Commander Hot rear brake

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paulwolf
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Commander Hot rear brake

Post by paulwolf » Mon Jul 22, 2019 7:00 pm

My rear brake has always ran hot,i have had the pistons out of the caliper and cleaned them and there is no corrosion on them and the wheel turns freely.I have just been out for a 10 mile run to test the temperature of the caliper & disc with a inferred thermo heat test run and i am getting a reading of 50c on the caliper & 45c on the disc.Is this normal ?.Thanks Paul

Clive603
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Re: Commander Hot rear brake

Post by Clive603 » Mon Jul 22, 2019 10:50 pm

I presume the pedal is returning fully and all the link pushrod adjustments are set correctly.

Both my Commanders have liked a bit of slack in the system.

When you pulled the pistons out did you look for corrosion / deposits in the seal grooves. Pretty much anything in there will make the pistons tight. Yamaha caliper bodies are notorious for such corrosion. I've been inside at least 20 calipers of this type and all needed serious cleaning in the grooves to work properly again.

Might also be the master cylinder not fully backing off. Had similar on a BMW decades ago that turned out to be early stage indication of a master cylinder rebuild being needed.

Clive

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Richard Negus
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Re: Commander Hot rear brake

Post by Richard Negus » Tue Jul 23, 2019 5:56 pm

It's always the master cylinder's fault! Or, more correctly, the owner's fault for not changing the brake fluid frequently enough.
Old fluid congeals to a sort of wax in the bottom of the reservoir or, in the case of the rear brake, in the black plastic elbow connecting the cylinder to the reservoir. This wax then blocks the feed hole, stopping fluid returning to the reservoir when the caliper heats up.
When testing customer F1's of unknown maintenance, I usually had an 11 mm spanner in my pocket to release the bleed nipple and release the pressure.
If not doing this, the inevitable result was warped rear disc.

The front brake can also suffer the same problem, as Wayne found when riding his F1 at Mallory. The wheel suddenly locked and he kissed the tarmac.

If your brake fluid has turned brown, you should have changed it years ago!

I have cleaned out blocked feed holes using very fine copper wire. Tricky when your eyesight is below par and your hands are a little shaky.
R.
Slower slower, no faster faster - the joys of old fogey mode to hooligan mode at the flick of a switch

paulwolf
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Re: Commander Hot rear brake

Post by paulwolf » Wed Jul 24, 2019 6:27 pm

Hi Richard,Thanks for the reply,I do change the Dot4 every couple of years but the previous owner may not have,I will now remove and clean out the master cylinder,Thanks Paul

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Richard Negus
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Re: Commander Hot rear brake

Post by Richard Negus » Wed Jul 24, 2019 8:41 pm

Odd how the Brembo master cylinders of the IP2 and Classic never seemed to suffer the same blockage, but the Yamaha ones do.
Maybe the feed hole in the Yamaha items is smaller than the Brembo.
R.
Slower slower, no faster faster - the joys of old fogey mode to hooligan mode at the flick of a switch

Charles Wilson
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Re: Commander Hot rear brake

Post by Charles Wilson » Thu Jul 25, 2019 8:59 pm

1. For general Information in regards to our favorite Norton motorcycles (Note: I don't speak Brembo), what is the Word on silicone based brake fluid?

2. Back in the Daze, when I ran my RE-5 into the dirt, I disassembled the front brake upon purchase and spent the next 3 months in Rehab over what I saw. It had been on a DOT-3 (American Classification) diet and never appeared to have had a change. The pistons were pitted and the label "brown" didn't really describe the color. There was a fine slurry of something floating in the liquid. DOT-3, of course, absorbs water. I felt lucky to get it home.

I bought some appropriate braided steel lines and used DOT-5. Silicone based, no water absorbed. Great stuff.

Is such approved for the NORTON? Anyone with experience with this?

Thnx,

Charlie

Clive603
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Re: Commander Hot rear brake

Post by Clive603 » Sat Jul 27, 2019 1:39 am

The big advantage of DOT 5 silicon brake fluid is said to be that it is not hydroscopic so it doesn't absorb water. Because of this it is claimed to be ideal for vehicles that are rarely used because the properties won't change in storage. Allegedly it doesn't degrade at all so can last "forever". Also said to be used on US military vehicles for this reason so they can go straight from storage, or overseas transport, into action.

All true up to a point but I wouldn't touch the stuff with a barge, let alone the pole.

The big practical complaint is spongey levers and pedals. Why? Entrained water from condensation and systems breathing. As the fluid isn't hydroscopic the water isn't actively absorbed and bound, probably electrochemically, into the fluid. It just floats around loose. So not only is the the wet boiling point dangerously low but you also have the normal vapour pressure effects of water to deal with. At normal temperatures there is always a little bit of water vapour floating around if its not bound up as in conventional brake fluids hence the spongey tendencies. Typical dry boiling point of DOT 5 is up around 260°C but wet boiling point at the standard 3 % concentration used for measurement is down around 120°C or less. For Glycol based DOT 5.1 the specification figures are 260°C and 180°C whilst plain old DOT 4 specifies 230°C and 155°C respectively. Many, both DOT 5. and DOT 4, are rather better.

If you are going to use silicon fluids the system must be totally dry before putting it in and totally sealed with an elastomeric cap "gasket" or floating piston covering the surface of the fluid with the actual breather on the other side so the air, and condensation, can't get at the fluid. If you are going to go to that much trouble you might as well stay with the standard stuff because that won't go off either. Systems designed for DOT 5 are properly sealed so its not an issue.

To quote TRW
"IMPORTANT: Never mix TRW DOT 5 brake fluid with conventional glycol-based brake fluids with DOT 3, 4 or 5.1 specifications.
Danger!
Even DOT 5 silicone brake fluid absorbs moisture from the air, but does not bind it. Therefore DOT 5 silicone must be changed regularly, like other brake fluids."

Generally ABS systems don't like it either.

Clive

paulwolf
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Re: Commander Hot rear brake

Post by paulwolf » Wed Jul 31, 2019 9:31 am

Top man Richard,you were spot on the 15 tho hole was blocked and the rear brake is now running a lot cooler.On the subject of silicon dot 5, a few years ago i restored an 1969 Aston Martin DBS and used Dot 5.The first road test i did the brakes jammed on and would`nt release and on investigation i found that the pistons in the servos were sticking on and the fact was that Dot 5 has not got the same lubrication qualities as Dot 4.After i flushed out the Dot 5 and replaced it with Dot 4 i never again had a problem.I also had the same problem with Dot 5 in my E type and when changed to Dot 4 all was OK.I wish i still had the DBS & E Type.Cheers Paul

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