Vibration @ 50 mph
 

Hi folks, here is an easy one for ya ... I hope.
54 PU, right around 50 there is a vibration of the frequency of the wheel rpm.
Couldn't tell if it was front or back as there was no transfer to the steering wheel.
First, I found a broken shock on the rear. Put 2 new ones on and balanced the rear wheels. One was out quite a bit as I had the spin them up before removing the original weights. Test drive .... still the same "shaking" vibration at around 50.
Decided to check and balance the front wheels. They were very close but one was a little "eggy" and didn't spin absolutely true but was balanced. At this time I also noticed some play in one of the kingpins. Test drive and same problem. Put 2 new shocks on the front .... same shaking but no noticeable transfer to the steering wheel.
I'm not sure if the eggy tire is matched to the loose kingpin or not. Could one or the other, or both be making me shake ?
Also, the front motor mount is turning to jelly. Could that contribute ?
So, 4 new shocks, 4 balanced, 1 eggy tire and 1 loose kingpin.
The spare is an old original bias-ply, guess I could try that in place of the egg
for a test, but the others are radials. Safe to do ?
Thanks.
Thanks

Re: Vibration @ 50 mph
 

Don't forget things like the drive shaft, look it over. And worn U joints can make that happen. I know it was my problem with my Rambler a few years ago. There was a little movement in them, changed them out with new and wham, vibration gone.

Brian

Re: Vibration @ 50 mph
 

move the eggy tire to the back and see if the problem moves with it
you may have a broken band or tread starting to separate

Re: Vibration @ 50 mph
 

I would check the drive line and u joints first like Brian suggested above.
I have had aftermarket wheels cause a similar vibration. Where the center bore of the wheel is larger than the hub so the wheel isn't centered. That can usually be fixed with a hub centric ring, if you can find the right size.

Re: Vibration @ 50 mph
 

Thanks jwed and Brian.
I've experienced driveline vibes before and am familiar with the higher frequency thereof. This is clearly at wheel speed frequency. (as mentioned earlier)

It's all original ... torque tube with original wheels.
I have another pair of mounted bias-ply's that I'll try on the front.
Thanks to Ogre also. I'll move them around and see if it calms down.
I'm ordering a kingpin kit too.

Thanks guys.

Re: Vibration @ 50 mph
 

are you running stock suspension with the torque tube? open driveline?
if possible, have a buddy drive behind you and watch the tires as you drive, when you get to the vibe speed tap the brakes as a heads up that the vibe is in progress. maybe he/she can see something happening with the load on the truck while driving. just curious, when it does this will the vibe go away if you step on it or let your foot off the gas? is it making any noise when the vibe happens-like a wheel bearing or trans bearing? does it change if you gear up/down, is it at a certain engine speed no matter what gear or even if you are moving? I have found a u joint is usually more of a hum and a buzzing vibration coming up through the seat and will come in at a certain speed, get worse, then fade out and come back again at a higher speed. a wheel is a slower thing, more like a shake and gets worse as you speed up. usually the whole vehicle seems to move a bit.
-jack it up and put it on some sturdy stands under the axles so the truck is sitting on stands just like it would be on the floor except higher. use the same height of block in the same position on both sides so you can check as close as possible to how it sits when on the floor
-spin the wheels one at a time and check for run out, like out of round-eggy, and also not running true, like a bent wheel. a block with a nail in it will scribe a small scratch mark all the way around the tread of the tire if the wheel is round, if not there will be a spot where the nail doesn't touch. don't use the nail on the sidewall, but a lumber crayon or even a felt marker or pencil will help you see how outta whack the tire is running, if at all. you can use the scribe mark to check your alignment later
-check the wheel bearings while you're there, park brake off. might as well do a complete suspension check on the front and rear. spring pins and bushings, springs, ride height the same on both sides, tie rods, drag link, steering box play and wear, etc
-start it up and run it up to speed where the vibe was happening, if possible. have a buddy check the wheels as they spin to see if one is going eggy from speed. that will diagnose the rear axle tires. if nothing found swap the front and rear tires and try again.

