Mark iv linked brake issues

[Bazil]

Hi all. Hope someone might have some pointers. Sorry for the long windedness.

My linked brakes have never been good, bordering on abysmal. I rebuilt the master cylinder a couple of years ago and replaced rear pads at that time along with replacing brake lines. No major improvements and my front hand brakes has always been we'll used as a result.

Recently I replaced front pads and was ecstatic to have great brakes. This was short lived, as halfway through the shakedown ride I lost linked brakes entirely. That was interesting. Strangely they came good again later in the ride.
Installed seal kits in both calipers and replaced crush washers on the lines.

When bleeding the brake pedal goes down to the exhaust pipe and I pushed through fluid until I didn't see bubbles.

So- it should be great right?

No. The pedal travels until it hits the exhaust and while the pads move, they won't apply any appreciable pressure to the discs. It's like there are no brakes at all.

Have I just got a case of of poorly bled brakes?

Or maybe I've connected the new brakes lines  incorrectly at the manifold. I have read conflicting advice on which line go where.  But they match whats in the manual. Mine are connected from top to bottom in the following order:
Front brake
Brake switch
Master cylinder
Rear brake

I've spent way too long on this! Anyone got any suggestions?

Thanks in advance.

Baz

[pete roper]

The lines are long and voluminous, the amount of fluid pumped by the master cylinder is small. Get a master-vac or at the very least elevate the calipers above the splitter as you bleed.

Also remember the master cylinder is now at least 33 years old. Has it ever been rebuilt or re-sleeved? New lines are not enough on a thirty five year old vehicle. Chances are the whole of the rest of the system is stuffed too.

Pete

[pete mcgee]

Bazil,
Yep you have air in the lines.
Follow Pete's advice.
Another trick after bleeding is to depress the brake lever and keep it depressed over night, how you do that I'll leave to your ingenuity.
It should make a difference.
Other things to look at after you've gotten all the air out of the system is worn linkages, elongated holes in levers and couplings and wear in the rear face of the master cylinder piston where the lever pivots onto it.
If the rear of the piston us worn a rebuild of the master cylinder will replace it, the end of the input leaver us also probably worn as well and should be replaced.
Finally lever adjustment will also effect brake performance.
Braided brakelines are a worthwhile addition as well.
I cant remember if the proportioning valve on the mk4 actually had internals that may be faulty, stuck gunged or was just a splitting manifold with a bleed nipple like on the mk3.
Good luck with it.

[guzzisteve]

Never had any problems doing brake bleeds. I always took off calipers and tied a wrench in between pads, stretched out lines w/caliper on a table or box above the master so all bubbles go up. Tapping on lines and fittings also helps to brake free the air trapped in corners.
First I bought a hand vacuum power bleeder, worked better. Now I have an air compressor assisted set up cause the holes in system got smaller and new systems are harder to bleed.

[jwinwi]

Has to be the Master Cylinder. Rebuilding didn't improve its performance and that was 'a few years ago' which, to me, means at least 5 years. Had a linked brake MC go bad over winter sitting in the garage. Worked fine when parked but in April, NFG. Replaced it cause it was almost 40 at the time.

[Bazil]

Thanks folks. Looks like I'll be trying to rebleed it first, then worry about master cylinder if that doesn't resolve it. The m/c did get a rebuild kit though so I guess it would have tp be a resleeve or replacement.
Cheers Baz

[Diploman]

I think Guzzi's linked "integral brake" system, introduced in the 70's, was a brilliant safety innovation for which the company does not receive enough credit.  Emulation of the concept by the likes of Honda BMW and others, albeit in more complex iterations, gives validity to the soundness of Guzzi's vision.  I love the linked brakes on my V50 and SP and would not think of de-linking them.  It's the next best thing to antilock, IMO.

In my experience, the only real downside to the linked system is bleeding them, an operation I have sometimes found tedious, difficult and lengthy.  When doing a refresh on my V50II last year, I decided to see if this situation could be alleviated:  I installed a junction with a manifold and bleeder at the highest point of the linked line. Now, when I fill the line at the calipers, the air in the system is forced upwards towards this junction from both ends.  A few quick bleeds from the high-mounted manifold and -bingo - a firm pedal.  I have bled the system three times now and the longest it has taken to get a firm pedal is 10 minutes.  This little junction device, I must say, works like a charm.  Incidentally, I used Magnum DIY brake lines from MG to get the right lengths.  The linked brakes on my V50, with EBC F47 pads at both ends, work excellently.



 

[Orange Guzzi]

Is there a screw in the master cylinder that controls how far the piston returns?  Is it adjusted correctly?  Also check the small bleed back hole in the master cylinder to see if it is plugged. 

[Arizona Wayne]

Don't recall my `87 LM IV having linked brakes like my `81 CX100. But I could be wrong.

But I like linked Guzzi brakes for street riding. Never had a problem with mine but never have taken them apart either.  Bought a `77 Convert a few years ago that needed it's linked brakes  filled with more fuid, but that is all.  I figure most riders who don't like them have never had them before and for that reason don't like them, instead of adjusting to their attributes.

[Bazil]

Thanks all - quick update.

Carefully re-bled both calipers the old fashioned way, running through a couple of master cylinders worth of fluid. Elevated both calipers above the master cylinder level. Finally got some firmness in the pedal. Tied the pedal down overnight. I reckon it's probably 95 % of what is should be, but haven't had the chance to road test yet. The vacuum bleeder is probably the way to go, if only to save wear and tear on the bleeder threads - if I went through that process every year I think they'd be wearing out !

Love the idea of a bleed valve at the top of the system Diploman - something Luigi should have done. Maybe something to think about when I dont have "bleed fatigue".

Thanks for your help.

[pressureangle]

There is a bleeder on a junction block behind the left side cover, where the line from the master connects to the line to the caliper. It's not easy to spot. It is a high place in the line and if you don't bleed it you'll never get them in.