GMC front wheel bearings

How can you be sitting in Big Jim right now as he is sitting in my RVPort
right now in Idaho.
Marlene Meineken
77Palm Beach
AKA BIG JIM
- ----- Original Message -----
From: Samuel Pickens
To:
Sent: Tuesday, September 07, 1999 1:53 PM
Subject: Re: GMC: GMC Front wheel Bearings

> Arch and all,
>
> Approaching one's vehicle. Familiarity breeds exempt. Exemption comes by
> knowing. How well do we know our vehicle? Have you recently purchased and
> assuming everything is OK? At the first Spring or Fall whichever comes
> first, pull the wheel, inspect the brakes and lubrication of the bearings,
> etc. If I have suspicion of anything, I have a tendency to attach an
> accelerometer and drive down the road gathering data for analysis before
> visual inspection. And/or from said analyses I may determine to replace
the
> bearing even before visual inspection. On the other hand said analyses may
> give me confidence to continue operation without visual inspection.
>
> Sorry about the rambling. Yes, I do analyses of bearings while driving
down
> the road. I've also performed testing on vehicles while on a rack. I did a
> Jaguar and determined the drive shaft was out of balance. They didn't
> believe me as they told me that was the drive shaft they just had
balanced.
> They were fully confident the DS was OK. I soured the problem to the DS
and
> maintained the transmission and hogs head were OK. The problem was
resolved
> when the DS was again balanced. Setting DS's up for race is interesting
but
> that's another topic. I have full confidence on those data.
>
> One bearing doesn't necessarily relate to the next. For example; the L
side
> can be OK while the R side is bad. Analysis can determine this. Now to the
> trick. Can this transfer from one person to another? NO! But, I believe
> basic guidelines could be established. A random starting point could be
> established; say at five g's 0-P overall.
>
> How to obtain that data. One approach is to instrument the vehicle with
> onboard monitoring. Another, portable monitoring device that could even be
> transported or swapped between GMCers. Breaking down on the highway can
> cost five days unless you're stinking, filthy rich. I only need to get the
> rich part right. One may instrument a vehicle for ~$1500 - I'm guessing
> (six transducers, cabling, electrical supply {either -18, -24 or -27
> volts}, and a digital readout). Once it has been determined that 5 g's is
> the flag point that alerts to inspection/replacement or whatever value
that
> is finally determined, then one could run with peace of mind. Lubrication
> can be a veribile, how much wet driving vs dry driving and do you drive
> through creeks? The overall approach won't allow monitoring of lubrication
> but FFT analyses will. Replace the digital readout with an FFT analyzer
and
> you're ready to run on Indy. Those data can also be transmitted via cell
> phone. Anyone wanting to replace their dash with a computer -- monitor all
> parameters. It isn't that difficult anymore. Where do you want to take
this
> thing? Money is the only limit, all else is easy. Very easy.
>
> I hope this helps to provide insight. This is pumping me up to want to do
> it. Good preventive maintenance should void or kill the project. But,
> predictive maintenance is does have cost effective virtues too. It will
> reduce maintenance while maximizing life. And, life is too short to drink
> bad wine. Besides, a motor home is throw away money for most. Unless,
> you're like me - single, travel all the time, play as much as I can.
That's
> right, I'm broke but enjoy bitching about it. I'm sitting in Big Jim now
> writing this thread. I travel every season, even winter in MI and summer
in
> FL. I will venture to say, there isn't anyone out there that spends more
> time in their MH that me. I have to depend on mine, it's a way of life. I
> hope I haven't bored anyone with my ramblings. May the good Lord take a
> liking to ya.
>
> With best regards; I'm
> Sincerely,
> Sam Pickens
> picksam
>
>
 
>
>Sam
>
>I want to start with the basics. What is a FFT analyzer?

