Author Topic: '86 LeMans IV brake de-link and rear shock questions with pics  (Read 252 times)

Offline brider

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Pulled my left sidecover to dis-connect the hot-wired coils so I could install a new ignition switch, and I learned how the PO plumbed the de-linked rear brake:





He retained the rear proportioning valve, which is good, so if I want to convert BACK, I can only hope he didn't destroy the threads on the top port with that big-ass bolt.

Front:




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So I would think that if I found the hard pipe that ran under the tank and a stainless braided line for the left front disc, and dis-connected the existing left front line at the T and plugged that port, I'd be back to stock linked brakes. Sounds easier than finding a V50 front master to swap to the rear, or having the rear re-sleeved.

Can anyone identify these rear shocks? They have close to 50 psi in them, which seems kinda high to me:



« Last Edit: June 14, 2018, 09:41:47 PM by brider »
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Offline canuck750

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #1 on: June 14, 2018, 09:48:09 PM »
The shocks look like FOX, I rebuilt several pairs years ago for my TT500 projects. Rebuilt Fox shocks are pretty popular with the vintage twinshock MX scene.



You can buy the steel brake line to connect the front caliper to the rear master cylinder, HMB in Germany and MG Cycle have had them in the past.
« Last Edit: June 14, 2018, 09:58:07 PM by canuck750 »
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Offline wirespokes

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #2 on: June 14, 2018, 09:53:20 PM »
Auto parts stores around here sell brake lines. They're easy to bend being soft steel

Try riding it as it is for a while and see if you get used to it. I've been riding mine for a year and a half - probably 15K - and it feels pretty normal. I could probably lock up the rear wheel if I wanted to. I'm also one of those odd guys who prefers de-linked brakes since there are times I don't want to apply the front brake, but do want some braking action.
« Last Edit: June 14, 2018, 09:56:26 PM by wirespokes »


Online Chuck in Indiana

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #3 on: June 15, 2018, 07:19:25 AM »
Auto parts stores around here sell brake lines. They're easy to bend being soft steel

Try riding it as it is for a while and see if you get used to it. I've been riding mine for a year and a half - probably 15K - and it feels pretty normal. I could probably lock up the rear wheel if I wanted to. I'm also one of those odd guys who prefers de-linked brakes since there are times I don't want to apply the front brake, but do want some braking action.

Yeah, fabricating the brake line shouldn't be a big deal.
Getting rid of the bodges might be a little more of a problem. Guzzi bodgers can be very creative.. :evil:
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Online SPScottNT

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #4 on: June 15, 2018, 07:57:58 AM »
I believe the pictured "valve" is just a three-way junction and does not have any proportioning effect.  If the threads are bodged beyond repair, finding one used should be pretty easy - it was used on many models.  MG Cycles carries the stock long run of hard pipe.  As long as the m/c's are stock/unaltered, getting back to the original, linked ft/rr brake setup should not be a problem.

Scott   

Offline Dukedesmo

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #5 on: June 15, 2018, 11:33:07 AM »


Quote from: SPScottNT on Today at 01:57:58 PM
I believe the pictured "valve" is just a three-way junction and does not have any proportioning effect. 
___________________ ___________________ ___________________ ___________________ _______

Agreed.
I de-linked my LM2 and it had a similar setup that I'm fairly certain is just a 3 way junction, I removed the junction BTW and fitted new braided hoses to suitable sized master cylinders to front and rear.


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Online rodekyll

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #6 on: June 15, 2018, 11:42:59 AM »
Yes, the junction has no special properties.  Yes, your local parts house will have both sae and metric hard lines in varying lengths.

You might consider replumbing to -3AN specs since you're redoing it end to end.  Easier to get fittings for AN than for metric, and you can easily convert to whatever end hardware you require.

