guzziriders.org - moto guzzi forum Homepage
Forum Home Forum Home > Technical > Technical services
  New Posts New Posts RSS Feed - V85TT bad rear brake
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

V85TT bad rear brake

 Post Reply Post Reply Page  <123
Author
Message
theone&onlymin View Drop Down
Senior Member
Senior Member


Joined: 14 May 2014
Location: United Kingdom
Status: Offline
Points: 1593
Post Options Post Options   Thanks (0) Thanks(0)   Quote theone&onlymin Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 11:30
Not getting into a fight about this so I'm not as I'm not qualified to do so. Showed the comments to my  MOT tester who would disagree. 

Cheers
Min
Back to Top
Stevex View Drop Down
Senior Member
Senior Member
Avatar

Joined: 24 Nov 2020
Location: North Yorkshire
Status: Offline
Points: 320
Post Options Post Options   Thanks (0) Thanks(0)   Quote Stevex Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 14:47
I de linked my LM2 brakes, all my other bikes have been / are conventional systems, so from this perspective alone it makes sense to me, but I've never been a fan of the linked system.
I run Goodridge hoses, stainless steel discs, carbon ceramic pads and have the very best tyres available for this bike's tyre sizes, Conti radials. Suspension also contributes to good braking and no one can say the poor dampers fitted to big Tontis are anything but barely adequate. I replaced mine with Showa cartridges from an RC36 and re oiled and resprung my Konis. I would class this set up as phenomenal, the braking is absolutely superb in performance. I would go so far as to say that seat of the pants they feel better than my Aprilia Tuono and my Honda CB1300, both of which have braided hose and SBS/Brembo pads.
It's a very individual choice to de link, I've noticed it's almost a mantra with some owners, 'linked is best', probably the same people who have yet to ride a de linked Guzzi. Interesting that Guzzi themselves gave up the linked set up a while back.
If you're happy that the brake has been properly bled then a change of pad material may help. Did you remove the caliper and position it above the rest of the system? Is it a dual piston caliper and did you push the pistons fully in with the bleed nipple cracked open to remove any trapped air?. It's amazing how even a small bubble or 2 will affect braking performance. Also bleeding an ABS equipped bike is no different to any other. I replaced my Honda 1300 rubber hoses for braided and it was one of the quickest and easiest bleeds I'd ever done.



Edited by Stevex - 15 Nov 2022 at 14:56
Steve
Back to Top
Simond View Drop Down
Senior Member
Senior Member
Avatar

Joined: 23 May 2021
Location: Kent
Status: Offline
Points: 624
Post Options Post Options   Thanks (0) Thanks(0)   Quote Simond Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 15:05
I’ve had my LeMans for 34 years, and am entirely happy with the linked brakes, they’re certainly more capable than I am.

Why did Guzzi give up, was it pressure from self appointed ”experts” writing in the biking press, or was it simpler and cheaper to go with the flow and do what everyone else did?  I guess we’ll never know.

But I would note that BMWs (at least the current R1250GS) have linked brakes, although from the hand lever rather than pedal, and cars seem to manage entirely fine with linked brakes.

I think Guzzi were way ahead, it worked well, it was convenient & easy to use, and if you wanted more, you’d got a whole spare front brake…

Fully agree re the braided hoses & thorough bleeding though.


Back to Top
Andy M View Drop Down
Senior Member
Senior Member
Avatar

Joined: 27 Jan 2015
Location: Leeds
Status: Online
Points: 1000
Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy M Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 18:36
Originally posted by theone&onlymin theone&onlymin wrote:

Showed the comments to my  MOT tester who would disagree. 

Cheers
Min

You mean a tradesman who owns a roller tester thinks they are great? Ask him to calculate the MFDD from a test result then carry out a road test to the same level as proof his tester is accurate. Any bets he doesn't know how?

Moto-Guzzi got rid of linked brakes because of market pressure. When you investigate crashes the data will usually show levels of braking way below what the vehicle is capable of. It's why AEB functions are now having a real effect, you need to decouple control from a monkey brain with a design speed of 8 mph. If the actual performance is never used, journalists use it as a stick to beat you and you can save cost by getting rid of a few odd fittings, not many will be sorry to see it go. Motorcycles are endlessly held back by a massively conservative market. 

Andy
Back to Top
theone&onlymin View Drop Down
Senior Member
Senior Member


Joined: 14 May 2014
Location: United Kingdom
Status: Offline
Points: 1593
Post Options Post Options   Thanks (0) Thanks(0)   Quote theone&onlymin Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 19:52
I don't really understand the MFDD from a quick glance at it. But I will read up on it.
What I was hoping to do for Pernao was find some level of comparison, and hopefully  reassurance that his brake was as designed to operate, rather than a seat of the pants/sole of the boot comparison that was offered to him , so I was.