FFT stands for Fast Fourier Transform. It's used for many purposes, but one
of the nice thngs about the FFT is that it can be used to crunch a bunch of
data and extract the "real" information. Let's suppose that the GMC front
wheel assembly turns 5 times per second. If noise is being generated by the
turning, all you need to do is sample the sound (or motion - vibration) at
a frequency of at least 10 times per second to get valid data. The FFT then
is used to find out how much energy is present at each frequency (according
to how the prograsmmer set up the FFT) so that you can determine the
strongest frequencies generated by the wheel. In practice the sample rate
is much higher than what I mentioned, but the principles are the same.

By using an accelerometer you can detect minute vibration. There's a lot of
work that has gone into bearing analysis using vibration analysis. I'm glad
that Sam has the experience with the frequencies etc.

Sam - what type of accelerometer would we need to instrument the wheels?
ADI makes some pretty good silicon accelerometers with condictioning
circuits in teh 5-10g range. I'm pretty certain that I can come up with FFT
S/W that will run on a PC (or cheap DSP board). (DSP is my primary business).

Henry

We have got to
>get you and Heinz together. I for one was not bored but I do want to
>hear your thoughts on why GMC front bearings have such a bad reputation.

"Lots" of failures in the 80s and then the fear of faiulure used as a
selling tool perhaps?

Henry
Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com
 
> >
> > "Lots" of failures in the 80s and then the fear of failure used as a
> > selling tool perhaps?
> >

I sure hope my rig hasn't heard anything about that.

I've put on about 210k on 3 sets of fronts and I'm hoping to get a few more
turns on the current set.

Heinz
...shhhhhhh
 
Arch,

The Fourier Transform is a mathematical function invented by John Baptise
Fourier in or around 1538 AD I think if memory serves. Basically, the real
time signal is generated from the transducer and is a sinusoidal wave much
or exactly like the time wave form seen on an EKG machine. If it were
possible to view the wave from the end, then one would be able to see the
frequency components.. So, it's a frequency spectrum of a time wave form.

The analyzer is a volt meter -- a very good high dollar volt meter with the
ability to display the frequency spectrum on the display as well as time
wave form. One may chose different analyses functions and different
processing formats. Cesptrum analysis became popular in the 80's. It's an
FFT turned inside out or an FFT of an FFT.

Bearings with a bad reputation! I guess it depends on where they hang out
and who they associate themselves with. Maybe they were abused as a child.
Who knows. It may be myth. I've rebuilt many pumps that wouldn't run past a
month or so after others did the rebuild. But, after I did the rebuild we
concluded that I must have gotten lucky because it gave good service.
Better lucky than good I guess. Why, even some people like to rub me for
luck. Boy! These know it all people. Some people think they know it all; it
really upsets those of us who really do. Everybody thinks they have a sense
of humor. Few do: here's the test. A man walks into the Shrink's office
with a duck on his head. The doctor walks out and says, "may I help you?"
The duck says, "yeah, get this guy off my ass".

With best regards; I'm
Sincerely,
Sam Pickens
picksam
 
Oh, it probably flies into the face of conventional and perhaps even
mythtical wisdom, but fact is fact. This is not supposition but actual
transpirings and hopefully the GMC gods will continue to be kind :-)

I've been working on a new page so as to minimize net clutter with ramblings
that may not be of interest to all (or even ayone :-).

http://www.bytedesigns.com/gmc/rambling.htm

Any and all comments welcome, private or public :-)

Don't hesitate to ask questions... I'll try to do my best to answer but
please keep in mind that I'm just a doer as in trial and error. No
professoring or enkineering in my background, just some slight envy of those
that have (professoring/enkineering background).

Heinz

> In a message dated 9/7/99 6:48:28 PM Central Daylight Time,

>
> >
> > I've put on about 210k on 3 sets of fronts and I'm hoping to get a few
more
> > turns on the current set.
> >
> Heinz
>
> Would you mind sharing your secretes? I for one would sure like to hear.
> If it fly's in the face of conventional wisdom then send it private.
>
> Take Care
> Arch
>
>
 
Arch,

The precision of the bearing is a science, and, I agree the installation of
the bearing is an acquired art. A bang up job in parts of the country means
good, while in others it means beat to death with a hammer.

