TR6 Brake Bleeding

[Gliderman8]

Not to change the content of this thread but I do have a related question…..
I have never seen my brake light illuminate on the dash with the ignition “ON” and engine not running. I know bulb is good because the handbrake switch illuminates the bulb.
Suggestions?

 

[poolboy]

Unplug the wire from the PDWA switch and ground the wire to the frame or any good ground with the ignition switch in the ON position.....the BRAKE warning lamp should be receiving the full 12 volts and be relatively brighter compared to the ordinary 'bulb test' condition.
If there is no illumination, you might want to check out Dan's troubleshooting schematic.

'

 

[Gliderman8]

Unplug the wire from the PDWA switch and ground the wire to the frame or any good ground with the ignition switch in the ON position.....the BRAKE warning lamp should be receiving the full 12 volts and be relatively brighter compared to the ordinary 'bulb test' condition.
If there is no illumination, you might want to check out Dan's troubleshooting schematic.

'

Thanks for the suggestion. Will give it a try.

 

[DrEntropy]

Could also be a higher wattage bulb so the lower voltage in the "test" position wouldn't have enough "oomph" (technical electrical term ) to produce a visible glow?

 

[Gliderman8]

Could also be a higher wattage bulb so the lower voltage in the "test" position wouldn't have enough "oomph" (technical electrical term ) to produce a visible glow?

I believe that there’s an LED bulb in the brake light position so the lower voltage should light it up. I’m going to do as Ken suggested and ground the wire and then I’ll know more.

 

[Govtslug]

Still working on my brakes. I re-bled both rear brakes and used the ’slam on the pedal’ method with the bleeder open. No change in pedal feel so I assume the valve didn’t move. I get very little brake fluid coming out of the rear compared to the front. Should I be trying the slam method on the front bleeders?

 

[Govtslug]

One more thing. I removed the nylon switch on the top of the PDWA and it looked dry Inside. It fits into a very tiny hole in the PWDA, I couldn’t see any valve in it. What happens if I remove the large plastic nut on the front of the PDWA? Will that open the brake system and leak fluid? Is that where I will see this valve that has moved off center?

 

[Tybalt]

First off, picture credits to Buckeye Triumph's Tech Pages.

Please note that if you do not have the PDWA switch connected, all the talk about using the warning light to determine shuttle piston centering is moot. No connection, no light.

With these cars, when the PDWA is in place, bleeding the brakes will shift the piston and it must be recentered.

The center volume of the PDWA should be dry unless one of the PDWA seals is leaking. This means that you can remove the switch without introducing air into the system. If you pull the swicth and see brake fluid, it is leaking and you need to replace the PDWA piston seals.

There were two styles of shuttle pistons used on the TR6 but with yours being a 1970, it should be the later style. The middle portion of the piston is much smaller in diameter than the rest of the piston body. There are ramps on either side of the small diameter center section of the piston. That is where the pin from the switch would sit under normal operating conditions. If pressure is lost in one of the two brake circuits the shuttle piston is shifted which in turn pushes the pin on the switch up as it rides up the ramp. If connected, that will trigger the warning light under normal driving conditions.

If the PDWA shuttle piston is shifted forward, then you need to open a bleeder at the rear. If the PDWA piston is shifted rearward, then you need to open a bleeder on the front. (IIRC)

I have heard of people using an awl or ice pick to manually shift the piston but I have always shifted the piston back to it normal "neutral" position by hydraulic means by having a helper open a bleed valve and slowly pushing the pedal until the piston is centered, then have the helper close the bleed valve. When connected, the piston is centered when both the oil pressure light and the PDWA light glow dimly. If the PDWA light is bright and the oil pressure light doesn't glow, then the piston is not centered. The bleeding and PDWA piston centering is described in section 70.25.02 of the Bentley manual if you have one of those. If not, you should get one, it is essentially a reprint of the factory shop manual.

If the switch is not connected, then you are looking at two helpers. One to crack open the bleed valve and one that knows what they are looking for to be watching the piston as it goes to the centered position.