Offline Stevex

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #7 on: June 15, 2018, 12:26:15 PM »
Much prefer my de linked LM2 brakes.
What are your mc sizes? If the PO did the job right you'll need to change both of them.
I fitted a PS12 to the rear single and a PS15 to the front twins, which, if your brakes are working properly is what you should have.
If you re link you'll need a PS12 and a PS 15 to the front and rear respectively.
Steve
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Offline brider

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #8 on: June 15, 2018, 03:51:02 PM »
I could have sworn I read in Guzzi literature that the foot pedal has a 70% front/30% rear bias, and that has to happen somewhere; are you saying that proportioning is not true?

Regardless, I never had an issue with linked brakes, and I think going back is the easier path for me.

Cool about the Fox rear shocks, but the only Fox shocks I remember back from the twin-shock days was their airshock.
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Online rodekyll

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #9 on: June 15, 2018, 06:07:31 PM »
There are some bikes with proportioning valves.  The manifold pictured is not one of them.  It is a simple splitter.
 The proportioning valves I have seen have bleeders or a separate valve in-line with the brake.

Offline brider

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #10 on: June 16, 2018, 07:29:14 AM »
There are some bikes with proportioning valves.  The manifold pictured is not one of them.  It is a simple splitter.
 The proportioning valves I have seen have bleeders or a separate valve in-line with the brake.

AHA! I looked in the owner's manual, and sure enough, there is no mention of any front/rear proportioning for the read pedal. So I'll be darned.

BUT, without starting another science discussion (I can search and read the physics behind it elsewhere), my head still can't understand how reducing the volume of fluid displaced by ~50%, but same pressure (pedal input) against same area (rear caliper) results in LESS force on the rotor (no braking effect with pedal input). I've demonstrated that it WILL lock up if I STOMP on it, so maybe the thing I'm not understanding is the modulation that has been lost.

Another problem with the speedo trip-meter, but I'll post that in another thread.
'85 Cal II Auto
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'74 White Eldo LAPD
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Offline Diploman

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Re: '86 LeMans IV brake de-link and rear shock questions with pics
« Reply #11 on: June 16, 2018, 10:37:21 AM »
In Guzzi linked braking systems without proportioning valves (eg. Lemans, early smallblocks and others), a front brake bias is achieved by using a larger diameter rotor on the front as compared to the Rear brake.  A simple splitter produces a 50/50 pressure split from the MC, but the greater rotor diameter in front creates more leverage on the front wheel than the rear for the same pressure on each.  Basic but effective.

If you are refreshing or modernizing such a linked system, it is not necessary to fit the OEM splitter or hard pipe.  The same effect can be achieved by using a double banjo at the MC, which will produce a 50/50 pressure split between front and rear.  In place of the hard pipe, a DIY braided brake line (eg. Goodridge Sniper II) can be fitted, routed any way that is preferable (eg, to free up some internal space in the battery compartment in conjunction with fitting a small lithium battery).  This line can run directly from the MC all the way to the front caliper with no junction.

On my V50, I chose to place a junction block on the tab which originally held the cable-operated front MC under the tank. This 3-way junction block (from MG Cycle) is equipped with a manifold and bleeder on top, and is positioned at the highest point on the linked system line.  This piece joins the line coming up from the MC to the line coming up from the left front caliper. When the system is reverse-filled with brake fluid at the front and rear calipers, air in the line is driven up to this junction, where it is easily bled.  I have found that this junction block greatly simplifies the once-tedious task of getting a firm pedal on the linked line.  This task which used to frustrate me now takes 10 minutes or less.

I am a huge fan of Guzzi's linked system, which enables stable and secure braking with less drama, nose dive and "stoppie" tendency than conventional brake setups.  The brakes on my V50, IMO, are outstanding, even compared to the extremely strong front brake on my KTM 390 Duke, featuring a 320mm Galfer rotor, a 4-pot Brembo- designed ByBre caliper, EBC HH pads and a 15mm Frando radial MC.  To preserve the V50's cast iron rotors, I am not using HH pads, but clearly it does not need them. 



« Last Edit: June 16, 2018, 10:55:47 AM by Diploman »
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