915 with Sachs 'Super' Clutch - Very Heavy Feel - Need Options

[asphaltgambler]

Hey all, Just finished my complete nut / bolt resto / rebuild 1985 911 Targa. The engine is heavily modified and with also upgraded fresh 915. I've installed a Sachs 'Super' clutch, all components are new, rebuilt pedal box, cables, etc.

I'm currently working out tuning / driving / suspension bugs.

The issue is heavy clutch effort. I replaced all the related springs and adjusted it per the factory manual. The problem is not so much for me but comfort level for my wife who is petit. I know it is going to be an issue. Really I would like to see less pedal effort as well.

Looking at the whole OE system, it seems to me there would be easier solutions than installing a whole aftermarket hydraulic conversion, which is something that I will not do. To me, if clutch long arm was @1" longer at the end where the cable hook goes and the short actuator arm was, say, 1/2"-5/8" shorter at the contact point that would be enough increase in leverage W/O sacrificing travel.

Has anyone else thought of this or make something along these lines?

[john walker's workshop]

A stock Sachs kit is not stiff. Probably your only option. A few hours R&R and sell the beefy one on the forum. I used a centerforce kit in my old '72 with a 3.2 and replaced it a few days later.

[asphaltgambler]

John - thanks for replying. The engine I have in there now makes substantially more HP / TQ. I'm fairly confident that the stock clutch would not hold or last long which is why I installed the performance Sachs kit to begin with. At the time, I do not think that Centerforce made that kit as I would have likely bought and installed that.

After some thought on this, possibly could find someone to do CAD scan of the current parts, and machine what I want W/O spending $1K+

[icarp]

Originally Posted by asphaltgambler

John - thanks for replying. The engine I have in there now makes substantially more HP / TQ. I'm fairly confident that the stock clutch would not hold or last long which is why I installed the performance Sachs kit to begin with. At the time, I do not think that Centerforce made that kit as I would have likely bought and installed that.

After some thought on this, possibly could find someone to do CAD scan of the current parts, and machine what I want W/O spending $1K+

What power and tq numbers are you talking ?
Engine specs for the build, Drag racing ? road racing ?
I may have some answers for you
Ian

[asphaltgambler]

^^^^ Ian, hi - The engine I built is as follows: 3.4, 9:8 pistons, Super Cup Cams, turbo oil pump, slight port work on stock heads, 964 Plastic Varioram intake with the Disa valve controlled by a MSD RPM 'pill' box, DBX programmable MAF integrated to Steve Wong modified DME/chip, B&B headers.

This combination should make 305 / 310 Flywheel HP. I don't what the TQ is, but the curve is very broad and pulls very strongly from 2500 to 7200RPM

It is a weekend fun / street car...............

[icarp]

Originally Posted by asphaltgambler

^^^^ Ian, hi - The engine I built is as follows: 3.4, 9:8 pistons, Super Cup Cams, turbo oil pump, slight port work on stock heads, 964 Plastic Varioram intake with the Disa valve controlled by a MSD RPM 'pill' box, DBX programmable MAF integrated to Steve Wong modified DME/chip, B&B headers.

This combination should make 305 / 310 Flywheel HP. I don't what the TQ is, but the curve is very broad and pulls very strongly from 2500 to 7200RPM

It is a weekend fun / street car...............

Ok great info , I agree with the 305 hp @ crank, TQ 240+ , and the tires ?
the stock clutch will hold the "go" that your engine produces , provided you drive without reckless abandon. The tires should spin before the clutch gives up.
You could beat the snot out of it with speed shifting to chirp the wheels and have problems , if you want .
I think the stock clutch will hold up well for you, I have a number of customer cars with 270 hp and a stock clutch with no problems .
Just my thoughts , call if you like
Ian

PS , if you play Dyno games you may get it to slip, the tires and the road are far more forgiving

[john walker's workshop]

Agreed.

