TR7 & TR8 Mailing List

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21
Wedge List / Re: Afterthought - Brake Bleeding/Pressure Failure
« Last post by David Massey on April 13, 2018, 05:00:11 PM »
This is just a shot in the dark but perhaps what goes unwritten is that the dealer had a tool to keep the shuttle centered during the bleeding process.  I.E. "Remove the switch, insert tool, bleed brakes, remove tool, reinsert switch."



Another option is using a screw driver to recenter the shuttle.  This may be workable on a TR6 which has a separate PDWA where the switch installs from the top and you can see what you are doing but on the wedge you will be working blind.



The more common practice is to reinstall the switch and slowly bleed the other circuit from the last on bled until the light goes out.



What ever works for you.



 



 



Dave Massey
22
Wedge List / Afterthought - Brake Bleeding/Pressure Failure
« Last post by William Smith on April 13, 2018, 04:34:28 PM »
At the risk of over-thinking, and being my usual anal self, another question entered my mind.If the purpose of the ROM's instruction to remove the pressure switchB  before brake bleeding was to not trigger the brake failure light, that doesn't make sense to me. If unequal brake pressure decenters the shuttle, I would thinkB  that will happen whether or not the pressure switch is removed. If that's theB  case, IB  would also think the failure light would not come on while bleeding the brakes, but would come on as soon as the switch is reinstalled and reconnectedB  as the shuttle would still be uncentered. What am IB  missing here? If anyone has the answer, I'd appreciate knowing.

Thanks from the over-thinking and anal lister,Bill SmithB '80 TR7B '72 TR6B







Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: William Smith <smithw1@optonline.net> Date: 4/12/18  7:33 PM  (GMT-05:00) To: fosmith@aol.com, jroe44@gmail.com, Wayne@last-chance-garage.com, jibrooks@live.com Cc: tr8@mercury.lcs.mit.edu Subject: Re:  Brake Bleeding/Pressure Failure Switch

Thanks guys.B  Sounds like the consensus is that there is no need to remove the switch.

B Fred, regarding the shuttle in the master cylinder, I assume that the shuttle is a P.D.W.A. shuttle which the ROM says is "self-centering". On my TR6, the P.D.W.A is a separate assembly that is not self-centering. If it is triggered by either a failure while in operation or while bleeding, it has to be re-centered manually by opening a bleed screw on the "opposite" brake circuit and gently applying the brake pedal - a real PIA.

Again, I appreciate all the input and will try bleeding without removing the switch.B  Keeping my fingers crossed,

Bill Smith'80 TR7 DHCB '72 TR6B



Sent from my Verizon, Samsung Galaxy smartphone

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23
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by William Smith on April 12, 2018, 07:34:12 PM »
Thanks guys.B  Sounds like the consensus is that there is no need to remove the switch.

B Fred, regarding the shuttle in the master cylinder, I assume that the shuttle is a P.D.W.A. shuttle which the ROM says is "self-centering". On my TR6, the P.D.W.A is a separate assembly that is not self-centering. If it is triggered by either a failure while in operation or while bleeding, it has to be re-centered manually by opening a bleed screw on the "opposite" brake circuit and gently applying the brake pedal - a real PIA.

Again, I appreciate all the input and will try bleeding without removing the switch.B  Keeping my fingers crossed,

Bill Smith'80 TR7 DHCB '72 TR6B



Sent from my Verizon, Samsung Galaxy smartphone

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24
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by Mark Elbers on April 12, 2018, 06:40:01 PM »
Additional suggestion:  consider  having a spare switch handy,  many are

original and as mentioned the aged plastic may break off.  Sometimes on the

threaded part but my experience is more with damage at the wiring plug end.



I believe TR7 and TR8 also use different switches to match the different plugs

in the wiring harness.







Cheers





Mark Elbers
25
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by "Philip Johnstone" on April 12, 2018, 06:38:05 PM »
If the shuttle does NOT move while bleeding then chances are that the shuttle

has seized (commonly with corrosion) and the brake failure warning light is

inoperable.



Maybe it is time to carefully inspect and rebuild the master cylinder !



The Rimmers rebuild kit (https://rimmerbros.com/Item--i-GRK1004 ) shows the 2

x O rings in the shuttle are included.



>

 The rationale is that you will decentralize the shuttle that operates the

switch and the brake warning light will come on after bleeding. To remove the

switch, merely unscrew it from the bottom of the master. It won't leak as the

switch is not in contact with the fluid. If it does, the shuttle seals are bad

and you need a new master.

>
26
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by Jack Brooks on April 12, 2018, 11:09:52 AM »
I've never done this when bleeding the brakes either.



Jack
27
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by fosmith@aol.com on April 12, 2018, 09:45:29 AM »
The clips are for attaching the harness connection.  The switch screws into the body of the m/c.  It can be removed using an open end wrench, I don't recall the size.  The switch is made from a white, nylon like material which is somewhat soft so go easy.  BTW, I've bled mine many times without removing the switch with no problems.  However, that may be because the shuttle in the m/c is seized and can't trigger the switch...  ???  



Fred
28
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by John Roe on April 12, 2018, 09:25:24 AM »
William,

 We just did this on my TR eight and I would imagine that your pressure

switch is similar. The housing for the switch is made of plastic and has

small clips that hold the clip in place. The plastic becomes brittle

overtime and the clips are easy to break off. Ask me how I know...



John
29
Wedge List / Re: Brake Bleeding/Pressure Failure Switch
« Last post by Wayne@Last-Chance-Garage.com on April 12, 2018, 09:21:36 AM »
FWIW, I've never done this and have not had any problems with the brake

warning indicator.



The rationale is thatb you will decentralize the shuttle that operates the

switch and the brake warning light will come on after bleeding. To remove the

switch, merely unscrew it from the bottom of the master. It won't leak as the

switch is not in contact with the fluid. If it does, the shuttle seals are bad

and you need a new master.



Wayne



SentB fromB myB BlackBerryB 10B smartphone.

B  Original Message B
30
Wedge List / Brake Bleeding/Pressure Failure Switch
« Last post by William Smith on April 12, 2018, 09:15:37 AM »
I'm in the process of replacing the rear wheel brake cylinders in my '80 Tr7 DHC and will need to bleed the system.B  The ROM says to remove the pressure failure switch from the underside of the master cylinder before bleeding and keeping it off until the bleeding is completed.My questions are:

1. Why does it have to be removed,

2. Won't the brake fluid in the master cylinder leak out if the switch is removed, and

3. How do you remove and reinstall it? Is it screwed in? Pushed in? Other?B  What kind of tool is needed?B  The ROM doesn't give this info.

Thanks in advance.

Bill SmithB '80 TR7 DHCB '72 TR6B

Sent from my Verizon, Samsung Galaxy smartphone

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