Loss of rear brake on 2021 T7 ?

[Ray Ride4life]

6 hours ago, RIDER GUIDER said:

I just upped the grade of the fluid

Mee too, i went for the DOT4 racing. I did it also with my Crosstourer, both rears went missing on a serpentine road.

[john_aero]

Had similar issues on my old ktm 950 adv and i changed fluid to a racing fluid

 

cant rember the name but i know was stupidly expensive

 

Also the camel-adv pedal is meant to be a good improvement.

[malcolmzilla]

The return spring behind the clip on is very weak, I had mine drag and lock up.  I disassembled the pedal assembly and wound the spring tighter, lubed the pivot.  I also added and external additional return spring from the lever to a zip tie off the case cover.  Has worked well since.  CamelADV pedal to go on.

[Black99S]

Exhaust mods that route the pipe close behind the master cylinder will add a lot of heat to the rear brake system. 

[concours]

my rear brake has done the "not available once in  a while" Shet too. 

[Windblown]

On 2/17/2023 at 1:38 PM, Black99S said:

Exhaust mods that route the pipe close behind the master cylinder will add a lot of heat to the rear brake system. 

 

That sounds like an off the cuff theory.  Am I wrong? I can see where one might come to that conclusion but I seriously doubt it's a factor.  Heck the stock exhaust runs right next to the entire brake system rather than well above it.  The high pipe only crosses close to rear brake system briefly. 

[Black99S]

57 minutes ago, Windblown said:

 

That sounds like an off the cuff theory.  Am I wrong? I can see where one might come to that conclusion but I seriously doubt it's a factor.  Heck the stock exhaust runs right next to the entire brake system rather than well above it.  The high pipe only crosses close to rear brake system briefly. 

Off the cuff? Heat is transferred via conduction, convection and radiation.

Radiation by the squared law of distance, conduction based on heat conductivity of the materials, and convection by the flow of air. 
Compare the distance between stock exhaust and brake components vs high pipe version with no heat shield. 

Distance gap or a heat shield make a world of difference. 
There is a reason Camel ADV makes a heat shield for the KTM 790/890 shock. 

[Windblown]

9 minutes ago, Black99S said:

Off the cuff? Heat is transferred via conduction, convection and radiation.

Radiation by the squared law of distance, conduction based on heat conductivity of the materials, and convection by the flow of air. 
Compare the distance between stock exhaust and brake components vs high pipe version with no heat shield. 

Distance gap or a heat shield make a world of difference. 
There is a reason Camel ADV makes a heat shield for the KTM 790/890 shock. 

 

So that would be a yes to off the cuff theory....

 

As for the 790 and the Camel heat shield - The exhaust piece in question was the CAT which runs hotter than any other part of the exhaust and it was positioned just in front and below of the shock in an area comparatively free of good airflow in an almost perfect position to transfer heat to the shock.  Plus the shock itself generates a tremendous amount of heat (unlike a rear brake MC).

 

Yet even with all that there were folks with heat shields installed that blew shocks and folks that never installed a heat shield and didn't. Why? Because the shock had issues and runs at a 3-1 leverage ratio so it's working it's ass off. The heat shield was a cool idea in an attempt to help keep the shock cooler. In other words trying to solve a known issue. Different bike, different situation, different parts.  Is there ANY evidence that a high pipe causes the rear MC on a T700 to overheat?  Sounds like the answer is no.

 

I got a box of donuts here that says the answer is "no" too.  

[Black99S]

3 minutes ago, Windblown said:

 

So that would be a yes to off the cuff theory.... 

Nope. Heat is bad, why promote it with an unshielded hot exhaust pipe close to a master cylinder. 

There was a post by a guy with left hand rear brake - he replaced the rear brake master cylinder with one that had a level sight glass - which cracked and bulged from the heat of his high pipe close by.

Feel free to take temperature readings - you can't argue with physics or engineering.

 

[Tenerider]

It's a hypothesis at the moment, unless the high temps are proven by measurements. Then it becomes a theory, which again needs to be proven by testing if this is the reason for a rear brake malfunction/disfunction.

