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Stiff Clutch - mid 80's 915 - Why?

The amount of pressure needed on the pedal to disengage the clutch on my 78 SC is high. The PPI indicated a possible pressure plate about to fail but the PO swears this amount of pressure has been needed during the 20k he drove it. The car is equipped with a mid 80's 915 and from a visual stapoint, all appear correctly setup .....see pic. I checked for bushing swelling at the pedals and there is no indication (although I am not sure I'd see it). The brake pedal does not suffer from this so I have ruled out the pedal cluster.

Could the cable itself be binding internally and other than replacing, is there a way to tell? If it is the pressure plate, is there a way to test this other than requiring a motor drop and visual inspection?

Other than the additional pressure, the clutch performs well, no slippage etc.

Any feedback would be appreciated.

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Old 01-02-2004, 11:41 AM
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I have read several times here that replacing the cable on a 915 car can/will drastically change the pedal effort required.
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Old 01-02-2004, 11:46 AM
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My guess is a broken horseshoe spring. While it looks intact in the picture, you should look at it closely to see if the inner part of the spring is broken.
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Old 01-02-2004, 11:49 AM
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I vote for the cable, if (when) the helper spring breaks it is so difficult to depress the pedal that it is nearly impossible. Or more accurately, it feels like you are going to break the cable.

My clutch pedal is stiff on my 915, it is either the cable, (age unknown), or a worn disc or both of these. A worn disc might still grab, but the action of the PP has to travel farther than it should, at least that is what I've been told by the people who know.
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Old 01-02-2004, 11:57 AM
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I vote for the cable also. Had my cable replaced last month and there was a significant difference afterward. Now easier and smoother to press.
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Old 01-02-2004, 12:10 PM
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The helper spring can lose its spring tension over time. Even if it looks ok, a new spring could make a big improvement in addition to a new cable.
Old 01-02-2004, 12:12 PM
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Three areas external to the 915 can cause stiff clutch pedal issues:

1. Worn, dirty clutch cable. Cleaning can help if the cable isn't frayed or worn out ... fresh lube job with moly grease is need. Otherwise, a new cable, properly lubricated along the last four feet next to the 915 end with moly grease such as Valvoline #985 or #986 ... is required.

2. Pedal box issues ... rust, worn or swollen bushings, cracked or worn arm on clutch pedal lever, cracked clutch pedal shaft, etc. You can't "rule out" the pedals unless the cluster has been removed, disassembled, cleaned and inpected for cracks or wear issues at the lever arm eyelet! Many times, when the eyelet hole wears ... it reduces the leverage available to the pedal to pull on the cable clevis, and effort increases significantly!!! Cracks can cause high pedal effort because only a percentage of pedal travel is transferred to the cable motion ... the lost travel is expended 'flexing' the crack. When the crack finally breaks, your pedal effort will be significantly reduced! Gear changes may be a bit 'graunchy,' though!

3. "Helper" spring cracked or binding ... corrosion, etc. ... OR, maladjusted!!!

Untill all three areas are addressed and brought up to new spec ... there isn't any reason to consider an engine and transaxle drop!
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Old 01-02-2004, 12:22 PM
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Warren, Excellent points on #s 1 & 2, but on #3, how can the helper spring be adjusted?? Or are you refering to the overall clutch adjustment? Thanks.
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Old 01-02-2004, 12:28 PM
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when the disc gets very thin, the release geometry of the pressure plate is changed, and a stiff pedal is the result. it's amazing the difference a new clutch makes on pedal effort.
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Old 01-02-2004, 12:29 PM
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Stiff clutch could be a number of things:

-guide tube or throw-out/release bearing
-helper spring
-clutch cable
-improper installation of cable
-pedal bushings
-pressure plate
-release fork shaft bushings

I'd start with the cable. If the cable isn't inserted properly into the bowden tube, the cable doesn't operate correctly and gets messed up.

