Is it the Torque Converter??

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68AusCUDA

68AusCUDA

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So, I got my 340 installed in my Barracuda a few weeks ago and have been running the motor in. I bought the engine built but don't know much about the specs other than I was told its 10.5:1 compression, mopar purple cam (no specs), forged pistons.
I added at 2000-2400 B&M converter not knowing much about the engine.

I'm wondering if the experts can tell me if the following symptoms are converter related:
  • Drops about 300rpm from neutral to drive
  • When I put it in drive you can really feel it with a firm clunk
  • Just as I pull up to stop it feels like its still really straining forward and gives a little judder against the brakes
Going from a \6 to the 340 has been awesome, its like a totally different car. I'm not a track racer, just a cruiser (and stop light acceleration freak:lol:) but I'm wondering if a higher stall converter would make a difference to the above.

Any help greatly appreciated.
 
Higher stall will sort of act like its slipping at RPM's under your flash rpm. You can sort of rev it a little and it wont do much until it reaches its break away torque level then it will really grab. first time I used my MP 175K convertor, I thought the bands were toast, but you get used to it. dropping RPM's in gear sounds like a A/F ratio issue, maybe too lean. fighting you when you stop sounds like an overrunning sprag or a VB issue? Lots af auto trans guys here, and I would not consider myself one. The clunk on drive may be a U-joint, best to get under there or somewhere you can see, and have someone you trust with your life stand on the brakes and drop it into gear while watching the driveshaft for any movement.
 
Thanks Guys, I'm not much at tuning and had planned to get it dyno tuned but didn't get the time to get it there yet. Pleased to hear this may solve most of my concerns.
 
That's a totally stock converter for a Mopar. That's why it's pulling through the brakes. You probably needed something on the order of 2800-3200.
 
Check/adjust the T-port sync. Make sure the secondaries are fully closed,but not sticking..Then
Do an idle vacuum test in Neutral @700rpm, then in Drive. Finally
Do a compression test.

The first will command your idle timing. Try and get it down to 650/700N
The second will reveal a bit about your cam. Include the rpm at which you measured it.
The third will reveal a lot about the Scr.

My guess is the T-port sync is off cuz like d55Dave said, you have not got enough initial timing, and therefore the throttle has been adjusted too far open . The transfer port exposure should be from square to slightly taller than wide. Set the idle speed with initial timing and Idle-air bypass. You are running a PCV right? The PCV is your idle-air bypass. That engine wants at least 12* initial, perhaps as much as 18*. But with a tight convertor, Like RRR said, I suspect 14* will be close.
The only way to get it to stop pulling on the brakes with that TC, is to reduce the torque input to the TC. Yet the torque has to remain high enough to keep the engine running. The first Go-To is throttle opening, with timing closely following, But above all, the T-port sync has a very fine window of operation. That's why you set it first. After it is set,do not mess with the speed screw.
Good luck
 
you don't say what your idle speed is in gear, just that it drops 300 rpms do you have a tach in it?
 
Not an expert, but 1200rpm idle in neutral is pretty high. I'm typically in the 600-800 range, but that's with a 4 speed.
 
68AusCUDA said:
So, I got my 340 installed in my Barracuda a few weeks ago and have been running the motor in. I bought the engine built but don't know much about the specs other than I was told its 10.5:1 compression, mopar purple cam (no specs), forged pistons.
I added at 2000-2400 B&M converter not knowing much about the engine.

I'm wondering if the experts can tell me if the following symptoms are converter related:
  • Drops about 300rpm from neutral to drive
  • When I put it in drive you can really feel it with a firm clunk
  • Just as I pull up to stop it feels like its still really straining forward and gives a little judder against the brakes
Going from a \6 to the 340 has been awesome, its like a totally different car. I'm not a track racer, just a cruiser (and stop light acceleration freak:lol:) but I'm wondering if a higher stall converter would make a difference to the above.

Any help greatly appreciated.
Click to expand...

You bought a junk convertor with a stall speed not much different than stock.

You idle speed is part of the issue. Base tuning may be part of the culprit as well. I mean mine idles at 800 so 500rpm would not be happy. That's with an automatic.
 
you need to find out or figure out what camshaft is in your engine a compression test from a cylinder might help figure it out if your compression is 10.5 to 1
 
Mine bumps into gear with a 3500 stall convertor. That's with an 800 rpm idle.
 
Thanks guys, I’m going to get the tune and curve sorted out first then go from there. Thanks for all the advice.
 
just FWI
I could pull my 292 cammed 367 down to 550rpm with the clutch, and she would hammer along on flat,hard,level ground without help from the gas pedal.
So yes,in your combo, 1200 is ridiculously high; something is not right, maybe more things than just one.

Get the rpm down and maybe things will get a lot brighter
 
Last edited:
AJ/FormS said:
just FWI
I could pull my 292 cammed 367 down to 550rpm with the clutch, and she would hammer along on flat,hard,level ground without help from the gas pedal.
So yes,in your combo, 1200 is ridiculously high; something is not right, maybe more things than just one.

Get the rpm down and maybe things will get a lot brighter
Click to expand...

That was my first thought when I saw the 1,200 idle.
It's probably trying to keep going through the brakes.
(not to mention building a good amount of heat)
 
Thanks everyone, got a tune and wow what a difference. Idles around 800 and drops about 50-100 rpm when I move it to drive. Not pulling through brakes anymore either. Still a little work to do, there's a vacuum leak at the brake booster so need to get it reco'd then back for a final tune up.

I don't post much here but read heaps and you guys that post regular are bloody legends!
 
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