transmission question
 

I have a 85 silverado. Orginally a 305/700r4. I took the 305 and replaced it with a 350 out of a chevelle. The question i have when i put the motor and trans back in my truck it will not go into 3rd gear. I think 3rd gear is burned up. The question i have is what size transmission will fit in place of my 700. I know some of these truck came with a 350 transmission. What size transmission is it and will a th400 work also. I do not want to make any mods to my driveshaft or crossmember. Can any body out there help me.

Re: transmission question
 

If you don't want to modify your transmission or crossmember you are going to have to replace it with another 700R4.

Re: transmission question
 

he is correct but i think when you say modify you crossmember do you mean you dont want to cut or weld on it if this is what you ment then purchase the crossmember with the tranny you choose then the only thing is bolting in the new member and tranny the drive shaft can either be shortend or replaced with a longer one and in some cases a longer tranny yoke can be put in and no modiftying to drive shaft itself other than dis-assemble and install of u-joint and yoke not a difficult thing to chang in these trucks, yuo may have to drill a hole or two in the frame rail to fit the member but not difficult again hope this help you out and good luck with the tranny swop

Re: transmission question
 

thanks guys for your help. So would i be able to use a crossmember from a truck that orginally had a 350 trans in it?

Re: transmission question
 

yes

Re: transmission question
 

The crossmembers are all the same for 2WD, they are just moved to a different location.

Re: transmission question
 

A long TH350 transmission will bolt right up with no surgery. Unbolt the crossmember and slide it to the next set of holes and re-use your existing driveshaft. You'll also need a vaccum line for the modulator valve. Just changed a 305/700R combo to a 350/350 in my '84 C10 last week and it's an easy swap. I've done four or five of these swaps.

I've also done several TH400's. They work pretty much the same but you do have to get a longer driveshaft.

Re: transmission question
 

i am looking at buying a 350 / 700r4 combo for my 83. isnt the 700r4 trans a better choice than a 350 or 400 since it has o/d ? unless you are going for all out strip performance.

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After buying my truck back in 97 and it coming with a 700R4 and 2.73 gears, I would say a 700R4 is a better combo if and only if you have a lower gear. I now have 3.73 gears and the 700R4 is perfect. If you have a high gear like I did stock, it's just about a waste of time to have OD. It won't stay in OD unless you are going down a freeway anyway. This is the simple reason most of the stock 700R4 truck owners hate them. They didn't last because of always going in and out of lock all the time, thus causing heat and burning them up. On top of this, if you even thought about towing in OD, it would kill it in a heartbeat.

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The other issue is cost. A rebuild of my TH350 cost me something like $325 with a converter about a year ago. A 700R4 will cost you more, but will get you better gas mileage and the ability to run lower rearend gears. I guess it all depends on whether you want to pay up front, or or stretch it out over the life of the transmission in extra gas payments. You'll pay one way or the other.

Slonaker

Re: transmission question
 

I replaced my 700R4 earlier ..around april i think, this year with a 700Raptor Jr, http://www.transmissioncenter.net/highperf700r4.htm so far i've been happy with it, not sure what gears are in the 10 bolt, from guessing they're pretty tall highway gears around 2:46 or so, I have a 2300 stall converter in and am running 295/50/15's on the back. I would like to put some 3:73's in with a posi, just haven't spent the money yet, but the truck will still plant you in the seat on a good launch. My od kicks in around 50 mph or so, and doing about 70 i stay around 2000rpm maybe a little over. But based on pure cost, i would've probably been just as happy with a stout turbo 350 for around 6or $700 instead of the $1500 raptor.

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With a 305, 3.08 gears, and a Bowtie Overdrives 700r4, I can run at 80+mph at 2000rpm. I have never topped out 3rd gear, nor 4th. I couldn't ever get close. I think aerodynamics stopped it from even topping out in 3rd. The tranmission wants something with at least 250 hp, which a stock 305 only gives about 165. With the Bowtie overdrive's tranny, it has the corvette servo in it so it won't let you downshift unless you about floor it. With a 305, you push the gas down on the freeway and it bogs down. Once it downshifts, then you get some speed. I love it though, in OD it acts civilized until you get mean with it. Put it in Drive and it shifts harder. Manually shifting in it provides very firm shifts, almost violent. But always fun. I also have a 2200 rpm stall converter, large external cooler, and deep sump aluminum pan for it to keep it cool. In summer her in CA, the tranny gets hot. As long as it stays under 90 degrees it runs at proper temps.

