Chasing Vibrations - ‘78 K10 Suburban

[RyanAK]

Hey gang. Working through my ‘78 Suburban drivetrain/suspension to try to get it as smooth and reliable as possible. I have one at 45-55mph that is especially irksome since most of the roads around here are 45-55mph speed limit. Heh.

So this is a cabin boom/drone/buffering at 45-55mph. It isn’t throttle/load dependent - it does it while coasting and in neutral. This indicates the vibratrion is not engine side. It’s low frequency... almost pressure-like. The vibration pulses slightly when it first starts, but by 50mph it’s a constant drone. Once you push through 55, it disappears.

Truck has a new crate 350, TH350 with full-time NP203. Stock suspension.

(Secondary question... what’s reasonable highway speeds with the NP203? Any reason I can’t drive 70 on the interstate?)

I can rotate the rear driveshaft 1/8 rotation while in park.

I replaced the rear U-joints. I replaced the front driveshaft u-joint, but haven’t done anything with the double cardan. Shafts went back in the way they came out. No evidence either have thrown a weight.

There’s occasionally a slight clunk when shifting from park to reverse. This isn’t consistent though.

Tires are 12 year old Toyo Open Country 235/75R15s on stock steel 15x6 wheels. I’m getting a plan to replace these. They’ve been balanced, but I’m not convinced they don’t have other problems... like not being round... that is contributing some of the problem.

Weather seals are ok. No serious water leaks, and wind noise is tolerable. They’re on my short-term list.

This thing is like a huge speaker cabinet... so whatever is going on is being amplified by the acres of sheet metal and huge cubic volume of air.

I have some suspicions, but thought I’d ping the forum for thoughts before I start spending what could be significant time and money chasing this. Other than this, truck is pretty great.

Thanks in advance!



Ryan

[dmack91]

Tired that old can have various problems, like flat spots, out of round, broken belts, and the rubber cracking and just plain getting hard. Not to mention, most tire shops won't work on anything over 6 years old.

Sounds like you are due anywa, so I would give the bullet and start with new tires and see if that helps. Tread design and depth has a big affect on fire noise and vibrations.

[bigdaddy4x4]

check the transmission and transfer case mounts and check the motor mounts for wear dried up rubber

[mongocanfly]

id be scared of the 12yrold tires..even if they wernt causing vibrations....ive had to many blowouts with aged tires...
and id get rid of the full time 4x4 transfer case..use part time adapters and hubs....lot of unneeded rotating mass

1.I can rotate the rear driveshaft 1/8 rotation while in park.(not uncommon)

2.There’s occasionally a slight clunk when shifting from park to reverse.(not uncommon)

[Greenlee]

I was thinking the same thing about the np203 full time transfer case. I’ve never owned one, but I used to keep up with the 4x4 magazines and forums and I remember a popular upgrade was to change to a np205 part time case. That might be worth doing anyway if you have to start spending money to chase the problem. Nice looking burb!

[RyanAK]

Thanks, fellas.

Tires are definitely in the near-term. Like, I’m ready to do it now. I don’t really trust them considering their age. I started a separate thread for tires since the 15x6 stock rims really limit my tire choice. So if probably consider new rims as well. Shame, since I really like the OEM steelies and hubcaps. Open to suggestions. I’d prefer a taller tire to fill the wheel wells and lower the RPMs on the highway. 3.73 gears ya know.

This rig has a GM Crate 350 the PO had installed, and I believe the mounts are new. I’ll have to recheck, but I don’t remember being concerned when I went over the truck when I first got it. When it was having the cab mounts and tailgate support replaced last month I had the guy do the ‘easy’ body mount rubber. I haven’t checked transmission or transfer case mounts though. That’s a good suggestion.

I go back and forth on the NP203. Keep it stock, convert it to part-time, or swap it out. Haven’t really decided what to do yet. I’m ok with leaving it full-time if it’s ok being spun up to 70 on the highways. It’s been doing fine for local driving. The double cardan joint on the front drive shaft is a suspect in my vibration hunt, even though it seems fine...