Re: Vibration @ 50 mph
 

sorry fred, just seen the bit about the stock driveline.
check the rear axle mounting pivots as well. the axle doesn't mount directly to the springs, correct? worn out bushings maybe?
do you know anybody with a spare set of wheels you could borrow for a test?

Re: Vibration @ 50 mph
 

Thanks raven.
I jacked the back up and it ran smooth after the new shocks went on and wheels were balanced. and they are round.
Would do no good to put the balanced egg back there to spin it. It is perfectly balanced on the computerized machine and the egg/out of round would only come into play if it was traveling along the ground at speed.
All 4 rims are good and straight, no problem there.
Back axle bushings are old, but are tight.
All front steering linkages are tight and the box is good. drives with 1 finger. Excellent for what it is.
I highly suspect the eggy tire .. it's just too much for the shock to handle.
It starts right at 50couple mph, and lets up over 55.
It's really smooth at 95 ... he he he :lol: just kidding, but, there is no gearing up or down in this thing at 50 mph, there is no 4th gear and to drop to 2nd ....... would be interesting. (no seat belts):lol:
I have depressed the clutch and the shaking continues until it slows to under 50 though. As I said, I do have a spare pair to try out. They are holding air but are quite old. I'll hang on and anticipate the worst.
Thanks.
Thanks

Re: Vibration @ 50 mph
 

I just did this on my mother in laws crv. vibration at 55 lasted through 60 then smooth. there was a separated belt in one (two year old) tire. she was sure it was the transmission! easy fix.

Re: Vibration @ 50 mph
 

I would suspect the out of round tire. Even if it's perfectly balanced the eggy tire will still induce a vibration. Personally, I would find a tire shop that offers "road force" balancing and get your tires there. Not every tire shop has the equipment. Here's a short video that explains the process.

http://www.motorweek.org/features/go...orce_balancing

Re: Vibration @ 50 mph
 

Well there ya go, that's a bit fancier than what I've seen, but basically what I had in mind. We don't have that here at my local tire shop in the hills, they just depend on a round tire, relatively straight rim and good "off car" balance.
Might just have to buy a new pair for the front.
Thanks !

Re: Vibration @ 50 mph
 

yeah i go along with blacksheep on the egg tire ......

Re: Vibration @ 50 mph
 

Very few tires are truly round, that's where match mounting can really help.

Re: Vibration @ 50 mph
 

Well if you were here we would spin the fronts up with one of my Hunter on the car spin balancers. That would tell you if you had a hub out of balance or other issue.

Right now I'd say try some different tires is probably the best for process of elimination. I would just change the one wonky one for the first test though. One change at a time so you know when you figured it out.

Re: Vibration @ 50 mph
 

OK, looks like we were all right.
It was an evil combination of the loose kingpin and the eggy wheel being on the same (right) side.
Swapped right tire w/left and all tests up to 70 mph were acceptable .... till I get a matched pair of new tires.
All in this regard is goo, thanks.
Now ... another issue.
When I bought the truck, the PO said the brakes will lock up on the first application after sitting a while. Well, it did it on the initial test drive, but never does it again till it sits a while.
While I was doing this tire diagnostic, I pulled all the wj\heels and drums and looked it over.
Front left was missing the the nail looking pin that comes through the backing plate that holds the shoe against the plate. The spring clip was still in there though and just tumbling along for the ride. I assumed I'd found the problem with this missing pin thinking the clip was jamming that one shoe/wheel cylinder and applying pressure to the other 3 causing the jamming, made a new one and tried it out.
SAME dang thing happened. After a a few firm apps of the pedal, it smoothed out and worked fine (perfect, actually) for the rest of the outing ... 40 or so miles with many stops along the way. Anxious to see what happens the next time out.
What the heck would make them jam up and lock like that ?
All the shoes were clean and dry with plenty of meat on em', the drums look
good and were dry except for the rear left that had a little oil from a leaking axle seal. It looks/acts like they ALL lock up though .... not just one. It's like a blast of hydraulic pressure is being applied to all .... but not from my foot.
Any ideas ?
Thanks again Gents.

