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6/18/10 10:08am - Original Message: 'Transmission not engaging when hot!'
fowler12
Former Member
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Toledo, OH - USA

Vette(s):
1977 auto.L48 383 stroker

Joined: 2/22/2007
Posts: 175

I have a 77 with original trans and shift kit.  The car shifts great when cruising around town and when it gets to normal operating temp.  Now, I noticed when I take it on highway for extended periods of time and when I really accelerate and rpms are up, the trans almost feels like it comes out of drive into neautral.  When I slow down it while then engage again but there is no loud noises or anything.  I thought it was because I needed new trans fluid so I had it changed with fresh.  The problem still exists.  Does anyone have any thoughts or ideas about this problem?  Thanks!

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6/18/10 11:15am - Reply: 'Transmission not engaging when hot!'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484
Matthew,
I'm no trans. expert but what you describe sounds like an issue with your Torque Converter.
I'm sure other members with more knowledge will weigh in on this.
I hope its an easy fix for you.


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6/18/10 11:34am - Reply: 'Transmission not engaging when hot!'
DaveM Lifetime Member
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Flanders, NJ - USA

Vette(s):
1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

Joined: 1/27/2004
Posts: 2530

Could be the clutch discs on thier way out. If Joel (Adam's Apple) does not come on with an answer try to PM him, he's the trans man around here.

Good luck,
Dave


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Dave's '82


   
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6/18/10 12:24pm - Reply: 'Transmission not engaging when hot!'
tonyb47
Former Member
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Suffern, NY - USA

Vette(s):
1976 restored,new interior,custom paint(purple),body kit,rebuilt engine,trans,upgraded sound system

Joined: 3/16/2005
Posts: 227
how was the color of the fluid when you changed it, was it still red or burnt. Sounds like your trans is slipping I had same tbl and had to get it rebuilt, my fluid was black

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6/18/10 1:05pm - Reply: 'Transmission not engaging when hot!'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
Not sure I fully unnerstand the description of the problem....
Are you saying it shift perfectly fine around town, under "normal" driving conditions?
The problem occurs when you are on the highway, and go to accelerate pretty hard? If this is the case, it sounds like the trans is downshifting"(passing gear), but it's not really catching the gear, but it's neutralizing. There can be a couple of explanations for that, as well as a problem with the "shift kit".
First, I'm assuming the car still has a 400 trans, so the kickdown(passing gear) is electric. It is possible the kickdown solenoid is bad, or maybe even loose inside the trans. The solenoid is bolted to the trans next to the valve body, on the driver side. With the pan off, just look for the wire.
Another possible problem could be the vacuum modulator, which is located on the passengers side, toward the front of the trans. It can cause silly stuff like this.
I'm also curious as to the condition of the fluid when you changed it...that might be a clue.
Also, what kind of torque converter do you have  for the trans? Stock? Higher stall? Usually, at cruising speeds, the tc will be about out of "stall", and just mostly be a 1:1 ratio. This depends on the stall speed, and the overall diameter of the converter...it may be slipping at higher RPMs, but that's kind of a long shot...tho still possible.
More info, please!

When did this start? 
When was the kit put in the trans?
What kind(brand) of kit was it?


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Joel Adams
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6/19/10 11:45am - Reply: 'Transmission not engaging when hot!'
fowler12
Former Member
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Toledo, OH - USA

Vette(s):
1977 auto.L48 383 stroker

Joined: 2/22/2007
Posts: 175

The color of the trans fluid was nice and red and did not smell burnt at all.  I thought initially that the fluid was old and was breaking down, thus having the fluid changed.  I have noticed my problem when I am really driving the car "hard" on the highway (repetitive hard acceleration and high rpms at speeds of around 80 mph.)  When the car is not being driven "hard" around town, the trans works perfectly. Also, when I am at consistent speed on highway at about 60-65 mph for a period of time, the problem does not exist.  Again, only when I drive the car "hard" for awhile and really bury the accelerator. 

Thanks to everyone for all the great insight, this gives me a little more info. , I will have to get it checked out. 
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6/21/10 9:39pm - Reply: 'Transmission not engaging when hot!'
yostusota
Former Member
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

Joined: 5/18/2010
Posts: 1518
If you have a line pressure gauge that's where I would go next,,sounds like you are losing it. Could be a weak pressure spring,,

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