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Infamous PDWA leaking

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Infamous PDWA leaking
#1
  This topic is about my 1975 Triumph TR6
gr8britt Avatar
gr8britt Andrew Blood
Grimsby, ON, Canada   CAN
Hey guys,

I know we have read a lot about these PDWA seals leaking but I changed mine and made the situation worse.

The PO had plugged the switch hole with an appropriate grub screw but it was weeping so I decided to do a major overhaul of my brakes which included these seals. Well....It leaked even worse than before so I pulled it out to check some measurements. I got fluid everywhere but at least it was DOT 5 so I still have paint!

I checked it against one I purchased from Ebay to find that the shuttle was shorter. Does anyone know why this would be and would this cause my leak a pretty fast leak at that!)? I have attached a photo with my PDWA on the left and my shuttle on top, the other is the spare (I know its the wrong spare but most of it is correct....lol)

I look forwarding to the answers on this.

Cheers
Andy

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Bpt70gt Avatar
Bpt70gt Brian T
Westmoreland, NH, USA   USA
Andrew, have you read the Buckeye Triumphs technical article on this particular PDWA? It might give you some help. Just one thing comes to my mind first from my experiences with the GT6 PDWA and that is I've yet to find one that the bore of the PDWA was good enough to just put new seals in it. Eye balling the bore isn't good enough, use a 10x eye loupe and good lighting to inspect the bore, It needs to be smooth and absolutely pit free or it will leak again. May not be so frequent with the brass bodied units but the aluminum ones on the GT are very prone to pitting after 45 years. Where did you get the seals for your unit.
I rebuilt my TR250 unit over 20 years ago and it's still working fine.

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1509026 by gr8britt Hey guys,

I know we have read a lot about these PDWA seals leaking but I changed mine and made the situation worse.

The PO had plugged the switch hole with an appropriate grub screw but it was weeping so I decided to do a major overhaul of my brakes which included these seals. Well....It leaked even worse than before so I pulled it out to check some measurements. I got fluid everywhere but at least it was DOT 5 so I still have paint!

I checked it against one I purchased from Ebay to find that the shuttle was shorter. Does anyone know why this would be and would this cause my leak a pretty fast leak at that!)? I have attached a photo with my PDWA on the left and my shuttle on top, the other is the spare (I know its the wrong spare but most of it is correct....lol)

I look forwarding to the answers on this.

Cheers
Andy

Andy:

The different shuttles require different seals.

The short shuttle requires square seals, the longer shuttle uses round seals.

I rebuilt mine with O-rings from the local hardware store, and it was fine for the 15 years that I owned the car, using DOT 5 fluid. Just be sure that the shuttle is a firm press fit into the bore (lubricate the O-rings with brake fluid before inserting the shuttle.) I brought home a couple of different sizes so I could experiment before settling on the right size. They are cheap - $0.40 each, as I recall, so I didn't mind tossing the ones that didn't fit.

If yours leaked after rebuilding, and the bore was in good shape, then the seals were the wrong size or they were defective. One problem we all face is the fact that many of the parts for our cars are produced in very small batches by tiny manufacturers in third world countries, so the quality is incredibly uneven. Rubber parts are always suspect. If the bore is not in good shape, get yourself a 'bottle brush' brake cylinder hone and clean up the bore, using a generous amount of oil on the hone. Clean the bore thoroughly and blow out the fitting openings.

Always use a fresh copper washer on the bore plug too. That is also available at a good hardware store.

You can re-center the shuttle after rebuilding and bleeding with a small screwdriver inserted through the hole for the switch. You will be able to feel the shuttle's position by tipping the screwdriver back and forth. You then lever the shuttle into the center of the PDWA and reinstall the switch.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

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Bpt70gt Avatar
Bpt70gt Brian T
Westmoreland, NH, USA   USA
Just a word of caution since we're talking about brakes and safety. There are only two rubber compounds designed to handle brake fluid---EPDM and Kalrez. The typical o-ring found at your local hardware store is Buna-N and has a poor rating for brake fluids. EPDM is THE common compound for brake related components, Kalrez is very limited in sizes we'd be using in our cars and not common except for special orders. If you are using common hardware O-rings you are rolling the dice. Be safe and do the research.

gr8britt Avatar
gr8britt Andrew Blood
Grimsby, ON, Canada   CAN
Thanks guys,

Brian, The bores on mine are perfectly smooth and I did learn about the O ring material after browsing the many forums relating to the PDWA and I'm right onboard with what you say. A good article from the Buckeye Triumph guys but it didn't really help me but I did see their shuttle which matched my shorter one.

