Hi folks, Still on the journey to get my combo back on the road. Only thing holding me back are the brakes.
Took off the rear master cylinder and fitted a repair kit. Put this back on the bike. Tried to bleed the brakes. Pedal still very little resistance. Handlebar lever seems to be still normal like it should be.
Is this likely something to do with the proportional valve?
If so might it need a refurb?
I’ve never come across a linked (dual) braked bike before so am starting from scratch with my knowledge.
Any ideas? & Happy Christmas to all.
When I had my 400 Bergman, I had to change the pads and fluid. The rear brake applied half the pads on the front, there were two small pads and separate pistons. I used two self bleed kits, first I bled the rear brake then while keeping the rear bleed pipe submerged and air free, I bled the front brake and then bled the rear brakes using the front bleed nipple.
This may help (From “This old Tractor”) https://www.thisoldtractor.com/moto_guzzi_tonti_brembo_brake_proportioning_valve.html
Gregory Bender also has the workshop manual for your bike here https://www.thisoldtractor.com/moto_guzzi_tonti_workshop_manuals___shop_manuals___service_manuals.html
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It can be quite difficult to bleed the rear brake. The proportional valve is unlikely to be the cause of the sponginess.
The front brake lever operates one front disk and is completely separate from the rear brake circuit so if this is working ok you can forget about it.
The rear master cylinder operates the rear disk and the other front disk.
Bleeding it can be a pain. The text book says bleed from master to proportional valve and then to rear and then to front (may be front then rear, I dont think it matters). In my experience I usually have to go through the cycle 2 or 3 times and pump the pedal a lot to remove all the air from the master to valve. Keep going until there are no more bubble to be seen in master cylinder.
Good luck.
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Just gone and studied the setup more closely and it does seem to be that the rear brake pedal only goes to the lhs front calliper, so thanks a lot for your help, I’ll carry on with that in mind.
Thanks for the reply. A lot to get stuck into here. Might take some time but hopefully I’ll get there. Happy Christmas.
Ha, getting the picture now. Step by step and I’ll get it sorted. First time I’ve encountered a split front brake control and therefore a linked up rear pedal control. I feel like I’m getting somewhere now. Many thanks for your input. I’ll post in the new year when and if I get a result. Happy Christmas
Merry Christmas to you too and yes do let us know how you get on
I’ve recently bought a vacuum pump for refilling brake system, just a few quid off ebay and it seems to work well. Just make sure you keep topping up the reservoir as it pulls fluid out at quite a rate.
It often needs quite a bit off pumping of the pedal to build the pressure up and to reseat the caliper pistons close to the disc.
Make sure the master cylinder piston is going back fully. Don’t allow the pedal actuator to press slightly on the piston when the pedal is at rest. You should be able to get a feeler guage blade between the lever and the piston.
I find unbolting the callipers and hanging them so the bleed points are highest( so air bubbles rise and don’t get stuck in awkward places) and bleeding in this position helps, always replace and anneal copper washers
I had the same problem with the linked brakes on my Le mans. Tried bleeding it the conventional way with the pedal without success so I got two large syringes off the bay and reverse bled by putting brake fluid in the syringe then making sure the pedal was up, and drew the fluid from the rear master cylinder then connected the syringe to the front left caliper and pushed fluid back to the master cylinder keeping my eye on the fluid level rising and drawing off when necessary. Repeated this with rear caliper and then tried the brake and it worked fine.
Sorry got the syringes from amazon. Just search ‘brake bleeding syringe’
Me too!
You get there in the end and it rarely needs attention thereafter.
If you are new to these linked brakes they are not like the modern variants. I almost crashed when doing an emergency stop 2-up. That was because I did not give the pedal enough pressure. The handlebar brake lever just gives top-up front braking. Practice recommended.
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Also the front brake stops the forks twisting under heavy braking!
You can feel them untwist when you release the lever before the pedal
I must say that I never experienced any fork twist and the fork brace is quite substantial on the 40mm Marzocchi forks. Then again I rarely rely on footbrake alone except minor speed adjustment prior to a bend and/or changing down.
Unless you want the infamous torque twitch - smoothly does it.
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