New to the forum. I bought yesterday a new V85TT and I have made some hundred kms of mountain roads. 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.

This is "normal", I mean do that V85TT has a bad rear brake or the motorcycle was delivered with a problem?

 I know that in the past the Guzzii rear brake also actuated the frontal brakes. It is still the case?

However rear brake has been improved somewhat by changing the pads to sintered, and adding a Harley type brake pedal extender to the pedal, this provides a large flat oval pedal that I can get a good stomp with. Sorry but I've concluded brake pedals that look like gear pedals are just daft. 

Don't know about the spongy thing  - you might want to take the caliper off and pads out for examination - two issues with the V7 850  - the caliper is single piston sliding type and could get hung up on the pins it's meant to slide on (but are seized)  - second issue, pads are retained by 2 pins that screw in with heads like grub screws with Allen key hex holes. - these must be removed and greased ASAP. They are held in with a locking compound (not Loctite) if not removed fairly soon will seize solid and Allen key will just round out the holes. 

If spongy then get it back to the supplying dealer to sort out. Spongy brakes are not right. Possibly just needs bleeding, but it does need sorting out and if you start modifying things on a bike that is only a few days old you void the warranty.

I've fitted a pedal extension like Mike H.

Guzzi went down the right lines 50 years ago with linked brakes and plain cast iron discs, but faced with the extra costs and angry toddler journalists rejoined the fashion herd. I've been selling and designing brake systems for 30 years and what racing has made the motorcycle market thinks it wants is honestly disgusting, but as a fashion product there is nothing much to be done. You've only to read all the "wah wah the linked brakes make my tum tum feel squidgy I'm going back to 1915" stuff on every forum related to bikes that have them to see what you are up against. 

Andy 

I recently borrowed a 1923 Matchless - the rear brake was much more useful than the front.

My 2020 BMW also has linked brakes, though all electronic & clever, with ABS etc., and controlled by my right hand rather than foot.  They seem pretty damn good too.

I too spent a few years of my professional life designing & developing disc brakes - big ones, for trains…

But I have raced raid type motorcycles for 15 years, occasionally also in roads, and I do use the rear brake to control the bike, more than for braking and I am truly disappointed with the V85TT rear brake. On the 1000km revision I will try to see if there is something wrong, I will mount better pads and see if the braking gets better. Again, thanks to all. It was relevant information.

Lets knock down the marketing guff one bit at a time 
 

The idea of twisting the forks of other means of brake steering is insane, every car, truck etc. has one disc on one side of a wheel. The structure is robust so this doesn't happen. 

A road bike and race bike have very different temperature profiles. The race bike does a warm up lap then multiple decels from high speed in a few miles . This keeps the brake warm. A road vehicle rarely suffers overheating, you ride miles with tiny decels then try an emergency stop, the twins are further below optimum temperature than the single. When I look at ECU data it's rare to see any road vehicle go over 0.4G, yet the occupants will tell you it was at the limit. Our monkey brains limit us except when we've done ten laps in practice. 

Wear can be caused by use or glazing. The latter is caused my making enough heat to soften the lining but not enough force to crumble off the resulting glass before it makes a thick layer that then either doesn't brake well or comes off in lumps. A single worked nearer capacity will glaze less, the underworked twin more. When the pads glaze replacing one pair costs less.

Feel is hard to specify. A twin disc will build deceleration faster so might feel better. You can get the same effect by changing pad materials or upping the size of the master cylinder, so why suffer wear etc. 

The only other vehicles that use multiple discs are off highway types and aircraft where the wheel has a much greater load and is limited diameter. It's still not a preferred solution because running costs are higher as is weight and cost. 

I'd be interested to talk to a race bike designer. The unsprung weight of twin discs is against their primary aim, so either they do still have an overheating problem from the multiple hard decels or the rules or sponsors force them to stick with them. The track isn't the road though. 

Left to my own devices I'd start with something like this

Disc as big as you like to set heat to the application and likewise choose a calliper for performance/feel. Split the calliper plumbing so the rear control gives 1/3 on the front. 

Andy 

Andy,

Thought I recognised the wheel -  here's one I bought earlier (and still have!) ..

One disk is plenty on this... There is a small one at the back too, just in case!!

Cheers,

Adrian

Bristol UK

I remember when I had my Spada III MOT test done, I heard the tester shout in surprise, the single front disc had acheived over 50% efficiency. It did work well.