Vance, I understand the different types of shuttle but the 2 you see in the photo are the same and both take the O ring type seals. I will just have to get another PWDA repair kit and try again, maybe with the longer shuttle, who knows, it might work!

Cheers
Andy

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
I think the key thing is to understand what the PDWA does, and understand the potential nuisance and potential danger of having a PDWA in less than perfect condition.

Personally, brakes are not something I want to fail on me (even if they fail while the car is in the garage!)

This is why my PDWA shuttle has been replaced with a loctited, threaded plug, and the warning light switch will soon be replaced with a low fluid level warning switch

gfe05111952 Avatar
gfe05111952 George Earwaker
Falls Church, VA, USA   USA
In reply to # 1509091 by Tonyfixit I think the key thing is to understand what the PDWA does, and understand the potential nuisance and potential danger of having a PDWA in less than perfect condition.

Personally, brakes are not something I want to fail on me (even if they fail while the car is in the garage!)

This is why my PDWA shuttle has been replaced with a loctited, threaded plug, and the warning light switch will soon be replaced with a low fluid level warning switch

That sounds like a great idea, Tony. thumbs upthumbs up I'd like to hear more details about it. Have you covered this in a journal entry?



George
1967 Triumph GT6
1967 Triumph Spitfire4 Mk2
1968 Triumph Spitfire Mk3

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
[/quote]

That sounds like a great idea, Tony. thumbs upthumbs up I'd like to hear more details about it. Have you covered this in a journal entry?
[/quote]


Sorry, this was done before the internet was what it is today.

My PDWA is the type where the centre link is accessable from both ends, so I was able to tap for pipe thread plugs and install them in each end.
If the link is only accessible at one end (as in this case) the link section would have to be threaded all the way through. A suitable length of threaded rod would then be cut, with a slot cut to drive it in within a straight bladed screwdriver. I suggest the threads are sealed with loctite.

I have yet to install the fluid level switch. I had made a new mater cyl mount to take a modern master cyl that incorporated a fluid level switch, but decided to stay with my old 'Big Lid' Girling since I have already had it re-sleeved.
I will need to cut the barrier between the front and rear reservoir sections away for a float switch to work, and play a little with the float level activation point (it will need to be quite high)

I think I will buy a new reservoir for this, then I can better sort this out on the bench before installing it.
I also do not trust the old plastic not to crack while I am working on it.

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1509078 by gr8britt Thanks guys,

Brian, The bores on mine are perfectly smooth and I did learn about the O ring material after browsing the many forums relating to the PDWA and I'm right onboard with what you say. A good article from the Buckeye Triumph guys but it didn't really help me but I did see their shuttle which matched my shorter one.

Vance, I understand the different types of shuttle but the 2 you see in the photo are the same and both take the O ring type seals. I will just have to get another PWDA repair kit and try again, maybe with the longer shuttle, who knows, it might work!

Cheers
Andy

I used Viton O-rings, which is a flouro-elastomer as opposed to Buna-N which is a simple rubber compound. I neglected to mention that. Viton is frequently green, but can also be black. It is much denser than plain old Buna. Said 'Viton' right on the package.

As to the round versus square seals; Andy, are you certain about that? There were two styles of shuttle, depending on the model year, one was for square, and the other was for round seals. The square seals were NLA as I recall, but that was 16 years ago so my memory is not to be trusted. I have used round seals where square ones were specified, and had good results, but then I am a bit cavalier about these things.

