Author Topic: Clutch shudder - tuning wuestions  (Read 296 times)

aaronz28

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Clutch shudder - tuning wuestions
« on: August 16, 2019, 03:06:21 AM »
Trying to tune out a clutch shudder on take off

Stock 1969 302.  With 1970 Lt1 cam
Manifolds, transverse exhaust
4053 with 72/76 6.5 and 8.5 and a 31 squirter

I don't believe timing is the issue as Ive had it everywhere frok 12initial/36wot to 20/42. With and without vac advance and no appreciable difference

The car is responsive and pulls great for being all corked up. 

The only thing i think is different in my carb,  previously i had 80 or 82 jets with a PV blockoff
And was running rhe 6.5pv up front when I had the 30/30 and it was smooth on take off

With the added 4-5” vaccuum at idle that the Lt1 cam creates, - do i need an 8.5 pv up front?At 900rpm idle, im getting 14-15”hg

Thoughts?

ko-lek-tor

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Re: Clutch shudder - tuning wuestions
« Reply #1 on: August 16, 2019, 12:58:20 PM »
If I understand? Just on takeoff and when clutch is engaged, there is a hesitation or stumble? I would check the clearance of the accelerator pump cam arm to make sure there was not too much slop (loose). If that is ok, possibly a size up on the “shooter” (accelerator pump discharge nozzle) 6.5 P Valve should be adequate.
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aaronz28

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Re: Clutch shudder - tuning wuestions
« Reply #2 on: August 17, 2019, 07:50:41 PM »
Def not the pump arm or the squirter. I have a 31 in it now   

Any ideas What else might be causing the chatter?

william

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Re: Clutch shudder - tuning wuestions
« Reply #3 on: August 18, 2019, 11:46:41 AM »
Incorrect motor mounts.

The 307/327 mount is a sloppy fit on the 302/350 frame bracket; about 1/4" too wide. In addition, it is shorter so the engine is incorrectly positioned.

If the balancer is very close to the front sway bar, may have the wrong mounts.

lakeholme

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Re: Clutch shudder - tuning wuestions
« Reply #4 on: August 18, 2019, 01:35:41 PM »
X2 to Willliam's suggestion.  A bad motor mount does feel like a transmission problem on straight or automatic.  It is most noteable on acceleration.
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Tinkerr

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Re: Clutch shudder - tuning wuestions
« Reply #5 on: August 18, 2019, 03:28:09 PM »
Assuming you have points, have you checked the gap. I use a dwell meter to set them right on 30 degrees. I've had a hesitation on another car that I couldn't find, turned out the points were out of adjustment, not significantly but enough to cause the hesitation.

aaronz28

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Re: Clutch shudder - tuning wuestions
« Reply #6 on: August 18, 2019, 03:31:55 PM »
i'm digging into it on monday -  its entirely possible the points have gone out of adjusment - but timing was still where I left it - so i don't think thats the issue.

the motor mounts could be the culprit - although i'm certain they are not the wrong ones - i would think that if they were shorter the fan would hit?

they were def snug on the frame when I installed th emotor last year - but i suppose one could have ripped some how.

will report back asap

thanks


olddragracer

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Re: Clutch shudder - tuning wuestions
« Reply #7 on: August 19, 2019, 04:37:36 PM »
 a shudder or chattering on pull away as the clutch is engaging is almost always caused by the clutch itself. If the clutch is the problem resurfacing the flywheel and installing a new clutch is the solution. Clutch chatter is often worse when pulling away in reverse. A stock "OEM" type clutch is what I would recommend. Aftermarket performance clutches have a much higher tendency to chatter but may be necessary if the engine is highly modified. Engine tune up and mount problems usually will show up at other times as well as when the clutch is engaging. Rough idle, under load at low RPM, engine acceleration while standing are examples. A new clutch will chatter if it gets engine oil, transmission lube or grease used during installation on the disc. A new pilot bushing is a "must have" when replacing the clutch. These are my opinions based on experience and I hope they are a help.

