G5 Brake Valve

[Scout63]

Is the rear-mounted brake splitter union a proportioning valve or just a three-way splitter for dividing fluid between the front and rear calipers?  I’ve installed this Brembo splitter in my build connecting the rear master cylinder, rear caliper and front left caliper and now am concerned that it will change the braking system:

https://www.mgcycle.com/index.php?main_page=product_info&products_id=3154

Thanks - Ben

[Antietam Classic Cycle]

If the original had a round rubber cap approx. 30 mm in diameter on one end, it was a proportioning valve. Otherwise it was just a splitter/manifold. The parts diagram shows a splitter/manifold.

[guzzisteve]

The integral slitter has no valve. Its a series of different size holes. The faster & harder you hit the foot brake it puts more pressure on back or front. It works on imput pressure to make the difference.

[Groover]

I believe the "proportioning" was done by using different brake pad grade as OEM on the front left, though we all change them to be all 3 (6) the same, but in reality to be correct braking per design, the pads on the front left should be harder grade, that's why I think you see a lot of left front disks maybe look more grooved than the right ones.

That's my conclusion at least 

[moto]

I believe the "proportioning" was done by using different brake pad grade as OEM on the front left, though we all change them to be all 3 (6) the same, but in reality to be correct braking per design, the pads on the front left should be harder grade, that's why I think you see a lot of left front disks maybe look more grooved than the right ones.

That's my conclusion at least 

Hi Groover,

With all respect, I believe you may be wrong about this, at least for the original T3 system. The part number for all three sets of pads is the same, namely 14 65 46 01, in the parts manual.

My understanding has always been that the front-to-back braking balance is 50/50 from the foot pedal in the original system, with additional force to be applied at the front for hard stops by pulling on the hand lever.

Moto

[moto]

If the original had a round rubber cap approx. 30 mm in diameter on one end, it was a proportioning valve. Otherwise it was just a splitter/manifold. The parts diagram shows a splitter/manifold.

Right. The G5 diagram shows the same, simple manifold with four threaded ports as my T3's, not quite functionally equivalent to the part you installed. Here it is, part number 17 66 80 50:





The difference is that your part lacks the fourth port for the brake light switch. (Edited to correct my initial oversight of the missing port )

[Groover]

Hi Moto, no offense taken. I am married, and "you're wrong" is an endearing word combination to my ears now 

In regards to the pads, not familiar with the T3 manual, but the G5 part manual shows the Front Left as Ferit I/D 330, and  Ferit I/D 332 for the Front Right and Rear.

Though, at this moment I don't recall if I ever did figure out if 330 is harder than 332, but that would make sense to me. The Moto Guzzi part numbers are 14654650 for the 330, and 14654601 for the 332 (same as T3 for these two)

[bmc5733946]

According to Guzziology (thanks Dave Richardson) the USA G5 had a 4 way manifold 1766 8050, no proportioning. Dave gives a complete list of valves/manifolds and their ratios. Guzziology is a most wonderful resource!

Brian

[1down5up]

Just to add to the conversation  - the SP1000 (possibly G5 though not sure) had a Brembo F09 rear caliper which had a 48mm Piston rather than the normal F08's (38mm) - so even though they had a standard 4 way cplitter with no proportioning valve the rear brake had a larger piston which changed the actual pressure application balance

[moto]

Just to add to the conversation  - the SP1000 (possibly G5 though not sure) had a Brembo F09 rear caliper which had a 48mm Piston rather than the normal F08's (38mm) - so even though they had a standard 4 way cplitter with no proportioning valve the rear brake had a larger piston which changed the actual pressure application balance

The G5 parts diagram shows the same part number for the front right and the rear caliper, indicating they are both F08's.

[moto]

Hi Moto, no offense taken. I am married, and "you're wrong" is an endearing word combination to my ears now 

In regards to the pads, not familiar with the T3 manual, but the G5 part manual shows the Front Left as Ferit I/D 330, and  Ferit I/D 332 for the Front Right and Rear.

Though, at this moment I don't recall if I ever did figure out if 330 is harder than 332, but that would make sense to me. The Moto Guzzi part numbers are 14654650 for the 330, and 14654601 for the 332 (same as T3 for these two)
...

Ah, big thanks to your wife for desensitizing you! 😁

So the T3 and G5 differ in that a different compound has been specified for the front linked brake, changing the front-rear balance when using only the rear pedal. The only reason I can see for putting less force on the front tire is when braking on dirt. That would require a harder compound. Is that your reasoning? Or something else?

I have to admit I am very fond of the great simplicity of the original system, where the selection of components and the use of the same compounds all around means that each disc contributes the same force for the same input pressure.

Moto

[Groover]

Yes, that would be my reasoning. Basically if hitting that rear brake hard with your foot, using the harder compound in my mind would have less friction than a softer compound, so everything else being equally, you get more braking/friction in the rear less in the front with the linked brakes (safer for various surfaces, such as gravel) in lieu of a proportioning valve, but you can then supplement more braking in the front as needed using the right lever (front right brake pads) like non-linked brake type bikes.

I also like the linked brakes, makes a lot of sense to me, and I also like they didn't link all three in case there is a failure in one system, then you have the other.

[Frenchfrog]

Just to add to the conversation  - the SP1000 (possibly G5 though not sure) had a Brembo F09 rear caliper which had a 48mm Piston rather than the normal F08's (38mm) - so even though they had a standard 4 way cplitter with no proportioning valve the rear brake had a larger piston which changed the actual pressure application balance

Not certain but that was only in certain markets...UK and France had 08's , Germany got the 09.Or the 09 bins were empty at some points 

[bmc5733946]

Guzziology lists the SP1000 with the F09 as well as a 4 way proportioning valve 1866 8560. While listing the SPII with 4 way manifold 1766 8050 and the SPIII with 4 way proportioning valve 1966 8565. Just trying to provide information. There are many variations, keeping them straight seems prudent.

Brian

[Scout63]

Right. The G5 diagram shows the same, simple manifold with four threaded ports as my T3's, not quite functionally equivalent to the part you installed. Here it is, part number 17 66 80 50:





The difference is that your part lacks the fourth port for the brake light switch. (Edited to correct my initial oversight of the missing port )

I ran a short brake line from the rear mc to the three way port and banjo’d the front left brake brake line off a Goodridge single banjo pressure switch in the second port.  The third port runs to the rear brake.

https://www.mgcycle.com/index.php?main_page=product_info&products_id=1583

Great feedback.  I feel better.