When using vibration analysis techniques for monitoring lubrication, there
are two main concerns. Is there a sufficient amount and is it an adequate
grease for this application. When the bearings' natural frequency is
excited it will usually be from one of these fundamental problems. Always
label your grease gun. Know how much one pump is: for example, one shot of
grease = 2 grams and does the grease gun have two adjustments? Get out the
handy mans secret weapon (duct tape) and apply to the side of said grease
gun and with your magic marker label those things. Record quanities and
time. If on one hand you know the grease is adequate, then increase quanity
or increase grease frequency interval. Now the left hand knows what the
right hand is doing.

I have a program I've written that covers presently five bands. I usually
set these bands to what interests me most of that particular machine. And
for that program, If a band monitoring the bearings natural frequency is
excited, alerted or alarmed then the print out automatically will display a
statement. If a bearing is set too tight that will be determined by ball
spin frequency (harmonics with high magnitudes). Or, if loose harmonic
content from the fundamental. That's right, if you can't dazzle em with
brillo, then baffle em with ?? Opps, I've used it all up.

With best regards; I'm
Sincerely,
Sam Pickens
picksam

- ----------
> From: Gcbr
> To: gmcmotorhome
> Subject: Re: GMC: GMC Front wheel Bearings
> Date: Tuesday, September 07, 1999 9:24 PM
>
> In a message dated 9/7/99 7:27:17 PM Central Daylight Time,

>
> > Who knows. It may be myth. I've rebuilt many pumps that wouldn't run
past a
> > month or so after others did the rebuild. But, after I did the rebuild
we
> > concluded that I must have gotten lucky because it gave good service.
> > Better lucky than good I guess. Why, even some people like to rub me
for
> > luck. Boy! These know it all people. Some people think they know it
all; it
> > really upsets those of us who really do.
>
> Sam
>
> WOW!! I love it! I will say it again I still define Lucky as when
preparation
> meets opportunity. I also think that bearing service is a matter of art
not
> science totally. Yeah the facts have to be right but-------so does the
art.
> Thats why some mechanics can make everything work and others cant.
> Sam I think I will leave the FFT stuff to you guys who like it. I would
just
> like to hear what the FFT is saying. What is the FFT saying about
> synthetic grease with its high drop point? Sam please translate what
> the FFT is saying.
>
> Take Care
> Arch
 
> Oh, it probably flies into the face of conventional and perhaps even
> mythtical wisdom, but fact is fact.
> I've been working on a new page so as to minimize net clutter .........
>
> http://www.bytedesigns.com/gmc/rambling.htm
>

Heinz,

I visited your "Front Bearings" website and found it very interesting. Your
setup is very similar to a 1951 Jaguar MK V that I owned. On that car, both the
front wheel bearings and the rear wheel bearings were lubricated by way of
grease fittings. The front grease fitting was located on the hub. The
procedure was to add grease with a hand held grease gun until a small amount
came out of a vent hole in the dust cap. The rear wheel bearing grease fitting
was located on the bottom of the axle housing. The vent hole was located on the
top of the axle housing. The bearings were very easy to lube and consequently
always got the proper attention.

Your setup may be the key to the whole problem. Why do your bearings defy
conventional experience and seem to last "forever" and only get changed when you
elect to do so? Probably because they are always properly lubricated.

Lorry
 
>In a message dated 9/7/99 5:53:32 PM Eastern Daylight Time,

>
>> PC (or cheap DSP board). (DSP is my primary business).
>
>Ok Henry, what now is a DSP board?--I probably have one laying around here.
>Is that something like a dihydrogen/silicon/phosphate board, I usually make
>in the morning and flush or something else?:) I have my halogen ears on and
>2 dendrites ready for the education-
>

Yes, but do you have your official, tin foil lined, beanie?

DSP is Digital Signal Processing. (or Digital Signal Processor depending on
whoi you talk to) It's fancy talk for modifying a signal using digital
techniques (as opposed to analog techniques). Signal In - modify - Signal
Out. No fuss, no muss. For some systems like digital cellular phones it
reduces cost and improves performance.