aaronz28

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Re: Clutch shudder - tuning wuestions
« Reply #8 on: August 20, 2019, 01:16:14 AM »
a shudder or chattering on pull away as the clutch is engaging is almost always caused by the clutch itself. If the clutch is the problem resurfacing the flywheel and installing a new clutch is the solution. Clutch chatter is often worse when pulling away in reverse. A stock "OEM" type clutch is what I would recommend. Aftermarket performance clutches have a much higher tendency to chatter but may be necessary if the engine is highly modified. Engine tune up and mount problems usually will show up at other times as well as when the clutch is engaging. Rough idle, under load at low RPM, engine acceleration while standing are examples. A new clutch will chatter if it gets engine oil, transmission lube or grease used during installation on the disc. A new pilot bushing is a "must have" when replacing the clutch. These are my opinions based on experience and I hope they are a help.

I would agree 100% except  -  this is my 3rd clutch and 2nd flywheel with less than 1500 miles and virtually no change in the shudder -

At first I installed a new McLeod 20# flywheel with their twin disk RST setup -    a lot of guys reported chatter so I wasn't worried - but couldn't live with it.  I contacted McLeod and they sent me their Super Street Pro which has a ceramic pad on the flywheel side and organic on the pressure plate side -   they said since it had such low mileage on the rST that I could easily get away without a resurface on a near new flywheel (we're talking less than 300 miles)

So - I put that clutch in - and made one error -  I put the Throwout bearing on incorrectly, as in, the fork's retaining clip on the back side of the TOB instead of in between the flange - stupid mistake, and I'm not a rookie at this -  - at first the clutch seemed smooth - but as it got warm, the TOB would not engage/disengage properly - and would make noise as I depressed the pedal -

SO - all that came out - and I learned that from the TOB not engaging the clutch properly, there was uneven wear on the flywheel -  so I pulled all that off - had the stock 40lb flywheel Blanchard ground, and installed an OEM type (made by Ram) clutch - fully organic with a bit more holding power.

That started off seemingly smooth but still had a very slight shudder -  I'm guessing nothing was solved but the problem slightly masked because fo the added inertia weight of the 40# wheel -  - but now a few hundred miles in - its still shuddering on take off.

When I put the car back together last year - I did replace the motor mounts with new rubber mounts and I had an energy suspension poly mount for the trans -  that's how the car sits.

tomorrow - I'm replacing the trans mount with an OE rubber mount - and I have 2 new Rubber motor mounts coming from HeartbeatCity - if the new mounts don't solve the issue - then it can only be the clutch fork or the bell housing - both of which are original and were not problematic before.   


I SUPPOSE I goofed up the fork when I had the TOB on incorrectly - but I highly doubt that -   I'm beginning to worry that I screwed up ANOTHER clutch with all this shudder - when its looking more and more like it never was a light flywheel or clutch problem to begin with.   

UGH - back under the car we go

Kelley W King

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Re: Clutch shudder - tuning wuestions
« Reply #9 on: August 20, 2019, 12:16:54 PM »
While you are under there look at your original clutch fork closely. I had one that had a hairline crack that gave me all kinds of problems. It seems the fork was flexing under pressure. The ball also deserves a good look. Just trying to save you another trip (under there).
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olddragracer

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Re: Clutch shudder - tuning wuestions
« Reply #10 on: August 20, 2019, 02:56:51 PM »
There has been no mention of the pilot bushing replacement. The pilot bushing is made of a material that is called "oilite bronze". The bronze is porous and contains a high percentage of oil. The oil will dry out over time and the bushing needs to be replaced when the clutch is replaced. A dry bushing even when not appearing to be worn can cause noise, [usually a screeching that sound like a bad release bearing] it can also cause an uneven clutch engagement that feels like a shudder. Engine and transmission mounts should be correct original type and not a type designed for racing. A new stock original clutch from a manufacturer like "Luk" is what I would recommend. The original type flywheel should be ground on a flywheel grinder that has the correct grit wheel to get the correct finish. There are many things to do during clutch replacement from cleaning the engine block to bell housing mating surface to the final clutch free play adjustment. If all steps of the installation are followed and a quality clutch is used you should end up with a smooth operating clutch.