Have you pulled the PDWA switch to confirm one way or the other if the shuttle piston is centered or not? If it is not centered is it offset toward the front of the car (rear brake circuit) or toward the rear of the car (front brake circuit)? Remember that the circuit to bleed for recentering the shuttle piston is the circuit opposite of that toward which the shuttle piston is offset. Is that well where the switch sits wet or dry? If wet, time to do something with the PDWA (replace, rebuild or bypass). If the well is dry and the shuttle piston not centered, try using the awl or ice pick technique to center the shuttle piston. My recommendation is that you use the slow push and bleed the circuit method as opposed to the slam method. The proverbial "bigger hammer" is not necessarily the answer.

Your latest post wasn't up when I first jumped on. If you remove the large plug at the end of the PDWA bore, it will leak brake fluid. You need to use a bright light shined down in the hole where the PDWA switch pin goes in order to have a prayer of seeing that small diameter "neutral" section of the shuttle piston. It is that small diameter "neutral" section that indicates the shuttle piston is centered. If you see any sort of taper, the shuttle piston is not centered.

 

[poolboy]

It’s installed but the wire isn’t connected. How can tell if there is a problem with it?

Really unless he has the switch connected to the electrical wire, it doesn't matter if the shuttle is centered or not.
The only thing that actually matters about the PDWA in this situation is if there is a leak around the plastic switch.
Govtslug mentioned a plastic nut on the front of the PDWA....if it's plastic someone had been messing with the PDWA..it's a steel hex head plug that resembles a 'bolt'...the only plastic would be the electrical switch.
And btw, there is no 'valve' in the PDWA, there is a shuttle but it;s not a valve that opens and closes to allow the passage of fluid...As long as the shuttle seals or O-rings have not perished, there will be no passage of fluid from the front brake hydraulic to the rear brake hydraulics and vice versa.....even when the shuttle is off center.
I really think you need to turn your attention elsewhere if there is no leak around the plastic plug.

 

[Deleted member 12064]

This is what a leaking PDWA switch looks like.

 

[Govtslug]

Well, I’m stumped. My switch is dry which means the PWDA o-rings are probably ok. I re-bled all four wheels, no change. No sponginess in the pedal but it doesn’t get resistance until near the floor. I get fluid at all 4 wheels. But I’m guessing I still don’t have rear brakes. I’m not losing fluid anywhere.

when I bled the brakes I tried a nice gentle push on the pedal A few times at each wheel, no change. then I tried a hard pump at each wheel when the bleeder was open. No change. And all this started just from my original brake bleed! Based on all the great feedback so far it’s probably a waste of time to tear apart the PDWA and install new seals. Is it possible the master’s seals blew out when I bled the brakes?

govtslug

 

[poolboy]

I don't know if you mentioned this yet, but is there any chance the flexible sections of the brake lines are expamding when you pressure up with the brake pedal ?

 

[Govtslug]

good question but i don’t think so. The brake lines are only 5 years old. And the pedal is firm, just not until it almost reaches the floor.

 

[poolboy]

How many clicks of the handbrake can you hear before the rear brakes lock up ?
And once they do lock, leave them locked and see if the brake pedal travel has lessened .

 

[Tybalt]

Well, I’m stumped. My switch is dry which means the PWDA o-rings are probably ok. I re-bled all four wheels, no change. No sponginess in the pedal but it doesn’t get resistance until near the floor. I get fluid at all 4 wheels. But I’m guessing I still don’t have rear brakes. I’m not losing fluid anywhere.

when I bled the brakes I tried a nice gentle push on the pedal A few times at each wheel, no change. then I tried a hard pump at each wheel when the bleeder was open. No change. And all this started just from my original brake bleed! Based on all the great feedback so far it’s probably a waste of time to tear apart the PDWA and install new seals. Is it possible the master’s seals blew out when I bled the brakes?

govtslug

It's possible, it is not unheard of for these master cylinders to bypass internally. With all the bleeders closed, does the pedal firm up and rise if you pump the brakes multiple times? If so, that is a typical sign of internal bypassing at the master cylinder if you are not seeing leaks anywhere. Just keep in mind that it is also a typically sign that you still have air in the lines as well. If you feel reasonably confident that you did indeed get the air out of the lines and that there are no leaks, then the next suspect would be the master cylinder.