The 915 I remember has a bit of resistance and the start of the pedal push and then partway down you feel the helper spring kick in and the pedal effort lessens. Very smooth and direct if I remember correctly. Lighter feeling and less effort than the hyd. setup in a G50 I think.
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Old 01-02-2004, 12:30 PM
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Denis,

Adjustment at the two-piece lever arm attached to the throwout bearing operating arm, and the 1.0 mm clearance ... was what I was referring to. Spline matching/alignment can affect the freeplay adjustment there, too ... as can the clevis position on the cable end and pedal stop ... up front at the pedals, and in the tunnel.
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Old 01-02-2004, 12:37 PM
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I can't speak for individual parts, but my clutch was fairly warn, so I did the full clutch kit from pelican including clutch cable, and I have to say it's like butter to push in now. I thought they forgot to connect something. It's tightening up a bit now but nowhere near the squat rack pressure it took me before to depress the clutch.

I couldn't believe I lived with it, but I thought it was suppose to be a little bit of a leg workout.
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Old 01-02-2004, 12:50 PM
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Do the cable, had the same problem on my '85 and it is 100% better.
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Old 01-02-2004, 01:50 PM
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Craig:

You have worn components. A comprehensive fix of a rebuilt pedal cluster with brass bushings, a new clutch cable, and a new horseshoe spring will result in an amazing feel. My hope is that the PO did replace the clutch so that you can exclude that, and the possibility of a cracked throwout arm.

Fixing this yourself is all of about $150.00. It is fun and just a bit challenging.

Pay particular attention to what Warren says about the clutch arm where the clutch cable attaches to it. The round hole will elongate, and you will have a notch feel to the clutch. Be prepared to take this part of the pedal cluster to a welding shop and have them drop a bead where the hole has elongaged. Buy a new rattail file and clean the hole to a round state again and then throw the new brass bushing in there for many faultless miles of use.

Love the RD400. I had a 350B with some TZ accents and I still cannot believe that the front brake was as nice as it was. Made the 400/4's brake feel like I was just grabbing air :<

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Old 01-02-2004, 02:01 PM
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If the clutch disk is thin, and all else is properly fuctioning, I'd go with what John Walker stated. The difference between a new disk and worn thin one is night and day. With a new one, it will feel as light as your Toyota, whereas with a worn one, due to the geometry of the pressure plate, the force seems like it increases by 3X.
Old 01-02-2004, 02:05 PM
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Thanks guys for the advice. I'll start with the cable and go from there. The helper spring is not damaged but I cannot speak to its functionability at this time.

If the clutch needs to be done, so be it. It's the excuse I need to pull the motor to replace the engine pad that's starting to fall apart and paint/detail the compartment in preparation of a new exterior color down the road. I would however like to get the suspension and front cooler installed first.....our first DE is in April and it will be here fast!
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Old 01-02-2004, 02:12 PM
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Here's more of the same: my '81 has always had a stiff pedal and I've kinda lived with it until now ... engine is out for a rebuild so while I'm in there I'm doing the whole enchilada - new disk, PP, TO bearing, release fork, pilot bearing, springs, cable and guide tube seal.

I drove KStylianos' 82 SC the other day and he did all of the same work. The feel was 10000000% better - I couldn't believe I had driven with mine like that for so long.

Now all I have to do is get mine back together so I can feel the magic as well
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Old 01-02-2004, 05:13 PM
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I would check the vertical throw out shaft that is in the bellhousing. The shaft gets dry and needs to be cleaned and lubed.
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Old 01-02-2004, 06:48 PM
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if you're going to replace the cable, do the helper (omega) spring at the same time. As said above, even if it "looks" good, it could be tired. Pretty cheap fix...made a night and day difference with mine.
Old 01-02-2004, 09:29 PM
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My 84 carrera had a very heavy clutch feel, no amount of tweaking ever helped (new cable, new PP/Clutch/TO bearing, adjustment, lubing the cluth arm tube etc.). Gave up and just ... took it.

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Old 01-03-2004, 07:54 AM
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