Solutions for the NLA PRV setup - T4 oil breather 022 115 303 A

[metahacker]

Ok,

so there's been a bit of fuss about this part.
it's not available. people come up with some kludge solutions.
some people have been trying to repro the valve or rebuild it.

instead, here is a relatively easy approach to use one of two currently available VW OEM equivalents.

parts list:

(1) valve--
(a) 25mm VAG PRV - 06A 129 101F
OR
(b) 20mm VAG PRV - 06A 129 101D
(try to get the OEM one. not the VAICO.)

they install slightly differently. see below.

(2) hose --
(a) buslab offers the molded breather hose.
022129973C
https://www.buslab.com/product-p/022129973c.htm
(if this is available/in stock i would go this route for sure)

(b) another option is to use 7/8" hose and a hose spring
the spring will allow it to make the tight 90º bend that normally necessitates the molded hose to avoid collapse

you should be able to use these...
hose: McMaster Carr 5155T64 (Tygon PVC, 7/8" ID, 5/32" wall) is good for this
hose spring: McMaster Carr 3138N17
you might be able to find something much cheaper at a FLAPS.

this will look more "breather-hose-y" than stock since it's clear PVC based.
---

if you are insistent on re-using the "OG" cloth-braided hose you already have, then you will definitely want to use the 20mm PRV
if you are using a hose like the buslab one, e.g. that is smooth on the outside, either the 25mm or 20mm should be able to work

(3) viton grommet
McMaster-Carr 1061T69,
"Silicone Rubber High-Temperature Grommets for 1-1/16" Hole Diameter and 1/4" Material Thickness, 3/4" ID"
https://www.mcmaster.com/catalog/1061T69
(P.S. Try not to use the electrical box grommet that some people have been eyeing for this job This McM-C one is MIL-spec rated for exposure to petroleum/oil.)

(4) breather hose coupling method
(a) for the 25mm, you need a section of 1" ID hose
i used McMaster-Carr 528K65 petroleum hose

(b) for the 20mm, you need a way to increase the nipple OD from 20mm to 22mm.
you should be able to use McMaster Carr 5119K47
which is a Viton 3/4" ID and 7/8" OD.... which should fit into 22mm ID hose.
you can just cut enough of this to slip over the 20mm PRV outlet and it will act as a bushing/sleeve to bring it up to 22mm.

other methods might be simply using silicone self-amalgamating aka self-fusing aka "rescue" tape, such as Scotch 70... and/or a way to "help" the 22mm ID hose to fit it tightly - e.g. worm gear hose clamp ... so if you are a super cheap person just try clamping the stock hose down on it .. GLWT if it's not fresh and flexible

Here's what you do.

(1) Remove the breather box: remove the hose from the old PRV (it should just slide off) and unclip the old breather box. Take it off.

(2) Remove the 10mm bolts and take the PRV off.
Note: You won't be using the nuts/wavy washers, so put them somewhere safe or just tighten them back down on the breather for safe-keeping.

(3) Insert the grommet into the hole in the breather. Notice that it fits/seals perfectly
Note: If you are using the 20mm, you may want to wrap the nipple feeding the intake boot now before you install it. The idea is to make it fit tightly into the breather hose.

(4) Insert the NEW PRV into the grommet, IN THE OPPOSITE ORIENTATION. The PRV is now rotated 90º vs. the original. If you consult the diagrams for the current VAG parts set, this is correct. This is NOT intuitive and easy to mix up if you use the 20mm unit instead of the 25mm.

(5) The end that feeds the intake boot (this will be the big fat nipple on the 25mm unit) now needs to mate with the hose... which isn't a direct fit.

For the 25mm unit, you will slide a length of the 1" hose over the large nipple on the PRV, and then slide the breather hose into the short 1" section. If you are using the Buslab breather hose, this should work and fit perfectly.

If you are using something else besides the Buslab hose, well, figure it out If you want to use the cloth braided hose, you will likely need a 1" to 7/8" barb reducer - GLWT (I mocked one up in CAD and 3D printed it...but didn't end up needing it) - they do exist but aren't very common.

For the 20mm unit, you will need to do one or both of the following: increase the OD of the nipple for the breather hose and/or use a hose clamp to cinch the hose down on the nipple and make a seal. The standard breather hose is 22mm and this will not fit tightly on the nipple as you desire. To increase the OD, you could use the self-fusing tape mentioned above. You may also get away with a hose clamp alone first. Perhaps a more classy method would be to make a "bushing" out of the hose specified above, or similar. This isn't a high-pressure fitting; it's a breather. As long as the pieces mate and seal, and you don't use something that will be murdered by oil/gas vapor, you will be fine with whatever method you choose.

Here are some pics that can help stir your imagination

This is a really ugly yellow spare breather box I am using to test fit, the viton grommet, the 25mm PRV, the BusLab breather hose and the 1" coupling hose.

This is how your PRV should end up in the breather box.
Notice that it's rotated 90º vs what you are used to with the stock one.
Don't fuck this part up unless you want blowby to blast splooge out of your dipstick.
With the 25mm part, it's pretty impossible to get wrong, since it won't fit.

