Going from TH700R4 to TH350

[Car'n'Guitars]

What all is involved in this swap? What all will need to be done to make it fit correct? All details are great, thanks. Oh yeah this is in a 4-wheel drive truck with a NP208 transfercase.

[Wellgeo03]

I just have one question...Why???

Ok, in all seriousness, it shouldn't be too tough. The TH350 will be shorter, so it will mean re-locating your tranny crossmember, as well as lengthening the rear drive shaft, and shortening the front one. If you had access to another truck with this setup for parts, it would be an easy swap.

[xrcr]

If you put a 9" tailshaft on the 350 they are within a 1/2-3/8 of each other.
http://www.maliburacing.com/auto_tranny_id.htm"][/URL]

[jjzepplin]

I would like to ask ...WHY as well?
What makes you want to do this?
I would get a newer 700r4 like 87 or above that has all the upgrades over the older unit and rebuild it and put it back together!
Oh and while your at it put in the adapter to install a np205 and kiss all your worries away!

[rs74]

Can you not take the 85 700r4 and take it to the transmission shop and have them put the upgrades in it or is it completely different than the newer models? I would think that they could just upgrade the one you have. I would like to know since I have an 85 700r4 as well.

My first thought was "why" as well on this swap.

[Edahall]

Originally Posted by rs74

Can you not take the 85 700r4 and take it to the transmission shop and have them put the upgrades in it or is it completely different than the newer models? I would think that they could just upgrade the one you have. I would like to know since I have an 85 700r4 as well.

My first thought was "why" as well on this swap.

The 87 and newer 700R4 has an auxiliary valve body that cannot be put on a pre 87 700R4.

[S10Fan]

The 700R in my truck is a 1985 version. My transmission guy said the 87 and newer ones were better to work with.

[Car'n'Guitars]

Okay for everyone who wants to know why, it's because I'm positive my 700r4 is toast and I don't have the money to fix it right now. Plus I have a chance to buy my grille, headlight bezels, a bench seat, and a TH350 4x4 trans for $150.

[Axle]

why? WHY? Let me count the reasons why....
1.The 700r4 sucks.
2.Costs too much for what you get in return.
3.See point 1.

Swapping to a th350 was the best thing I ever did to my truck.

Heres my basic summary C & G; http://www.oldengine.org/unfaq/leadfoot/th350in.htm

Alex.

[S10Fan]

Originally Posted by Car'n'Guitars

Okay for everyone who wants to know why, it's because I'm positive my 700r4 is toast and I don't have the money to fix it right now. Plus I have a chance to buy my grille, headlight bezels, a bench seat, and a TH350 4x4 trans for $150.

No harm what so ever in doing that swap for the reason you gave. I have a good friend that did the same thing. Our "truck" hobby can be expensive so some decisions have to be dollar influenced.

[Edahall]

Have you thought about rebuilding your 700R4 yourself? You can buy a rebuild kit for these units for under $100

[Car'n'Guitars]

Originally Posted by Edahall

Have you thought about rebuilding your 700R4 yourself? You can buy a rebuild kit for these units for under $100

Yes I have, but I don't have the special tools or experience. Plus I've heard from tons of people that the TH350's and TH400's are way better than the TH700R4's.

[Pyrotechnic]

Originally Posted by Car'n'Guitars

Yes I have, but I don't have the special tools or experience. Plus I've heard from tons of people that the TH350's and TH400's are way better than the TH700R4's.

Depends what you are doing and what kinda motor you have. For most stock to mild 350's, a stock rebuild 700R4 with all the fixes,a good transmission cooler and a properly set TV cable will live just fine.

Yes, a Turbo 350 can be made super strong for cheap. Problem with a 4x4 is, you gotta adjust drive shaft lengths and you have to hook up the transfer case. This will cost you.

Not only that, you just lost your overdrive gear so now your costs to drive the truck will go up from all the extra gas you will be using.

Yes, the 700R4 may be a bit more expensive to rebuild but in the grand scheme of things I think it will be cheaper and less time consuming than a Turbo 350 swap. After all the years they've been out and used in GM vehicles, and still used today (as the electronic 4L60E) the people who rebuild them have really figured them out and can build them to last.

[Pyrotechnic]

Originally Posted by Axle

why? WHY? Let me count the reasons why....
1.The 700r4 sucks.
2.Costs too much for what you get in return.
3.See point 1.

Swapping to a th350 was the best thing I ever did to my truck.

Heres my basic summary C & G; http://www.oldengine.org/unfaq/leadfoot/th350in.htm

Alex.

For a 2WD truck, a 9" tail Turbo 350 will drop right in place of a 700R4 with no driveshaft mods. Slide the crossmember forward and hook up the vacuum modulator. A nearly no cost swap, besides the trans itself. I'd do it too!

On a 4x4, that's opening a quite costly can of worms, especially for our OP here who is strapped for cash. Unless he can find a parts trucks for cheap with everything he needs to do this in workable condition, it's going to be time consuming and nearly as costly in the end as it would have been to pay for a rebuilt 700R4.

