3B diaphragm replacement

[lynchmob]

Thought I would post some pics of this. I did one earlier this summer and had some issues finding info on removal. Specifically, the nut that holds it to the shaft is an 8mm.

Pics might be useful to someone.

This engine is hanging on a hoist and the edic motor and mount is removed for better access.

1. Where to find the diaphragm
2. With the cover removed
3. Close up so you can see where the nut goes - you can see the threads on the right side of the shaft inside the housing.

[lynchmob]

The nut is tough to get to. Its an 8mm and I didnt see the size posted anywhere on mud - maybe I missed it. If you are removing a bad diaphragm its a little easier to cut the leather section with a razor knife just to get it out of the way.

[lynchmob]

1. Diaphragm removed. The shaft there (rack) is what the diaphragm connects to.
2. Diaphragm with attachments
3. Why I replaced this one.

[Big Blue 84BJ60]

what are the symptoms of a bad diaphragm?

[lynchmob]

Originally Posted by Big Blue 84BJ60

what are the symptoms of a bad diaphragm?

black smoke under load, high EGT and/or coolant temps. My 70 also had a flat spot in the power around 2500 RPM that seemed to be gone after replacement.

[wesintl]

usually it's high idle...

[Scoot Jockey]

Thanks for taking the time to post those pics. The diaphragm on my 2H is fine right now, but I sure need to do a replacement on my old Mercedes!

[lynchmob]

Originally Posted by wesintl

usually it's high idle...

that too, but mine only changed about 75 rpm after the install. I put new injectors in the 70 and it only seemed to help my black smoke issue a little so I was looking for other things to change.

I couldnt find any holes in the diaphragm on that one. It was just old and stretched a bit. It runs quite a bit different and I really have to try to make it smoke now.

It can be a time consuming procedure with the engine in the truck, but Id recommend it. I got the part at a local diesel shop for $26.

[lostmarbles]

You can test your diaphragm easily by sucking on that clear plastic tube attached to the cover (on the end of the injector pump). You should be able to build up vacuum quickly and easily (with your mouth) and feel the diaphragm hold that vacuum (if it's not torn).
I replace my diaphragm "in situ" but it IS tricky and you need a SMALL spanner (I have a tiny ring and open-ender set) and lots of care/patience.
It is easy to drop things inside if your not careful but I've successfully replaced mine twice now and I've never had the engine out of the vehicle.
(I did drop something inside during one of the diaphragm changes but I got it out successfully with a magnet.)

[brisveganbj42]

whats the consequences of not having the 8mm nut on the end of the diaphragm??

I recall when i replaced mine (due to excessive black smoke under load), that it slipped right off and was a matter of slipping it back on the rod (that was the hard bit) before doing it all back up again. this is while the engine is in the truck, no edic removal and banana arms..

[lowenbrau]

I've never removed the nut but rather pulled the cotter pin from the other side. The tricky part is not dropping the washer.

[Big Blue 84BJ60]

should i remove the HAC or will i be able to work around it

[lowenbrau]

HAC should be OK. I'd pull the EDIC though.

[Flatdeck]

I agree that the symptom of a damaged diaphragm is slightly higher idle. If you do not deal with it it will just get worse until one day your 3b will just rev till its screaming .... I've heard one do it.

[Rig of Mortis]

Originally Posted by Flatdeck

I agree that the symptom of a damaged diaphragm is slightly higher idle. If you do not deal with it it will just get worse until one day your 3b will just rev till its screaming .... I've heard one do it.

I'd have to agree with Flatdeck.

When I had to replace my diaphragm, the symptoms were high idle and the last day I could drive it (which was to the mechanic to swap out the diaphragm), white smoke was pouring out of my tailpipe and my RPMs were so uncontrollably high, that at every traffic light, I had to shut down my truck via the key ignition, or my idle would have just kept climbing and filling the intersection with white plumes of smoke.

That was ten years ago, been flawless ever since.

[Tapage]

I just replace ( ok ok ok ok not me the Shop ) mine 5 years ago or so .. the only issue that I have with my old one it's the smoke .. coul be not much worse at all ..

[lostmarbles]

Helps to understand how it works I feel.

Unlike most diesels, our Toyotas have the accelerator pedal controlling simply a butterfly valve in the air intake manifold. (Most connect the pedal directly to the injector pump.)

The injector pump then varies the fuel quantities according to the amount of vacuum created by a "venturi device" that is situated at that butterfly valve.

When the butterfly is closed, the increased pressure drop across it (and across the venturi device) creates increased air speed (m/sec) through the venturi. And this in turn increases the vacuum applied to the diaphragm.

The injector pump varies the fuel by having its "rack" connected this diaphragm.

