is my th350c trans not the best to keep with my engine? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

datguysaL · 02-14-2010, 12:13 PM

my truck is a 1985 chevy C10 swb. i got a 1995 carburated 350 bored to 355 with a perfomer intake, 750 carb and melling mtc-1 cam, stock heads. the transmission is a th350c. and 2.73 rearend. ( i always thought it was a 3.73 till i was under there yesterday and checked it ).

And i feel as if my transmission is eating what my engine is feeding it.

i will be redoing my exhaust and modifyin my transmission crossmember to clear it, and figured since ima make my own crossmember, well i might as well upgrade my transmission since i will be spending quite some time under the truck.

whats the best setup with this? should i get a new transmission? what kind will work the best? or does anybody know of any kits for this transmission?

i wanna get the best out of my engine. and feel the torque and still be able to drive on the highway with low rpms.

camshaftgsxr · 02-14-2010, 12:21 PM

TCI would be a good place to start i've got about the same mill you do with a 7004r behind it, and if it wasn't for the overdrive i would have a th350 (less power loss) a rebuild or a new tranny would be my suggestion, freshening it up will make it last longer, get you better mileage, and more of teh horsepowers to the wheels

its not good to beat up on a stock tranny with that high a rear gear, the heat will destroy it
bassically the only bad thing about lower gears is more stress on the axles everything elses load is lightened

since your looking for low end plus highway gears a 7004r should fit well with a 3.42/3.73 rear end gear mines a 3.42 and it won't hook till third (it keeps ME happy) turns about 2400 at 70 i think (it's been awhile since i drove it)

datguysaL · 02-14-2010, 12:29 PM

will the 7004r bolt right up, or is there any mods needed? wiring, driveshaft, etc....

so since my gears are 2.73, will i have to upgrade them? or will these help or hurt with the 7004r?

i plan on adding posi rear end in the future.

camshaftgsxr · 02-14-2010, 12:38 PM

drive shaft will have to be shortened and crossmember will need to be moved (back i believe)
it'll bolt to the motor just fine
on a late model truck i don't know about wiring (mines an 84 and stock tranny was a 700r4)
you should be able to run just the vacuum lines and the TV (throttle Valve) cable to the carb and it'll shift right (after all its a freakin sbc they haven't changed since block 1 rolled off the line in the 50's)
as for the gears, they're highway gears (low rpms) if you lower them i would do the posi at the same time (convience) but unless you add another gear (in the tranny) your gonna be turning pretty high on the highways
your really into reworking the whole drivetrain here it's not gonna be easy or cheap

700r4's are geared lower in first than the th350's

basically 2.73+th350=highway 3.73+700r4=highway+lowend

Damien · 02-14-2010, 01:51 PM

Actually the blocks did change in '58. GM added the side engine mounts that we all use.
The drive shaft will not have to be shortened if you have a long tail shaft th350. The long shaft has about a 9" extension housing. The spline count is also the same, so you can use the same yolk too. There is no vacuum line that goes directly to the 700r4. The vacuum line goes to a solenoid that controls the tq. converter lock up. The TV cable must be adjusted correctly or the trans will be junk in a few miles.

camshaftgsxr · 02-14-2010, 01:58 PM

props to the expert!
i'm pretty much right on the other stuff right? i don't want this guy to mess up his project cause of me

Pyrotechnic · 02-14-2010, 05:19 PM

A 700R4 and 3.42 gears (assuming the stock 28" tall tire) would work well. With a 30" or 31" tire I would go with 3.73's.

You will have to change the 2.73 gears out if you get a 700R4. If you run a short 26" tire you might get by, but if you are going to install a posi then you may as well do a gear change and use the correct gears.

datguysaL · 02-14-2010, 10:28 PM

thanks guys, i went earlier today to look at some transmission and posi-rear ends, but since they are from 1989-1999 chevys, the guy wouldnt sell them to me, said they wouldnt work for my application.

so, ok. wanna make sure im gettin the right stuff..

So i need a 700r4 trans, from before 1989, and also change gears to 3.73 to get the best out of it? is this correct?

oh, my old man told me i could yank out a 400 trans out of his old 4door 84 chevy western hauler dually truck. will that one work for me, or am i better just to keep searchin for the 700r4?

Damien · 02-15-2010, 04:36 PM

Quote:

Originally Posted by camshaftgsxr

props to the expert!
i'm pretty much right on the other stuff right? i don't want this guy to mess up his project cause of me

Yeah, for the most part. He may need a shorter driveshaft, and will have to move the cross member.