[asphaltgambler]

Thanks all. I am still setting the fuel map with an onboard wide-band and am getting very close to completing that. From a a roll-on in first gear, WOT starting at 2500, it will squat hard and spin the tires, pulling hard until I shift. It really is a monster with torque everywhere, I love it! This combination could easily make more power with additional cam timing, compression, more head work with larger valves. But I built it to do exactly what I want it to do, and it has exceeded my expectations.

Now I need to address the few things that don't suit me.

[Jeff Higgins]

I hate to say it, but I think your 915 is going to give you problems before a stock clutch ever will. I have had the same stock clutch in my 3.0 liter '72 hot rod for over 105,000 miles so far with absolutely no issues. I have, however, broken components in the transmission twice. First time was disintegrating the 2nd gear synchro, second time was breaking two teeth off of the big gear in the 2nd gear set.

Both times, while I had the tranny out and John Walker was repairing it for me, I pulled the clutch apart to at least put a new disc in it "while I'm in there". Both times the disc looked brand new and mic'd within just a few thou of the brand new one with which I was going to replace it. The broken teeth were just last Christmas, so the clutch had about 100k on it. And it looked unused.

I'm not making as much power as you are (about 255-260 hp, maybe 235 ft lbs), and my car is probably a lot lighter (under 2,200 lbs), which are both factors helping me out. But, I do run it on slicks, on the race track for DE days about a dozen times per year. Oh, and it has a limited slip in the diff as well, adding to the "stress" on the clutch. It's taken that "abuse" with nary a problem.

The stock clutches are pretty tough in these things.

[asphaltgambler]

I've had mine gone through completely, added the 4-speed double bearing setup. I don't plan to hole-shot or speed-shift at all. Just accelerate like crazy, then disengage the clutch, select the next gear, softly engage the clutch. lather, rinse and repeat. I already know the limitations and was unwilling to perform the surgery and spend even more money on a G50

[rumlyne]

I replaced a stock 1981 clutch, PP, and flywheel with a
Sachs super clutch & light flywheel to adapt it to a
1997 V-ram. I noticed no difference in pedal pressure.
In my 27 years with my 1981 911 a "stiff or Heavy clutch pedal is usually
a bad or knarly about to go bad clutch cable.
I've replaced 2 in 27 years. 1 or 2 strands of the cable break then ball up in the tube
and the clutch gets stiff.
Might not be your problem but you might check it before popping for
a new clutch.
Good luck!

[Sboxin]

Our Sachs experience:

The pressure plate failed in our 3.8L/915 race engine
- photos show the PP spring that broke and the 915 damage
- it also froze the engine when the spring cought on the starter hole
- The Sachs disk looked in very good condition
- the PP is probably 8 years old
- we will be switching to a Kennedy clutch for future use
.
The 915 was welded and machined to like new condition by CMS.

Regards,
Roy T

[mikedsilva]

Originally Posted by asphaltgambler

Hey all, Just finished my complete nut / bolt resto / rebuild 1985 911 Targa. The engine is heavily modified and with also upgraded fresh 915. I've installed a Sachs 'Super' clutch, all components are new, rebuilt pedal box, cables, etc.

I'm currently working out tuning / driving / suspension bugs.

The issue is heavy clutch effort. I replaced all the related springs and adjusted it per the factory manual. The problem is not so much for me but comfort level for my wife who is petit. I know it is going to be an issue. Really I would like to see less pedal effort as well.

Looking at the whole OE system, it seems to me there would be easier solutions than installing a whole aftermarket hydraulic conversion, which is something that I will not do. To me, if clutch long arm was @1" longer at the end where the cable hook goes and the short actuator arm was, say, 1/2"-5/8" shorter at the contact point that would be enough increase in leverage W/O sacrificing travel.

Has anyone else thought of this or make something along these lines?

did you replace the clutch cable with a new one?

[asphaltgambler]

Yes, see my OP, thanks.

[gled49]

I had the same experience with Sachs clutch in my race car as Roy did, but mine only lasted 15 min. Went to Kennedy ALU ALU light diaphragm and street race organic disc, with outstanding results.