Are you saying that both are for round seals because when you disassembled them they both had round seals? You cannot depend on that of course, since who knows what evil SOB (like me!) substituted round for square to get things working. grinning smiley

If you are certain about that, then I stand corrected. It wouldn't be the first time I got some detail incorrect. sad smiley

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

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Bpt70gt Avatar
Bpt70gt Brian T
Westmoreland, NH, USA   USA
Vance, in the interest of safety and I'm not criticizing you but every 0-ring manufacturer has a chemical compatibility chart in their technical library. Easily referenced online. Viton is worse than using Buna-n compounds. Viton is rated NOT RECOMMENDED//NOT ACCEPTABLE depending on the technical manual referenced. Specifically referencing AUTOMOBLE///AIRCRAFT applications Viton should not be used. It has the lowest compatibility rating with brake fluids. Good for fuels but not brake fluids. I've written a non-published technical article on these PDWA units. I've done weeks of research, O-rings appear to be simple devices but there is quite a bit of engineered science in them. Information available in the technical libraries of the manufacturers. Just want people to be safe here. I do a lot of research as a retired mechanical/structural engineer and a fair amount of experience with devices utilizing O-rings. Brakes are pretty important so please be careful. EPDM has an "EXCELLANT" rating.
Regards, Brian

Krom Avatar
Krom Paul K
San Rafael, CA, USA   USA
In reply to # 1509091 by Tonyfixit I think the key thing is to understand what the PDWA does, and understand the potential nuisance and potential danger of having a PDWA in less than perfect condition.

Personally, brakes are not something I want to fail on me (even if they fail while the car is in the garage!)

This is why my PDWA shuttle has been replaced with a loctited, threaded plug, and the warning light switch will soon be replaced with a low fluid level warning switch

Tony- I'm often confused, but it sounds as though you are talking about disabling the PDWA. If so, aren't you concerned that a bad wheel cylinder or caliper leak might take down your braking front and rear at the same time? Just trying to understand.
Thx,
PK

poolboy Avatar
poolboy Ken D
Sandy Hook, MS, USA   USA
The brake fluid reservoir on the brake master cylinder is divided into 2 compartments.
If a leak in the front brakes were to drain all its fluid reserve, there would still be fluid for the rear brakes..and vice versa.
You might discover the circumstance the hard way without the PDWA, however.



Edited 1 time(s). Last edit at 2018-01-23 05:20 PM by poolboy.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
ALL the PDWA does is to light a light on the dashboard AFTER you have pressed the brake pedal and found that one circuit in you braking system is not working. Belive me, you will something has happened even witout looking at the light!

A fuid level sensor will tell you the same thing BUT if your braking fluid has leaked while the car has been parked (as is often the case with a small leak) the light will light BEFORE you drive away.

We also see form this thread how difficult it is to service/rebuild the PDWA unit. I belive a 40+ year oil braking system component or one that is serviced with questionable seals that may be prone to fail, may be worse than no dashboard light lighter at all.

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1509169 by Bpt70gt Vance, in the interest of safety and I'm not criticizing you but every 0-ring manufacturer has a chemical compatibility chart in their technical library. Easily referenced online. Viton is worse than using Buna-n compounds. Viton is rated NOT RECOMMENDED//NOT ACCEPTABLE depending on the technical manual referenced. Specifically referencing AUTOMOBLE///AIRCRAFT applications Viton should not be used. It has the lowest compatibility rating with brake fluids. Good for fuels but not brake fluids. I've written a non-published technical article on these PDWA units. I've done weeks of research, O-rings appear to be simple devices but there is quite a bit of engineered science in them. Information available in the technical libraries of the manufacturers. Just want people to be safe here. I do a lot of research as a retired mechanical/structural engineer and a fair amount of experience with devices utilizing O-rings. Brakes are pretty important so please be careful. EPDM has an "EXCELLANT" rating.
Regards, Brian

Brian:

I did as you suggested, and indeed there are quite a few ratings out there that show Viton as marginal. But some show it as good or excellent with Glycol brake fluids too. Very confusing. The big thing I noticed is that all the ratings for brake fluids are for glycol based brake fluids. I did not find any for DOT5 silicone brake fluids. I did find ratings for silicone oils, which showed Viton as excellent. So there is no (?) data for DOT 5 out there that I could find.

EPDM is out there in the various spec sheets, and is rated excellent for DOT3 and DOT4. Once again could not find anything on DOT5, but I am guessing that EPDM is forwards compatible with DOT5 or it would never have received a DOT rating. But that is a guess.

Well, I ran Viton in my TR6 for many years with DOT5, and I have a few Viton in my TR8 with DOT5. <sigh> Hopefully I will fall apart before the O-rings do.

Thanks,

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

Bpt70gt Avatar
Bpt70gt Brian T
Westmoreland, NH, USA   USA
Vance, glad you took the time to investigate. Just want us Triumph folks to be safe as possible.

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