2014 4RT poor rear brake

[brucey]

Still can’t lock the back wheel on tarmac. I have:

Replaced pads for Apico items

Bled system and replaced fluid with fresh Dot 4 (nice place to put the reservoir!)

Rubbed disc with wet & dry on a flat surface plate and cleaned with carb cleaner. 

Pedal seems there and doesn’t pump up but brake is no where as good as my old gas gas (or even older Tiger Cub come to think of it!)

Is it new master cylinder or different/longer aftermarket brake pedal time?

Any advice appreciated 

 

Bruce

 

Edited June 13, 2018 by brucey
grammer and spelling corrections (Original done on Iphone!)

[jrsunt]

Bent disc? Check the spokes of the disc for cracks/trueness

[brucey]

1 hour ago, jrsunt said:

Bent disc? Check the spokes of the disc for cracks/trueness

Thanks for the suggestion.

Disc looks o.k.  I rubbed both sides on a sheet of 360 grit wet and dry on a surface plate (Ex Toolmaker!).  However, it is a little bit scored (I rubbed the worst bits off)

[jimmyl]

Presume pistons are free in Calliper.

what pads have you got in?

have you tried get disc pads  hot through short sharp braking then chucking water on them?

 

[brucey]

1 hour ago, jimmyl said:

Presume pistons are free in Calliper.

what pads have you got in?

have you tried get disc pads  hot through short sharp braking then chucking water on them?

 

Yes, I cycled both pistons in the caliper by clamping one and using the lever to push the other one out.  I then cleaned the bit sticking out and gave it a quick wipe with brake fluid.  Both pistons move easily when the brake is applied.

I put new Gold Fren Ceramic Carbon trials pads in.

I haven't ridden the bike in anger yet, just up and down the road briefly.  I will try the 'get it hot and dowse it with water'  thing if I can do it without upsetting the neighbors! :-)

Nothing to do with the rear brake but I also fitted an Apico clutch kit (dimpled steel discs and new friction plates) to try and stop the irritating clutch drag.  This included putting 1/2lt of expensive HTX 740 gear oil in.  2 of the new Apico friction plates looked slightly different from the rest so I put these in the first and last positions.  The old friction plates were approaching their wear limits.  First impressions are there is definitely less drag, especially when warm (I'm anticipating it will improve further when 'bedded in a bit more).  I also think the new clutch and/or oil have made the operation significantly less fierce which can only be a good thing.  

Thanks for the suggestions.

Are poor rear brakes common on 4RT's?

 

Bruce.

Edited June 13, 2018 by brucey
correcting typo's

[jimmyl]

5 hours ago, Nebulous said:

  All this buckets of water and short , sharp rot - never heard such twaddle.     

 

I did think the same but Adam raga does as part of his bike prep.

i find the sintered pads can be poor when dry and hot - seem to glaze. A bit of water seems to improve the braking effect .

i deglaze my pads after every ride as well 

[imexian]

Use galfer red pads, and drag rear brake to get hot then pour cold water on them, it’s not twaddle, I and many others have done it for years! But what would I know from a new member that obviously knows everything!

the new fren are a terrible pad. 

Edited June 14, 2018 by imexian

[brucey]

6 hours ago, Nebulous said:

Surprised you didn’t go for a new disc - to go with those trick-pads.   Go and buy the trickest , most space-age new one you can find.  Then bed them in properly - by riding the thing , and adjusting as necessary.     All this buckets of water and short , sharp rot - never heard such twaddle.     Once you get it right - then pat yourself on the back with a new , fancy , forged pedal.

You will like the Apico dimpled clutch-plates.  They give a nice , more progressive feel to the action. The expensive oil is an essential part of the lessened-drag process. Something to do with molecular-sizing , and more efficient dispersal thereof.

 

Are they trick pads?  Seem like a pretty common OEM replacement to me?

I’m not sure a replacement expensive disc would make much difference on a trials bike if the original one is in reasonable condition. 

But a nice expensive red anodised brake pedal?. Now your talking?

I guess I need to give it a proper test to let everything bed in but I’m sure a new bike wouldn’t have this problem. 

[brucey]

51 minutes ago, imexian said:

Use galfer red pads, and drag rear brake to get hot then pour cold water on them, it’s not twaddle, I and many others have done it for years! But what would I know from a new member that obviously knows everything!

the new fren are a terrible pad. 

Thanks imexian, food for thought.

It seems like there is basically a lack of friction between the pad and disc (unlike yourself and Nebulous :-) ) 

Also the old pads I replaced look like Fren which would explain why they weren't so good even though they were hardly worn!  I just assumed they were contaminated.

[crashmonkey]

If you've got brake pressure but no bite get the brakes really hot by riding them them dragging then quench rapidly with water -- repeat 2 to 3 times if nessessary.

Will sort it - doing it for years - no warped disks or anything else.

Loads do it.

[jimmyl]

Evidently Raga's mechanic does this as final preparation of Adams bike before every event so not a field trick but part of normal service and preparation - how it works mind is another matter- 

[jrsunt]

Heat them up and cool them down, it might not be the way to treat metal........  But it gives a good brake. Try it. Just riding around the street in 1st gear will generate enough heat, then stick the hose pipe on it.

[jonnyc21]

19 hours ago, brucey said:

...

Are poor rear brakes common on 4RT's?

 

Bruce.

No I would not say poor rear brakes are common on a 4RT.  Both my 07 and my 2017 300RR have great brakes.  One of our other group riders has a standard 2017 4RT that is great brakes, my friends 05 has no issues as well.  Have seen a few 2014 and 2015's at some events with great performance.  

I suspect its just a little ware in time or maybe some other edge case issue.  Heat and the quench cycle worked great on one set of pads on my 07 that gave me a small bit of trouble when I first changed them but they set in quick.

Edited June 14, 2018 by jonnyc21

[baldilocks]

12 hours ago, brucey said:

Thanks imexian, food for thought.

It seems like there is basically a lack of friction between the pad and disc (unlike yourself and Nebulous :-) ) 

Also the old pads I replaced look like Fren which would explain why they weren't so good even though they were hardly worn!  I just assumed they were contaminated.

Red galfers are the best pads ?

[baldilocks]

10 hours ago, Nebulous said:

“Gold Fren Ceramic Carbon”? Was late at night , and it just sounded expensive to me. Thanks for putting me straight.  All that glitters is not Gold I guess.   But whatever the pad’s pedigree - it didn’t really stand a chance of success anyway.  Guess my next question would then be - why install such cheap muck on a 4RT? And then why post on here when it doesn’t work with a scored-disc , that has been prepared with grit?

As for the water-treatment - I would be concerned about quickly cooling any metal parts. Such as the plates of those pads , and especially the caliper itself - when wrapped around a freshly retracted red-hot piston. Not to mention the disc itself.  Any “professionals” doing this in the field- I would point-out that whilst it may be a quick fix - don’t forget that they have a shed-load of new parts to slap-on the bike later.

I’ll respectfully change “Twaddle” to “Inadvisable” - and impractical for long-term integrity and performance.

It works and isn't dangerous in my experience. No different to crossing a stream at the foot of a long descent