Henry

Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com
 
> >There is the group that is adamant that you have to replace the bearings
> >every 25,000 miles or suffer bad things. On the other hand, there are those
> >that say you can run them for a very long time if they are not wearing and
> >that they just may be better then the ones in the box that are untried.
> >
> >Pretty heady stuff for this lowly computer salesman.
> >Richard Waters '76 PB, Troy, MI
> >-----

I posted this comment quite awhile back: I have a GMC owner friend who was an
airforce mechanic. He stated that they never replaced wheel bearings on an
aircraft related to mileage. If the bearing looked good, it was repacked &
reinstalled. I have close to 100k miles on my Bower bearings & agree with Ken
Thoma - if they look good, why replace. I'm not a mechanical expert (my field is
electronics), just my personal experience.

Along the same line, I read recently that the life expectency of a gas engine in a
motorhome is 100k miles. I guess I better replace mine. It has 200k miles on it.

I think we have all read the "theory books" in our prospective fields. What should
one believe, theory or experience. Anyone who's been around the barn knows the
answer to that.
 
>
> Thoma - if they look good, why replace.>>
>
> one believe, theory or experience. Anyone who's been around the barn knows the
> answer to that. >>
>
> Richard - I respect your right to make your own decisions on anything you
> want. However, there are several people whose "experience" has been pretty
> bad with the front bearings. I think that those of us who follow GM's advice
> on replacing the bearings every 25,000 or 30,000 miles are not expecting that
> at 30,001 miles they are going to immediately fail but rather find it an easy
> way not to have too much worry about when and if they will fail. This
> approach is called "preventative maintenance" and though it might cost a
> little more, in the long run it gives peace of mind and, if there were to be
> a failure, the repair costs could exceed the periodic replacement cost many
> times over. The loss of a wheel could also mean the loss of lives.
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM

______________________

Shakespeare said it: A rose by any other ....... The name's Edgar. No reprimand
intended.

I agree w/your thoughts. Many people will feel safer & possibly be safer. I'll
relate a little story (distantly related to the above & not to argue against).
I worked for many years in the videotape room of a major TV station in Baltimore,
MD. I started in there when "tubes" (you remember them), were in existence. In
those days videotape machines were very "touchy." Scopes & meters were constantly
hooked to monitor operation. Adjustments were often made while a tape was "on the
air."
One day the chief engineer came through & declared all of the tubes should be
replaced because they had X number of hours on them. The tape techs, my being one
of them, new from experience this would be a disaster. We would have to spend days
tuning all of the circuits to get them to function again. The tubes were never
changed. The chief engineer was never told.

OTOH, these were quad tape machines. Video heads were notorious for short life. 50
hours was considered fantastic. Cost to refurbish a head, if I recall correctly,
was $1K. We had a head that had achieved 100 hours - a milestone. RCA would have
replaced it free. The chief wanted to get a "few more hours" out of it. It failed
virtually within minutes after the 100 hours.

Take your pick.
 
> if there were to be a failure, the repair costs could
> exceed the periodic replacement cost many times over.

As a data point here, when my father toasted the right side wheel bearing,
the parts alone from Zeb Frady were over $1,000(not including core charges).
Contrast that with when, one month later, we pulled off the left side
hub/knuckle assembly and carried it up to Zeb for service and the total tab
was around $300 including a new bearing, rebuilt knuckle and CV boot(which
we replaced ourselves).

To paraphrase the old oil filter commercial, "You can pay me now, or pay me
a lot more later".

BTW, Zeb charges a flat one hour labor plus necessary parts to rebuild the
assembly. Not a bad deal at all if you feel the job is beyond your ability
or you don't want to buy an expensive tool that you'd only use every 25,000
miles. The assembly is simple to remove(although fairly heavy) by
disconnecting both ball joints, the tie rod end and removing the spindle
nut.

I'll say it one last time(this time at least), if you don't know
absolutely, positively that your front wheel bearings were properly serviced
within the last 25,000 miles, service them NOW! You can't afford not to.

My $.02,
Patrick
 
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