Mystery shudder

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ChrisRom

ChrisRom

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Don't know if this is a transmission or engine problem, so I am sorry if this is posted in the wrong group.

I have a 65 Dart, originally came with a slant 6 but I did a swap to a 340 I had laying in my garage from an earlier project.

So it is a 340 SB from a 73 Challenger, stock cam, Edelbrock AVS carb, Chrysler distributor with HEI ignition conversion, 904 Transmission with lockup (A999 I think it is called), it has B&M flex plate for external balancing and neutral TQ, standard stall. Lockard KD cable, B&M shift cable kit.

The car run great for few months, nice cruiser. But it developed this shudder at low speeds, under 40/50 mph. Above that you don't feel it anymore.

It idles great in Park and Neutral, no shudder when reving it like that. But once in gear it bogs and shudders.

I pulled down the the VB and did a TF-TC kit install that was supposed to fix the shudder. I added the "magic" lubeguard fluid.... nothing. But these were supposed to fix the lockup TQ shudder which happens at 45mph or so. My shudder is up to 45...

It may be an engine issue - too lean, the wires were triple checked for the correct order, don't know what else to do.

Hope I don't need a new TQ or transmission.

Any ideas?
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. edit. rest of the post came up. If it developed recently could be anything from u joint to flutter at a certain cruise spot in the throttle... or a tire weight was lost.
 
You say it bogs and shudders as soon as you put it in gear... I've had those Chevy style hei modules over heat and act all kinds of funny (or not so funny) ways..
I've only noticed unbalanced situations to get worse and worse not know themselves out at a certain RPM...
But again things are always hard to diagnose over the internet..
 
I have a 3/8" aluminum plate on the firewall where I installed the HEI module. I'll try to change it with a spare one and see if that will improve anything. It may be the HEI thing....
 
ChrisRom said:
I have a 3/8" aluminum plate on the firewall where I installed the HEI module. I'll try to change it with a spare one and see if that will improve anything. It may be the HEI thing....
Click to expand...
If you have a spare one then trying a free option is always my favorite... And the process of elimination has to start...
 
ChrisRom said:
I have a 3/8" aluminum plate on the firewall where I installed the HEI module. I'll try to change it with a spare one and see if that will improve anything. It may be the HEI thing....
Click to expand...
Is it a custom converter or stock?
How are you operating the lock up?
Does it shutter in or out of lock up? Or both?
 
I’m not sure I follow the OP but if it starts to shudder when you pull it into gear it could be a bad TC. Check the timing and make sure it doesn’t pull timing at or just off of idle, meaning when you go from park or neutral to gear the timing should not drop. If it does you need to fix that. I’m allergic to the HEI in any form. Had way too many of them that weren’t that good over the years. The last point is just my opinion. I can’t say that that’s an issue or not. I just don’t like them.
 
j par said:
U joints..
Click to expand...
I would tend to agree, but the OP states that it is happening at slower speeds and then it goes away. U joints typically get worse the faster you go.
I think this my be converter related.
 
It is the early 904 with lockup and it engages automatically. It has a hydraulic circuit built in the transmission and I think is a function of fluid pressure.
The TC is standard stall that came with cars in the mid 70's with this type of transmission.
 
I am thinking is the TC too..... wonder if one can install a standard 904 non-lockup TC in a lockup transmission?
 
Nope not without changing a bunch of other parts like the input shaft and valve body at a minimum.
 
If the converter clutch is glazed it will shutter at times when it is applied. I have replaced many of the over the years for that problem. No special fluid I have ever seen fixed it. If it is the converter just have it rebuilt. You could have it rebuilt and leave the clutch out but I wouldn't want to get rid of a LU convertor if I had it in mine.
 
Last edited:
ChrisRom said:
I am thinking is the TC too..... wonder if one can install a standard 904 non-lockup TC in a lockup transmission?
Click to expand...
So it shutters when?
A) Before lock up?
B) During lock up engagement?
C) After lock up?
D) All of the above
 
512Stroker said:
I would tend to agree, but the OP states that it is happening at slower speeds and then it goes away. U joints typically get worse the faster you go.
I think this my be converter related.
Click to expand...
Yeah I kind of covered that in post 4..
Lota times it's kind of spitballing when you can't see it..
 
Thank you guys, I think I solved the mystery..... Bad miss-fire on one or more cylinders.
I changed the HEI module and went for a ride around the block. Same shuddering and bogging.
Then when I came back home, I didn't turn the light on in the garage and open the hood. Looking careful at the cyl.1 I could see spark arching to the exhaust manifold.
Because the driver side manifold for these early darts is really tight and going up before merging into the exhaust, I used some short sleeves cut from longer heatshield tubing with velcro to protect the wires. See the picture. I didn't realize these heat sleeves are good electrical conductors.
So a combination of maybe one or two bad spark plug wires and these sleeves getting in contact with the ex. manifold and the wires at the same time just created a path for the spark to go haywire.
Tighten up the spark plug wires, took all the sleeves out and went for a ride again. No more bogging....
Time for some good spark plug wires and some spacers to keep them away from each other and from that ugly manifold. Lesson learned.

Thanks again for all your help.
engine1.jpg
 
Fantastic! I had a Honda that had a bad plug (2 cylinder) and it would run great at 4000 or better but miss terribly at anything lower. New plugs fixed it. Those sleeves are fiberglass, they are a great insulator.....? That is a beautiful color, same as my SC400. Whats it called?
 
pishta said:
Fantastic! I had a Honda that had a bad plug (2 cylinder) and it would run great at 4000 or better but miss terribly at anything lower. New plugs fixed it. Those sleeves are fiberglass, they are a great insulator.....? That is a beautiful color, same as my SC400. Whats it called?
Click to expand...
It is actually a Mercedes color - It is called Firemist Red and it was used on 2000's sportier Merc's. Homemade paint job thou with O'Reilly's paint. Cheapo....
 
I've tried numerous brands of spark plug wires. Really like the feel of the Taylor's I installed a few months ago. I have maybe 300 miles on them. Time will tell but they feel and look like a quality wire set.
 
66fyssh said:
I've tried numerous brands of spark plug wires. Really like the feel of the Taylor's I installed a few months ago. I have maybe 300 miles on them. Time will tell but they feel and look like a quality wire set.
Click to expand...
They are.
Had them running for over 15 yrs .
Msd are okay too except the boots rip and gouge too easy. Always the 1st place I look with an msd wire ..is the boot.
I've found the 135 degree boot Taylor spiropro is my fav for headered small block dodge.
 
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