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Happiest when Tinkering
 
gsmith660's Avatar
 
Join Date: Jun 2007
Location: Missouri
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4th gear rpms redline fast

I need some help from the group. I was accelerating in 4th gear and about 4000 rpm the revs jumped really fast to redline and again in 5th. Is my clutch slipping? I think I already know the answer but also would like to know if I have reached the limits for this clutch and need a better clutch?
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 10:45 AM
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Max Sluiter
 
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Do you smell anything? Clutch slipping only gets worse.
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Old 08-01-2010, 10:54 AM
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Happiest when Tinkering
 
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No I dont smell anything but then I only let it go for only a sec the funny thing is it hooks up fine at the launch it only happens when I am making good hp at boost. I think I will back out the adjustment on the clutch as I check it and I only had to move the pedal a quarter to half inch to disengage the clutch. I have to lean out the mixture a bit I had an AFR of 9.9 at 5-6 psi boost. I think the target is 10.5 at boost so not much.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 11:59 AM
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Yes it's clutch... that's typical in that the higher gears provide much higher resistance than the lower gears, hence the slippage
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98 Tahoe ,2007 Saturn Vue
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Old 08-01-2010, 12:46 PM
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Happiest when Tinkering
 
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Thats what I thought but wanted to confirm now how do I fix it? Am I making that much more hp that I am overwhelming the stock clutch?
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 12:49 PM
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yes, my car does the same thing. The clutch is fine 1st - 3rd but hammer it in 4th and it blows right thru the clutch
Old 08-01-2010, 12:57 PM
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Happiest when Tinkering
 
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I will try adjusting and report back
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 12:59 PM
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I'll defer that question to Brian (Rarlyl8), he's running close to 400 hp with a 915 clutch IIRC.
Could be a couple of things,, clutch wear, pressure plate getting weak, too much HP, how much do you think you're generating ?
I had a weak pressure plate and had to replace mine.
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"Todd"
98 Tahoe ,2007 Saturn Vue
86 930 black and stock, 80 930 blue tracdog
91 Spec Miata (yeah I race a chick car)
"life"ll kill ya" Warren Zevon
Old 08-01-2010, 01:00 PM
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Happiest when Tinkering
 
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I dont have any idea what kind of hp I am generating I have 2 clutches and when I drop the motor I switch clutches after checking the wear which was fine this time. I suppose the pressure plate could be weak the clutch is old but not many miles on it.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 01:12 PM
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Sounds like the clutch. The started slipping on my 930 shortly after I bought. I drove it way too long with the clutch slipping, but it never completely let go so it's pretty robust. When I did finally change it the flywheel was covered with cracks.

If you buy new, buy Kennedy.
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Old 08-01-2010, 02:31 PM
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What would have caused the cracks in the flywheel? Heat?
Old 08-01-2010, 02:57 PM
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Happiest when Tinkering
 
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Yes I would think heat. The good thing is it has not slipped more than 5 or 6 times and I let off right away and haven't smelled burned clutch plate mat. so I will adjust and hope that takes care of it I didn't have this problem before I pulled the motor for the cam nut so I am thinking I just over adjusted the clutch.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 03:02 PM
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Happiest when Tinkering
 
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Got the clutch adjusted will see if that takes care of it as clutchs go it was alot of adjustment.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 05:29 PM
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OFF THE BOOST PIPE NOW...
 
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Sounds like a slipping clutch. Mine started to slip when I was overboosting. A new wastegate fixed that. The next time it started slipping (with a new disc) was after I rebuilt my engine (400 rwhp). A KEP stage 2 PP and their disc fixed that.

Long story short, check your boost gauge and clutch linkage.
Old 08-01-2010, 05:43 PM
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Been there done that. New clutch time. Kennedy works very well for me.
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Old 08-01-2010, 06:09 PM
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Happiest when Tinkering
 
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Def. not overboosting gauge is right on 6 psi when slippage starts. I am thinking possibly 250 to 270 hp is what this is turning out this is a very mild build as I didn't go into the motor internals on this go around but next summer or possibly this winter I will start on the short block for a higher output motor and will need if my clutch is not going to hack it then I will need to replace it before the new motor goes in. wastegate by the way is new and works great (Tial).
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 06:15 PM
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Happiest when Tinkering
 
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Quote:
Originally Posted by mark houghton View Post
Been there done that. New clutch time. Kennedy works very well for me.
Got a link to the Kennedy products with prices?
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 06:16 PM
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BTDT as well though I choose a brand new stock unit for a 911 with a 915 tranny. I spoke with don at EBS (we do business together) and he mentioned some great deals on something that would work for me when I drop the engine next time. it really was not that expensive. Make sure no oil is weeping on the disc as this would cause it to slip
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Old 08-01-2010, 07:01 PM
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Happiest when Tinkering
 
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Quote:
Originally Posted by mb911 View Post
BTDT as well though I choose a brand new stock unit for a 911 with a 915 tranny. I spoke with don at EBS (we do business together) and he mentioned some great deals on something that would work for me when I drop the engine next time. it really was not that expensive. Make sure no oil is weeping on the disc as this would cause it to slip
Good advise Ben. EBS? Got a link? I dont think it is oil getting on it but I can check if this adjustment didn't work.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go!
76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3
76 Blazer also restored by me
Old 08-01-2010, 07:17 PM
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Quote:
Originally Posted by gsmith660 View Post
Def. not overboosting gauge is right on 6 psi when slippage starts. I am thinking possibly 250 to 270 hp is what this is turning out this is a very mild build as I didn't go into the motor internals on this go around but next summer or possibly this winter I will start on the short block for a higher output motor and will need if my clutch is not going to hack it then I will need to replace it before the new motor goes in. wastegate by the way is new and works great (Tial).
It's torque, not HP, that the transmission cares about.

Nearly stock 930/60 making 310 ft/lbs ate a Sachs Power Clutch very nearly down to the rivets in ~ 15,000 miles. Couldn't tell it was slipping, the 915 gears were so short.

Once making upwards of 375 ft/lbs (flywheel), it ate a new replacement Power Clutch up pretty much as soon as the motor was broken in - very obviously broke free @ peak torque and thereafter it just got easier and easier to do with less and less throttle... It was in there less than 3,000 miles.

Sachs competition pressure plate seems OK - although the first one mysteriously lost spring tension around 12,000 miles and was replaced for free by the Sachs distributor despite the fact I bought it on another continent...
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Old 08-01-2010, 07:28 PM
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