Scubapro D300, D350 & D400 Overhaul: Theory and Practice

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rsingler

rsingler

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I didn't realize that the diaphragm had been improved. Thank you! I'll look for that on my various models.
 

Clashswims

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Spring Contour - While it is not common, if evaluation of the spring revealed a gap between the lever and the spring’s most forward position in the Pre-Dive position, you will have to re-bend the spring.

To start, with the spring laying on its side, trace the contour of the spring on a piece of paper. Then add a short line that shows the ideal final position of the crossbar once the spring is bent an amount that will bring it in contact with the back of the lever.
View attachment 624928
Taking a pair of needle nose pliers, grip the spring just below the 90° bend in the long arm, and then place the second set of pliers approximately 1/4” further away from the 90° bend.

This will allow a new slight curve to be added to the steel without stressing the spring at the sharp bend - brittle from when the spring was originally formed. It will take very little added curve to restore contact with the lever, and it is better to do repeated slight bends rather than attempt to undo an excessive new bend. By setting the lever against the tracing after each attempt, it is easy to return the spring to optimal shape in short order.

Reassembly:
If the Pre-Dive Switch was not removed for service, skip to post #7 below.
Challenge #3: Pre-dive Switch Reassembly
The reassembly of the Pre-Dive Switch is, after cover removal, the most frustrating thing about D-series service. Two tools are required: a small flat-bladed screwdriver and a wire-claw small parts grabber. The first step in reassembly is to insert the inlet tube at the same time as the pre-dive spring. While it is possible to thread the spring into place after the inlet has been installed, it is difficult, and risks permanently deforming the spring.

First, ensure that the top crossbar of the spring is inserted in what will be the lower slot of the switch retainer (22). The part is bidirectional, so either slot can be used. Next, grasp the head of the retaining ring screw with the claw grasper and set it aside.
View attachment 624929

Examine the pictures below to aid in orienting the spring. From the diaphragm side of the case, the left (long) side of the spring is on the hose side of the inlet tube, and passes over the tube. The short arm of the spring is on the right, and ends under the inlet.
View attachment 623628
View attachment 625279

Place the spring high in the case with the retainer clipped to the spring (in the lower slot), with the convex side facing toward the switch. Then place a lightly lubricated 2-016 Duro 75 o-ring (18) in the land of the inlet tube (32). Insert the inlet tube retainer end first, with the spring high inside the housing and the inlet passing underneath the squared top of the spring. Take care that the sharp inlet flanges do not catch the spring as it is inserted. Before you seat the inlet in the far side of the case, cock the spring so the short arm of the spring passes under the other side of the inlet tube. Then seat the inlet tube fully. The spring will be dangling loosely over the inlet tube. Now place a second lubricated 2-016 o-ring in the recess for the inlet retainer (19). Place a little lube on the threads of the inlet retainer (to facilitate the next disassembly), and screw the inlet retainer into place, tightening hand tight with a Scubapro tool or a small pin face spanner. If the switch retainer has popped off the spring, press it back into place now, with the convex side facing toward the switch, and the spring in the lower slot.

Confirm that the spring is correctly (if loosely) oriented around the inlet tube. Confirm that you can position the retainer over the rectangular switch hole in the front of the case with the mouthpiece up. Set the case aside.
Take the switch (34, 35) and o-ring (33) and without lubricating the o-ring, place it in the land of the switch. If you are using the service kit’s square o-ring, this is a straightforward matter.
View attachment 625668
If you are using a 2-116 o-ring, it will be a slight struggle to force the round o-ring into the square groove. Don’t even try for all four sides. Not lubricating the o-ring provides just enough grip to fit the bottom and sides into place. The 2-117 recommended by other DIY'ers is even harder to install, and depending upon which switch molding you have, occasionally cannot be completely wedged under the switch edges into the land.
View attachment 625277
Here is the difficult part: with the switch capturing the o-ring on at least three sides, with your third hand carefully pick up the case and press the switch firmly against the front of the case. At this point, if you aren’t using the square o-ring, you can use the forked end of a brass spade to push the bulging top of the 2-116 o-ring under the switch edge into the land, and with firm pressure on the switch, the o-ring will remain in place, trapped between the case and the switch.
View attachment 625278
With the square o-ring that fits the land perfectly, great pressure isn’t necessary.
But you need to maintain pressure while you attach the spring, which is why the wire-claw grabber is so helpful.

