Removing PDWA, thread size/flare type of fittings

Talk about the E-Type Series 3
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Mephistopheles
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#1 Removing PDWA, thread size/flare type of fittings

Post by Mephistopheles » Sat Aug 13, 2022 1:12 pm

Hello all,
I would like to remove the PDWA and instead connect the two brake lines for the front circuit / the rear circuit with screw fittings connectors.
Since I want to order the necessary connectors and have them on site before I start work, here are my questions:
What are the thread sizes of the 4 fittings on the PDWA (see picture from the parts catalog)?
I assume that the brake line flanges are each bubble flare type (see picture), correct?
Thanks for the support!
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1973 manual LHD OTS E Type
Holger

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MarekH
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#2 Re: Removing PDWA, thread size/flare type of fittings

Post by MarekH » Sat Aug 13, 2022 6:27 pm

If the bit in the middle is gummed up and seized anyway, then there is no harm in simply leaving it.

If you are feeling lucky, then you can bend the pipework to fit the brake booster directly as so there is no need to buy any new parts. It will fit if the front and back circuits are swapped. That isn't as odd as it sounds - the early s2 cars are back to front like this aswell. It changed half way through the s3 run. Don't ask me why, because I don't know. Perhaps someone wants to weigh in with the difference in the two failure modes and which is deemed safer.

kind regards
Marek

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Mephistopheles
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#3 Re: Removing PDWA, thread size/flare type of fittings

Post by Mephistopheles » Tue Aug 16, 2022 12:30 pm

Hi Marek,
Thanks for your answer.
Best regards
Holger
1973 manual LHD OTS E Type
Holger

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lowact
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#4 Re: Removing PDWA, thread size/flare type of fittings

Post by lowact » Fri Aug 19, 2022 2:58 am

Thread size is 3/8NF24. Yes they are bubble flares. You might have to search a bit to find connectors for bubble flares, more commonly available for double flares …
I wouldn't do this. Tampering with brakes, removing designated safety devices, not a good idea. Don’t tell your insurance company or registration authority.
In my experience the PDWA is simple, robust and reliable. If it is not working should be easily fixed by pulling it apart, cleaning thoroughly, if the NLA square section o-rings are deteriorated, replace them with circular section rings that are not a tight fit.
There is a lot more variation that just the type of flare. Notice in your diagram, the double flare nut has thread all the way to the end while the bubble flare nut has a spigot. My understanding, it used to be most commonly the other way around while these days spigoted nuts are used almost universally, including for double flare connections because there is then no requirement to cut thread below the top of the inverted taper (cone). Notice in your diagram, the hole for the bubble flare nut has a reduced diameter below the thread to accommodate the spigoted end of the flare nut. If a spigoted nut is used in a hole without this reduced diameter (i.e. a fully threaded hole) there is risk that over-tightening the nut will spread the spigot making it irremovable; example in the photo.
Note in yr diagram, the bubble flare nut has a protruding taper on the end of the spigot. I have never seen this before, older style had the opposite, inverted taper, newer nuts have virtually no taper and the spigots are less likely to spread …
Image
Regards,
ColinL
'72 OTS manual V12

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Mephistopheles
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#5 Re: Removing PDWA, thread size/flare type of fittings

Post by Mephistopheles » Fri Aug 19, 2022 5:28 am

Hi Colin,
Thanks for your detailed answer.
However, in the meantime I decided to keep the PDWA.
Best regards
Holger
1973 manual LHD OTS E Type
Holger

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