Mind you he then went on to fail the "back" brake at 24%. Wouldn't be told to take the front left disc into account.

borderer wrote: i remember getting into a bit of an argument regarding the CARC bikes someone insisted that you have to drill and lockwire the rear wheel bolts! he was quite happy with unlockwired bolts on his car.

And yet the stresses on the car wheel are far higher.

Trains have (well, had, I’ve been out of that business for many years) multiple discs per axle in some cases. 

Typically, medium speed & freight have one disc per wheel (which are fixed to the axle) but high speed trains may have three or four discs per axle.  Diameter isn’t the issue, it’s energy, and how hot the disc (and pads) would get under a full emergency deceleration from Vmax.

The limiting deceleration is, as with motorbikes and cars, determined by the grip between wheel and rail.

Atb

Simon 

Again, re V7 850, not specifically V85TT, but service manual says brake bleeding can be done in the conventional manner.

Brian UK wrote: If spongy then get it back to the supplying dealer to sort out. Spongy brakes are not right. Possibly just needs bleeding, but it does need sorting out and if you start modifying things on a bike that is only a few days old you void the warranty.

Actually it is a bit worse than when I bleed the system (the pedal brakes further down).

Cheers

Min

Cheers

Min

That's reletively easy to do in the UK Min, but I don't know what the system is in Portugal.

But certainly a check of the actual braking efficiency would be useful.

A roller is measuring both tyre and brake friction. Assuming the roller isn't shiny, wet and lubricated with years of debris, you'll achieve the 30/25 percent level with rashers of bacon fitted instead of pads. What you are mostly measuring is the balance of tyre to brake, the tester assuming a fixed relationship to determine the brake's influence. Get a heavy operator and low tyre pressure and it won't peak fast enough to interpolate 30/25. Too light and a good stomp on the pedal and lock is too fast. The MOT isn't a serious test (It's years out of date), it's there to trap the ones with the cardboard packaging fitted instead of the pads. If you want to see the real number you need to strap the bike down and measure the load as part of the calculation.

25% decel is typical at the bottom of a motorway slip road with an underpass that restricts vision and results in overconfidence then slight panic. It feels uncomfortable, but isn't teeth in the headstock stuff. If that's the  performance stood on the pedal you won't be happy.

What everyone wants is a change of feel which isn't measured. Less travel to the point decel is detectable is desired. Faster build up to temperature and thus less pedal variation to achieve a steady state. Most bikes would benefit from a bigger master cylinder (or smaller calliper) but would then need adjustable controls to stop them feeling too vicious to riders wearing size 12 diving boots and the service intervals might not be acceptable. Changing the pads for the temperature relationship can help, so can making the pedal adjust.

Personally I don't feel Piaggio accept any warranty, so have no problem using non-MG solutions, but you have to gauge that yourself.

Andy 

Cheers

Min

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.

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.

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

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

But the question was

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.

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 

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 

I buy direct from EBC.

Rear, FA256HH - https://ebcbrakesdirect.com/motorcycle/partno/fa256hh" rel="nofollow - https://ebcbrakesdirect.com/motorcycle/partno/fa256hh

Front, FA244V - https://ebcbrakesdirect.com/motorcycle/partno/fa244v" rel="nofollow - https://ebcbrakesdirect.com/motorcycle/partno/fa244v

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" rel="nofollow - https://www.ebay.co.uk/itm/284159172062

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

I changed for racing EBC HH and improved a bit. Bought from moto Guzzi an accessory to replace that silly brake pedal and improved a bit. Changed the brake fluid and carefully bleed all the system and improved a little bit.

It is far away from the racing motorcycles I used to ride, but I can already use it for controlling the motorcycle. The biggest problem is that, without being spongy the brake pedal movement from the moment it starts breaking to max breaking is too long and the foot is too deep for being comfortable. I tried to regulate the cursor but I was not able to do so, looked to the manual for the mechanics and it is not there either.  

How do you regulate the course of the pedal? Before it starts to break?

Went to make the first revision, the mechanic said that the brakes cannot be bleed the traditional way without disconnecting the ABS...he put it "right" and it was terrible again breaking too low on the pedal. When I arrived home I bleed it properly...and stayed without ABS. 

.

So if it doesn’t work, there’s something wrong with it, and it wants to be fixed properly.  

I think I’d recommend finding another mechanic.

And the one thing I’d have on any bike (except off road on something little) is ABS, because the day you need it, you really do need it.

Many owners with V50s found the front brake useless, due to the wrong master cylinder being used, in that case it was too big, a smaller one from a jap bike worked far better.

Do they learn?