 

[Govtslug]

I‘m pretty confident I’ve got all the air out of the system. No sponginess, the pedal holds when it stops. And if I pump the brakes to build pressure, there’s no change in the brake feel.

the handbrake has always been weak. It barely holds the car. But it’s always been that way. Related?

 

[poolboy]

I‘m pretty confident I’ve got all the air out of the system. No sponginess, the pedal holds when it stops. And if I pump the brakes to build pressure, there’s no change in the brake feel.

the handbrake has always been weak. It barely holds the car. But it’s always been that way. Related?

Do that test. Let's see what happens.

 

[Tybalt]

I‘m pretty confident I’ve got all the air out of the system. No sponginess, the pedal holds when it stops. And if I pump the brakes to build pressure, there’s no change in the brake feel.

the handbrake has always been weak. It barely holds the car. But it’s always been that way. Related?

OK, let's take a step back since the handbrake works reasonably well on these cars when everything is adjusted. Here are some questions to answer:

1) How were your brakes before you started this bleeding exercise, were they working and you were shooting for a fluid flushing (what it sounds like from post #1) or was there a definite braking problem that initiated this exercise? If there was a braking problem that initiated this exercise, what was it?

2) Have you looked under the MC/servo interface for any evidence of brake fluid leakage there?

3) How is your rear brake shoe adjustment?

4) Reiterating what poolboy said, how many clicks to lock the rear brakes and once locked, does that change anything? Are the rear brake cables properly adjusted? Brake shoe adjustment and brake cable adjustment complement each other, if one is out of whack, things are somewhat compromised at the back.

5) You indicate that you have a "long" pedal. When you pump the brake pedal, I realize that once it has pressure, it has pressure but does pumping it raise the pedal to shorten up the pedal travel? Other than the obvious changes in the MC reservoir fluid level from the bleeding process itself, has that fluid level changed as you have pumped the pedal?

6) Have you taken a look at the brake pedal, the servo pushrod (TR PN 516891) and the clevis pin that attach to the brake pedal to check for wear (hole elongation on the pushrod and/or brake pedal, and wear on the diameter of the clevis pin)? Excessive wear on these items can cause a long pedal thanks to pedal lever effect on relative travel between the pedal pad and the servo push rod (~a 4:1 ratio). I think this is probably the unlikeliest of the bunch, but have seen it before. While the clevis pin is readily available, it looks like the pushrod is NLS as a serviceable part from the usual supplier suspects both in the US and the UK. I have seen pushrods repaired by welding washers to them and using a longer clevis pin but note that will probably require dismantling of the servo. There are various hydraulic houses around that could probably do that for you. My handy dandy big book of almost all things Girling does not list the servo so it evidently came from a different source that I cannot identify.

7) Something else I have seen cause a long pedal is if the front wheel bearings are not properly adjusted. If on the loose side, the pads in contact with the rotors knock the caliper pistons back into the calipers and it takes a pump or two to get the caliper pistons out to where the pads bite. If you had the front hubs off during this exercise, that is something to consider.

8) Do you have the Bentley manual? If not, you should seriously consider rounding one up.

 

[Govtslug]

I did the flush just because the fluid was looking pretty dark. No other problems. The brakes were working fine just before the flush and I had a much less travel in the pedal before the brakes engaged.

I pulled up the handbrake, 7 or 8 clicks until it stops. With the handbrake on I get no different feel in the pedal. And pumping the pedal makes no difference in the pedal travel. That’s why I think I don’t have air in the system (plus no spongy pedal). Could it still be the master? No leaks around the master or servo.

 

[poolboy]

3 or 4 clicks would be better....once you get the pedal situation straightened out, you may want to take some slack out of the cables....And to make the E brake hold better, try full depressing the brake pedal, then pull up on the handbrake before lifting your foot off the brake pedal.
Back to the subject...As in Tybalt's #6, I was also thinking that the servo pushrod might need adjusting...but that's not something that just goes out of adjustment PLUS I don't see mention of you fooling with the servo in the first place, sooo ....closely related would be a problem within the master cylinder...maybe an internal seal is getting bypassed now.