Re: transmission question
 

A T-350 with a 9" tailshaft housing is the same length as a 700. There are also 6" & 12" housings.

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My son's truck had a set of 3.08 gears and with the 700R4 that we put into it, the truck ran like a pig. The cruise control worked hard to keep up and the engine was sloppy on gas mileage. We update the rearend to a 12 bolt posi unit with 3.73 gear and it picked up in performance and gas mileage. We actually gained two MPG getting the motor into it's RPM range. The 350s like that 2100 to 2700 RPM range for optimum operation. I also have a 700R4 in my 64 truck with a set of 3.73 gears and I love the performance. I originally had a 350C in my truck and it was restrictive on my horsepower application. I average 15 MPG on a bored and stroked 383 motor and con eat up pony cars on the highway (imagine that as a surprise). I run down the highway at 2500 RPM at 70 MPH and when I really get into it and push it I still maintain RPMs around 3000 to 3500. Going back to a 350 tranny is NOT in my book, but run what you want.

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right now my truck has the straight six with 350 trans. not sure about the rear gears but i only get about 15 mpg on the highway. ill have to check the gearing. doesnt sound like the o/d trans likes highway gears. the six only has around 74,000 original miles on it but it is starting to puff a little smoke on start up and has a few leaks. shame to send it to the boneyard but thats most likely where it will go.

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Why do you want to replace your 700r4 with a th350 or a th400? Why not just get it rebuilt? It'll more than handle the power of the 350.

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With today's age of higher gas prices, I would seriously consider an overdrive tranny. The 350/350 combination of the 70s is a dead issue with the ability of an implant of OD. There is no getting by the fact that the Turbo 400 is a nearly indestructable tranny, but it is death on your wallet for parts, mileage, and horsepower. It takes more horses to turn over compared to the 350 Turbo, not to mention a 700R4. The 700 is an upgrade 350 and is virtually a T-350 with an extra gear. There are parts out there to make a monster 700 and I can relate to you that it can get somewhat expensive to put them in. I built mine to take everything that my stroker could give and then some--for a pricey bill. With that aside you can get into a 700 R4 rather cheaply or even rebuild one reasonably, but I would recommend looking at some of the quality upgrades for the tranny like a hardened seperator plate and upgrades to the shift components for long life. I would NOT go back to a 350 tranny for daily driving, because you have to give a lot of things (lower fisrt gear, Overdrive capability, longivity of motor components due to running lower RPMs, gas mileage, and last but not least, more fun.

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Lets take a look at this dead issue using my truck as an example.

700R4 /2.73 gears/ 28" tires = 1600 rpm @ 70 mph (A turd from the factory)
TH350 /2.73 gears/ 28" tires = 2300 rpm @ 70 mph (Just about right)

Most will agree that a gear change is needed to make that 700R4 work best so let's install some 3.73's and have that 700R4 built. Alright. We've spent $2000.00 (or more) now let's see what we've accomplished.

700R4 / 3.73 gears/ 28" tires = 2200 rpm @ 70 mph.

I spent $2000.00 (or more) for 100 rpm's @ 70 mph? But I'll save on gas mileage won't I ? Sure, if you haul tomatoes cross country for 20 years. What about my lower first gear? Not really an issue unless you like to leave the line first/fast and then the gas mileage becomes a mute point. What about the overdrive capability? If the D with the circle around it means that much to you then go for it. The motor will wear less due to the lower rpm's. If you drive 300,00 miles, maybe. The fun factor? The 700R4 or the TH350 don't have anything to do with that. Fun is a state of mind. :cool:

Re: transmission question
 

Everyone is failing to see one benefit of a 700R4 over a TH350 other than gas mileage. If you have 3.73 gears think of how much more get up and go you will have. Then, when in OD, it's about the same as having 2.73's and no OD.

Myself, I think I'll keep my 700R4 and 3.73's. With my cam, torque converter and other related parts, my truck would be a total dog without the lower gears. Also, have any of you tried to drive a vehicle around with 3.73 gears and no OD?

Of course if you don't care anything about performance then yes, this is probably a dead issue. But remember, if you are after gas mileage, you are in the wrong type of vehicle to begin with.

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I've driven my 1980,(over 300,000 miles!), 4x4 for 25 years with a T350 and 3.73 gears. It has a 406 and a 205 transfer case. The motor and tranny has been rebuilt once.It's spent all these years running 33/12.50's without problems. I almost forgot to mention, an 8.5' Western ProPlow in the winter. The T350 is the best driving tranny around town! I like my T400's for their strength in my other trucks but, the 350 is more user friendly. I've had a lot of vehicles with 700R4's and had more trouble than I like to think about.

