Author Topic: Front disc options  (Read 574 times)

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Offline D Peacock

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Front disc options
« on: November 21, 2021, 06:01:00 PM »
Hi A/all

I’m putting together parts for my 250/400C front end conversion. I have read that LC discs are a straight swop for the hefty aircooled disc, can anyone confirm this is the case, using the original twin pot caliper?

Thanks  :D
For speed add lightness!

GSXR1100 - Big boy’s bike
GSXR400RKSP - Track / Race bike
YR5 - 52bhp - Ported RD barrels, 28mm carbs, Mick Abbey pipes, Powerdynamo with Zeeltronic DC controller, premix, Euro CR 6 speed box.
GT200X5 - Bog standard.

Online GAZZATT2

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Re: Front disc options
« Reply #1 on: November 21, 2021, 06:55:16 PM »
1 wouldn't think LC discs are much lighter
they are the same diameter but only 5mm thick compared to an A/C 7 mm
XSR900  350lc 400F 400f special 2nd 400F special
it did look good in a photo lance ?
Picture026" border="0

Offline 5port

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Re: Front disc options
« Reply #2 on: November 21, 2021, 09:20:40 PM »
Hi Dan,
Yamaha used the early RD and TZ discs with alloy carriers so, possibly they are lighter than the all-steel later RD and LC disc?  You can get the steel disc of the earlier type ground down a bit, and drilling would shave a bit more off. 
Without doubt, a modern type floating disc is better and can be lighter but, I think the early RD250/350 disc is pretty good.  Certainly, with the SBS Carbon race pads, mine are powerful and with great feel with the iron caliper and 1/2 inch 250LC master cylinder and Hel braided line.  :)
Cheers

5port     
5port

Offline D Peacock

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Re: Front disc options
« Reply #3 on: November 21, 2021, 09:56:55 PM »
Thanks Chris. I’m just floating ideas around, sent the front wheel assembly off to my engineer this week, I’d forgotten how beasty the original discs are  ;D

I might just get another disc and play around slotting / drilling it for a giggle.
For speed add lightness!

GSXR1100 - Big boy’s bike
GSXR400RKSP - Track / Race bike
YR5 - 52bhp - Ported RD barrels, 28mm carbs, Mick Abbey pipes, Powerdynamo with Zeeltronic DC controller, premix, Euro CR 6 speed box.
GT200X5 - Bog standard.

Offline 5port

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Re: Front disc options
« Reply #4 on: November 22, 2021, 08:00:53 AM »
Yes, I just had the TZ type lightening holes drilled in the inner dia of the disc, like the YPVS as well.
I toyed with getting the disc ground down to 5mm, early TZ disc is 5mm and bigger dia, but I haven't done it. I might try that in future?
The early RD disc is thicker on the outside face so, you want to be careful to take the metal off that side or the inner dia that bolts onto the alloy carrier could be very thin.
Cheers

5port
5port

Offline 5port

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Re: Front disc options
« Reply #5 on: November 22, 2021, 08:32:07 AM »
Here is the way mine is at the moment.  :)



BTW, how are the rest of the forks going and, what springs will you have?  Mine are the linear rate 0.8kg/mm.
Cheers

5port
5port

Offline D Peacock

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Re: Front disc options
« Reply #6 on: November 23, 2021, 10:22:07 PM »
Here is the way mine is at the moment.  :)



BTW, how are the rest of the forks going and, what springs will you have?  Mine are the linear rate 0.8kg/mm.
Cheers

5port

Still at the engineering mock up stage, have all the bits except for master cylinder and brake hose. Need to sort out the damaged fork bottom then dry build the forks to figure out the emulator conversion and at that point I’ll look into springs. I run .9kg/mm on my GSXR400 but as the 350 is lighter (as is myself these days) .8 might be a good start.
For speed add lightness!

GSXR1100 - Big boy’s bike
GSXR400RKSP - Track / Race bike
YR5 - 52bhp - Ported RD barrels, 28mm carbs, Mick Abbey pipes, Powerdynamo with Zeeltronic DC controller, premix, Euro CR 6 speed box.
GT200X5 - Bog standard.

