Bucking after new clutch install
 

I had a stage 2 SouthBend clutch installed a few months ago after the TOB failed. This is an Exedy clutch with 6 segments of their Feramic compound.

14 FRS at 87k manual trans car for reference. Put all new parts in down to a cerakoted bearing retainer, Verus fork and new subie TOB and flywheel. Only part I didn’t replace is the clutch pivot boss if I missed something.

Since then I can get some nasty bucking if trying to launch hard. It gets worse when after spirited driving for a good session. It’s tamed a bit since installation, but still occasionally it gets obnoxious. I was thinking it was break in norms, but it it has not stopped yet.

Also, I did have a Whiteline trans mount bushing installed. And lately, an HKS supercharger which has shown me how soft the bushing package really is making the issue more prevalent.

Now, to the solution space. I’m not sure if this is the engine/trans mount set or the rear end suspension bits. Any comments appreciated as to where to start. Which might just be buying a GoPro to see the problem.

My car is stock suspension wise other than the Whiteline trans bushing. I’d prefer an STI parts solution, but not sure if they address the rear end bushings with different parts like the STI grade engine and trans mounts.

Nasty "bucking"?

Please describe "bucking" in reference to an automobile?

:confused0068:

Clutch chatter. Stock clutch is rated to let go before the transmission frags, and engages smoothly.

Feels like wheel hop on a leaf spring suspension. It is clutch chatter of some sort, just expected it to wear in by now and go away. The feeling from the driver's seat is that the tailshaft of the trans is moving, or the rear suspension connection to the unibody is bucking to and fro its range of motion.

It is a 350 ft-lb clutch.

So on one drive I purposely gave it a lot of clutch slip a few times to wear it in a bit more. Not obnoxious, just a few slow engagements making it slip a lot. It is improving the 1st gear takeoffs.

This clutch doesn't make it easy. Feels the same weight wise to the leg, but engages like rock compared to stock. Learning curve on the break in, I think I'll be fine in another month or so of commuting.

It's the Whiteline trans mount 100% I had the stage 2 sb clutch in prior to doing the mount and Perrin insert. Take offs are still smooth but I do get some low speed bucking in 1st gear. Never had that before. So guessing that's what your feeling. Clutch feels OEM and take off is the same for me

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I had my suspicions, I'll have to yank it and test again to be sure. I have slipped the clutch a bit figuring I was having a long break in as I'm pretty easy on clutches. But I never felt any shuddering that way, just first gear or reverse when trying to be brisk on take offs.

I had my suspicions, I'll have to yank it and test again to be sure. I have slipped the clutch a bit figuring I was having a long break in as I'm pretty easy on clutches. But I never felt any shuddering that way, just first gear or reverse when trying to be brisk on take offs. The bushings on this car seem really soft, I'm considering some STI bits.

Go with the STI n-group stuff. I have gotten used to my Whiteline+Perrin mount. It seems to have broken in but the bucking is there from time to time in low speed first gear driving.

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@jeepmor you might need the whiteline positive traction kit (subframe and differential bushing) to stiffen the rear. IMO it makes my car much easier to drive at low rpm, can lug the engine and the (stock) clutch doesn't make a peep on my 130k mile car. Though will make the car stiffer than coilovers and very loud and sometimes you'll get noisy vibrations from the rear.


I also notice that the clutch might act differently after some heat has gotten into the clutch or bushings. Maybe more deflection, compliance, etc.

Was thinking I was all alone with this issue. I'm getting used to it as well and it has greatly reduced. I definitely put a large bit of that on breaking in the clutch. 350 ftlb of holding power is a lot more than stock, and when it bites, there is zero slip. My new routine of slipping the clutch on purpose is in 6th gear going 60ish. Not tortuous, just making it slip a bit, run a few miles to let it coole, slip it again routine. This helped a lot more than trying to do it in lower gears.

That said, It hasn't disappeared just yet, but I'm adapting well and not as concerned about it now. Pretty new to sports car stuff like this, but an old hat in regards to my jeep. And, now that I've driven enough, it's very similar in nature to wheel hop on the jeep leaf springs.

Thanks for the STI parts reference and Whiteline rear bushing suggestions. I've read the STI parts are stiffer, but still have low NVH. Not thrilled about the NVH feedback from radroach, but good to know it addresses a lot of this issue. It always felt like it was in the back end, not the clutch, but this type of issue can be difficult to pinpoint.

As stated before, it really feels like leaf spring wheel hop.

I had the clutch opened back up recently, this root cause was the Verus fork with sloppy tolerances. The shop put in an OEM fork and all is well again, no more serious bucking.

Expensive mistake, but finally have this issue resolved. Also, the OEM throwout bearings still suck. At 30k, it's throwing rust dust out of it. Had the Exedy throwout bearing I saved from the Southbend clutch put in this time.

What in the tolerance was sloppy?

That is an extremely weird source for something like this...

I was thinking the same.

Consider an imaginary plane intersecting the top and main pivots along the longitudinal axis. That plane must bisect the line drawn between the contact points on the tines of the fork.

Is it really the issue? I don't know, but I've considered it.

:( I have a Verus fork I am about to put in...

but how many verus forks have been sold, and this is the first related issue to surface here since they developed it in early 2014?

I wouldn't hesitate. I didn't want to say anything, but this sounds more like a shop who makes mistakes is taking an easy scapegoat. I've heard ' oh yeah, we've seen failures after installing those" when it's really just bad installation practices.

