1968 302 / C4 Vibration Issue Mystery

jsbenami

New Member
Apr 7, 2019
3
0
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43
Alexandria, VA
Hello, wondering if anyone has advice/experience in this area.

I have a 68 that I bought taken apart but with a rebuilt 74' 302 and rebuilt C4 transmission. Got it all put together but there is a pretty bad chatter vibration at moderate RPMs. This is parked or in neutral. If you take a short drive it is of course pretty impossible to drive faster than 25 or 30. Origninally this car had that same c4 and a 289.

I have access to a full lift shop. Already replaced the harmonic balancer and flexplate (28 oz offsets). Took the c4 out twice this weekend removed and drained torque converter. Ran the motor with new balancer and flexplate installed but with torque converter purposefully left off. Engine ran smooth as a baby's behind. No problems at all RPM ranges.

R&R the tranny again today with the new (brand unknown) converter installed and fluid. Vibration came back immediately. Infact it's even worse now. So thoughts are that there is either a bad or incorrect torque converter (all bolts line up through the flex, even the drain plug and yes it has some play....not too tight) or the tranmission input shaft or something else inside the trans. Our shop foreman said he felt the vibration was coming from the bell housing when he was under the running car.

Stock type torque converters seem like they are hard to find! Anyone else have this issue where it was down to converter or tranny?
 
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grimi64

New Member
Mar 22, 2019
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76
N C
Check your flex plate and make sure you have not lost the balance weight on it, I accidentally grabbed the wrong flex plate (for a 6cyl) fits great however it will cause a vibration when it is running, not good to say the least.
 

2Blue2

will be trying this sex one when I can find it
Mod Dude
Mar 5, 2019
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Oahu
My guess is bad torque converter. Twice!?!
 

jsbenami

New Member
Apr 7, 2019
3
0
1
43
Alexandria, VA
Yes, we are going after the torque converter. You've had bad converters before? I talked to a guy who had two bad ones on his Ford F150. But I've not heard of many doing this on Mustangs. Have a quality rebuilt one from a factory in the Midwest that specializes in converters and they really knew their stuff and were great on customer service and all the particulars of the year I have on the C4. Swapping that out this weekend. The one that is in it now was new out of the box. Though it had no branding or papers with it. Came with the sale. Could be Chinese junk.

No it did not throw the weight. It's a new 28oz flexplate that I installed myself. The old one I pulled probably was too....old well I guess I'll have a spare now :p
 

tos

Founding Member
Apr 27, 2001
896
68
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Cincinnati Ohio
Just a thought but are you sure your drain plug on the converter is lined up with the hole on the flexplate? I made this mistake once and it drove me bats.
 

Onetim

New Member
Sep 14, 2018
26
1
3
61
Farmington MI
Any further results? Fighting the same problem, is the pilot size the same on your old TC as the new one? waiting on a trans jack shipment to start checking things on mine. So far I have only found a Hughes Performance 2500 RPM stall converter that is correct for the 65 application 11" diameter, 10.5" bolt pattern, 24 spline. I am told the trans pump can be changed to the newer 26 spline version for more TC options
 

jsbenami

New Member
Apr 7, 2019
3
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43
Alexandria, VA
Mine was just a bad or incorrect converter plain and simple. Mine was a 24 spline input shaft and I kept it there because I’m not running an especially high horsepower motor, but yes a swap to 26 is common and possible. The stock converter stall speed is well below 2500 rpm. There is no pilot bearing on a automatic transmission. That is a clutch/manual term. I bought a replacement from these guys:

 

Onetim

New Member
Sep 14, 2018
26
1
3
61
Farmington MI
Thank you for the supplier info, I will contact them. While there is no bearing, if the converter has a nub in the center, it locates in the crank end, if no nub it locates by the converter studs, with neither, well that could be a problem. I can see there is no hole for a drain plug in the flex plate, so I will be looking at that as well. Still waiting on the trans jack to know what I have. The higher stall converter works really well with my set up, you wouldn't know it's there unless you really jump on it, and it's a match for the cam i'm running. Thanks again for the input.