I want to put overdrive in 72 Blazer 4x4, which tranny?

[GuyO]

Guys, I want to replace TH350 IN MY 72 Blazer 4x4 CST with an OD, which one do I need 200-4r or 700?? HELP!

[fxdxharley]

the 700 r4 is what you want.

[Firebirdjones]

If you are sticking with the carbed 350, then you'll probably want the older 700R that is TV cable operated to simplify the swap.

If you want computer tunability then you'll want a 4L60. But with the carbed 350 you'll need a seperate controller that adds about $600 to the cost.

Or you can just scrap the entire drivetrain and go with an LS swap and 4L60 and have one computer control everything Ultimately this is the route I chose when the original TH350 started slipping and I wanted an overdrive.

Either way you go you'll need several hundred dollars worth of adapters to mate the 205 transfer case to the overdrive trans.

Many have done it,,,,alot of good info here.

[AJs72K5]

Originally Posted by Firebirdjones

Either way you go you'll need several hundred dollars worth of adapters to mate the 205 transfer case to the overdrive trans.

Or....swap in an NP241. Its a direct bolt in (with the correct spline count) to the 700R4.

Even if you don't do the 241, you'll will need new front and rear drive shafts as the 700r4 is about 4" longer than the TH350.

[GuyO]

Thanks guys, I am sticking with a carbed 350 (Edelbrock 1406 w/Perfomer intake. Also have MSD Blaster 2 coil and a Crane Cams pointless module with built in rev limiter). I have swapped a Powerglide for a 200-4r in my 70 SWB and am familiar with the cable hook up and related upgrades. I understand the 200 vs 700 debate and the TH350 and 200 are the same length but wasn't sure of the transfer case stuff. Am I right that the 205 transfer case and 200-4r are better matched together? It seems that the longer 700 in would require the 241 and different drive shafts too. What can I expect for problems e.g. cross member location? or motor mount holes, etc?

[jjzepplin]

200r has no removable tail-shaft and will not accept a bolt on case. Any 700r pre-1986 are junk. Later models had many upgrades. I bought a video and a rebuild kit from B-M and went to town. Pretty easy and added lots of upgrades. You have to take it all apart to get the Advance Adapter shaft in anyway. Bought a TCI torque converter that was supposed to be high performance and it blew up within 3000 miles. I also did a np203 crawl box from ORD mated to the np205. Overdrive and Underdrive=wicked.

In most cases you will have to move your cross-member back and get your shaft shortened. I put a CV type joint in the front of my rear shaft for the angle issue and also dropped the cross-member bout 2". (4"axle lift)
All these things cost money so weigh your options. I have not mentioned all the things necessary- that being said I love it and it will tow anything or climb anything and it has for ten years. 406 sbc / 700r4 / 203-205 / 14blt-dana60-4.10's.

[Firebirdjones]

There is no need to move the transfer case back,,,that opens an entire can of worms,,,,driveshafts,,,shifter relocation that will hit the console (if you have one) cutting the floor, and in my case it would hit the exhaust system if I moved the case back.

It's much easier to simply move the engine forward. It only has to come forward about 1 1/4". Actually after doing it on mine I wish it was done like this from the factory, it makes rear access to the engine a little easier, I always thought the engines sat too far back into the firewall in the stock location.

The 241 case idea has been discussed before, It's a weaker case in most peoples opinion but has a better gear reduction. Good and bad points,,,if you aren't an avid hard core off roader it doesn't really matter much.

I prefered to keep the 205, I just like the overkill rugged design, and it was leak free and noise free and I didn't want to install an unknown case with potential issues.

[Steven B]

I also will put a 700r in the burb. Use the stock trans mount and just move the motor forward. More clearance for the HEI.

[Firebirdjones]

Originally Posted by Steven B

I also will put a 700r in the burb. Use the stock trans mount and just move the motor forward. More clearance for the HEI.

Yep, and that clearance you gain will come in handy. I ran the stock points in mine (when I had the 350 in it) and even that little cap was close to the firewall.