Re: Vibration @ 50 mph
 

if its all 4 wheels your brake pedal may not be returning all the way back to allow a neutral pressure situation ...when the piston in the master cyl returns past the ports it should relieve the system pressure...some use residual valves to hold a few lbs of pressure as well

Re: Vibration @ 50 mph
 

Thanks Greg, but it ain't that. All of that's good.
As soon as very slight pressure is applied to the pedal ... BAM, they all lock up.
Let off the pedal and all is fine. Might do it a time or 2, then all operates as normal.
I even seen 4 skidmarks in the gravels, and once all 4 on the pavement. I live on a dirt road.
Thanks .... still wondering,
:confused:

Re: Vibration @ 50 mph
 

are you sure the primary and secondary shoes are installed in the correct place, as well as the correct return springs on the shoes? the long shoe lining usually goes on the rearward side. the weaker spring usually goes on the frontward side. also check the backing plates to ensure there are not worn out grooves where the shoes sit against the backing plate. this is common and the shoes "fall into" the worn grooves and then when they come out, with a little pedal application, they can grab the drum and cause erratic brake action. a smooth backing plate and some brake lubricant applied in that spot is normal, not lube on the linings, just the steel backing part of the shoe. it usually has a small expanded area where it rubs on the backing plate. below is a link to the original manual and it explains self energizing brakes better than I could.basically the front shoe has a weaker spring so it tends to push out first, grabbing the drum and slightly turning the shoes on the backing plate so they jam against the mounting pin at the top of the backing plate. that's the reason for more lining on the rear shoe as well. maybe just read the link, lol
how far does the pedal travel before you get some feedback? you may want to check all the linkages and return springs right from the pedals down. ensure all the pivot points etc are all free and easy moving, no binding etc. ensure the pedal returns fully but also ensure the master cylinder returns fully. all it takes is a little slop in a linkage point and a sticky pivot so the master cyl doesn't return

http://chevy.oldcarmanualproject.com...4ctsm0502.html

Re: Vibration @ 50 mph
 

another thing to adjust is the toeboard clearance

http://chevy.oldcarmanualproject.com...4ctsm0508.html

Re: Vibration @ 50 mph
 

and brake adjustment

http://chevy.oldcarmanualproject.com...4ctsm0511.html

Re: Vibration @ 50 mph
 

then park brake adjustment

http://chevy.oldcarmanualproject.com...4ctsm0513.html

Re: Vibration @ 50 mph
 

this page shows the brake contact areas of the backing plates. some old trucks will have those grooves worn into them from years of use. a replacement backing plate is the fix.

Re: Vibration @ 50 mph
 

Hey, thanks for the info. I am going to go into it later this week with this manual and hope to find something amiss. Maybe the pri./sec. shoes are reversed.
With the manual as a guide, I hope something is quite evident.
New seals and shoes are on the way.
Thanks again.

Re: Vibration @ 50 mph
 

Or just grind it smooth in that area. I remember seeing my brother (a mechanic) doing that years ago when I was a kid, and it's the norm for me, just clean those areas up.

Brian

Re: Vibration @ 50 mph
 

I've smoothed out hundreds of grooves in backing plates where the shoes rubbed in the years I was doing brake jobs. I did most of them with a file then as I didn't have access to a grinder. I'd use a flap wheel now.

Following behind someone else's brake job can always be a challenge as you are always having to check and see what they might have done wrong. Springs in the wrong place or missing, contaminated lining, shoes on backwards as far as primary/secondary go. The shoe with the least lining always goes in front, the one with the most always goes in back and some budget lining came with two different compositions that were marked primary and secondary. kind of like a tan lining and a gray lining.