[Stickman]

Originally Posted by Pyrotechnic

Depends what you are doing and what kinda motor you have. For most stock to mild 350's, a stock rebuild 700R4 with all the fixes,a good transmission cooler and a properly set TV cable will live just fine.

Yes, a Turbo 350 can be made super strong for cheap. Problem with a 4x4 is, you gotta adjust drive shaft lengths and you have to hook up the transfer case. This will cost you.

Not only that, you just lost your overdrive gear so now your costs to drive the truck will go up from all the extra gas you will be using.

Yes, the 700R4 may be a bit more expensive to rebuild but in the grand scheme of things I think it will be cheaper and less time consuming than a Turbo 350 swap. After all the years they've been out and used in GM vehicles, and still used today (as the electronic 4L60E) the people who rebuild them have really figured them out and can build them to last.

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[jjzepplin]

Buy all the stuff and sell that t350 for $150.. Get where I'm goin? I have had a 700r4 behind my built 406 for some ten years.. and yes it's 4wd and yes I LOVE burnouts And yes it's driven hard and tows etc. Stay out of lockup when towing and your good. I think you may need to change the output on that t350 to fit your case anyway could be wrong.. By the way this is the first tranny I ever rebuilt and It's nice. B-M kit was about $350 and it has extra clutches and tweaks to make it even better. 1989 trans by the way. Cost $50 at the junk yard as a core. Adapter for 205 was about $200. Tools about $100 and I can rebuild it again!

[Car'n'Guitars]

Originally Posted by jjzepplin

Buy all the stuff and sell that t350 for $150.. Get where I'm goin? I have had a 700r4 behind my built 406 for some ten years.. and yes it's 4wd and yes I LOVE burnouts And yes it's driven hard and tows etc. Stay out of lockup when towing and your good. I think you may need to change the output on that t350 to fit your case anyway could be wrong.. By the way this is the first tranny I ever rebuilt and It's nice. B-M kit was about $350 and it has extra clutches and tweaks to make it even better. 1989 trans by the way. Cost $50 at the junk yard as a core. Adapter for 205 was about $200. Tools about $100 and I can rebuild it again!

That's actually not a bad idea. Maybe some people can give me the pros and cons of each transmission.

[Edahall]

Originally Posted by Car'n'Guitars

That's actually not a bad idea. Maybe some people can give me the pros and cons of each transmission.

700R4 Pros
-Overdrive (for better fuel economy)
-Lock up torque converter (for better fuel economy)
-Can be built up much stronger than TH350
-Lower 1st gear

700R4 negatives
-Weak 4th gear overdrive (easily overcome by keeping it in 3rd when towing)

TH350 Pros
-Takes abuse a little better
-Simpler to rebuild

TH350 Negatives
-No overdrive
-No lock up torque converter
-Expect to lose 20% fuel economy

[clinebarger]

TH350 are great transmissions, The only con besides no OD is they Grind themselves to death if not rebuilt every 100K to 150K miles to correct endplay, They start to make metal that destroys the bushings, Governor stem & Governor bore. I have to sleeve the governor bore on at least half of the TH350's I build.
99% of used TH350 will need a rebuild, Even if they have had "clutches" installed recently, Because installing frictions is NOT a rebuild. Will need to replace ALL bushings & thrust washers, Replace Governor. Check the governor bore, & Set endplay with selectives.

Mods I do to a TH350.....

New 700R4 center support & low roller clutch.
Hardened intermediate sprag race.
New intermediate sprag.
Machine the Direct piston to allow 1 more direct clutch (for 5 total).
Trans Go shift kit (also double feeds the directs).

700R4

Anybody that says 700R4's are junk...Never had one that was right.

Stock 700R4's shift like crap, Break sunshells, Burn 3-4 clutches, Have a weak forward sprag, The front OD & rear output planets blow up from torrington bearings coming apart or lack of lube, The TV system needs alot of attention, They wear bushings, Input drums form small cracks.
Replace ALL bushings. (sonnax where listed)
Replace ALL Torrington bearings.
Replace ALL Thrust wahers.
Use late 4L60E Molded input drum pistons, 3-4 apply cage, 3-4 apply plate.
4L60E forward sprag assembley.
HD 29 element sprag. (Borg Warner/SKF Only)
8 or 9 3-4 clutches. (Alto)
New 10 vane pump kit. with hardened pump rings.
Trans Go SK 700-G shift kit.
Wide Sonnax sun gear bushing.
HD GM sunshell.
Wide Sonnax stator shaft bushings.
.472 boost valve.
.300 reverse boost.

[Beetle]

I will take the old 700R4!

[clinebarger]

Sonnax input housing......http://www.sonnax.com/system/pdfs/37...pdf?1350308246

[Car'n'Guitars]

Okay so I am looking at doing this again, and the told me he would sell it with the np208 and a trans crossmember for $100 out of a 81 chevy, He also said he'd sell the driveshafts for another $100. What else would need to be swapped out? And what about the trans cooler and cooler lines?