[jjzepplin]

I did move the engine forward in my new truck..No problem ,,, just pull it out measure carefully,, get a 90 degree drill , hope you marked the holes right and go for it...Oh yeah and it helps to have the whole front clip off of the truck.???
First time around I dropped the t-case and moved the x-member and got my drivelines rebuilt.
But this time the engine is easier to work on and the dist has lots of room and I can get to those last header bolts near the firewall without an issue.
6 in one half dozen in the other.
Do both and you have the whole carton!

[GuyO]

Thanks guys, I will buy a later model 700 R4 with an advance adapter kit, keeping the 205 transfer case. When the Blazer goes in for paint I will take off the front clip, paint the fenders, hood and valance seperately making moving the engine forward easier. I really appreciate all the help! Guy

[AlaskaMatt]

Have any of you gone with the 2inch spacer and cut the shaft on the 700r4 method vs. the Advanced Adapters shaft?

If you were to go with the idea of moving the engine forward, you would now be moving it close to 4 inches correct?

[Firebirdjones]

Originally Posted by AlaskaMatt

Have any of you gone with the 2inch spacer and cut the shaft on the 700r4 method vs. the Advanced Adapters shaft?

If you were to go with the idea of moving the engine forward, you would now be moving it close to 4 inches correct?

Cutting the shaft doesn't work,,,not enough splines on the 4L60's I've seen.

I used the Advance Adapters setup with their shorter output shaft. The only adapter (per say) on my setup is a rather small piece that holds the VSS,,,and at the same time changes the bolt pattern so I can bolt the same 205 mount that bolts onto the cross member.

When it's all done,,,I only moved the engine forward about 1.5". The only real fab work is cutting the exhaust system and installing a short piece of pipe to take up the difference. I have some pics if it would help.

[AlaskaMatt]

Understood, I think that is why the 2 inch spacer is used. It's used in combination with the factory th350 adapter. You only end up cutting about 1/2 inch off the shaft that way. The supposed advantage (aside from not having to crack into the case) is that you don't have drive shaft/ oilpan clearance issues with the double cardon on the front drive shaft.

Did you run into any clearance issues on your setup?

Not sure I need photos, but some more information about how your 700r4 mated up to the 205 would be nice. What and how to find the "adapter" that changed up your bolt pattern. It sounds like that goes to the stock th350 adapter that rides on the cross member. But perhaps I am missing something.

I may end up going the way you did if driveline clearances are not an issue. Only moving the engine forward an 1.5" is very attractive. I keep up coming with 5" forward (not really feasable) to do it the way I mentioned above. ~2" longer for the 700r4, 2" spacer, and the block I am using is at least an inch longer.

I guess I could bite the bullet and move everything and go with the 208 from the donor vehicle but all the headaches that come with that I would like to avoid.

[Firebirdjones]

Originally Posted by AlaskaMatt

Understood, I think that is why the 2 inch spacer is used. It's used in combination with the factory th350 adapter. You only end up cutting about 1/2 inch off the shaft that way. The supposed advantage (aside from not having to crack into the case) is that you don't have drive shaft/ oilpan clearance issues with the double cardon on the front drive shaft.

Did you run into any clearance issues on your setup?

Not sure I need photos, but some more information about how your 700r4 mated up to the 205 would be nice. What and how to find the "adapter" that changed up your bolt pattern. It sounds like that goes to the stock th350 adapter that rides on the cross member. But perhaps I am missing something.

I may end up going the way you did if driveline clearances are not an issue. Only moving the engine forward an 1.5" is very attractive. I keep up coming with 5" forward (not really feasable) to do it the way I mentioned above. ~2" longer for the 700r4, 2" spacer, and the block I am using is at least an inch longer.