Cheers
Min

Back to Top
Brian UK View Drop Down
Moderator Group
Moderator Group
Avatar

Joined: 13 May 2014
Location: Surrey
Status: Online
Points: 16836
Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 2022 at 22:51
This topic has digressed more than just a bit. Discussions about what sort of brake tester or delinking brakes don't answer the original question.
Brian.

Better 5 minutes late in this world than years early in the next.
Back to Top
Simond View Drop Down
Senior Member
Senior Member
Avatar

Joined: 23 May 2021
Location: Kent
Status: Offline
Points: 624
Post Options Post Options   Thanks (0) Thanks(0)   Quote Simond Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 2022 at 07:59
Well, to be fair, he did ask about whether the brakes were linked!

But the question was

“Liked the bike with the exception of the rear brake that is incredibly bad.

Very, very weak, without sensibility and spongy, going deeper and deeper with prolonged use.”

To which I would respond

1. You should be able to lock the rear wheel using the foot brake, unless the ABS prevents you doing so.  (Not sure I’d risk turning the bike off whilst riding to check). Worth checking if there is a mode to disable rear ABS for off-road use, then try it.

2. The brake should not be spongy, this suggests air in the fluid.  Bleed required.

3. “Going deeper and deeper with prolonged use” is more concerning.  Assuming the pad isn’t actually crumbling, this suggests a fluid leak.  If so, need to fix this first.  Note that the leak could be within the system, so fluid may not actually be lost.

Back to Top
Andy M View Drop Down
Senior Member
Senior Member
Avatar

Joined: 27 Jan 2015
Location: Leeds
Status: Online
Points: 1000
Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy M Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 2022 at 10:08
MFDD is Mean Fully Developed Deceleration. It's the straight bit of the decel curve after all the mechanical lash and pressure build-up and before anything cooks off. It's the type approval standard. A roller test at variable weight fixes the time period to look at and interpolates, hence you can trick them or introduce errors. It's like taking the steering angle as you pull off your drive and using that to predict your journey will end in your neighbours living room.

If the ABS can be made to cycle the limit of adhesion rather than the brake is the limit, so yes, almost certainly as good as it needs to be.

The feeling part leaves engineering and enters ergonomics and psychology. If you can produce 25% decel with your heel on the pedal, 8 inches down the travel, it's a pass but isn't right. Most motorcycles seem to be designed with way more travel and control force required in the area of main use (1-5% decel) than riders desire. I can only assume this is though the use of standard parts, maybe to help untrained (US) riders who fear the front. This means it's really hard to tell if it's got problems.

If we think there is air, bleed it.

Andy 
Back to Top
Speciality View Drop Down
Falcone
Falcone
Avatar

Joined: 31 Aug 2022
Location: Bucks
Status: Offline
Points: 97
Post Options Post Options   Thanks (0) Thanks(0)   Quote Speciality Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 2022 at 10:59
Not qualified to comment on the first part but empirically as I said earlier most modern bikes seem to have relatively inefficient rear brakes, though changing the pads usually helps. Should not be spongy though.
Back to Top
Tris View Drop Down
Senior Member
Senior Member


Joined: 01 Jun 2015
Location: Lincolnshire
Status: Offline
Points: 336
Post Options Post Options   Thanks (0) Thanks(0)   Quote Tris Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2022 at 06:44
I found the rear brake on my V9 to be very poor when compared to the Breva 1100 I'd just come off.

Cleaning and lubing everything made little improvement 
Changing the pads did  but they're still not in the class of the V1100

That being said,  it dosn't stand out as a problem now so either it's not an issue or I've adjusted to it 


2017 V9 Roamer
2005 Breva 1100 - sold
1994 California - sold
Back to Top
Mike H View Drop Down
Senior Member
Senior Member
Avatar

Joined: 21 May 2014
Location: East Anglia
Status: Offline
Points: 8370
Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2022 at 16:38
Originally posted by Pernao Pernao wrote:

Hi,

It seems you are right (see the previous post). It seems that the brake is OK, or at least it is what the Guzzi mechanic says. He compared the breaking of my bike with other V85tt he had in the shop and says it is about the same.

So, I am going to change for EBC HH,
I buy direct from EBC.

Rear, FA256HH - https://ebcbrakesdirect.com/motorcycle/partno/fa256hh
Front, FA244V - https://ebcbrakesdirect.com/motorcycle/partno/fa244v

Quote and about that extension, I cannot use anything that is not from moto guzzi without voiding the warranty,

I can't entirely believe that. it's only literally a bolt-on thingy. I used this, just goes on top of the existing pedal, easily removeable...
https://www.ebay.co.uk/itm/284159172062

But I had to make a curved plate to go underneath and be fixed by the screws.





"Chicken nuggets don't dance on a Tuesday."
Back to Top
 Post Reply Post Reply Page  <123
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.082 seconds.