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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> Hitting Hard When Shifting into Drive at Idle
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Topic Review (Newest First)
09-06-2009 06:14 PM
reflog I have the same problem on my 400. Is it possible that the low vacuum signal given by the bigger cam causes this problem. When I had the vacuum advance on the distributor disconnected the tranny shifted like a dream. Smooth into reverse and drive. As soon as I hooked up the vacuum advance to the distributor, it started to hit hard again. Is this possible??

Steve
08-07-2009 05:19 AM
My68Vette
Quote:
Originally Posted by ericnova72
Have you done anything to tune the carb beyond just turning the idle speed and mixture screws??
I also did some tuning with the secondary throttle plates to cure the off-idle stumble.. They are now open slightly, which cured that issue.. I tried a bunch of different configurations between the 4 corner idle mixture screws, opening of the secondary throttle plates and the idle eaze screw in the center and the setting I have now not only obtained the highest vacuum reading but also gave me the best idle at the lowest RPM.. I know I dont have any vacuum leaks and even went as far as unplugging all vacuum lines to the carb and then plugging the ports to see if the vaccum would increase and it didnt.. I also sprayed around the carb and intake.. My Vacuum reading is 8hg at idle with a cam profile that has 260 degreees @ .050.. I farted around with it again last night and managed to get a good idle at 1000 rpm but it still seems to slam hard when I put it in Drive. I turned the vacuum module screw 1 full revolution but it didnt change anything.. By the way, I have a Might Demon carb..
08-06-2009 05:18 PM
ericnova72 Have you done anything to tune the carb beyond just turning the idle speed and mixture screws??
08-06-2009 04:59 PM
NEW INTERIORS
Quote:
Originally Posted by My68Vette
The lope is just to much to idle at 950 and at 1000 its just enough to keep it running and 1100rpm is perfect.

What size cam are you running ???? I have ran some Pretty big cam's,And never had to Idle them that high..
08-06-2009 01:51 PM
ericnova72 It will soften the blow but may not be enough. Why do you expect it to idle cold, without a choke, at the same idle speed as when it is warm?? It never will. Without a choke and fast idle cam on the carb, a hot rod engine will never idle without you "babysitting" the gas pedal. You are expecting too much.
08-06-2009 12:55 PM
My68Vette
Quote:
Originally Posted by ericnova72
Almost all aftermarket modulators are adjustable by reaching down into the hose nipple with a small flat blade screwdriver, in your case turning it counter clockwise to "soften" it, 1/2 turn at a time. Can't go too far though, only maybe 3 full turns out. This will also lower the shift points a lttle too, though. Have you worked on the carb and the distributor advance curve to try to get a stable 950-1050 rpm idle speed?? This is where most of the problem probably is.
The lope is just to much to idle at 950 and at 1000 its just enough to keep it running and 1100rpm is perfect. I already locked the timming in at 36 and tuned the carb idle circuit to achieve the lowest idle possible without it stalling.. The motor itself runs great and has a great off-idle response. Here's the problem, when the motor is cold I need to have the RPM set 100 rpm higher or it will stall. But by doing so I cant shift it out of drive until its fully warmed up or it will hammer the rear end when I shift into drive. If I shift directly into reverse first it wont do that, then I can shift from reverse to drive and its fine. I have no problem making my shft points lower, since I mostly shift manually anyways. So if I adjust the module counter-clockwise, that will soften the blow?
08-06-2009 12:36 PM
ericnova72
Quote:
Originally Posted by My68Vette
No changes were ever made from when the Trans was recieved new from TCI.. They dont say what type of kit is in it, they only say that it has crisper shifts.. It does not have a full manual shift kit it in because it stil shifts when in drive.. Is something like this adjustable in the vacuum module? The vacuum is hooked up and working because with out it, it wont shift.
Almost all aftermarket modulators are adjustable by reaching down into the hose nipple with a small flat blade screwdriver, in your case turning it counter clockwise to "soften" it, 1/2 turn at a time. Can't go too far though, only maybe 3 full turns out. This will also lower the shift points a lttle too, though. Have you worked on the carb and the distributor advance curve to try to get a stable 950-1050 rpm idle speed?? This is where most of the problem probably is.
08-06-2009 12:20 PM
My68Vette
Quote:
Originally Posted by ericnova72
Did the trans builder discard the wave plate from the forward clutch, under the guise of increasing holding power?? Is the vacuum modulator hooked up and adjusted correctly?? What brand of shift kit??
No changes were ever made from when the Trans was recieved new from TCI.. They dont say what type of kit is in it, they only say that it has crisper shifts.. It does not have a full manual shift kit it in because it stil shifts when in drive.. Is something like this adjustable in the vacuum module? The vacuum is hooked up and working because with out it, it wont shift.
08-06-2009 11:49 AM
ericnova72 Did the trans builder discard the wave plate from the forward clutch, under the guise of increasing holding power?? Is the vacuum modulator hooked up and adjusted correctly?? What brand of shift kit??
08-06-2009 08:27 AM
NEW INTERIORS
Quote:
Originally Posted by My68Vette
I'm having a problem when shifting from Park to Drive at idle.. I have large cam that will just barley idle at 1000rpm and actually prefers to idle at 1100rpm.. However, if for any reason it climbs just 100rpm to 1200 and I shift into drive, its like doing a neutral drop and hits really hard... My set-up is a SBC with TCI streefighter TH400 trans and 3000 stall.. The converter works fine when I mash the pedal and will flash to 3000.. Its allot smoother if I go to Reverse first and then quickly up to Drive.. Anything I can do?

With a 3000 stall,There's no way it should be Idling that high,It's Idling to high,That's why it's hit when you put it in gear..Make sure you don't have a bad vacuum leak.Check a few things and try to get the idle down..And you will fix the problem.The 3000 stall should take care of the big cam...
08-06-2009 05:51 AM
My68Vette
Hitting Hard When Shifting into Drive at Idle

I'm having a problem when shifting from Park to Drive at idle.. I have large cam that will just barley idle at 1000rpm and actually prefers to idle at 1100rpm.. However, if for any reason it climbs just 100rpm to 1200 and I shift into drive, its like doing a neutral drop and hits really hard... My set-up is a SBC with TCI streefighter TH400 trans and 3000 stall.. The converter works fine when I mash the pedal and will flash to 3000.. Its allot smoother if I go to Reverse first and then quickly up to Drive.. Anything I can do?

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