NP205 - possible problem

[71Blaze]

Hi guys,

I need some help , hopefully you can point me in the right direction.

A while back I bought a seal kit from North West Fab for my NP205. While I had the 205 apart I installed a 32 spline front output shaft along with all the new seals/gaskets in the kit. Everything seemed to have gone together properly. I also installed a rear driveshaft from High Angle Driveline w/ a double carden joint on the 205 end and single 1350 joint on the rear end along with one of their drive flanges on the rear output shaft. This was coupled to the stock 12 bolt w/ 3.08 gears. So far so good.

I drove it like that for a short while with no noticeable issues. I then replaced the 12 bolt with a 14 bolt rear w/ 4.10 gears (freshly built by Boyce Equip). On the very first drive with the new rear, I heard a loud growling type vibration at freeway speeds when I let off the gas. Thinking it was the new rear not being set up properly, I contacted Boyce who very graciously shipped the rear back to their shop, rebuilt it again (they said the pinion gear was slightly out of spec), and shipped it back to me.

I reinstalled the rear, took it for a spin and experienced the very same loud growling vibration! During my inspection I noticed that the rear output flange on the 205 seemed to be loose. I dropped the driveshaft and sure enough the flange nut had backed off! I removed the nut, cleaned the threads, applied some blue loc-tight and reinstalled the shaft thinking I was good to go. Wrong. On the first test drive the noisy vibration was still there.

Is it possible the transfer case needed to be rebuilt and the 4.10 gears are amplifying something that has always been there?

Should the rear output flange have any wiggle to it when its torqued to spec (150 ft/lbs)?

What should I look for to determine if the 205 needs to be rebuilt? According to the paperwork that came with the truck, it only had about 70k original miles on it.

Any help is greatly appreciated!

 

[thatK30guy]

This belongs in the Garage and Tech forums...

 

[stevos67k20]

maybe your drive shaft is out of balance. or some of your angles are bad, but you mentioned you have a cv or somthing so i dont think its that. my 205 has a tiny bit of "play" on the rear output. its hasn't broke yet and its never been rebuilt. i'm sure the play is supposed to be there but get an expert opinion on that one.

the only thing i can think of is driveline out of balance or driveline angles off.

 

[tRustyK5]

X2 on driveline angles being off.

Rene

 

[Hogback Fabrication]

Yep, a driveline vibration will make your 205 noisy.

 

[4X4HIGH]

You have a couple problems to deal with. First off, when you run a CV rear shaft you need to have the pinion pointing just shy of straight inline with the driveline (i like 2* down so when you drive it is about inline with the driveline). If you hadn't done that with the 12 bolt that could be part of your problem. Secondly, if you did do that when you changed to the 14ff the pinion nose is longer so the angle has changed and once again needs to be corrected.

 

[Mudstud]

If I member right the pinion on the 12 bolt and 14 bolt are the same distance forward from the axle tube center, therefor that should not have a hand in this.

Is your 205 twinsticked and if so who ground the shift rails? Reason I ask is that my 205 makes a bunch of racket when I lay off the gas and coast. I have a regular d-shaft though, not a CV and my angles are textbook. What inch lift are you running? Mine is 6" with no t-case drop. I ground my own rail (only one) and later it came out that both rails should be ground so I shocked the rattling noise up to that.

FYI- I have had the case apart since running it like this and there seems to be no premature wear on any parts- no metal in the oil either so I'm just living with the noise. Not my DD though.

 

[RingMaster4x4]

I have had a this issue you need to take the t-case out and check the internals of the 205.

I replaced the rear yoke and then shortly after that the noise started. I have the t-case out of the truck now ( swapped to SM465 with differnt t-case) I can turn the rear yoke and hear the noise. I feel that it is the rear bearing but have not taken it apart yet.

 

[71Blaze]

If I member right the pinion on the 12 bolt and 14 bolt are the same distance forward from the axle tube center, therefor that should not have a hand in this.

Is your 205 twinsticked and if so who ground the shift rails? Reason I ask is that my 205 makes a bunch of racket when I lay off the gas and coast. I have a regular d-shaft though, not a CV and my angles are textbook. What inch lift are you running? Mine is 6" with no t-case drop. I ground my own rail (only one) and later it came out that both rails should be ground so I shocked the rattling noise up to that.

FYI- I have had the case apart since running it like this and there seems to be no premature wear on any parts- no metal in the oil either so I'm just living with the noise. Not my DD though.