I have one installed, many people have them. Go ahead and Google " Verus clutch fork issue" and watch as nothing pops up..

I have a Verus fork and pivot and south bend stage 2. Works perfectly for about 4 years now.

Was still planning on installing it lol. All valid points though. I've never heard of anyone else having issues either.

I think it'd have to be pretty bad. I'm skeptical too. They switched to a forged design but I don't see any finish machining in the pics.

Per the mechanic, the clutch wouldn't completely disengage which was my difficult shifting issue.

So the pivot points of contact were less than needed. This could be a pivot pocket too deep or the seesaw contact points not being far enough from the pivots in the parallel plane. This also hints to me my throwout bearing never took any time off.


I agree, it has baffled me, but it is now a night and day difference. I could put it in reverse on cold days and the drivetrain would shake because the clutch was not fully disengaged. Please tell me how this could be installed improperly, there is no room for adjustment on this assembly. And the shop that fixed it said they've seen several as they are a subi specific legit dyno speed shop. It was not the shop that installed it.

I agree, but how could this part not be installed properly. Blame it all on a worn pivot or such. All other parts were brand spanking new. Wear marks on everything were normal, the fork didn't slip off the the TOB at all.



Bottom line, I replaced that part back to OEM and I'm good. You can defend Verus and doubt me all you want. The mechanic said the previous install was sound, and had seen these before. Call Surgeline yourself and ask them to elaborate.

I wonder if pedal travel was checked/readjusted after changing out clutch fork.

This would be my guess. The aftermarket clutch might have some increased thickness somewhere as well. Also, the oem fork might be flexing a bit more than the forged one. An extra mm could make up the difference.

#4...

?

From post #4, one of mine.

"Feels like wheel hop on a leaf spring suspension. It is clutch chatter of some sort, just expected it to wear in by now and go away. The feeling from the driver's seat is that the tailshaft of the trans is moving, or the rear suspension connection to the unibody is bucking to and fro its range of motion.

It is a 350 ft-lb clutch."


I really thought it was just the beefier clutch causing the chattering due to the extra torque impulse exceeding the stock bushings design and the stock bushing were now too soft. Namely the rear diff bushings that connect the subframe to the back of the differential.

Also, I have no axe to grind with Verus, I was just told by the shop they've experienced this before with this particular part. They had no negative feedback on other Verus parts, just this one.

Knowing how this clutch goes together, there isn't any adjustment to the fork engagement. If like my old CJ7, I have an adjustable threaded section in my linkage to set the clutch fork hold off clearance so it isn't touching the TOB and spinning it while running. I have no adjustment on the throw distance of the jeep system either, the bellcrank (linkage) assembly controls that, and is fixed.

Subarus don't even have that, and the first shop tried to fix it when I complained about it. All I found on my own was that I can adjust the pedal height with adjustable linkage in the cab at the pedals, but this is not an adjustment of throw distance, or even the clearance setting to keep the fork off the TOB when in gear and clutch engaged, there isn't any adjustment on these like that. But it is nice to lower the pedal a bit so you don't have to lift your heel. If you do this, be careful, it does not take much adjustment to have the clutch engage while the pedal is barely off the floor.
I tried some of this setting both high and low to see if it would change the condition, it did not.

I share this only because I finally got this issue fixed and found the root cause and thought it relevant in this forum.

There are no finishing/machine marks, zero, it was 100% cast. You can now see wear on the ball pivots and where the fork touches the TOB. And again, mine exhibited the problem from day one.

Do you still have the fork? I'd like to examine it if you are game.

It's forged 100%, not cast. I have one sitting on my desk waiting for install. You can't just base it solely off the surface finish at first glance. Looking at it you can see the parting line from the die and you can see the draft for the dies in the edges. Cast parts usually come out cleaner to be honest. Ever see a forged rod that doesn't have surface finish machining? This is an eagle forged rod for a SBC.

https://www.competitionproducts.com/...0BPLW_1500.jpg

Forged, okay I see it now. How do I share pics? It does have two holes and some pockets milled at fork end for clip retention. The pivot clip is milled open. I do see what looks like a mold part line, or rather a forge line like a high pressure stamping.

The interesting bit is the wear, the pivot pocket has significant wear you can feel with your fingernail like a button from the drilled open top of the pivot ball. I'd guess 10-20 thousandths of an inch.

Like this ? This is a used fork I picked up.

https://uploads.tapatalk-cdn.com/202...9f12711077.jpghttps://uploads.tapatalk-cdn.com/202...3ee3ff027d.jpg

For shits n giggles I ran back and threw it in my hardness tester. Granted I didn't sand in a smooth spot and level it but it's pretty hard. I would say it's in the range of 34-38 hrc. A decent high carbon knife or a truck leaf spring is about 42 hrc for reference. I would shoot Verus a message. They are pretty responsive and care about the product they put out.

https://uploads.tapatalk-cdn.com/202...7a9be0b54b.jpg

are the fork tines symmetrical about the center plane?

In my 4 handed attempt at taking a picture of it, it's close but it looks like it's off a smidge. Hard to tell without another set of hands. Could have it off the peak a bit on one side. I didn't check the lengths.



https://uploads.tapatalk-cdn.com/202...ff1a012794.jpg

Use the right measure.

It's ok. I would set up a jig with a camera and plug that into inkscape.

Right?! JFC, what a cruel joke!

Would be nice if I could just scan it and port it into solid works. Even nicer if I could scan the stock one too and have SW merge the two and match points.....but I sold my scanner.