Offline tim steele

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Re: Front disc options
« Reply #7 on: November 24, 2021, 03:10:13 AM »

R6 disc with original RD disc center cut-out used as a spacer. R1 caliper with a simple bracket. Yamaha Zuma 11MM master cylinder and steel braided line. Perfect feel and 1 finger braking. I have less than $100  in all the parts bought used off Ebay.
I Love The Smell Of Blue Marble In The Morning!!!
Tim Steele in Front Royal. VA

Offline tim steele

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Re: Front disc options
« Reply #8 on: November 24, 2021, 06:32:22 AM »

I bought a 2015 if memory serves SR400 Yamaha front fender off of Ebay as well used for $50 and it fit easily with a little persuasion at the bolt holes as I couldn't run one the fender stays and I didn't like the way it looked with one missing.
I Love The Smell Of Blue Marble In The Morning!!!
Tim Steele in Front Royal. VA

Offline 5port

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Re: Front disc options
« Reply #9 on: November 24, 2021, 11:15:17 AM »

Still at the engineering mock up stage, have all the bits except for master cylinder and brake hose. Need to sort out the damaged fork bottom then dry build the forks to figure out the emulator conversion and at that point I’ll look into springs. I run .9kg/mm on my GSXR400 but as the 350 is lighter (as is myself these days) .8 might be a good start.

Norbo still doing the new 250LC Yamaha copy mastercylinder for £45 and the Hel custom made braided hose is about £35 inc post.  The olive in the Yam caliper comes out, allowing use of the simple male swivel screw-in fitting.  :)
Cheers

5port

5port

Offline Barnett

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Re: Front disc options
« Reply #10 on: November 25, 2021, 06:37:43 PM »
Sorry slightly off post but this chap at Castle Coombe used what was possibly the biggest and most beautifully made, (in france or hungry, can't remember), front drum brake I have ever seen. Made from billet. Thought you would like to see the pic, I have others but can't find themM

Offline robrd

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Re: Front disc options
« Reply #11 on: November 25, 2021, 07:10:40 PM »
In my opinion, that drum brake looks far better than any disc brake. But!!! looks don't stop you.

Offline 5port

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Re: Front disc options
« Reply #12 on: November 25, 2021, 09:52:00 PM »
Sorry slightly off post but this chap at Castle Coombe used what was possibly the biggest and most beautifully made, (in france or hungry, can't remember), front drum brake I have ever seen. Made from billet. Thought you would like to see the pic, I have others but can't find themM

That front drum brake is the Yamaha 4LS racing brake from the 1969TD2/TR2 onwards, through TD2B/TR2B, TD3/TR3, TZ250/350/A/B, replaced by the single disc on the '76 Model TZ250/350C onwards using the RD type Iron caliper!  In fact, remember that the TZ750 came in in '74 with effectively twin RD iron-caliper discs from the XS2.   
Those big 4LS drums are rare and expensive, that may well have been one of the repro ones.
The big 4LS brake could certainly work well on a 250 and is impressive.  However, it required to be well set-up and I guess if it was better than the single disc, they would have been seen on later bikes.  ;)
Cheers

5port 
5port

Offline german

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Re: Front disc options
« Reply #13 on: November 25, 2021, 10:28:58 PM »
Chris,
many riders swapped to RD discs back in the day and ditched the big drum. They are too heavy(only the brake, without rim and spokes, weights 8,7kg) and not lasted the race distance. In period the races were much longer than now in classic racing. We still have some guys which use the drum brake but even in our 20 minutes races they have problems in the last 2-3 laps to have acceptable brake power.
Back in our RD racing days we used thinned RD discs. A team mate had access to a grounding machine and over winter he always did a batch for us. Grounded down to 5mm and drilled like swiss cheese. On my own RD I had removed 2 of the 6 mounting arms of the disc stay aswell. Such a brake disc holds maximum 2 seasons before it was worn, if you raced much at airfield tracks with there stop and go characteristics it could be that the disc was worn out after 2-3 races as we braked it blue. But a lot lighter than a standard RD disc. I was always happy with the genuine RD caliper, RD master and such a modified disc. Nowadays I wouldn't bother and to use a EBC floater aftermarket disc if the regs allow it.
Will have a look tomorrow if I still have such a modified disc in my part boxes. Will weight them then. My guess is near the half of the weight of the standard RD disc.
Regards Uwe
« Last Edit: November 25, 2021, 10:45:16 PM by german »
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Yamaha RD250, RD400, Yapol TZ250B, Daspa TZ350, FZ750/1000, Honda RS125, Jackson Special 250, Höpfner-TD3, Hejira PE250, Broadstock F350 Sidecar, Siroko TZ250

Offline german

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Re: Front disc options
« Reply #14 on: November 26, 2021, 11:23:15 AM »
Found and an old worn out to 5mm grounded down and drilled disc. Could only weight it without a carrier. It comes in at 1,3kg.

In the same box I found a drilled only standart one. It comes in at 1,95kg(with carrier)


Regards Uwe
Classic Racers do not hide the ashes, they keep the fire burning
Yamaha RD250, RD400, Yapol TZ250B, Daspa TZ350, FZ750/1000, Honda RS125, Jackson Special 250, Höpfner-TD3, Hejira PE250, Broadstock F350 Sidecar, Siroko TZ250