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V85TT bad rear brake

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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2022 at 21:43
Originally posted by borderer 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.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Simond Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2022 at 22:11
Originally posted by Andy M Andy M wrote:


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. 

Andy 



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 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote borderer Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep 2022 at 10:52
Some tractors have multi discs on the axle running in Oil? in a sealed unit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep 2022 at 12:41
Yes, most off-highway equipment has multi-plate wet discs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote borderer Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep 2022 at 16:58
I suppose this isn't much help regarding the original questionSmile. Yep the V85 brakes appear to be soft, I stripped the caliper and lubed everything than needed doing. Its a little better but improves with use. I think its a dealer job to bleed the brakes with the ABS system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 29 Sep 2022 at 18:51
Again, re V7 850, not specifically V85TT, but service manual says brake bleeding can be done in the conventional manner.


Originally posted by Brian UK 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.


Originally posted by Pernao Pernao wrote:

... have made some hundred kms of mountain roads.
... without sensibility and spongy, going deeper and deeper with prolonged use.


Does sound like should go back to dealer.

Mine did take nearly 100 miles to stiffen up and start workng properly, with new pads of course, but he says hundeds of km.




"Chicken nuggets don't dance on a Tuesday."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pernao Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 00:18
Some news about this problem: I changed the oil fluid, bleed the system and it become slightly better. Took the bike for the first revision, complained about the rear brake, they changed the fluid again, tried the motorcycle, comparing with other V85TT that were in the shop and said to me it was ok. 

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

So I am changing for EBC brake pads. I found some on Ebay but on the reference  they say that they are suitable for models between 2019 and 2020. They changed the rear brake in the 2021 and 2022 models or are the pads the same for a 2022 model?

"EBC FA256 737.09.50 For Moto Guzzi 850 V85 Tt 2019-2020 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pernao Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 01:55
Originally posted by Mike H Mike H wrote:

Mine isn't the 85TT, but the V7 850 - however similarly the rear brake is next to useless. No it is not linked to the front. Guzzi stopped doing that a while back, can't remember when exactly. 

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. Shocked

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, and about that extension, I cannot use anything that is not from moto guzzi without voiding the warranty, but they have this:


It only increases marginally the size of the lever, but will give the foot more support.

By the way, do you know if the EBC right pad for the rear brake is the EBC FA256?
They say they are for the 2019 and 2020 models. They have changed the rear brake or it is the same for the 2021 and 2022 models?



Edited by Pernao - 14 Nov 2022 at 01:59
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Speciality Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 08:15
I doubt that anyone will have the definitive answer to that, but I have found that suppliers can be slow to update the years to which parts they sell apply and that unless the new year model is obviously a significant refresh the existing parts usually fit the previous model. Unless someone knows for certain I suggest you order them and compare to the originals and if they look like they won’t fit, return them. Best to confirm with the supplier beforehand. FWIW the rear brake on my V7 850 is not brilliant but it does work. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote theone&onlymin Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 08:34
Has it been on an MOT brake tester ?

Cheers
Min
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Speciality Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 10:28
Not mine, no. The bike isn’t old enough to need an MOT yet. FWIW I find that most disc rear brakes on the bikes I’ve owned are not particularly powerful or progressive. The one on my V7 850 is a bit better than the one on my NC750X. The last really good rear brake on a bike I’ve had was on my 2015 RE UCE Classic. That had a drum rear brake that was great once I’d taken it to bits and reassembled it properly. That said it’s a long time since I’ve owned a cruiser type bike or an old British bike, which usually had far more effective rear brakes than front ones…
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pernao Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 13:01
No, never been tested in a MOT brake tester.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote theone&onlymin Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 13:09
But you could go and discuss it with them so you could. 

Cheers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 13:34
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.

Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy M Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2022 at 14:11
It will almost certainly pass.

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 


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