Ok guys heres the deal, my truck in my sig, a 1994 F-250 (converted to dually) about 4 years ago while driving, I downshifted into third from 4th, the "tranny" started slipping and making a REALLY high pitched whining/grinding sound. As soon as I came to a stop I was able to shift up into every gear, no noise, no slipping, no problems at all. But as soon as you tried to downshift into any gear you would get the whine/grind/slip (slipped so bad the truck wouldn't move) I assumed at the time that it was without a doubt the tranny (ZF-5) and swapped it with a junk yard tranny, trading in my core. As soon as it was back in, took it for a test drive and NOTHING changed. I chatted with a hillbilly at a gas station about my problem and he said its your transfer case, change it. SO I changed the transfer case, and it was like new again. $500 at this point.. Fast forward to last month, while on leave from Afghanistan, driving my truck, the very same thing happened that happened 4 years ago. Alas, it was 4 days before I had to return to Afghanistan so I didn't have a chance to tear it apart. So here is the question, WHAT is broken in the transfer case, WHY did it break? CAN it be rebuilt? And what can I do to prevent this from happening again? And no, the power stroke is not stock, but I am making probably around 400 HP. I've pulled it a few times, a trailer here and there, but mostly a DD. I'm returning in January and would just like to know what is wrong ahead of time. So far I have found nobody with any guess what could be wrong in the transfer case. I'd be super glad for any imputs/educated guesses. THANKS!
Sent from a sand box paradise called Afghanistan

 

Tim, Thanks for your service. Do you know what T/C you have? If it is the BW 1356 it is not a very strong T/C. Most likely the reduction gear. How to prevent it look for a heavier duty T/C.
Craig

 

I had looked it up the first time I changed it, however I cannot remember what it is. What would be a heavier T/C without going divorced?

 

I believe they started using the 1356 in 87? Either way you should have the 1356 if you replaced your factory case with the same model.

As far as a stronger case goes, an NP205 will bolt up to your ZF5 with minor trimming for shift rail clearance and is the strongest case Ford used in there fullsizes. It took me less then 10 minutes with my angle grinder to make the necessary clearance cuts, but keep in mind you will have to modify your driveshaft lengths and fab up a way to support the extra weight of the all iron case. I simply used the factory torque mount from the 78 I pulled the case from.

 

A 205 is all gear driven right? Will that change my gear ratio at all going to the 205? I could stand higher if so, but my truck has 4:11 gears right now.

 

The only thing that will change is your low range gear. Your high range will be the same.
The np205 is a badass piece, but its not the most high speed hyway friendly from what I hear. I haven't had any issues with mine at 100mph but I'm wondering how long it will last.
The 1356 is a decent unit, I haven't broken mine yet but that truck is mostly stock. My 87 truck with a zf5 and hd clutch with about 450hp/650tq has an np208 behind it and its been rock solid throughout all its abuse truck pulling, mudding with 40s, towing 20k+ and plowing. I've blown up 2 ford 10.25 diffs and break d60 axles in pairs (Detroit locker) and I don't even think I've checked the fluid level in 13 years.
So..... I don't know what your doing wrong. LoL
I'd say just replace it with another bolt in friendly 1356 and call it a day. Unless you're planning on adding more power and start abusing it more, don't bother wih all the retrofitting and conversion.

 

You'll be going from a 2.7:1 to a 2:1 low range ratio, although since you are blessed with the 5.7:1 first gear in the ZF5 (assuming you have a wide ratio trans) you shouldn't be too disappointed with the difference.

I have never heard anyone mention that NP205s have problems running at highway speeds. I used my F250 on a daily basis for my maintenance job, which required driving 2-3 hours at a time on the interstate with zero issues.

 

Good to know first hand info. When I was building my 76 highboy 15 years ago everyone kept telling me to ditch the 205 and use the 208. I had used the 205 in my other truck but they never got above 55 usually around town.

 

I've had to rebuild my 1356 t/c three times now and it is almost always to range reduction fork. The plastic inserts hold your reduction sprocket in place and dealing with long hauls (Washington state to alabama) they almost always give in. I've gotten to the point i carry the replacement parts in my truck so if i have to i can rebuild it at a hotel. All you need is a t50 star drive for the case, snap ring pliers, and a basic set of tools. It takes me about 45 min to drop the t/c rebuild takes about 30 min and about an hour for the install. do yourself a favor and try to get factory plastic tabs because the crap the part stores sells you don't last but about 1000 miles. some high temp long term grease helps a lot. Good luck.

 

My truck must have something wrong with it, then. 148K miles, lots of freeway running and my 1356 xfer case hasn't failed.

I agree with the observation to install another 1356 and call it good to go. If you felt industrious, rebuild the pump before you install it.

Just my humble opinion,

Ray

 

Thanks guys, I can't wait to get home and tear it apart and see what the problem is. Hopefully it really is just the forks