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Author Topic: 350 trans gears??  (Read 7082 times)

Offline Socal_GMC

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350 trans gears??
« on: September 13, 2009, 02:15:27 pm »
Hi i need a little help with some issues i have with my trans. First off i have a 77 Gmc c25 3/4 with a 350. How many gears does the 350 trans have? I just changed my old one with a rebuilt one and it shifts 3 times but it seem when im cruising at 40-45mph the rpms are to high. is this normal? Also ever since i swapped it out my MPG when down about 4mpg? Sorry about all the questions but i dont know much about transmissions. One more question my Speedometter is off by 8-10mph i have 33 inch tires but it was never off this bad. Thanks for the help i really appreciate it..
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Offline zieg85

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Re: 350 trans gears??
« Reply #1 on: September 13, 2009, 03:33:58 pm »
3 gears in a TH350.  There are different plastic gears to drive the speedometer cable so you just have to get the right one for your gear/tire combo.  As far as RPM's in 3rd, we would have to know gear ratio of the rear end.  If you went from a TH350 to a TH350, nothing should have changed RPM wise.  BTW Welcome to the site...
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Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
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Offline VileZambonie

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Re: 350 trans gears??
« Reply #2 on: September 13, 2009, 08:47:41 pm »
Are you sure you had a 350? Was there an electrical connector on it?
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Offline Socal_GMC

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Re: 350 trans gears??
« Reply #3 on: September 14, 2009, 12:15:33 am »
electrical connector? i dont believe so
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Offline Irish_Alley

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Re: 350 trans gears??
« Reply #4 on: September 14, 2009, 01:44:28 am »
sounds like a 350, it does only have 3 so your rpms might be a little high. if you knew the rpms it might be a little better to help you out
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Offline Socal_GMC

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Re: 350 trans gears??
« Reply #5 on: September 14, 2009, 10:35:54 am »
is there a way to change shift points??
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Offline zieg85

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Re: 350 trans gears??
« Reply #6 on: September 14, 2009, 05:38:01 pm »
There are some adjustments that can be made however when you are in high the rpm's won't change no matter what you do.  Make sure your rebuilt trans isn't slipping in 3rd.
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Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline Irish_Alley

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Re: 350 trans gears??
« Reply #7 on: September 15, 2009, 12:54:54 am »
i know my 350 would shift into 3rd but if you gave it too much gas it would slip into 2nd. there is a way to change what rpms it shifts at but i haven't don't it so i cant tell you. but if i can remember right it was a screw/bolt on the side of the trany. your rpms being high would effect your mpgs
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If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline rick_c

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Re: 350 trans gears??
« Reply #8 on: September 19, 2009, 10:21:40 pm »
You can turn the screw inside the vacuum modulator on the back of the trans. by the pan. Turn it in (to the right) to stay in gear longer. you need a very small flat head screwdriver.
Mine runs at 3000 rpms at around 80mph but I have a stall, so I think that has something to do with it.

Hope that helps...
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Offline Irish_Alley

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Re: 350 trans gears??
« Reply #9 on: September 20, 2009, 01:55:56 am »
i thought a stall just changes the rpms when the t/c kicks in
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If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline rick_c

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Re: 350 trans gears??
« Reply #10 on: September 20, 2009, 10:49:41 pm »
You are probably right about that, I'm not sure.
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Offline malibu795

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Re: 350 trans gears??
« Reply #11 on: September 22, 2009, 09:35:08 am »
Quote from: Irish_Alley on September 20, 2009, 01:55:56 am
i thought a stall just changes the rpms when the t/c kicks in
stall change with the t/c goes into fluid coupling. and hold the engine.

if you are sliping in 3rd gear direct clutch is bad
2nd gear intermediate clutch
1 forward clutch

th350 shifting 3 times... did you get a th350"C"?
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adam wildman
75 K25 383/400
79 malibu 454/T56 305rwhp/432rwtq 15.6@92.8mph
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