[winddown]

20 hours ago, Windblown said:

 

That sounds like an off the cuff theory.  Am I wrong? I can see where one might come to that conclusion but I seriously doubt it's a factor.  Heck the stock exhaust runs right next to the entire brake system rather than well above it.  The high pipe only crosses close to rear brake system briefly. 

 

I'd like to hear from OP as to whether the pipe runs close myself. 

 

Here's my off the cuff theory.  What about the ABS system?  I'll admit I haven't a clue how it works in detail but I do know it disables the brake when the sensor detects the rear wheel is not rotating.  Has this issue occurred when the ABS was disabled?  Could the ABS unit be having a digital brain fart from time to time?

[Windblown]

31 minutes ago, winddown said:

 

I'd like to hear from OP as to whether the pipe runs close myself. 

 

Here's my off the cuff theory.  What about the ABS system?  I'll admit I haven't a clue how it works in detail but I do know it disables the brake when the sensor detects the rear wheel is not rotating.  Has this issue occurred when the ABS was disabled?  Could the ABS unit be having a digital brain fart from time to time?

 

Based on the ops description I'd guess ABS is not the culprit because he comments that the brake pedal just keeps going down with no braking action.  ABS does not (cannot) bleed off the fluid between the ABS pump and the brake lever. So even if it was activating without the op feeling the feedback pulse at the lever it would not cause the lever to move like it was not connected to anything.

 

My arm chair thinking would be...

1) Air stuck somewhere in the system that only rears it's head occasionally (unlikely)

2) Physically dragging the brake causing fluid to boil in the Brake caliper (Not uncommon but the ops description seems to rule it out)

3) A problem with the brake lever or MC not allowing the MC to bleed fluid back into the reservoir and thereby keeping the brake line pressurized and causing fluid to boil as mentioned above.

 

As others have pointed out already. #3 seems the most likely and #3 could manifest itself as an intermittent issue.  Braking systems can get pretty odd when they get intermittent.  I'm a big fan of checking the physical action of the entire system (Brake lever, MC plunger, piston action at caliper) and giving the entire system a good flush. Any oddball issues after that I reach for a new MC.

 

 

The whole exhaust pipe theory was interesting but unless the op is running a "one of" system different than what is commonly available there is simply no precedent to suspect it. Far too many existing high pipe systems out there with zero issues, with the apparent exception of the one mentioned where where the fellow apparently had a "one of" brake system he had cobbled together.  I believe Occam's razor likely applies on that one.

 

 

 

 

Edited February 28, 2023 by Windblown

[NeilW]

18 minutes ago, Windblown said:

 

Based on the ops description I'd guess ABS is not the culprit because he comments that the brake pedal just keeps going down with no braking action.  ABS does not (cannot) bleed off the fluid between the ABS pump and the brake lever. So even if it was activating without the op feeling the feedback pulse at the lever it would not cause the lever to move like it was not connected to anything.

 

My arm chair thinking would be...

1) Air stuck somewhere in the system that only rears it's head occasionally (unlikely)

2) Physically dragging the brake causing fluid to boil in the Brake caliper (Not uncommon but the ops description seems to rule it out)

3) A problem with the brake lever or MC not allowing the MC to bleed fluid back into the reservoir and thereby keeping the brake line pressurized and causing fluid to boil as mentioned above.

 

As others have pointed out already. #3 seems the most likely and #3 could manifest itself as an intermittent issue.  Braking systems can get pretty odd when they get intermittent.  I'm a big fan of checking the physical action of the entire system (Brake lever, MC plunger, piston action at caliper) and giving the entire system a good flush. Any oddball issues after that I reach for a new MC.

 

 

The whole exhaust pipe theory was interesting but unless the op is running a "one of" system different than what is commonly available there is simply no precedent to suspect it. Far too many existing high pipe systems out there with zero issues, with the apparent exception of the one mentioned where where the fellow apparently had a "one of" brake system he had cobbled together.  I believe Occam's razor likely applies on that one.

 

 

 

 

FYI every one of the times it happened to me the rotor was extremely hot. I stopped and checked it. ( wouldn’t that rule out air in the line) 4 out of 5 times the abs was off. Last time Abs was on and like I have said, I hadn’t touched the rear brake in about an hour as my feet were up on my highway pegs on a long stretch of Idaho highway. 