I’d like to have the drive shafts balanced, but there isn’t a shop in the area to do it.

What else? I have a very long list of possibilities, ranging from tires, driveshafts and rearends to stuff like weather seals and missing carpet pad in the cargo area. Trying to be logical in my approach to keep from throwing time and money away. I have the flow chart that Kieth Seymour posted and I’m trying to work my way through it.

Thanks again. Ain’t this place great?

[dmack91]

You can pull the front drive shaft and see if that cures your vibration problems. Not completely familiar with the 203, but you may have to put it in 4high lock if you do pull it.

[RyanAK]

I’ve considered doing that. It would need to go into H Lock to engage the differential in the case. Otherwise it would try to spin the front shaft only. At least that’s my understanding.

[Ziegelsteinfaust]

Originally Posted by dmack91

You can pull the front drive shaft and see if that cures your vibration problems. Not completely familiar with the 203, but you may have to put it in 4high lock if you do pull it.

Do not just pull the front drive line. The np203 needs it as it is a full time transfer case. It supposedly will try to send the power to the front, and will not move the vehicle well.

I had one, but I had both my axles working.

Also most shakes on a leaf spring truck are the tires. Not enough movement in the bushings to get terrible shakes supposedly.

Use balance beads in the tires since they will constantly change to suit dynamic needs. I use them exclusively now, and never have issues of tire balance.

[RyanAK]

Balance beads, huh? More research needed...

Not sure what you mean by not enough movement in the bushings to get the shakes... can you tell me more? I’m trying to educate myself as I go through this rig.

Appreciate the suggestions, fellas.

R

[Ziegelsteinfaust]

Originally Posted by RyanAK

Balance beads, huh? More research needed...

Not sure what you mean by not enough movement in the bushings to get the shakes... can you tell me more? I’m trying to educate myself as I go through this rig.

Appreciate the suggestions, fellas.

R

I have very little 4x4 experience as I only had a K20 for about a year, but I did a bit of research when I converted my C20 to K20. Also I didn't get a Jeep JKU due to the same issues appearing on stockers, and I kind of preferred a truck.

Link suspensions are notorious for shakes. Type in favorite model with the term death wobble, and you'll get alot of stories.

My K20 had non existent bushings for the first few months I drove it, but it tracked perfectly fine. My tires were really nice AT's on pyo rims with balance beads. The rear had 2" spacers to match front track width.

[akart]

If you think it is your drive shaft here's a trick/Get some hose clamps,maybe 5 and attach them to your drive shaft all w/the weight ends together maybe opposite your attached weights. Better,worse?? See how it goes.

[demian5]

I thought I had driveshaft problems, it was the flat spots in my 20 year old 31 11.50 15 goodyears. New tires, all gone.

[RyanAK]

The hose clamp trick is definitely worth trying. I found front and rear driveshafts somewhat local with a guy that has a stockpile of squarebody stuff. I’m considering getting one of each and having them rebuilt/balanced and swapping them in. But the hose clamps are a good idea to try.

demian5 - what symptoms were you experiencing? I need tires anyway, and will be springing for them as soon as I can decide on a good-looking set of 16” wheels for this rig. I assume driveline somewhere since the vibration is specific to 45-55 (and I’ve now discovered it’s back between 65-70) and I think tire issues would occur at all speeds, getting worse as you go faster. But maybe I’m wrong...

Decided to take the Suburban out of town for work this week. Other than the vibrations, it did well. Here’s a couple photos.

[1976gmc20]

Tires can definitely have vibration issues within a certain speed range.

Absent any obvious driveline problems, I would get new tires before chasing down anything else.

[RyanAK]

Ok... tires definitely first. The more I drive this truck, the more I believe it's the almost 13 year old Toyos. I'm looking for a good looking 16" wheel and then run a 32"-ish tire. Even if it doesn't cure the vibration, overall ride has to improve. I'll report back once the rig has new rubber. Thanks guys.

