Th350 ?
Thread Starter
Pro
Joined: Nov 2019
Posts: 599
Likes: 55
From: Dover, Delaware
Th350 ?
Hey there all C3 Gurus:
Was driving along the interstate and was in the process of passing a TT at around 65mph..
I nailed the pedal and it did accelerate ok even for my L48 but noticed that the kick-down surge was not there??
Not sure there is an issue but I was under the impression that at whatever speed ya floor the pedal something should be noticeable from
the transmission...
Any clues out there in Vette Land??
JJ78
Was driving along the interstate and was in the process of passing a TT at around 65mph..
I nailed the pedal and it did accelerate ok even for my L48 but noticed that the kick-down surge was not there??
Not sure there is an issue but I was under the impression that at whatever speed ya floor the pedal something should be noticeable from
the transmission...
Any clues out there in Vette Land??
JJ78
Safety Car
Joined: May 2001
Posts: 4,721
Likes: 1,626
From: Fairfax Virginia
What is the background of the car? Any important details or information? The more you tell us about the car and it's history the easier it will be to get it fixed with you. What transmission does it have right now? My only automatic experience has been a 700R4 transmission in my 1988 C4 Corvette and if that extra (Tv?) cable mounted at the throttle is out of wack it can cause problems for the transmission. I thought that earlier automatics with lockup torque converters used a vacuum signal. Old vacuum hoses are the biggest PIA sometimes. I would verify that your vacuum hoses are all in good working order along with any linkages between the carburetor and any sort of kick down device.
The experts on the L48's will start chiming in soon and the problem with be resolved hopefully!
The experts on the L48's will start chiming in soon and the problem with be resolved hopefully!
Le Mans Master
Joined: Jan 2007
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From: Omaha NE
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With a Turbo 350 any surge you would feel comes from the downshift to 2nd.
At 65 mph that ain't happening..
At 65 mph that ain't happening..
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
I also am no expert on the Turbo Hydromatic 350. But back when I was much younger I did have them in some passenger cars. Not exactly the gearbox I'd want in a Corvette.
That said, they can be improved a bit with a shift kit. So even at that speed they would down shift.
But would likely shift back up pretty quickly anyway.
There again, I'm no expert on fun sucker transmissions. I'd just pull it out and start buying parts for the manual conversion.
That said, they can be improved a bit with a shift kit. So even at that speed they would down shift.
But would likely shift back up pretty quickly anyway.
There again, I'm no expert on fun sucker transmissions. I'd just pull it out and start buying parts for the manual conversion.
Race Director
Joined: Mar 2017
Posts: 11,807
Likes: 4,431
From: Virginia
I also am no expert on the Turbo Hydromatic 350. But back when I was much younger I did have them in some passenger cars. Not exactly the gearbox I'd want in a Corvette.
That said, they can be improved a bit with a shift kit. So even at that speed they would down shift.
But would likely shift back up pretty quickly anyway.
There again, I'm no expert on fun sucker transmissions. I'd just pull it out and start buying parts for the manual conversion.
That said, they can be improved a bit with a shift kit. So even at that speed they would down shift.
But would likely shift back up pretty quickly anyway.
There again, I'm no expert on fun sucker transmissions. I'd just pull it out and start buying parts for the manual conversion.
3rd gear in the TH350 is 1:1. That's what an OD transmission would be downshifting to at highway speeds. I don't think you'd ever see 2nd at 65 mph. 45 mph, perhaps, for a stock transmission?
I took @4-vettes advice, though. No automatic transmissions in any of my cars now!
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 8,901
Likes: 4,075
From: US-PNW
Does the kick-down work as expected at lower speeds? If not you may need to check and adjust both the kick-down cable from the carb and the accelerator cable from the pedal; here's what Lars had to say a few years ago on the subject addressing the kick-down cable:
It doesn't sound like you are adjusting the cable correctly. You need to pop the adjuster release tab on the cable at the carb bracket "up." When the tab is released and "popped up," you put the carb at wide open throttle. In this position, you then press the lock tab back down. Before you do this, have someone in the car push the gas pedal to the floor and verify that you are actually achieving wide open throttle. It is very common for these cars to not get to WOT due to the throttle cable not being installed in the correct throttle position, or due to misadjustments of the pedal & linkage. If it's not going to WOT, it won't downshift, in spite of the correct adjustment as outlined above.
Lars
Lars
Le Mans Master
Joined: May 2007
Posts: 5,007
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From: North tonawanda NY
So my 74 has the t400 but if your th350 setup is the same, 2 things are supposed to aid with signaling to the trans to downshift when flooring it. One is the switch located on the accelarator pedal arm with depresses when floored IF adjusted right and the pedal is not hindered by carpet. and the second is the vacuum modular switch mounted between the vacuum line and trans at the transmission. I believe the th350 uses different methods depending on year. It might even use a cable from the carb.
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Drifting
Joined: Aug 2019
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My 1980 with T350C will downshift at 65 with 3.08 gear . Not sure what gear you have but easy enough to reset it and like mentioned have someone floor the throttle (engine off) and verify Carb opens all the way up so hold the choke wide open if the engine cold