A$$ Backward 203?

[6 Door King]

Figured I'd post this here since it will end up being 6 wheel drive... I am looking to add another t-case to run my two rear axles. The plan is to turn the case backward in the frame so that the original rear output will now be the input from the trans, and the original input will run one rear drvieshaft while the original front axle output will run the other rear axle's driveshaft. Similar things have been done so I feel I can make it work, but I need a few questions answered first. If I take the reduction box off what will end up being the back of the box, what kind of output shaft will I be left with? Will it be a female splined hole or a monsterously long male splined piece with no support bearings. Second, the differential in the case, will it allow one axle to spin while the other goes nowhere? Effectively unloading one axle if it breaks loose? If that is the case it will defeat the purpose of powering both rear axles. If it does work the way I am thinking, is there any way to "lock" that diff to stop this problem? I can see benefits to both situations, in on road driving the split drive speeds could be better, but seeing as I plan to use the rig for hauling junk cars out of the woods I do not want to lose the added drive of one axle or the other. Any help would be appreciated. I"ll add a pic of what I have in mind, hope it helps.

[mrolds88]

I would look for a divorced 203 for what you want to do. Saves a gob of hassles. I wouldn't worry about dropping the reduction box either. If you are worrying about it shifting on you, just build a link and a bolt on bracket to lock it in gear.

[Ziegelsteinfaust]

I thought the guy's who did this used V drives of some sort.

There was an article in trucking magazine years ago where the guy from Spectre accessories did that with a Dually. I can't find it online now.

[Redcap]

Wouldn't even mess with a boat anchor NP203.

http://www.pirate4x4.com/forum/gener...puts-done.html

[6 Door King]

Only reason I was considering the 203 was the fact that by the time I get the reduction box off it would be about the smallest case size that I have found that is readily available and parts are cheap for. The case will have to tuck into a relatively small space between the rear rails, hydraulic ram supports, supply lines and crossmembers. I am not panning to wheel the 30 ft long truck on any hard core trails, so I think the chain will hold up ok, and it will be seeing highway duties so I ruled out the NP200 since it has a reputation of overheating on long journies. I have access to a 205, but it seems like a waste/overkill to me. I am looking for divorced cases for the simple fact that it will already have a driveshaft yoke versus a slip yoke or flange, and since the shafts will have to be custom anyways I can tailor them to whatever my outputs have on them. Not at all worried about the case shifting from hi to low, I plan to use this feature to get me out a jam if need be. Hopefully 6 rear tires digging will get me free. Only reason I was considering removing the reduction box was to slim down the length of the output shaft/case section.

Anybody have any knowledge about the differential action inside the case, and if running power through backwards would interfere or cause premature detonation?

[OrrieG]

I would go with a 205 too. 203 chain will not hold up in the situation you are using it for. The chain was used to compensate for the two axles being full time but does not take long with the constant loading and unloaded to stretch and start jumping gears under load.

[6 Door King]

So it sounds like the answer to my problem is a divorced 205 turned around backwards. Such a simple solution is why I always ask you guys first, to save me the pain and expense of figuring it out on my own.

[ryanroo]

i dont think anything will be solved doing that over running the 200/205 hybrid. you are still going to have the same gearbox running power through all the gears all the time.

additionally you will have another driveline to make and maintain and another link to possibly fail. you will also have less room behind the case to work with the two drivelines going to the rear

[mrolds88]

One issue that you have a good chance on running into with a 205. Heat. With a 205 it is all gear to gear, which we all know and like. But when running the truck on the road, there is a good chance of you getting that thing hot. As all 4 rear tires are not exactly the same size and cornering, etc. This puts a load on the geartrain. The same thing happens with big rigs when the inter axle lock is left on going down the road. The 203 would eliminate that with its internal differential. It would allow that small amount of movement and keep things cooler. Plus if you throw a new chain in it before you install, it should be good to go for a long long time.

[6 Door King]

I was just pondering the two rear axles being locked together at the same speed. If I use the 203, and run power "backward" through it ie power in through old rear output, and running rear drive shafts one through the original front output and the other off the original input shaft with a custom yoke. I want to remove the reduction box to shorten it up some, but it will be mounted in the frame instead of on the axle like I planned before. The offset output will run to a front axle (8 lug 44 or 60) running backward so the housing will be offset also to avoid having two center sections inline and having a driveshaft staggered around the middle pumpkin.

Is the 205 subject to the same heat problems as the 200? As many of them as there are behind 465s in heavy trucks, I can't believe they would fail in over the road use. Also, if I was to disengage the "4x4", would the altered configuration of the t-case prevent it from functioning properly? The advantage of using my front axle in the rear idea is that I could easily turn the hubs out and disengage the axles if needed.