[demian5]

Originally Posted by RyanAK

demian5 - what symptoms were you experiencing?

Vibration going down the road at 55-65 MPH, no matter accell or decel, in gear or out of gear. Checked everything, when I got new tires, it went away. Smooth up to 120 now... In a burb you have all that room inside, that it will also have a sound like a buffering.

At least have them balanced and have the tire buster look at them and see if they are OOR (out of round).

[RyanAK]

Well, that about seals it! Thanks, man. I’m definitely experiencing a buffering-type sound at a specific speed band. I had the Toyos rebalanced, but the couldn’t (or wouldn’t...) check for out-of-round or lateral runout. Makes no sense... I would have been an easy sell!

Needless to say, I’ll buy tires somewhere else!!

16x8 Cragar wagon wheels and 265/75R16 General Grabbers. Yeah... that’s the ticket!

Appreciate everyone’s input! Fingers crossed!

[demian5]

Originally Posted by RyanAK

265/75R16

Those aren't cheap anymore. Such a bummer.

Take this for price matching: Hankooks are decent

https://www.walmart.com/ip/Hankook-D...114T/570246074

[RyanAK]

Yeah. I had a good case of sticker shock. Hence the fairly modest wheel choice.

[demian5]

Find a set of 17" toyota FJ cruiser or nissan titan steel wheels (17 and 18 I beleive) and check prices of tires. That would look really cool and you can put clips on for caps.

[1976gmc20]

Originally Posted by demian5

Find a set of 17" toyota FJ cruiser or nissan titan steel wheels (17 and 18 I beleive) and check prices of tires. That would look really cool and you can put clips on for caps.

Are you sure the backspace would work ????

IFS wheels won't work on solid axles that I'm aware of. Not without spacers anyway which adds more expense and complication.

[ShortHaul]

Yeah be sure to check for fitment with any Toyota/Nissan wheels... the bolt pattern matches (almost) but backspace and center bore could be a different story...

Before you commit to wagons, I was searching a few more possible steelies options and found a few other possibilities.

Hot Rod Wheels offers a handful of steelies in 6x5.5 lug 16”

https://www.uswheel.com/wheel/12211/...?finishID=3880

Us Mags has these Squarebody Ralley style wheels. Offered in every size under the sun...

http://us-mags.com/sierra-u706-6-lug-w-7843.htm

They also have a “steelie” type called the Plain Jane which you could drill to accept clips to hold on OE caps.

http://us-mags.com/plain-jane-u475-w-4947.htm

Detroit Steel Wheels has smoothies, ralleys and artillery style, but the smallest they go is 18”. They do, however sell the clip sets for holding oe caps on.

Most of these options are a bit pricier than wagons, but it might be worth looking into. As I like to say, buy once, cry once...

Anyways, good luck!

[RyanAK]

Appreciate the breadcrumbs. I spent a lot of time looking and thought I found all possible options but hadn't come across the US Mags. Pretty neat. The Sierra especially looks great. The budget is tight (two amazing little ones... 4 and 3...) so I'll see what I can do. I had thought about wagons and saving up to have Stockton punch out my OE 15x6 to 16x8. This is still probably the direction I'll go.

"Fred" ain't no "Sweet Pea", but we're moving in the right direction.

R

[1976gmc20]

I know just everything has aluminum wheels now but after cracking an OEM aluminum wheel on my 1500 Suburban, I wouldn't have anything more to do with them. I've got three of them that are still "usable" sitting out by the garage but I won't ever use them again for anything other than an emergency spare-spare.

I even swapped out the factory 17" aluminum wheels on our 2006 HHR for 15" steel junkyard wheels from a Malibu/Saturn. Main reason was to get rid of those damn low profile tires that also cost a fortune, but now I get better ride, mud/snow traction, and gas mileage. Also a steel wheel will bend, maybe to the point of needing replacement, but an aluminum wheel might just shatter.