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post #1 of 9 (permalink) Old 09-08-2019, 05:53 PM Thread Starter
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Rear brake conundrum.

Hoping for some advise .. I've just rebuilt my rear brake caliper after it had seized , smoked the pads, melted the brake line where it entered the caliper. I installed new pads, brake line and seals. Using a Mitivac I drained the old fluid and added fresh but for the life of me I can't get any hydraulic pressure under the pedal. It almost feel as though there is nothing in the master cylinder but I know I was drawing the fluid from the reservoir to the bleed nipple. If I spin the rear wheel I can hear the pads dragging and can see that they are touching the rotor. Another weird thing is that I can't get the rear brake light to turn on. The front works, signals are fine, headlights etc., all the fuses are good. Is the switch activated by pressure ? So, before I pull the caliper off the rotor again to check for obvious owner errors has anyone run into issues like this.
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post #2 of 9 (permalink) Old 09-08-2019, 09:35 PM
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I cannot speak on the light.
Assuming you have brake fluid in the reservoir, in the line and in the caliper then you most likely have air in the system and you must get it out. Their are various ways to get it out. I connect a clear hose to the caliper nipple and submerged the other end in brake oil in a jar. With the nipple open pump the brake pedal and you should see oil running out and down into the jar if you look very closely you will see tiny bubbles in the oil ..... keep adding oil to the reservoir and keep pumping the brake until the flow of bubbles is near non existent you should now feel resistance on the pedal but you are not done yet. Tighten the nipple and remove the tube. Keep weight on the brake pedal then every 10 minutes burb the nipple (quickly open and close the nipple) do this until you are satisfied with the results.

TTP Tune#3, NH Toga's.

I'm no Gynecologist but hey I'll take a look.
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post #3 of 9 (permalink) Old 09-08-2019, 10:44 PM
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In the T100 the rear brake light is operated by a hydraulic pressure switch (Part number T2023120). It's located on top of the master cylinder and doubles as a banjo bolt for the hose connection.
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post #4 of 9 (permalink) Old 09-09-2019, 06:26 AM Thread Starter
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Quote:
Originally Posted by Forchetto View Post
In the T100 the rear brake light is operated by a hydraulic pressure switch (Part number T2023120). It's located on top of the master cylinder and doubles as a banjo bolt for the hose connection.
Thanks, that makes me wonder if maybe I have a pocket of air trapped in the master cylinder ....
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post #5 of 9 (permalink) Old 09-09-2019, 10:11 AM
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You can try this: Get the reservoir off its mount and have a helper hold it and watch it. Lower the fluid level in the reservoir to near the bottom and put the lid on loosely so it's covered but vented. Gently push the brake pistons in to force fluid up the line into the reservoir. If you're lucky, any stuck air will go up with it. Some tapping on the caliper might help and won't hurt.

Remember that air wants to go up, so it's best to push as much of it as possible up the brake line before you start pulling it out at the caliper end. Keep the caliper unmounted so you can position it to your best advantage.

You can use a syringe with tubing to push brake fluid into the caliper.

I do the above before I start bleeding with the Mity-Vac, so I start with a system which hopefully doesn't have too much air, because it is indeed tedious to get it all out.

When bleeding with the Mity-Vac, have a helper watch the fluid level and add fluid to ensure that no air gets in at that end, or you're wasting your time and brake fluid.

It's a messy process for us amateurs, but you will eventually get the air out, and the Mity-Vac is the easiest way to do it. Once you've done it once or twice, you'll have a better feel for how to go about it.

Finally, about the light. Yes, it's a pressure switch in the banjo bolt. Don't worry about it until you get the brake working. No pressure > no light. They are known to go bad and get stuck in the on position--dangerous--but you have no way of knowing that until you have a working brake. If it ever does get stuck on, disconnect it; your front brake light switch will take care of things until you replace it.
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Last edited by Baltobonneville; 09-09-2019 at 10:15 AM.
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post #6 of 9 (permalink) Old 09-11-2019, 07:40 PM
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Hey Dave! Did you finish bleeding it? How did you get it done?

Marty
2005 Bonneville Blue 790cc, AI removed, Staintunes RC, no snorkel, inlet enlarged, 118/40/NBZT needles/1 shim/3 turns, Ikon 7610s, Ricor Intiminators, Barnett green clutch springs, Michelin Pilot Activs, D9 gauge panel, tachometer.
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post #7 of 9 (permalink) Old 09-14-2019, 04:55 PM Thread Starter
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Brilliant advice, worked like a charm ! I had to use a magnet to pull the pistons out of the caliper body but once I'd forced them back in we got a just enough resistance under the pedal to push them out and little, we repeated that, using a piece of wood to stop the pistons coming all the way out, until it was working correctly. Since it feels right under foot I didn't bother with the Mighty Vac. Just got back from a quick spin around the neighborhood, all seems good with the world. Forcing the air up .. who'd have thunk it ! Thanks again for the advise, invaluable as always.
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post #8 of 9 (permalink) Old 09-15-2019, 09:09 AM
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Does the brake light switch work now?

Marty
2005 Bonneville Blue 790cc, AI removed, Staintunes RC, no snorkel, inlet enlarged, 118/40/NBZT needles/1 shim/3 turns, Ikon 7610s, Ricor Intiminators, Barnett green clutch springs, Michelin Pilot Activs, D9 gauge panel, tachometer.
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post #9 of 9 (permalink) Old 09-15-2019, 04:28 PM Thread Starter
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It does indeed, correct on all counts so far .. got out into the world for a longer ride today .. no leaks, brakes braking, lights blinking appropriately ... except the horn .. now that's another story !
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