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My experience with 700R4/NP205 combo swap

Desert Rat

Desert Rat

Fetch the comfy chair
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Ok, saw a couple of other posts about 700R4's and thought I'd share the experience I just went through. For most of you, this may be old news, or maybe you never dealt with it, but when I was doing my homework, I thought I'd done it well. Not. I bought a 76 Blazer that is my project and I will post a complete report on what I did to it when I finish it. However, one of the things I did was to swap out the TH350 in favor of a built 700R4. Why? Because I drive long distances to wheel, don't like shifting a clutch anymore and anticipate wheeling when I'm an old fart and can't, and want decent gas mileage and performance on the highway while I'm headed to the desert and the OD accomplishes that.

So, Shucks Transmission in Dublin, CA has always done me very well and I have them build me basically a Bowtie Overdrive copy. I was very good at reading every post I could find on this conversion on CK5 and Pirate. The PO had installed an NP205 and a Gear Vendors OD. I removed the OD and sold it. I was pleased to already have the NP205 which is in good shape. The vast majority of posts recommended going with an Advance Adapters short shaft to mate up the 700R4 to the TC. I could find no downside to this, but may have missed it. So, the tranny gets built and installed. The crossmembers have to move about 1-2 inches back but no biggie.

The shop installs it and gets everything hooked up. I haven't purchased drivelines yet so I tow it back home. I have a Corp14ff in the rear and wanted 1350 CV's so a call to High Angle Driveline gets me a nice rear shaft. 1350 CV up front, 1410 yoke out back with the strap style yoke for the diff. Now it comes time for the front shaft. I planned on a 1350 CV up front. Not to be. The 700R4 tranny pan is waaaaaaaaaaay too close to the front TC yoke to accomodate it. Now I'm really pissed. I posted this before and solicited opinions but apparently too late. Turns out that the better way to go is not with the Advance Adapters short shaft, but with a spacer that simply moves the TC farther back. Doing so gets you plenty of room for a 1350 CV to fit.

Now, there is a minor downside to the spacer. As it is, I had to heat and bend my TC lever to make it work with the existing boot setup. This wasn't a big deal for only about 1.5 inches of movement. With the spacer, you can figure at least a three inch drop backwards, maybe a little more. This would mean a serious tweaking of the lever, or perhaps even a custom setup. But, I would have chosen to go that route and obtained the 1350 CV.

It now looks like I'm going to have to run a 1310 CV up front. I have a D60 and 315/75R16 MTR's. I am a little worried that the weak link will be this 1310 CV shaft. I pulled off a 1310 from my 74 and put it on just to check the clearances today. The D60 has a 1350 yoke but I was able to bolt it in temporarily to check it out. You can see from the pics that the clearances are pretty tight even with the 1310. I jacked up both sides and played iwth angles to see if it would hit the pan. I don't think it will, but it is close. I'll be having a 1310 CV for the TC and a 1350 for the diff built for me I guess. I'm pretty bummed out because I've gone heavy duty on everything for my rig in the name of durability. I don't rock crawl or mud run, I mainly do remote desert exploration and the name of the game is making it back out.

Just thought I'd pass along my experience for anybody considering this same swap. I suppose I can console myself with knowing that the "fuse" in my driveline will be that shaft and better to break a front shaft and drive out in 2 wheel drive than with something more critical in the axle snapped I suppose. If I would have read anywhere that clearance was going to be an issue, I would've gone with the spacer. I still may down the line after the missus calms down from all the money I've spent on this project.

8443Front_driveshaft_001.jpg


8443Front_driveshaft_002.jpg


8443Front_driveshaft_004.jpg
 
sorry to hear of the difficulties.. :(

if its any consilation, i'm planning this swap myself with the Highangle cutting brake and i'll be keeping your post in mind...
 
Thanks for the heads up!!! I'm going to be installing a 700r4 into my 79 here in the next week or so... Any other words of advice???
 
I wouldn't worry much about the front 1310 shaft. It is a weak link but it is still pretty tough. Matt (az-k5) runs a stock front 1310 driveshaft that he cut the stops out to get more flex. He did break the actual CV ball but the joints are still holdin up and he runs it pretty damn hard. He has a D60, doubler, and 37" MTR's. He rock crawls the piss out if it.

Fred (FWP) also runs a pretty stock front driveshaft in his truck. He absolutely hammered it all the time with 38.5" TSL SX's, doubler, D60, heavy truck and heavy foot. He snapped 30 spline D60 stubs with it and wallowed out 35spline inner and outer axleshafts with it. The driveshaft holds up to being beat on heavily in the rocks alot.

I personally have been running a stock front driveshaft in my truck with 35" MTR's, poorman's doubler, and TPI 350. I rock crawl it as much as I can and I have put a fair amount of hurtin on a 20 year old driveshaft without any problems. Contrary to popular belief and some people's preaching 1310's do not instantaneously explode on contact with dirt and larger tires.

