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PostPosted: Sat Apr 25, 2020 6:07 am 
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Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Greetings all! Please could anyone tell me how to successfully uprate a standard GT380 clutch? My 1975 GT380M has EBC clutch plates (new) and new heavy duty EBC springs fitted. It slips the clutch when under hard acceleration. This is most likely related to the bike having a little more power than standard due to GT550 carbs being fitted. I have fresh Castrol Power 1 4T motorcycle oil in the box.
I am wondering if anyone knows of an alternative set of stronger springs or some other professional bodge that will work


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PostPosted: Thu Apr 30, 2020 5:02 am 
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You could try putting a penny washer or two on top of the springs to further compress them a little.

I'm surprised it is slipping, my 380M had J&R spannies and 0.5mm milled off the heads and was MUCH stronger from 5K rpm upwards, but I never had a problem with slip (before adding the spannies, I rebuilt the clutch with EBC friction plates and fresh springs from Crooks, because the PO hadn't tightened the big centre nut properly, and it was coming loose!)

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1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
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PostPosted: Thu Apr 30, 2020 5:37 pm 
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To the on ramp
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Joined: Sun Jul 13, 2014 7:55 pm
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Location: Greendale Vic, Australia
Country: Australia
Suzuki 2-Strokes: AS50, GS500, GT500, ex GSXR750 slabbie
Bit of a long-shot I'm sure, but I wonder if the GS500 clutch would fit.
Excellent clutch, zillions around.


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PostPosted: Fri May 01, 2020 2:08 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2350
Location: The Republic of South Yorkshire
Country: England
Suzuki 2-Strokes: 2 x GT550s GT750, T200, TC200
I got a set of EBC plates for the 550 and when I checked them, they were only minimum thickness, so as I needed the bike quickly, I put another steel plate in as well. So check the plates with a vernier to make sure they're ok.
I've fitted better plates during the current rebuild.

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PostPosted: Sun May 03, 2020 7:08 am 
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Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
That is an interesting idea Allan. I may give that a go. Thank you. I have noticed another clutch related glitch. After revving it fairly high for a fast take-off the clutch needs adjusting. I have had to do this a few times. At first I wondered if it was just bedding in, but I am starting to wonder if it is something more.
What were the better friction plates you installed?


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PostPosted: Sun May 03, 2020 1:13 pm 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
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Location: The Republic of South Yorkshire
Country: England
Suzuki 2-Strokes: 2 x GT550s GT750, T200, TC200
Unfortunately some unmarked NOS ones from my 'stash'. Similar colour to the 'normal' EBC ones, so possibly heavy duty or sintered. We'll see how they go when I get it sorted. Still having issues with the oil pump on the 550A and the weather is crap so I can't get 3 bikes out of the garage to work on the one I need to.


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PostPosted: Thu May 07, 2020 4:11 pm 
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Location: New Hampshire
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Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
I did the GT550 carb mod also (couple other items :ssh: ) and my gt380 clutch now slips too.

I bought new clutch springs, since mine were a little compressed per spec... but still slips!

I am going to try these springs which are allegedly 15% stiffer. That should be more than enough in my case

https://www.ebay.com/itm/CSK-Series-Clu ... SwF3Begh9n


I just order this 3 into 1-> 8) Since it has chamber, kind short tuned length it supposedly preserves top end but boost lower RPM power. That would be nice if so. And if so, clutch is going to slip even more unless I do something!

https://www.facebook.com/messenger_phot ... x4qArjd2qh

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),


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PostPosted: Sat May 09, 2020 9:30 am 
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Moto GP
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Location: Illinois
First. Check the specs and new plates and calculate the complete clutch pack thickness- maximum and minimum.
Now measure your clutch pack. As mentioned above, sometimes it will take an additional plate.

Next" Measure spring dimensions and compare to specifications to see if they are sagged. Try new springs and see if that fixes it. If not, you need LONGER springs, not stronger springs. That way, they provide more pre-load but similar lift pressure.

The reason the clutch cable needs to be adjusted is usually because the motor/transmission got hot. Does it need to be backed off again after it cools down? If not then it's something wearing way to fast - might be the end of the pushrod or the pressure plate.

Third: and this should have been first... What oil are you using. Our old clutches do not like friction modified oils. The additive packages often cause the old clutch designs to slip. Try an oil designed for 2 stroke transmission. I use Honda oils

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PostPosted: Sat May 09, 2020 1:01 pm 
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Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Vintageman wrote:
I am going to try these springs which are allegedly 15% stiffer. That should be more than enough in my case

https://www.ebay.com/itm/CSK-Series-Clu ... SwF3Begh9n" onclick="window.open(this.href);return false;

Those are what I already have fitted. They aren't strong enough to stop the clutch from slipping under hard acceleration.


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PostPosted: Sat May 09, 2020 1:22 pm 
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Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
tz375 wrote:
First. Check the specs and new plates and calculate the complete clutch pack thickness- maximum and minimum.
Now measure your clutch pack. As mentioned above, sometimes it will take an additional plate.

Next" Measure spring dimensions and compare to specifications to see if they are sagged. Try new springs and see if that fixes it. If not, you need LONGER springs, not stronger springs. That way, they provide more pre-load but similar lift pressure.

The reason the clutch cable needs to be adjusted is usually because the motor/transmission got hot. Does it need to be backed off again after it cools down? If not then it's something wearing way to fast - might be the end of the pushrod or the pressure plate.

Third: and this should have been first... What oil are you using. Our old clutches do not like friction modified oils. The additive packages often cause the old clutch designs to slip. Try an oil designed for 2 stroke transmission. I use Honda oils


I'm using Castrol Power 1 4T engine oil. Supposed to be ok for wet clutches, I thought. Maybe thicker gearbox oil would be better. As for adjusting clutch too often; No it doesn't need backing off again after cooling down. Perhaps pushrod is faulty. I think perhaps I forgot to harden the ends when I made it. Will have a look at that tomorrow if I have enough time. Don't worry, I'll give myself a smack round the head for being stoopid if it's my fault. :roll: :oops:


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PostPosted: Sat May 09, 2020 2:58 pm 
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Joined: Tue May 18, 2010 5:38 pm
Posts: 1471
Location: New Hampshire
Country: USA
Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
I bought new clutch disks and springs, plate seemed like new to me so did not change (yet) . I run 15-40 oil. I can still slip ... my case gets a lot better when engine warms up. Never any issue before mods ...so I will see if the 15% spring work for me. See If I can check if they really are stiffer or BS :evil: . I'll report back. For Yamaha you could get Barnett's truly stiffer than OEM and fixed slip on Yamaha R5 which should have had one more disk/plate set like RD350 if I recall.

Since I have to drain oil I'll consider trying something else

I'll watch this post
Good luck

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Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),


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PostPosted: Sun May 10, 2020 1:09 pm 
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Joined: Wed Jul 10, 2013 12:04 pm
Posts: 1087
Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Think I'll try the extra plate to give it more preload and see if that works well enough. Don't want to make the clutch too heavy unless it is necessary. Didn't have time to fiddle with clutch today, only carbs. Will see what she runs like tomorrow with carb alterations. Then play with clutch at the weekend.


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PostPosted: Sat May 30, 2020 8:28 am 
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Joined: Wed Jul 10, 2013 12:04 pm
Posts: 1087
Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
OK. After adding an extra plate and fitting a brand new genuine Suzuki cable, there is no clutch slip at all, despite carb revisions making the motor more powerful than before. Clutch is a little heavy with the extra stiff springs and extra plate in but feels very strong now, both cold and hot. Now if only it was possible to make it lighter...


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