So I am back to my original problem, is the 203 better or the 205? I have a deal in the works for a 205, and it seems like less modifications would be necessary to the 205. I do not need permanent 4x4 capabilites, just want to be able to power the axle when needed to get me through the rough stuff. HELP!

[ryanroo]

running a dual output 205 will have power to both rear outputs all the time. mechanically there is no way that i know of to disengage the lower shaft from the upper. the engagement collar is for the front half of the shaft, the front output. the heat issues in a 200 stem from the fact that it is driving with pressure against the entire geartrain all the time. i also think it has to do with the strait cut gears. there may be additional heat in the 205 due to the fact that you will have drive pressure on all the gears. since the load will be split against both outputs it will be half of what the 200 sees normally. i think the helical gears in a 205 help as well. you would be able to shift the front output in and out normally. the rear two would always be powered. i would use the 205 if i was doing this.

[6 Door King]

So if I understand 205's the gear workings properly, if I were to run the t-case as I propose and I shifted out of 4x4, it would effectively put the entire rear of the truck in neutral since the front output (my input) would not be connected to the rest of the gear train?

I have also heard rumors of making a 205 with two rear outputs with traditional 205 parts and in the standard input configuration. How would that work? I do not need a front output as the truck will only be powered by the rear axles. Would I be better off going this route? Could I just bolt another rear bearing setup in place of the cover with the same pattern/number of bolts? Would the gears mesh ok, or are the helical gears not going to line up? Are the gear diameters compatable? I don't care about hi/low or 2WD/4WD shifting and the binding with two driven axles issue can be solved with locking hubs when on the road.

I wish I had a 205 in front of me to tear into to answer these things for myself!

[ryanroo]

i dont know why you would tun the case upside down. you would not gain much... if your plan was to run the case backwards using the rear output as an input and the normal input as an output and the front output as the other output, which again, i would not do, you would have the ability to shift one rear axle into neutral the entire case into neutral and low range would act in reverse. that sounds like a good thing, except you loose front wheel drive.

using the normal rear output of the NP200 which is on the lower shaft in the case and the normal NP205 output you can create a case that acts like any normal 205 but has two constantly powered rear outputs and a front that acts normally,

[jjzepplin]

I was told once that gears in differentials are made to go in one direction. Just the way they are cut. Watching some jack turd doing a burn out in reverse got me thinking when I saw him drop the rear end o the ground in pieces.
Could that be a possible issue here?

[6 Door King]

Thank you again for all the knowledge.

Am I right in thinking that a front differential and housing running in the rear of a vehicle (pinion facing the t-case) would still be spinning in the same direction? I am sure that helically cut gear would have to be stronger in one direction than the other, so I want to stay in their good graces and use them as intended. Also, I don't want to do all the work and end up with one rear axle fighting the other!

I shouldn't have to flip the t-case upside down for any reason that I can think of, I can switch rear outputs to fit the final differential layout versus flipping the case.

[mrolds88]

Just looking back over my ideas on the 203. For the way I want to run it, it will not work. The axles will be locked together and the differential would be between the chain and the transmission. You would have to run in hi lock all the time. Looks like it's going to have to be a gear case.

[6 Door King]

I finally have my 205 here on the ground, and after tearing it apart I have concluded two things, it will be more than up to the job, and that I need a divorced 205 just to simplify the process of converting the input from splines to a fixed yoke so my second rear driveshaft will bolt up. Back to Craigslist to find someone with a divorced case, awesome part about finding this out now is that a Ford or Dodge case will work as I can move the driveshaft to either the straight through or offset output to accomodate the offset rear axle...


I did read on pirate4x4 about a member using ford guts in the Chevy case and using a rear output bearing retainer on the ford input shaft after drilling out the holes in the case and the flange. Could I simply swap in the Ford input shaft into my Chevy housing without changing all the guts? Will the Ford input shaft fit the Chevy output shaft and are the internal tolerances the same?

[mrolds88]

That I'm not sure of. But also don't forget to check out any old Internationals. Pretty sure they had divorced cases too.

[6 Door King]

Another noob question! I unbolted the rear output housing and the cover from the offest shaft also on the back of the tcase, if the front output shaft was removed, could I bolt in the rear output shaft into the offset side on the back? If so, I could source parts from any case for the rear housings and make it work with normal input shaft, no front output and two rear outputs all with stock Chevy parts. I only worry about the gear loading with nothing supporting the internal end of the second rear output shaft since the front output would be removed. would this cause too much deflection on the second shaft/housing or are the two bearings inside the rear output housing strong enough to take this king of loading?

[ryanroo]

i believe the rear upper output and lower cover/shaft support have a different bolt pattern. it also wouldnt work internally. there is really no way to do it without a front output and you have to use a lower rear output from the np200. at least to my knowledge.