Vibration. K20 '76 th350 NP203 and a 400 motor.

[75gmck25]

When a converted case is in 2H it does not run the internal oil pump and there is a risk of insufficient lubrication. I doubt that many folks follow the directions for a converted NP203, where they tell you to run it in 4H about once a week to engage the pump and ensure the case is fully lubricated.

There used to be a chainsaver kit for the NP203 (took out the slack?) and several places sold replacement chains. Although many/most NP203 chains get noisy as they get older, I've never heard of one actually breaking.

Bruce

 

[Dooley]

When a converted case is in 2H it does not run the internal oil pump and there is a risk of insufficient lubrication. I doubt that many folks follow the directions for a converted NP203, where they tell you to run it in 4H about once a week to engage the pump and ensure the case is fully lubricated.

There used to be a chainsaver kit for the NP203 (took out the slack?) and several places sold replacement chains. Although many/most NP203 chains get noisy as they get older, I've never heard of one actually breaking.

Bruce

I have run a few part timed 203's well over 100k without issues of oiling.
I always added a bit more oil to the transfer case as instructed by one of the kit manufacturers back in the day.
It seems to have worked well.
Also when looking for a better 203 for replacement part way through 1978 and all the 1979 units had a narrower 2" chain but with a steeper cog/tooth and gear angle to match.
It seems that stopped the issue of a worn chain from easily skipping over teeth in high torque instances.

A pic of the fill plug modification that allowed enough oil for splash lubrication.
I still locked in 4H every now and then when not needed just to be sure.

You must be registered for see images attach

 

[Pavin]

Well I replaced the np203 with another one. Friday I had finished, Monday test drive, No difference in the vibration. Tuesday jacked up the rear of the truck and ran it in gear to look at things again. Slowed the motor down to a crawl and used a test indicator on the driveshaft. It is .02 out in the rear and .025 out in the front. Took the truck to a driveline shop Wednesday and was told it would be 110.50 per hour and $850 for a new driveshaft if it needs it. (screw that!) Might need to be clocked they said, I am thinking that I put new u-joints in the front drive shaft then take out the rear driveshaft and run it in 4H with the front hubs locked. If no vibration then I can say it is the rear driveshaft. I called a transmission guy of 40 years and he said there is no way a transmission will cause that kind of vibration. Thanks for posting Dooley, I took that T.C. quite a ways apart and saw the kit they used to convert it. It's this kind of solid thing. It's got 4 solid shafts in a holder. I should have taken pictures. I will be at the driveline shop and will ask for the clocking of the rear driveshaft and the front u-joints replaced for my $110 today in 2 hours from now. I will buy the new u-joints at O'Reillys auto parts and take them with. By the way Dooley I have that filler mod on my T.C. maybe you worked on my truck at one time? Do you live in San Diego?

 

[dvdswan]

Hell, for $850 that driveline better add and extra 200 HP! There are plenty of driveline shops online, I had 2 drivelines custom made by Woody's Driveline from TN or KY, somewhere like that for 300 shipped.

So vibration is under load, generally a u-joint. Clunk when shifting into gear, remember with all pieces added together you can have quite a bit of "slop". Greased, u-joints and gear oil help maintain the noise from these clearances. Figure trans has .1" from park to drive, connection from trans to t/case .1", slip yoke on d/line .1", pinion to ring gear .1". Yes these are not actual figures just an example.

Things I would look at if d/line is good, check your engine and trans mounts, check your pinion angle and u-bolts on rear axle, check t/converter bolts on flywheel. If the t/case is not 2wd converted check the u-joints on front axle.

 

[bft305]

Ya $850 for a driveshaft, head to the junk yard and get one out of a truck. I seriously don’t think it is the driveshaft. I have a huge drive shaft out of a wrecker in my K20, I don’t have any vibrations like your talking about. Had a bad one once and it was the double cardin u-joints in the front driveshaft. Replaced those and the terrible vibration was gone. Like I commented before, replace all u-joints and tranny and motor mounts. Then let us know if it still is happening. I would start with the cheap stuff first.

 

[Dooley]

Well I replaced the np203 with another one. Friday I had finished, Monday test drive, No difference in the vibration. Tuesday jacked up the rear of the truck and ran it in gear to look at things again. Slowed the motor down to a crawl and used a test indicator on the driveshaft. It is .02 out in the rear and .025 out in the front. Took the truck to a driveline shop Wednesday and was told it would be 110.50 per hour and $850 for a new driveshaft if it needs it. (screw that!) Might need to be clocked they said, I am thinking that I put new u-joints in the front drive shaft then take out the rear driveshaft and run it in 4H with the front hubs locked. If no vibration then I can say it is the rear driveshaft. I called a transmission guy of 40 years and he said there is no way a transmission will cause that kind of vibration. Thanks for posting Dooley, I took that T.C. quite a ways apart and saw the kit they used to convert it. It's this kind of solid thing. It's got 4 solid shafts in a holder. I should have taken pictures. I will be at the driveline shop and will ask for the clocking of the rear driveshaft and the front u-joints replaced for my $110 today in 2 hours from now. I will buy the new u-joints at O'Reillys auto parts and take them with. By the way Dooley I have that filler mod on my T.C. maybe you worked on my truck at one time? Do you live in San Diego?

Sorry, I haven't been near this thread since I last posted here.
No, I am a long ways from San Diego.
From your description someone might have installed a "Rough Country" unit that was popular back in the day.
It was much cheaper than the kits I used. It used most of the original parts. removing the spyders and installing a "lock ring" gear. Maybe a later "Mile Marker" kit.
It's a shame that your drive shaft shops are so expensive out there.
I can get a new shaft done for my Bobb'd deuce and a halfs for just under $200 bucks around here.
I hope you have gotten your problem sorted out by now!

 

[nabeshin]

Ya $850 for a driveshaft, head to the junk yard and get one out of a truck. I seriously don’t think it is the driveshaft. I have a huge drive shaft out of a wrecker in my K20, I don’t have any vibrations like your talking about. Had a bad one once and it was the double cardin u-joints in the front driveshaft. Replaced those and the terrible vibration was gone. Like I commented before, replace all u-joints and tranny and motor mounts. Then let us know if it still is happening. I would start with the cheap stuff first.

I have a K10 with the same configuration as the OP, and a vibration starting at 50-55mph that feels like it will shake the truck to pieces.

I think there might be side to side play in my slip joint on the rear, tighter after greasing, but I guess I should still try replacing all u-joints first. Would a trans mount cause this vibration issue as well? Under very hard acceleration, there is a clunk when the trans shifts, like the whole thing is bucking under there. All mounts are severely oil soaked, lol.

 

[Snoots]

Oil degrades the mounts. All of them.

 

[Memaloose]

I had a vibration in my '79 K20 after I replaced the 400 with a 350. The 400 flexplate is externally balanced whereas the 350 flex plate has no weights on it. It's something to check. I found the weight tearing off the flex plate.
This was all 40 years ago so maybe I'm remembering wrong but I do remember installing a different flex plate for a 350 and it cured it.
You can probably look it up somewhere.