High vacuum (foot off accelerator) pulls the rack against spring-pressure (via the diaphragm) towards the "idling-fuel-quantity" end. Low vacuum (foot hard down) allows the spring to move the rack back in the opposite direction towards the "full-power-fuel-quantity" end. So when the diaphragm is torn and you have your foot off the accerator, the butterfly is almost closed starving the engine of air but the injector pump doesn't know your foot is off the accelerator anymore. It thinks your foot is still "hard down" (because the tear tends to equalise the pressures across the diaphragm rather than allowing the vacuum to suck-and-move the diaphragm) so it supplies more fuel.

Understanding this explains all the symtoms.

[golfinw71]

I just received the part did the install and what a difference. I bought the cruiser with this symptom and couldn't figure it out for the life of me until i found this forum. Feels like a brand new motor now that she is finally back to normal. Who knows how long it went without the fix. Thanks for pics posted, was a big help!

[ohrly?]

I ripped my diaphram out, it was all rottenish; i ripped it into 6.37 pieces with my hands. This is not necessarily a hard job, but it isnt easy. I had to do it twice because I installed it upside down

[lostmarbles]

Originally Posted by lostmarbles

Helps to understand how it works I feel.....Understanding this explains all the symtoms.

Sorry. Looking at this post some months later made me see that I had been talking a bit of sh*t.

So I've edited that post.

And here is a photo that helps explain what I was rabitting on about. I welcome any comments pointing errors I may be still making.





PS. Ya never stop learning

[lostmarbles]

And here's another photo that would be a good addition to this thread and my earlier reference to "sucking on a hose" to test your diaphragm:

[RufusTheDufus]

Sucking might help if there's serious issues. A vacuum gauge is very helpful and far more accurate.

FSM provides a test for the diapgragm: put a vacuum gauge on it at 36.8 mmHg. It should take longer than 10 seconds to drop below 35.3 mmHg. My vacuum gauge isn't that sensitive but it's close enough to be able to see if there's a leak in the diaphragm.

[lynchmob]

Originally Posted by lostmarbles

And here's another photo that would be a good addition to this thread and my earlier reference to "sucking on a hose" to test your diaphragm:

Attachment 213419

Whatever you do - DO NOT remove the line on the right side in this picture while running. I did this once and the engine races to max RPM. I quickly shut it down, but it scared the crap out of me.

[lostmarbles]

Originally Posted by lynchmob

Whatever you do - DO NOT remove the line on the right side in this picture while running. I did this once and the engine races to max RPM. I quickly shut it down, but it scared the **** out of me.

The lines cross over each other so it is hard to tell which one you're referring to Lynchmob.

But I would think it must be the "vacuum" line that connects from the LH side of the intake-manifold-throat to the RH side of the diaphragm because removing that one would make the injector pump think your foot was "flat to the floor - and then some".

I don't think I'd be game to try that

[american psycho]

Originally Posted by lostmarbles

the increased pressure drop across it

Trying to understand this phrase makes my brain hurt.

[lostmarbles]

Originally Posted by american psycho

Trying to understand this phrase makes my brain hurt.

Sorry. I'm not too good at explaining things sometimes. My years spent in refrigeration/air-conditioning (where pressures/vacuums are studied in detail) probably means I've left stuff out of the explanation. Try this:

When the butterfly valve is wide-open, it is like a "wide-open tap" within a water pipeline. The pressure either side of the tap is roughly the same. But when the "tap" is closed - you normally have "supply pressure" on the upstream side and "little or no pressure" on the downstream side. So the valve "closing" has increased the "pressure-drop across itself".

So I was trying to say that closing the butterfly valve increases the pressure drop across the "venturi tube" and this forces a higher air speed through the venturi. (A higher pressure drop across a tap would force more water through it.)

A Venturi is also used in a paint spray-gun (where the "pot" hangs down below the gun). The air speed through the gun (when you pull the trigger) then sucks up the paint from the pot by means of the vacuum produced by the venturi. Pulling further on the trigger further increases the air speed and this further increases the vacuum/suction to suck the paint up faster.

In the air intake of a diesel engine the "supply pressure" is "atmospheric pressure" and downstream of the butterfly valve, the engines pistons and valves are together trying to pull a vacuum (below-atmospheric pressure).


My apologies - I used to teach in a polytech and maybe writing all this sh*t is just me "playing pretend" at being a teacher again. (I'm fully aware that I'm IGNORANT in comparison to many others who post on MUD.)

[rchalmers3]

Originally Posted by lostmarbles

My apologies - I used to teach in a polytech and maybe writing all this sh*t is just me "playing pretend" at being a teacher again. (I'm fully aware that I'm IGNORANT in comparison to many others who post on MUD.)

I think you did a great job of explaining pressure differentials and how they are used. Thank you for your willingness to contribute. No more apologies needed!

Rick