper Diaphragm Replacement
« Reply #15 on: September 18, 2022, 02:14:27 »
I'm glad you turned me on to the diaphragm support technique, because as I mentioned above, I didn't know about it, installed it unsupported, took it back apart a couple days later, and of course, the diaphragm was out of position.

I think that pulse idea is probably pretty accurate.  As the driver goes from idle, to a more fuel consuming throttle position, and back to idle, or lower consumption, and the electric pump is still supplying a liter every 15 seconds (because it runs at only one speed), that would certainly produce some sort of pressure wave, or flow wave, in the system?  I'm not very knowledgeable in the area of fluid dynamics.