Hold the case/oring/switch sandwich in one hand with the mouthpiece tube facing up, and the switch slid to its highest position in the slot. You may find it easier to push the sandwich against the edge of a padded table top. Use your other hand to position the spring/retainer assembly inside the case with the retainer (22) positioned precisely over the screw hole in the switch. With the retainer in position, insert the grabber holding the retainer screw through the mouthpiece tube, and partially thread the screw into the switch.
View attachment 625276
With the parts loosely connected (and with pressure maintained on the switch and o-ring), switch to your screwdriver for final tightening. As with the grabber, insert the screwdriver through the mouthpiece tube, with the switch maintained in the uppermost predive position. This brings the screw head into view from behind the inlet tube.
View attachment 625275
Trying to do the assembly with a screwdriver alone is an exercise in frustration. But however you got the screw into the switch, perform your final tightening with the small flat-blade screwdriver. Lube on the screw threads is probably not helpful here, as you need your switch retaining screw to remain where you set it. Firm tightening will bring the back of the retainer into contact with the switch mount for the screw, so that net tension is provided solely by the compressed o-ring, and not by additional tightness of the screw. If switch action is sloppy with your particular switch, consider reinstalling with a 2-117 oring, though this is only rarely needed.

If the o-ring pops out as you are installing the screw, all may not be lost. If the screw is in the switch at all, you may be able to use your spade to push the o-ring back into position and add more pressure to the switch to trap the o-ring while you complete tightening. If not, swear loudly and start over.

Your guide to proper screw tightness is the slight resistance with which the predive switch slides up and down. At this point, it is appropriate to add a small line of lube to the case above and below the switch. The o-ring will then pick up the lube as you slide it back and forth.

(Discussion continued in next post...)
 

RyanT

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I'm stunned at the amount of time you've put into this. Thank you!
 

scrane

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Having enough experience in life to understand my own limitations, I sent my D400 to rsingler for a full makeover. He knows these regulators inside and out and is sitting on a treasure trove of parts. He quickly returned my reg to me totally gone over and better than new.
Instead of sitting on one of these fantastic regulators thinking you'll sometime get around to it, PM Rob and send it off so you can take it on your next trip.
 

scrane

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I recently received my second D400 off of ebay as a spare. It is in like new shape, but it looks like someone sucked on it too hard without being pressurized and the exhaust valve wedged in below its sealing surface on the main diaphragm. Then it probably sat like that for a decade and the valve took a permanent set and is deformed. I managed to track down a new valve, but I'm wondering if this is a "thing" with the D series.
Also, is there any way to tell if you have a metal or plastic orifice without disassembling the reg?
 

lexvil

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I recently received my second D400 off of ebay as a spare. It is in like new shape, but it looks like someone sucked on it too hard without being pressurized and the exhaust valve wedged in below its sealing surface on the main diaphragm. Then it probably sat like that for a decade and the valve took a permanent set and is deformed. I managed to track down a new valve, but I'm wondering if this is a "thing" with the D series.
Also, is there any way to tell if you have a metal or plastic orifice without disassembling the reg?
Don’t know the answer to question 1, question 2 is no.
 

axxel57

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I recently received my second D400 off of ebay as a spare. It is in like new shape, but it looks like someone sucked on it too hard without being pressurized and the exhaust valve wedged in below its sealing surface on the main diaphragm. Then it probably sat like that for a decade and the valve took a permanent set and is deformed. I managed to track down a new valve, but I'm wondering if this is a "thing" with the D series.
Also, is there any way to tell if you have a metal or plastic orifice without disassembling the reg?
If you look into the mouth piece shaft you can see the white Delrin 'legs' which are crimped over the 'valve edge'.
If it's a metal orifice you cannot see any.....
 
OP
rsingler

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Here's what @axxel57 is referring to:
Round inner hole = metal orifice (looking thru the hose connection).
20210814_174524.jpg

Oblong hole with white tab from the Delrin orifice = last edition
IMG_20210814_174836.jpg


And no. Exhaust diaphragm collapse inside the spokes is very uncommon. And Pilot Error to suck it so hard it leaks and then leave it that way.
 

scrane

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OK, Thanks. As a data point I can confirm that the d400 I received marked CE0098 / 96 serial number 7020101652 has the new style orifice.
It also has an interesting lever lock mouthpiece I've not seen before.
 

Open Ocean Diver

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OK, Thanks. As a data point I can confirm that the d400 I received marked CE0098 / 96 serial number 7020101652 has the new style orifice.
It also has an interesting lever lock mouthpiece I've not seen before.
One of these?

upload_2021-8-15_9-21-10.jpeg
 
https://www.shearwater.com/products/peregrine/

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