Carry a spare driveshaft and you will be fine unless you are doing something that you shouldn't be doing or are a total throttle jockey.

Harley
 
You can remedy your troubles by installing an ORD doubler. Just a thought, i'm sure you would enjoy the crawl ratio as well as being able to run a 1350 CV up front. Sorry about your misfortune but it is in black and white everywhere on this site that doing a 205 behind a 700R4 causes front driveline issues if you want to run a 1350 CV. Like i said, if you decide to go with a doubler then you can run a 1350 CV without any troubles.
 
I wouldn't worry too much about using the small joint. The torque that it sees is WAY less than what the axle joints see. The driveshaft comes before the biggest torque multiplier in the drivetrain; the axle gears. :cool1: If you're running 4.10's, the driveshaft will see less than 25% of the torque than the axles will.
 
Couldn't You just modify that corner of the pan for some clearance? Im not real up to date on 700's but it seems like notching a small corner of the pan could clear up some room for You. All it would take is a welder and a couple small pieces of sheet metal.
 
same thing I was thinking...

Yeah--if the pan is all thats in the way,why not modify the pan slightly--either custom build that corner of the pan,or maybe check and see if anything internal interferes,(tranny filter,etc)and smack it with a BFH to gain a little more room?--so near yet so far--must be frustrating to have done all that work,only to have lack of one inch be such a pain--I'd be about ready to use the BFH on it if it were me!:blush: --would be nice to be able to use the beefiest U-joint there too if possible..


But as the others said,even the "weak" 1310 joint isn't exactly made of glass--a good brand of U-joint that size will take a lot of tourque--I've plowed with lots of trucks,and all had the stock 1/2 ton style shaft and joints,and not had any failures of the yokes or U-joints,even with badly worn splines on the slip yoke....and thats pretty demanding of it-

-I think most offroad failures are from the wheels leaving the ground momentarily and speeding up quickly,then the "shock" load when the wheels suddenly regain traction is what breaks them--that and the weight of the truck being supported some by the shaft itself while going thru mud and ruts,while its under torque stress...of course extreme angles caused by lift kits are a big factor too...when it binds,they break..:crazy:
 
Thanks for all the replies.

For White-Ryno, I may look at running a non-CV but I think the angles are going to be too much. I have 6 inches of lift, 7 if you count the D60 extra inch, and it may not be feasible. But, I will be looking at that option.

For undr8ed, I'd go with the spacer instead of the AA shaft. Just take your TC lever, heat it up, and make more of an S shape out of it and you can still use the existing boot location without cutting into the sheet metal of your tunnel. The shop that built mine took a look at the Bowtie Overdrive specs and basically built me a similar tranny. We made some changes since BO 700R4's tend to lean more to the hot rod use and not so much offroad. I didn't want a tranny that was shifting really harsh like you would for street/drag racing.

For 4X4HIGH, trust me, I did tons of searches here prior to the project. I never saw a post about clearance issues. Had I seen one, I would've done things differently. Perhaps I just missed them, but this is why I made my post obvious for the next guy.

As for the pan, I thought about modifying it, or having a custom pan built. In another thread somebody posted a picture of the inside of that area and there is a round gizmo that is right on that corner. I might be able to knock it in about a quarter inch but that's it. Not enough to facilitate a 1350.

For all the other responses, I'm heartened to hear that this isn't as big a deal as I perhaps thought. I won't be beating on the truck so I may be ok. Even Jess at HAD tells me I shouldn't worry too much and he would know.
 
I wouldn't worry about the 1310cv in your case. I ran that joint on mine for years with 38'' swampers and a dana 60 front. Broke the 30 spline outer on the 60 and the driveshaft held up fine.

Brent
 
The only thing I can add is maybe look into fabbing up a driveshaft loop, like a upside down "U", so if the joint does break it won't take the trans with it.
 
Leadfoot said:
I tried to warn people in past posts:

http://coloradok5.com/forums/showthread.php?t=29882&highlight=Leadfoot+700r4


http://coloradok5.com/forums/showthread.php?t=42366&highlight=leadfoot+205



You can modify the pan, but there is an accumulator in that corner so modifications will only yield a little more clearance (although it may be just enough)....

Hopefully it works out for you.
Click to expand...

Crap, I must not have gone back far enough for those threads. Clearly I didn't search long or hard enough. I had toyed with the idea of doing a doubler at some point. Maybe that will be sooner rather than later. By modifying the pan, can you get a 1350 in?
 
No chance on a 1350 CV. Luckily most of the stress from truck pulling is on the rear driveline as the "stock" class is not allowed front weights. I am currently planning on jumping up a class, but also going to upgrade to a full manual 4l80e so that should take care of my pan clearance issues.

As far as not searching far enough back...I have done the same :blush:
 
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