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Maybe I should have made myself a little more clear. Have any of you tried to drive a vehicle around with 3.73 gears and no OD with 28 or 29 inch tires.

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well cost is not an issue. i just bought a monte carlo with a rebuilt 350 and a rebuilt 700r4 . $700 for basically the eng. and trans. also has a b+m shifter in it and a brand new radiator ( that i doubt would work in my truck). ill use the 700r4 trans. NOT looking for performance just better mileage. ill still have the 350 trans to put back in if i dont like the 700r4.

Re: transmission question
 

If your truck has 2.50 - 3.08 gears and your daily commute includes the Bonneville Salt Flats you'll love that 700R. Swapping from a TH350 to a 700R doesn't always guarantee better gas mileage. Engine, tire size, driving style, and many other things have to be considered.

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84 Pumpkin---Just a tad bit cynical, aren't you? Put any darn thing you want under the body of the truck, I did what I wanted to and I cover a lot of ground with mine. I have driven all over the country and it was worth the change. You want a city street basher or a hay hauler the NON-overdrive trannys will work. Salvage yards are full of them for just a few bucks. I happen to have a garage full of the 700R4s and I like the ability to leave the line first and then cruise home at lower RPMs. I also built my truck to gobble up Mustangs and even some Camaros for entertainment. Creativity is just a figament of our minds....and Dude you seem to dislike ours. Just what is your vision of what we should do on this thread for fun?

Re: transmission question
 

Cynical? Not in the least bit. You stated that the 700R4/TH350 swap was a dead issue. I simply disagreed and gave you facts and figures that backed up my claim. I DID put the tranmission I wanted under the body of my truck. I also have vehicles with the TH400, 4L60E, 4L80E, Richmond, and the old reliable Muncie 4 speed so I'm not a TH350 salesman. As a matter of fact the best transmission of them all is the 4L80E in my humble opinion. Eating Mustangs and Camaros is something that I can appreciate. I drag out my blown big block '33 Coupe for those ocassions and enjoy every minute of it. Dude, I have no dislike for your creativity since I have no idea if you have any or not. I also don't have a "fun" vision for this thread. I think the original thread started with "which transmission can I replace my 700R4 with and not do any modifications" ?. The answer is a TH350 with a 9" tailshaft. Although this TH350 is 1/8" shorter than the 700R4 it will bolt right in and work out great. Use your same driveshaft and move the crossmenber and you're all set.

Thank you and God bless




Ladies and gentlemen, Elvis has left the building. :five:

Re: transmission question
 

well i have a bone stock 85 305 700r4 and a 84 400 with a rebuilt th350. My shop teacher goes on and on and on about how the 80's 700r4's were just a whole mess of prbloms but mine has 114k on it and seems to work like new. However i have heard so much bad stuff about them i just don't trust it. As for my th350 well it is sweet i wish it had had overdrive for the long trip i took driving it from texas to my house but oh well. I was thinking of a B and M shift kit for it or a th400 with shift kit swap in the 84 not the 85 what do yallthink ???

Re: transmission question
 

Then there's the issue of low gear ratio. My Suburban has 2.73 gears & a T-350, and it takes forever to cross an intersection from a dead stop. The T-350 has a 2.5:1 low gear, and the 700 has 3.06:1. Might be worth considering, since the 700's low gear would make mine think it had 3.31's in the back.

Re: transmission question
 

The 3.08 and 350 that was in my son's truck was a fair combination, but it wasn't a stormer by any means. The 3.73 gears in the rear and the 700R4 that we put on the 350 motor woke the truck right up. It runs the streets decently and does good on the highway. A 700R4/4l60e tranny and a set of 3.42 gears is a common setup from Chevrolet in the late eighties and early 90s trucks, this is a good all around ratio for everyday driving.

Re: transmission question
 

Thanks guys for all the info? I found another 700r4 over the Thankgiving weekend. The question i have now is that its a newer 700 and has the electronic speedometer cable. My old one has a screw in cable. Can i do anything about this.

Re: transmission question
 

I believe the tailshaft housing can be interchanged and the gear can be installed on the tailshaft for the older style speedo. Contact a tranny shop and see.

Re: transmission question
 

Yes, swapout tail shaft housings. You will also need to swap out the signal generator disk on the shaft with your speedo gear. Pretty simple swap and you will be good to go.