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02-06-2015, 11:18 PM
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#1 |
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Registered User
Join Date: Oct 2012
Location: Philly, PA
Posts: 540
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TH350 Downshift
For those with a TH350 tranny and 3.73 rear ... Love the transmission, with the exception of the kickdown. Above 35mph it will not down shift when given WOT. I have full kickdown cable pull at WOT, so I'm left scratching my head. I'm curious if this is the norm for a truck with a 3.73 rear and can it be increased to kickdown at a higher speed by changing the governor weights.
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02-08-2015, 12:10 PM
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#2 |
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Registered User
Join Date: Oct 2012
Location: Philly, PA
Posts: 540
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Re: TH350 Downshift
Anyone with a TH350, would you share the max speed for a kickdown from 3rd into 2nd and your trucks rear end gearing.
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My truck ain't dead, it just smells funny. |
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02-08-2015, 12:57 PM
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#3 |
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Senior Member
 
Join Date: May 2007
Location: Doodah Kansas
Posts: 7,774
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Re: TH350 Downshift
make sure your pedal is opening the carb to WOT, setting the kickdown to WOT only works if your pedal opens the carb that far, and aftermarket carbs with factory linkage seldom work together perfectly in this respect.
If you need to, adjust the stop on the kickdown cable on the carb side a little. this will allow the kickdown to operate at full pedal instead of WOT on the carb.
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02-09-2015, 03:08 PM
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#4 |
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Registered User
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Location: Philly, PA
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Re: TH350 Downshift
The kickdown is hooked up to a Rochester B. The kickdown cable is set to fully extend when the pedal is on the floor, at which point the linkage is fully forward on the Rochester and I believe is also WOT.
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My truck ain't dead, it just smells funny. |
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02-09-2015, 04:28 PM
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#5 | |
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Senior Member
Join Date: Jul 2000
Location: North Texas
Posts: 3,597
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Re: TH350 Downshift
Quote:
Is that true for 3rd to 2nd, and 2nd to 1st? The governor controls full throttle up-shifts. When do those occur?
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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02-09-2015, 04:50 PM
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#6 |
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Registered User
Join Date: Oct 2012
Location: Philly, PA
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Re: TH350 Downshift
The trans will downshift from 3rd to 2nd at 35mph or below.
Under normal acceleration, 2nd upshifts to 3rd at 35mph, when gunning it, 2nd to 3rd upshift has been as high as 55mph. I've read the TH350 is designed to kickdown from 3rd to 2nd, but not 2nd to 1st. 1st gear upshifts to 2nd around 15mph – at that speed, no need for a kickdown  . As a side, the tranny shifts smoothly, no noises, and I changed the transmission fluid & filter about 2 years ago and didn't find any metal in the pan. Also, vacuum is good.
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My truck ain't dead, it just smells funny. |
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02-09-2015, 05:27 PM
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#7 |
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Registered User
Join Date: Jan 2015
Location: Santa Monica
Posts: 264
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Re: TH350 Downshift
I don't remember too much hassle with setting it up when I had a TH350 but that was a while ago...
I do remember downshifts from 3rd to 1st under certain conditions though. I was running a Lokar type cable, vs OE, but the theory is the same. Try this link http://www.chevelles.com/forums/showthread.php?t=95549
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02-09-2015, 06:18 PM
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#8 |
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Registered User
Join Date: Jun 2010
Location: Upland Ca
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Re: TH350 Downshift
I don't know what max speed is but mine will kick down from 50-60 at least. And mine will also kick down from 2nd to 1st.
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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02-09-2015, 07:11 PM
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#9 |
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Registered User
Join Date: Aug 2009
Location: S.C.
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Re: TH350 Downshift
Sounds like either it's way out of adjustment or not connected in the transmission. Just my thought. Maybe someone "in the know" will be along.
Mine would kick down around 50 or so (don't remember) and this was with 4.10's
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02-09-2015, 08:55 PM
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#10 | |
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Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
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Re: TH350 Downshift
Quote:
Have you installed a "shift kit"? Did this involve governor springs and advertise better fuel economy? Sound like you are shifting too early all the time and maybe fighting a governor issue. Last edited by mechanicalman; 02-09-2015 at 09:12 PM. |
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02-09-2015, 11:56 PM
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#11 |
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Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,147
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Re: TH350 Downshift
If memory serves me correctly, (probably not), stock THM350 WOT shift is 4,500 RPM.
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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02-10-2015, 09:07 AM
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#12 |
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Registered User
Join Date: Oct 2013
Location: Maine
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Re: TH350 Downshift
You should play with that cable some more. Make sure it pulls smoothly and springs back with no binding. It should downshift when you floor it at a speed below your 2nd gear top speed. Mine goes almost 70 in 2nd and it will easily kick down to 2nd if I floor it at 55 mph. Yours may not be working at all. I think without the cable the governor will downshift from 3rd at 35 mph, like yours is doing.
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02-10-2015, 03:35 PM
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#13 | |
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Registered User
Join Date: Jun 2014
Location: Glendale, Arizna
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Re: TH350 Downshift
Quote:
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