I guess I could bite the bullet and move everything and go with the 208 from the donor vehicle but all the headaches that come with that I would like to avoid.

regarding your first paragraph,,,if going with the thick spacer so as to not cut so much from the output shaft,,,You would have to move the engine so far forward you might run into other unexpected issues. One issue that I know off the top of my head is the front balancer/pulley setup starts to get very close to another cross member that runs under the radiator. Another issue that you definately don't want is getting the engine crossmember and engine oil pan too close to the front diff. If you off road and articulate the front diff,,,or even a good bump at speed on the road could ruin your day. Just some things to think about.

I never ran into any clearance issues on mine with the front double cardon shaft, and I even run a factory deep sump GM transmissin pan,,,cleared fine. I think where some guys might run into issue is maybe re-using their sagging stock rubber transmission mounts. I upgraded all that to poly mounts so it's all nice and solid and doesn't move around.

The 208 might be another option for you. I didn't go that route for alot of reasons. I like the robust 205 with it's gear-to-gear setup. The 208 has a better gear reduction however if that matters to you. The 1.96 in the 205 is more than enough for me, with 3.73's and 4-low along with the 3.06 first gear of the 4L60 I can creep over anything I care to tackle.
Also my 205 works perfectly and doesn't leak a drop of fluid,,,,so I didn't want to mess up a good thing I figured any 208 I grabbed could have more potential problems to deal with (leaks/noise etc..) so I didn't want to increase my chances of that.

I can certainly understand wanting to do it as cheap as possible though. Hang on and I'll grab some pics of my setup and the clearances I have.

[Firebirdjones]

Not sure how long these pics will stay up (photobucket issues) so save them if you wish...

Here is the Vehicle Speed Sensor adapter. At this point I already have the short output shaft installed. This adapter changes the bolt patter to accept the factory 205 mount as well so it's accomplishing a couple things.



A couple pics of the factory mount. I bought a new one from Advance however because their kit required modification to the stock mount, I believe there was a lip in the coupler area? I'd have to look at the instructions again. But in the interest of keeping my stock stuff stock and in one piece with the original drivetrain, I simply bought a new one from Advance with the modification already done.




Here are a couple of shots with driveshaft installed. You can see that factory GM deep sump tranny pan (truck transmission pan) has a recess towards the back, that gave me some addtional clearance. I figured GM put that there for a reason on the new trucks,,,,and it worked out slick for this retro swap too.

[BBrendal]

I was thinking of putting a 700r4 in mine last year when I pulled the trans and my friend (builder with over 40 years experience) said the cost to do it would really not be worth it because it would only raise my MPGs by like 3-4. He said rebuild the TH350. Keep it original and all that extra $$$ you were gonna spend to do the conversion put in the gas tank. I get 12-14 MPG on my rig. He said with the 700 Id get 14-17 so the time and money, downtime and headaches to do the swap really is not worth it. He said I might as well do an LS swap instead because I would br 1/2 way there and would get much better results for the work involved. For those who are running a 700r4 with a 350 engine what kind of MPGs are you getting?

[Firebirdjones]

Originally Posted by BBrendal

I was thinking of putting a 700r4 in mine last year when I pulled the trans and my friend (builder with over 40 years experience) said the cost to do it would really not be worth it because it would only raise my MPGs by like 3-4. He said rebuild the TH350. Keep it original and all that extra $$$ you were gonna spend to do the conversion put in the gas tank. I get 12-14 MPG on my rig. He said with the 700 Id get 14-17 so the time and money, downtime and headaches to do the swap really is not worth it. He said I might as well do an LS swap instead because I would br 1/2 way there and would get much better results for the work involved. For those who are running a 700r4 with a 350 engine what kind of MPGs are you getting?

This is one reason why I did the 4L60 and the 6.0 LS swap at the same time.

My 350 turbo was slipping, and since this is my daily driver I knew I wanted an overdrive no matter what the cost, it would pay for itself over the years.