If you find the girth of the 25mm PRV outlet threatening, then you can use this smaller PRV instead
It will install the same, and even slip into the breather hose...it will just need help sealing against the hose.

This is what the final product will look like, with the 25mm PRV.
The 1" ID sleeve should be trimmed to a minimum length so that it has a more pleasing appearance but this picture of the initial fitment should clearly demonstrate the arrangement.

In case you are wondering, the "updated" 25mm OEM VAG 06A129101F part is nice, it has metal sleeving inside of it, etc. It looks relatively sturdy.
My 06A129101D test unit is not OEM VAG so I'm not sure what the "genuine" 20mm looks like inside yet. I believe they will both function similarly.

This should get you fixed right up.

Cheers

EDIT: 12/18 better instructions for 20mm PRV and new hose options

[raygreenwood]

Nice!

Ray

[Jetfxr69]

very detailed and easy to follow. thanks for that. i was just waiting for Rays opinion.
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[SGKent]

it works, I proposed the solution 10 years + ago and even bought some of the factory valves and offered them for my cost of like $5 a piece. No one was interested so I tossed them. It is a good solution.
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"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[aeromech]

10 years ago I bought one. Still have it. Never could get it to work. Someone has more attention to detail than I do. Good job
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[metahacker]

thanks guys

i made some updates to the instructions above to improve the 20mm details and offer a proposed alternative to the buslab hose (which is having supply chain issues)

ive been running the 25mm PRV and it works great... my motor is very happy now. seemed to take a day to "break in" the valve.
im surprised how much of a difference that little thing made

my idle AFR (mixture) adjustment in the AFM has MUCH better resolution now, not to mention finally having a very consistent AFR at idle.

the old PRV alone was responsible for making the motor around +0.6 to +1.0 AFR leaner at idle.... but honestly fueling under load did not really seem significantly impacted by the PRV either way.

now i don't have to compromise and choose between an ideal target idle AFR (about 13.6 in my case) and having perfect AFRs in real operation... e.g. 12.8 - 13.6 load AFRs (with a max swing between 11.8 and 14.0). before, one of them had to budge ... now it's easy to do both. it's so nice. (god, i really have to say - jetronic is unbelievably awesome for 70s tech...... when it's all setup properly... particularly with a 123 distributor).

i have to say...the inside of the latest VAG PRV looks waaaaaay nicer than the 2 old original Jetronic ones I have......

the original ones look somewhat crude and less trustworthy, IMO, in comparison (lots of rubber to sit in oil/gas vapor spluge)

given a NOS one as an option at this point, I think I would choose the new retro-fit part instead unless i needed a museum-worthy presentation

[raygreenwood]

I know its just bitching on my part....but I HATE the way the original part worked on L-jet and digifant.

This problem was not just with L-jet. The PCV valve system on D-jt...earlier...had similar issues. This was early PCV systems with early injection.

As metahacker notes....yes...it made the engine run slightly leaner than it should....at idle....which can mean a screwy idle and coupled with other age or tuning related items it can mean stumbling off the line. Just damned annoying.

Later systems that employed lambda or 02 sensor had much less issues as it could tune around the issue.

But you got to have PCV....a good thing really as it got rid of "draft tubes" and the oil slick center of each lane we were famous for in the 50's and 60's.

An intermittent vacuum bleed to purge crankcase gases seemed to be the simple way to go. On L-jet....it causes intermittent lean spots. On D-jet ...just the opposite because we use MAP for load metering.

But...on D-jet we have a workaround because our MAP sensor is pretty adjustable and so is our fuel pressure. We get rid of the intermittent part of teh valve and just make it a small constant vacuum bleed that constantly scavenges the crankcase into the oil breather and then into manifold vacuum. Like 2-3mm maximum.

Yes....this cause about 1.0+ rich.....across the board because its constant. We can dial that back with either the MAP sensor adjustment or fuel pressure or a smidgeon of both.....then simply adjust idle at the TB. It gets rid of the idle "cascade" effect and greatly smooths off the line and idle response.

I would suggest...something similar for L-jet...like dump the guts of the valve and just put in an orifice...like maybe 1mm to 1.5mm....which would scavenge the crank case full time....and also make it slightly lean full time.

But I am not sure on L-jet how to accurately tune the fuel curve richer to compensate for the lean factor.

And....I would NOT want to screw with the AFM....as while that could fix it...it also just slides the response curve upstream.

A suggestion would be an adjustable rising rate fuel pressure regulator. Not for the vacuum response portion...dont want to change that...but for the baseline pressure.

At a 29-36 psi range....every 1 psi of pressure addition is 2.77% of gross fuel. At idle...29 psi is 3.44% of gross fuel.

Just some thoughts.

