Brembo brake conversion - P08 to P4

Hi All,
I’ve seen a few conversions out there of older big twins with more modern calipers and was considering converting my T3 from the old P08 calipers to the P4 30/34C single pin calipers used on the EV, Centauro, Daytona etc.
I have a P13 brake lever from a Cali on the bike so the front is a bit spongy and I’d like to improve the stoppers.

Stein Dinse sell a conversion bracket for the 40mm mounts and the calipers are also available new.
However, the brakes appear to be directional, with the smaller piston being at the lead end of the caliper. If the calipers are fitted to the T3 they will have to be switched left to right so the lead caliper will then be trailing.
I can’t see this being a real problem, as the reason for differing sizes is an attempt to even out disk wear.

Have any of you done this conversion ? Any ideas or comments appreciated.



I’m surprised you say the front brake is spongy, The front lever brake is usually very solid and wooden with the standard handlebar master cylinder acting on a single front P8 Brembo caliper.
I assume you are still linked on the brakes.
I know someone who de-linked the brakes and connected 2 discs to the original master cylinder on a T5 Guzzi and said it made a really good brake with a good amount of feel. He never could get the rear to work any good.
Have you tried some braided hoses, that makes things a lot firmer.
Could there be a bit of air in the system or could the cylinder need a new seal kit fitting?

The bike has Goodridge hoses, P08 calipers, EBC disks and the PS13 master cylinder / brake lever. It isn’t exactly standard though the rear and LH front brakes are still linked using the standard rear PS15 master cylinder.
The master cylinder was brand new 2 years ago, the brake caliper has been reconditioned with new teflon type pistons and new seals fitted. It’s been OK for 12 months but has recently started leaking (again - which is why it was rebuilt).
To be honest the front (RH) brake has never been anything but spongy and a bit Harley like in effectiveness since I changed to the later master cylinder so I decided to upgrade to something I know works.
My main concern is that I could be rushing into a project that isn’t properly feasible.



Hi All,
In order to answer this for myself, and to help anyone else with the same daft idea I’ve been doing some digging and had a good read of Guzziology.
Basically, don’t, unless you are loaded or have a machine shop.

If you have a 13mm brake master cylinder, the P4 30/34C (aka 5165) is OK for the RH (hand) brake using a conversion mount provided the pad retaining spring is fitted the correct way. This is similar to the standard EV setup and should be a vast improvement over the P08. OK if you don’t mind a P08 on one side and a P4 on t’other.

With the T3 linked braking system, the rear/front P08/P4 combination would require a 16mm rear master cylinder at least or it would be too soft in feel and also potentially dangerous. The rear to front breaking effort would be very different to the standard ‘feel’, having a lot more bite at the front, but not as pronounced as a P09 front/P08 rear.
Using a Brembo 16mm rear master cylinder would need a remote reservoir as well, adding to the cost.
The standard late Cali type brackets won’t fit due to the side panel lower mount so custom brackets would also have to be made.

Using a P09 in the rear with a P08 at the front without a suitable proportioning valve could cause the rear wheel to skid so is not advisable.

Using a P09 in the rear with a P4 in the front would restore most of the balance (still a bit too rear biased) but would require an 18mm master cylinder - I can’t find one so that’s out.

There is one more alternative keeping the linked brakes. Use two P4’s plus an EV rear brake caliper. That would also require a later proportioning valve to work plus even more expensive brackets and a 16mm rear master cylinder. (Might as well buy an EV).

I hope this helps someone out there (or at least provides entertainment).
Looking all this up and crunching numbers has at least kept me out of the pub and saved a few hundred ponds !



That was an interestin read. Meddling with the linked system would throw up all sorts of issues with the balance of the system. My old twin is a Spada and that has the P9 rear and a proportioning valve. Never quite known what it does, I know I can feel a piston moving up and down inside as you press on the pedal.
To be honest, I find the standard set up fine for the road so long as it is working well, you have all the air out of the system and a decent set of pads, I always stick with Ferodo’s.

Like Don, I’m also surprised that the front is spongy with the standard size master cylinder - normally very little travel and a hard wooden feel. I would suspect a problem with the master cylinder, even though it’s new. I’ve just changed my SP to an 11mm master cylinder and find it much better. This is another modification from Guzziology.

I dismantled my proportioning valve (to deal with a broken bleed nipple). I have a photo somewhere, but it’s basically a piston with a spring behind it, that closes off a port (rear caliper outlet I think) at whatever pressure the spring is set to.

Brilliant post Vinsdad :bulb: :nerd:
I have an 1100i motor in a T3 frame and the brakes are up to it. When I ‘downsized’ from the EV it was a bit of a relief as I found the EV to be a bit overbraked even when two up with luggage.
The EV calipers are also after the DIY era and rebuild seals/kits weren’t available the last time I tried to get some.
Despite this I had been giving it some thought :astonished:
Thanks again

Thanks for the replies everyone.
I’d missed the point about the PS11 front master cylinder - that should give more feel than the PS13 with a P08 caliper according to Mr Richardson. I’ll see if I can get my paws on one to play with.
Anyone got one they need to be rid of ?

In the meantime I’ll be stripping down the whole lot and finding the cause for the spongy feeling.