I was getting 13 mpg city and 16 mpg highway with the original mild 355 and 350 turbo,,,,so it wasn't horrible by any means. When the trans started to slip however,,,I knew I wanted a 4L60 (not a 700) because I like the simple control of the transmission with a few key strokes. Rather than buy a stand alone controller to run the trans,,,,it made more sense to tear it all down, do the LS swap and have one factory computer control the entire package,,,hence the reason for the LS swap. I've been tuning these things for years with Hptuner (I have 2 other LS vehicles) so really it just became a no brainer to do the swap.

In the end I'm glad I did it. I now get 17 mpg city and 22 mpg highway. But there is more to it than a gas mileage gain with the overdrive. You also cut down on the wear and tear of the engine over a long period of time. If you go with the 700/4L60 you also get a 3.06 first gear and a 1.62 second,,,so the truck also becomes a little more peppy around town.

You are right in your thinking,,,,,an overdrive alone with no other changes will give you about 25-30% more fuel mileage,,,,so the gain isn't huge by any means.

Rebuild cost is about the same between the 350 or the 700. It's the adapters for a retro swap that add up. I think I spent about $800 for everything to swap it in, but I spent a little extra for a new 205 mount to keep from modifying my original,,,,so that's an added $200 that you don't really have to do. Looking at it that way you'll spend about ~$600 for adapters,,,,in my opinion it's not that overly expensive. It's all about how bad you want it

[BBrendal]

Hmmm! 800.00 for adapters is not overly expensive to me either. Plus a doner eng and trans 1800-2500ish. Now youve got my wheels turning...

[Firebirdjones]

Originally Posted by BBrendal

Hmmm! 800.00 for adapters is not overly expensive to me either. Plus a doner eng and trans 1800-2500ish. Now youve got my wheels turning...

[AlaskaMatt]

Thanks for the photos! Sadly many of them are not displaying, but thanks regardless. I hear you on moving the engine that far forward. Headaches for sure.

I am glad to hear you didn't have clearance issues.

I am curious about the VSS. I as understood it the 700r4 with the AA shaft will bolt right up to a 27 spline 205 using the stock th350 adapter. I was unaware of the need for the change in bolt pattern. Can you clarify this one for me?

Thanks again.

[Firebirdjones]

Originally Posted by AlaskaMatt

Thanks for the photos! Sadly many of them are not displaying, but thanks regardless. I hear you on moving the engine that far forward. Headaches for sure.

I am glad to hear you didn't have clearance issues.

I am curious about the VSS. I as understood it the 700r4 with the AA shaft will bolt right up to a 27 spline 205 using the stock th350 adapter. I was unaware of the need for the change in bolt pattern. Can you clarify this one for me?

Thanks again.

It could depend on the year of the transmission as some are 4 bolt and some are 5 bolt. I swapped in the 4L60 which is completely electronic control. It also has the 5 bolt pattern tailhousing.
The VSS is the vehicle speed sensor, which basically tells the computer when the trans needs to shift. That adapter also has the necessary 4 bolt pattern for the original mount (or th350 adapter).

[AlaskaMatt]

Ok gotcha, sounds like I wouldn't need the VSS for the 700 and my application. I was just cleaning up my 700 and it's 4 bolt. Thanks again.

[GuyO]

Thanks guys. I did put in the 700r4 because the 200 4r does not work for this application. I drilled oversized holes in the frame and moved the engine forward 1 3/4" inches. I tried to cut the output shaft as many have suggested, but I couldn't get the original output shaft to match up to the NP 205 transfer case. So I bought the Advance Adapters shorter output shaft and watched a You Tube video on how to teardown a 700r4. Got the AA shaft in OK, and it mated up to the NP205 beautifully. Added a trans temp gauge by drilling a 3/8" hole in the pan on the drivers side. Also used the Bowtie Overdrives Edelbrock TV cable system. All works great but was a hassle switching from the TH350. Would think twice before doing it again. I didn't find it easy and questionably cost effective.

[BLUE THUNDER]

Man I was just thinking about this today. I have a TPI set up that I wanted to put in along with a 700r4. I was told that I should go with the 4l60e if i'm going to run the ecm on my motor and have it manage both. Who has this set up?