PCV sucked with all early injection that did not have exhaust sampling and tuning capability.
Ray

[SGKent]

they run leaner when they perforate. Also the crankcase becomes a huge vacuum can.
_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[honkadori]

just fyi if someone is still looking for a working one. today i visited a used parts seller here in la. his name is ed. super super friendly. he has quite a few. selling them on here too but listed as breather boxes.


https://www.thesamba.com/vw/classifieds/detail.php?id=2379121
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[metahacker]

after going through this experience studying all the various options (including two original PRVs) i would recommend to avoid using the original part instead of the updated VW part (with the metal internals) unless you find a NOS one and want it to look 100% original
the original part was just not very good, and a used one with ~45 years behind it is not going to be trustworthy
they can "seem fine" but impact your idle mixture and introduce undesirable behavior - particularly if you have less than brand new rings (e.g. blowby) - such as oil leaks/ seal failure/ greatly diminished response from idle adjustment screw
IMO & YMMV

[metahacker]

a little update --

simplified cheat sheat from above:
a $10 method ... or a $70 method.
Only two parts, simple...

(1) VW PRV ....
use the smaller one, part number 06A 129 101D

here is the Genuine VW one (~$50)
https://www.ecstuning.com/b-genuine-volkswagen-aud...6a129101d/
OR
cheaper, pick another brand of your liking (about $7 here or similar @ FLAPS)
https://www.ecstuning.com/Search/SiteSearch/06A129101D/

(2) Grommet
either the Viton grommet listed above ($15)
https://www.mcmaster.com/catalog/128/4233
"Silicone Rubber High-Temperature Grommets for 1-1/16" Hole Diameter and 1/4" Material Thickness, 3/4" ID"
OR
cheaper, use a standard 3/4" grommet (like a Home Depot electrical box grommet for $2)
https://www.homedepot.com/s/3%252F4%2520grommet?NCNI-5

unbolt the old breather valve, pop the grommet in, carefully push the PRV into the grommet, then hose... check your PRV to hose fit, use a hose clamp if necessary....
(keep in mind that the new VW PRV installs with the disc shaped head turned 90º compared to the bolt-on unit that the Bus came with...)

couldn't be easier....

[metahacker]

Just a reminder, do not install the valve the "wrong" way - the orientation is opposite the original Bus PRV

If you look very closely at the first pic above... you can see that the new PRV's ports are clearly labeled "K" and "F"

K Kurbelgehäuse (crankcase)
F Filterschlauch (filter hose)

Also, here is a diagram AshB kindly linked, showing the VW diagram with the bottom port ("F") of the new PRV feeding the intake and the side port ("K") drawing from the crankcase breather fitting:

To reiterate the earlier post: the smaller valve (06A 129 101D), a hose clamp and the grommet are all that's needed for the simplest install (retaining your original hose)

p.s. I have sourced an OEM VW marked version of the smaller diameter PRV to verify it's construction, and it's sturdy with metal inside as well. Both newer VW PRV parts covered here appear to be of a significantly more durable design than the original.

[Good Old Dusty]

I need to replace the PRV on my 78 bus with L-jet FI system.
It has been a year since the last post on this topic. Can Metahacker give us an update on how his replacement PRV part #06A 129 101 F, is working? I think the followers of this forum would like to hear how it's working after a year in service. Thank you.

[SGKent]

I imagine his workaround would be working fine. There is no reason it would fail.

I know of 5 NOS factory breathers that have been discovered in the last 15 years,. Bob Hood got one and me four. I sold one for what I paid. The others no one wants to pay the value so they will probably end up in a land fill. The solution MetaHacker followed will work just as well. I proposed it 15 years ago. Later VW / Audi engines use the later part, and there is no reason that it would not last as long or longer than the originals. The workaround is less expensive then the NLA part. Just pay attention to what direction faces the S-Boot. The only thing it does is cut off vacuum to the engine case when the pressure is the same as outside pressure. Otherwise the engine case would become a big vacuum can and do things like suck valve cover seals in so they leak. If someone runs carbs, they can also run an early style which has a metering hole.
_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[dodger tom]

i tried it, and it’s been working just fine.
_________________
1978 Champaign Edition 2 Westfalia
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[metahacker]

it works great!

it's OEM VW/Audi!

the new ones are perfect and much better made. just look inside of them compared to the OG bus part. not anywhere near as cheaply put together

any old PRV is likely junk. NOS or not I don't see the point in chancing it

personally, for the retrofit, i'd go with the smaller one (20mm)....don't need to adapt the hose just clamp it on and go

like steve said, make sure you don't orient it wrong!
visually it looks backwards vs stock.

[SGKent]

[otiswesty]

Not sure how I missed this before, but I appreciate the tutorial
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[Wildthings]

I suspect people could get by with putting a 6mm orifice in the breather hose, that is what the later watercooled Vanagons had once the breather tower itself failed, which all of them eventually did.

[metahacker]

since we're bumping this thread, here's an update

my original post was way too long, here's the TL;DR version:

1) buy the current-issue VW breather (the smaller one, PN 06A129101D, used on '96-'05 VW 1.8T and others)
2) get a grommet
https://www.mcmaster.com/catalog/131/4387/1061T69
if you're a cheapskate i believe an electrical box grommet from home depot works
3) install the breather in the opposite orientation as stock, so it looks rotated 90º (it will have a "F" for intake/air-filter side and "K" for "k"rankcase side)

here's what it will look like (geebee hose shown but fits same as stock, smaller breather "D" part shown)