Trans "bumps" hard when put into gear ...

[Mike Brichta]

I have a 70 monte with a stroked 383 and TH400 trans with a shift kit. When I move the car from Park into any gear, the trans "bumps" really hard into gear and the rpms drop from around 900 to around 400 and the engine almost stalls. Should I be looking at a different torque converter to address the problem? I'm not sure what torque converter is in it now. Am I on the right track thinking it needs a different torque converter or should I be looking elsewhere?

 

Thanks,

Mike

 

[kc8oye]

hrrm, i would say you problaby could use more stall. my 700r4 does that (did) it had a stupidly low stall converter in it. even at 1000 rpm off the fast idle you had to be standing on the brake when you put it in gear. and at 650 rpm in-gear idle, (as low as my engine will idle stable) on the snow/ice, the rear wheels would push you forward with the front tires locked up

 

[wallaby]

When I move the car from Park into any gear, the trans "bumps" really hard into gear and the rpms drop from around 900 to around 400 and the engine almost stalls.

 

The solution might be simpler than that. If the engine will idle down to 400 against the load of trans being in gear, why do you have it turned up to 900 in neutral?

 

Maybe the solution is to try and get the idle and in-gear speeds closer to one another. That way there won't be such a drastic change when you move the lever. At first you wouldn't think it would work, but try slowing down your neutral idle speed. I would guess maybe around 600? Then when you put the trans in gear it doesn't make such a bang, and won't be working so hard to idle against the engine.

[Mike Brichta]

Hi Wallaby,

 

Thanks for the response. I already tried what you suggested. When I turn down the idle adjustment to around 600, it stalls out when I put it into gear. I usually try to set it at 600 in park at idle and then around 400 when in gear.

 

Mike

[wallaby]

Ok, so you've tuned the engine to run at 500 in gear, and then it just happens to jump up to 900 when you put it in neutral?

 

That seems logical, but it's kinda backwards. Instead, you should adjust the neutral idle to something in the 600-700 area, and tune it so it doesn't die when in gear. I know it sounds like the same thing but it isn't. Once the idle speed is where you think you want it, you may have to play with the mixture or the timing to make it happy in gear. The theory is that if the engine will idle at just 400 for example, then there will only be a minor drop in rpm when its put in gear..maybe down to 350.

 

If your engine will idle in gear at less than 1000, you should be able to use a stock converter. I guess the trick is to reduce the slam into gear.

[Heckeng]

If there is actually a problem, it could also be the idle fuel mixture, or more likely a vacuum leak.

 

That doesn't sound that out of the ordinary to me though. Your cam will have an affect there like KC and Allan were saying, torque converter could be too tight for your cam like you were saying.

 

I'd probably just check for a vacuum leak at first, just so you don't do any tuning and then find out that all of your tuning efforts are worthless because your PCV valve wasn't plugged in or something! Then I'd try adjusting your idle mixture to get the highest idle speed and see if that fixed things.

[Sam (Bones)]

timing may have a effect here too (not enough int timing)