[icarp]

Originally Posted by gled49

I had the same experience with Sachs clutch in my race car as Roy did, but mine only lasted 15 min. Went to Kennedy ALU ALU light diaphragm and street race organic disc, with outstanding results.

I believe the "Kennedy " products are the ones to go to . There products are top notch,
well thought out , and durable . That said the Sachs should perform without any problem. I'm not sure what it is, that is causing the heavy feel for you.

Ian

[Jeff Higgins]

I must admit to a bit of surprise reading about Kennedy clutches for our applications. I didn't realize they even made them. I'm equally surprised to learn of everyone's misfortunes with Sachs. They are all I have ever used in my VW and Porsche applications, with outstanding results.

My only experience with Kennedy was back in the late '70's to early '80's when I was actively drag racing. I ran a series of big block MOPAR "B" bodies (Road Runner and Super Bee) cars with 383's and 440's. The "launch" was carried out by running the motor to about 6,800 RPM as the Christmas Tree lights worked their way down, then simply stepping off the clutch on the green light. They seemed to hold up well to that kind of (ab)use, so I imagine they must hold up quite well to relatively "gentle" use (by comparison) in our cars.

[spuggy]

I ran multiple (cough) Sachs clutches in my 915 with a 930 at increasing power levels. Apart from wearing out quickly with 330 crank HP - I replaced one with ~15,000 miles on it - they were fine. Although for that clutch, the PO loved to build boost holding against the brakes - which in retrospect really can't have helped the clutch life.... It was a lot of fun to launch that though, LOL...

The Stock/Power clutch dismally failed to hold peak torque once I got to 370HP & 350 ft/lbs at the wheels. Fitted another, then tried a trick friction plate, not realizing the car was making that much until I got to a dyno... They both broke free ~3500 RPM with more than 1/3 throttle or so and would just polish the flywheel.

So puck friction & Sachs Sport/ZF Race Engineering pressure plate it was. Another league entirely. Pedal pressure was a bear after 20 minutes in traffic. Probably 3x, 4x pedal pressure of stock. But it didn't slip under power, ever - it was also fun (not!) slipping the puck on hill starts (it hated that)...

Sachs make a range of pressure plates, so you can get progressively higher clamping force if necessary... The pressure plate I ended up with, my wrenches said was the highest clamping force quoted in the catalog, and the closest thing to an RSR pressure plate still available.

Minus the puck, that sounds like the clutch you have. I think that's probably more clutch than you really need. I'd think that with ~310 crank HP in an N/A car that revs - eg doesn't make 80% peak torque @ 3000 RPM - you would be fine with a relatively mild clutch upgrade. Sachs Power Kit is the stock clutch, but cherry-picked to be in the top 10% of spec, apparently. Seemed to work with the 930 at 10% over stock. Perhaps a slightly higher-tech friction plate and/or pressure plate would hit the sweet spot for you.

One thing a competition clutch guy did tell me when I was selecting clutches and exotic friction materials - Sachs have probably a 20% margin on their quoted spec, whereas most aftermarket clutches tend to get rated with relatively little margin in comparison.

[asphaltgambler]

Interesting, thanks. There is more in the engine combination through larger valves and a little more port work, but I felt at the time, and now I'm about at the limit of the transaxle already even with the upgrades. Honestly I'd like explore casting / modifying the short actuator arm with @ 1" less reach, cast the long arm with the contact pad moved closer to center to increase the leverage.

[Gordo2]

Seems things went sideways from your OP - discussing clutch vs. HP/TQ vice clutch vs. wife's ability to depress the clutch pedal.

I think a good part of the force required to depress the clutch pedal is due to the pedal assembly itself. The spring at the clutch pedal is quite strong and is somewhat difficult to depress even with the clutch cable detached.

You could consider trying options to reduce the pedal spring tension, but I would be concerned with how it impacts overall clutch performance (pedal return).

Just a thought to get the conversation back to your original Q - how can you reduce force to needed to depress the clutch pedal?

Good luck, Gordo

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Side note - I think I have a Sachs "Super Clutch" but can't tell the difference in pressure needed to depress the clutch pedal, between the super clutch and stock.