[Windblown]

15 minutes ago, NeilW said:

FYI every one of the times it happened to me the rotor was extremely hot. I stopped and checked it. ( wouldn’t that rule out air in the line) 4 out of 5 times the abs was off. Last time Abs was on and like I have said, I hadn’t touched the rear brake in about an hour as my feet were up on my highway pegs on a long stretch of Idaho highway. 

 

From everything you have described I am definitely inclined to believe something is causing the brakes to drag -> That in turn builds up enough heat to boil fluid at the brake caliper which creates air in the line as the water content in the fluid boils off (BTW, when was fluid last changed?)   -> That air then causes your "no break action" at the lever.  When things cool back down the brake works again. 

 

I'm the first to admit the above is just speculation -  When I find myself scratching my head  and ask for opinions  I take what others say, mix in my personal bias, shake the magic 8 ball, and get to work until I solve it. LOL. 

Edited February 28, 2023 by Windblown

[NeilW]

1 minute ago, Windblown said:

 

From everything you have described I am definitely inclined to believe something is causing the brakes to drag -> That in turn builds up enough heat to boil fluid at the MC which creates air in the line as the water content in the fluid boils off (BTW, when was fluid last changed?)   -> That air then causes your "no break action" at the lever.  When things cool back down the brake works again. 

 

I'm the first to admit the above is just speculation -  When I find myself scratching my head  and ask for opinions  take what others say, mix in my personal bias, shake the magic 8 ball, and get to work until I solve it. LOL. 

Yamaha replaced everything at the rear and then I immediately added the camel brake pedal. Probably only have 800 miles since then but no rear brake issues so far and I am convinced I won’t. 

[Hollybrook]

@Windblowndescribed the same thing I am thinking.  Having raced a sports car with unvented rotors, I am intimately familiar with brake heat issues and how they manifest themselves. 

 

I think he is 100% right about how the typical T700 rear brake issue occurs.  Not that there aren't other ways to have a brake problem, but this makes the most sense to me given the symptoms and conditions.

[roygilbo]

58 minutes ago, NeilW said:

Yamaha replaced everything at the rear and then I immediately added the camel brake pedal. Probably only have 800 miles since then but no rear brake issues so far and I am convinced I won’t. 

At no cost to you NeilW?  (Yamaha replace)

[NeilW]

20 minutes ago, roygilbo said:

At no cost to you NeilW?  (Yamaha replace)

@roygilboyes. Warranty. 

[roygilbo]

24 minutes ago, NeilW said:

@roygilboyes. Warranty. 

Excellent.  The first post was about the dealer wanting to charge you and it being dicey around warranty.  Glad it got sorted.  

[Tenerider]

7 hours ago, Windblown said:

 

Based on the ops description I'd guess ABS is not the culprit because he comments that the brake pedal just keeps going down with no braking action.  ABS does not (cannot) bleed off the fluid between the ABS pump and the brake lever. So even if it was activating without the op feeling the feedback pulse at the lever it would not cause the lever to move like it was not connected to anything.

 

My arm chair thinking would be...

1) Air stuck somewhere in the system that only rears it's head occasionally (unlikely)

2) Physically dragging the brake causing fluid to boil in the Brake caliper (Not uncommon but the ops description seems to rule it out)

3) A problem with the brake lever or MC not allowing the MC to bleed fluid back into the reservoir and thereby keeping the brake line pressurized and causing fluid to boil as mentioned above.

 

As others have pointed out already. #3 seems the most likely and #3 could manifest itself as an intermittent issue.  Braking systems can get pretty odd when they get intermittent.  I'm a big fan of checking the physical action of the entire system (Brake lever, MC plunger, piston action at caliper) and giving the entire system a good flush. Any oddball issues after that I reach for a new MC.

 

 

The whole exhaust pipe theory was interesting but unless the op is running a "one of" system different than what is commonly available there is simply no precedent to suspect it. Far too many existing high pipe systems out there with zero issues, with the apparent exception of the one mentioned where where the fellow apparently had a "one of" brake system he had cobbled together.  I believe Occam's razor likely applies on that one.

 

 

 

 

A decent writeup mate - Occam's razor

[winddown]

Good, glad we have that problem sorted.  Now can we discuss the real problem here, namely those "Highway Pegs"