The newer rear ends have been made to work. They are a couple inches wider than the stock one, which makes the rear track width the same as the front. The spring perches need to be moved. I think GLOCK did this swap and a few others have too. The TH400 has a lower first gear, but absorbs more power. So you may have better acceleration. Third gear is still 1:1 like the Th350, so highway cruising will not be affected.The tranny cross member will still have to be moved back and you will definitely need a new driveshaft. I would still swap to a lower rear gear ratio though. Here is a link to TCI's website giving dimensions for the different transmissions.
http://www.tciauto.com/Products/TechInfo/trans_dims.asp

datguysaL · 02-15-2010, 10:32 PM

thanks guys, guess ima park my truck for a while.. till i finish it off...

oldschool18 · 02-15-2010, 11:48 PM

I got 2.73 gears in my 85 with a 400 turbo with a shift kit and runs great, its no shot out of the hole but it has no end. But i would like to upgrade to 3.42s

cableguy0 · 02-16-2010, 09:23 AM

Those gears are killing you. The transmission isnt eating your hp its the gears. You need at least a 3.07 gear in a truck. Im sure its a complete dog off the line and not so great on the highway but the faster you go the more power it seems to have. Start with the rear gears and go from there. You can either swap the gears or just swap out the entire rear. A rear shouldnt be too terribly hard to come by anything from a 2wd 1/2 ton 73-87 is a direct bolt in. A 3.42 gear is probably your best bet with keeping the th350. rpms on the highway wont be bad and it will still have enough guts to get moving down the road.Btw your carb is too big. A 600 carb will also improve your low end performance. The carb does not match the rest of the engine.

datguysaL · 02-17-2010, 10:33 PM

hey thanks, yeah thats how it performs.

the carb i bought brand new cuz i got it for dirt cheap from a performance shop that closed down over here. i wonder if theres a way to convert this one into a 600 or 650. i need to look into that.

i been searching for a complete rear end, so far no luck.

looks like ima have to build it.

but i was debating on the gears but it sounds like the 3.42's are my best bet... thanks

i been hearing rumors of a swap meet down here, i also need to look into that..

02-14-2010, 12:13 PM	#1
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	is my th350c trans not the best to keep with my engine? my truck is a 1985 chevy C10 swb. i got a 1995 carburated 350 bored to 355 with a perfomer intake, 750 carb and melling mtc-1 cam, stock heads. the transmission is a th350c. and 2.73 rearend. ( i always thought it was a 3.73 till i was under there yesterday and checked it ). And i feel as if my transmission is eating what my engine is feeding it. i will be redoing my exhaust and modifyin my transmission crossmember to clear it, and figured since ima make my own crossmember, well i might as well upgrade my transmission since i will be spending quite some time under the truck. whats the best setup with this? should i get a new transmission? what kind will work the best? or does anybody know of any kits for this transmission? i wanna get the best out of my engine. and feel the torque and still be able to drive on the highway with low rpms.

02-14-2010, 12:21 PM	#2
camshaftgsxr Registered User Join Date: Feb 2010 Location: Asheville, N.C. Posts: 785	Re: is my th350c trans not the best to keep with my engine? TCI would be a good place to start i've got about the same mill you do with a 7004r behind it, and if it wasn't for the overdrive i would have a th350 (less power loss) a rebuild or a new tranny would be my suggestion, freshening it up will make it last longer, get you better mileage, and more of teh horsepowers to the wheels its not good to beat up on a stock tranny with that high a rear gear, the heat will destroy it bassically the only bad thing about lower gears is more stress on the axles everything elses load is lightened since your looking for low end plus highway gears a 7004r should fit well with a 3.42/3.73 rear end gear mines a 3.42 and it won't hook till third (it keeps ME happy) turns about 2400 at 70 i think (it's been awhile since i drove it) Last edited by camshaftgsxr; 02-14-2010 at 12:27 PM.

02-14-2010, 12:29 PM	#3
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: is my th350c trans not the best to keep with my engine? will the 7004r bolt right up, or is there any mods needed? wiring, driveshaft, etc.... so since my gears are 2.73, will i have to upgrade them? or will these help or hurt with the 7004r? i plan on adding posi rear end in the future. Last edited by datguysaL; 02-14-2010 at 12:34 PM.