Thanks for all the ideas. I gave the 12 bolt to a friend so I'll have to go to his place and measure it for comparison with the 14.

My 205 is stock (no twin stick mods) except for the 32 spline front output I installed while I had it apart for the new gaskets and seals.

My lift is technically a 4" but the rear springs are 6" because I don't like the a** dragging look Blazers usually have, I'm a hot rodder at heart so I need a little rake.

I haven't had much time in the last few days to do much with my truck but I did stick an angle gauge on the driveshaft last night just out of curiosity and it read 18*. Now I need to check the t-case and pinion angle.

One thing I noticed when I drove it last is that if I let off the gas and then hold it to maintain my speed it makes a lot of noise, almost like there's too much lash between the gears. With my hand on the floor between the seats I can feel it. If I let off the gas completely, it makes noise for a second or so, almost like it takes that long for the lash between the gears to be taken up. I noticed it at slower speeds two, just not as loud.

Other than the noise, it seems to drive ok. I'll post some more as I dig into it.

 

[Mudstud]

OK sounds good. I'll keep an eye on this post. RingMaster, I have had the case apart and found nothing.

 

[71Blaze]

Ok, I think I found the cause of my problem and a possible solution.

After reading all of your comments and suggestions (much appreciated BTW), I did some digging around online and found some great info from High Angle Driveline and Tom Woods web pages.

As a reminder, I’m running a rear shaft with a double cardon joint (C.V.) on the t-case end and a standard joint on the axle end.

According to both sources, if running a C.V. type shaft the proper angles should be as such:



Naturally, I don’t have it set up like that. What I currently have is this:



At first, I thought this couldn’t be the problem because when the stock 12 bolt was in place, there was no noise or vibration. The more I thought about it, I came to realize that the most likely reason the noise & vibration started after the 14 bolt was installed was due to the 4.10 ratio.

The 12 bolt had 3.08 gears, so at highway speed the driveshaft never reached a high enough rpm for the harmonics to become noticeable. Drop the gear ratio down to 4.10, and voila, the shaft rpm is suddenly high enough to cause the noise & vibration.

That’s my theory and to this point, it’s the only thing that explains why there was no noise or vibrations until after the 14 bolt was installed. Because the rear joint angle was wrong all along, the missing ingredient was insufficient rpm. If you think I’m out in left field please let me know because I intend to cut the leaf spring pads off and re-clock the rear axle to the recommended angle.

 

[Mudstud]

Everything you say seems reasonable. Unless you have a plasma cutter those perches are a BIOTCH to get off. You might try buying some degree shims instead of all that work. If you can determine ho much you hav eto rotate the pinion you should be able to get the shims you need. This guy makes them.

http://www.jkwoffroad.com/offroadproducts.php

 

[71Blaze]

Thanks Mudstud! I bought a pair of aluminum 6* shims last Saturday and when I got home and looked at my setup, the springs already have what looks to be 6* shims. That's why I figured I should reclock the spring pads. Now that I know I can get custom shims made, I'll get the angle finder down there and see how many more degrees I need to get the angle right. This will save me a lot of work to test my theory.

 

[Mudstud]

Sounds like a plan. You K5 in your avatar is georgious! You have some more pics lurking somewhere?

 

[71Blaze]

Thanks for the compliment. It's more of a 30 footer actually. That's the nice thing about the avatar, its size makes the truck look a lot better than it really does!

 

[Mudstud]

ARG! Can't see the pics cuz I'm a cheap sum biotch and can't afford to pay attention let alone CK5.

 

[71Blaze]

Mudstud, I sent you an email w/ the pics.

 

[71Blaze]

I'm finally back in the garage working on the Blazer. I was originally going to add degree shims to the leaf springs but when I got under the truck to figure out how many degrees it was going to need, I found that it already had degree shims! I'm not sure but they looked like at least 6*. I decided to cut off the spring pads and relocate them instead of stacking shims. Last night after work I got the driver side cut off, smoothed the axle tube and positioned the new pad. This morning I'm going to get the passenger side done and reclock the housing...

 

[71Blaze]

It's fixed!

After I finished the back breaking job of cutting the old spring pads off and grinding the remaining welds down smooth, I clocked the axle so the pinion and drive shaft are straight. A couple spot welds to make sure nothing moved, followed by a quick run down the highway, and voila, the noise and vibration are gone! The only thing left to do is fully weld the spring pads to the axle tubes and it'll be done.
Boy do I feel better!

Thank you guys for the helpful suggestions and comments!