02-14-2010, 12:38 PM	#4
camshaftgsxr Registered User Join Date: Feb 2010 Location: Asheville, N.C. Posts: 785	Re: is my th350c trans not the best to keep with my engine? drive shaft will have to be shortened and crossmember will need to be moved (back i believe) it'll bolt to the motor just fine on a late model truck i don't know about wiring (mines an 84 and stock tranny was a 700r4) you should be able to run just the vacuum lines and the TV (throttle Valve) cable to the carb and it'll shift right (after all its a freakin sbc they haven't changed since block 1 rolled off the line in the 50's) as for the gears, they're highway gears (low rpms) if you lower them i would do the posi at the same time (convience) but unless you add another gear (in the tranny) your gonna be turning pretty high on the highways your really into reworking the whole drivetrain here it's not gonna be easy or cheap 700r4's are geared lower in first than the th350's basically 2.73+th350=highway 3.73+700r4=highway+lowend Last edited by camshaftgsxr; 02-14-2010 at 12:40 PM.

02-14-2010, 01:51 PM	#5
Damien Registered User Join Date: Mar 2007 Location: Farmington, MN Posts: 928	Re: is my th350c trans not the best to keep with my engine? Actually the blocks did change in '58. GM added the side engine mounts that we all use. The drive shaft will not have to be shortened if you have a long tail shaft th350. The long shaft has about a 9" extension housing. The spline count is also the same, so you can use the same yolk too. There is no vacuum line that goes directly to the 700r4. The vacuum line goes to a solenoid that controls the tq. converter lock up. The TV cable must be adjusted correctly or the trans will be junk in a few miles. __________________ I can still count my vehicles on two... wait three hands.

02-14-2010, 01:58 PM	#6
camshaftgsxr Registered User Join Date: Feb 2010 Location: Asheville, N.C. Posts: 785	Re: is my th350c trans not the best to keep with my engine? props to the expert! i'm pretty much right on the other stuff right? i don't want this guy to mess up his project cause of me Last edited by camshaftgsxr; 02-14-2010 at 01:58 PM.

02-14-2010, 05:19 PM	#7
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: is my th350c trans not the best to keep with my engine? A 700R4 and 3.42 gears (assuming the stock 28" tall tire) would work well. With a 30" or 31" tire I would go with 3.73's. You will have to change the 2.73 gears out if you get a 700R4. If you run a short 26" tire you might get by, but if you are going to install a posi then you may as well do a gear change and use the correct gears. __________________ 1977 GMC Sierra Grande

02-14-2010, 10:28 PM	#8
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: is my th350c trans not the best to keep with my engine? thanks guys, i went earlier today to look at some transmission and posi-rear ends, but since they are from 1989-1999 chevys, the guy wouldnt sell them to me, said they wouldnt work for my application. so, ok. wanna make sure im gettin the right stuff.. So i need a 700r4 trans, from before 1989, and also change gears to 3.73 to get the best out of it? is this correct? oh, my old man told me i could yank out a 400 trans out of his old 4door 84 chevy western hauler dually truck. will that one work for me, or am i better just to keep searchin for the 700r4?

02-15-2010, 10:32 PM	#10
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: is my th350c trans not the best to keep with my engine? thanks guys, guess ima park my truck for a while.. till i finish it off...

02-15-2010, 11:48 PM	#11
oldschool18 Registered User Join Date: Jan 2010 Location: Hollidaysburg, PA Posts: 785	Re: is my th350c trans not the best to keep with my engine? I got 2.73 gears in my 85 with a 400 turbo with a shift kit and runs great, its no shot out of the hole but it has no end. But i would like to upgrade to 3.42s

02-16-2010, 09:23 AM	#12
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	Re: is my th350c trans not the best to keep with my engine? Those gears are killing you. The transmission isnt eating your hp its the gears. You need at least a 3.07 gear in a truck. Im sure its a complete dog off the line and not so great on the highway but the faster you go the more power it seems to have. Start with the rear gears and go from there. You can either swap the gears or just swap out the entire rear. A rear shouldnt be too terribly hard to come by anything from a 2wd 1/2 ton 73-87 is a direct bolt in. A 3.42 gear is probably your best bet with keeping the th350. rpms on the highway wont be bad and it will still have enough guts to get moving down the road.Btw your carb is too big. A 600 carb will also improve your low end performance. The carb does not match the rest of the engine. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

02-17-2010, 10:33 PM	#13
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: is my th350c trans not the best to keep with my engine? hey thanks, yeah thats how it performs. the carb i bought brand new cuz i got it for dirt cheap from a performance shop that closed down over here. i wonder if theres a way to convert this one into a 600 or 650. i need to look into that. i been searching for a complete rear end, so far no luck. looks like ima have to build it. but i was debating on the gears but it sounds like the 3.42's are my best bet... thanks i been hearing rumors of a swap meet down here, i also need to look into that..



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