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post #1 of (permalink) Old 12-11-2003, 11:41 AM
jzack
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Buzzing from front axle/diff \'95 Tahoe

This is my first post and first visit to this board.
HIYA ALL!

I've got a buzzing comming from the front axle of a 1995 4x4 Tahoe (2dr). I bought this truck 4 months ago. This past weekend we got 2 ft of snow, and I used 4wd high & low for the first time.

The following day I noticed a buzzing from the front, and it goes away if I engage 4-low, but it's present in 4-high/2-high. It gets loud and goes quiet, and doesn't seem too bad at high speed. In fact, it explains the very faint buzzing noise I (very) occasionally heard prior to this incident, which I had thought might be the rear diff but wasn't. In its now-worsened state I don't feel comfortable driving the truck.

So it seems I've got a problem with getting the front fully disengaged. Does that sound right?

I don't have any manual so I have no idea how this thing is put together. (the darn hood latch just decided to quit also...go figure). Does it use a linkage or electric? Internal or external actuator? Can this be fixed by replacing some sort of bolt-on axle shift motor, or am I going to eat a big repair bill by some who's going to rip the diff apart? (I have air tools, impact wrenches, torches, etc., so I can do mediaum size jobs, but it's cold and wet here in Boston <sigh> and I can only stand so much out in my driveway).

If anybody has a URL or PDF of an exploded view of this axle / diff assembly then please send it to me.

Thanks
Jay - [email protected]

BTW, I just found this - does it apply to me? (sound like a sinch, eh?)

http://forums.vmag.com/suvtahyuk1099/messages/7506.html

In Reply to: Re: 95 tahoe not engaging 4 wheel drive posted by mike on January 11, 03 at 19:06:23:

1995 has the front axle with the thermo shift solenoid in the front axle. Has a fluid that must heat up to shift. Bad engineering. Chevy replace approx 75,000 of them in 95-96 but no recall. Go to a dealer and get the electric conversion solenoid and harness. Takes about 1/2 hout to install. This will make a solid shift every time. Try http://www.gmotors.com/ (Brasington Cadillac) Got my conversion there last yr for $76 with shipping and it works flawlesly.
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post #2 of (permalink) Old 12-11-2003, 12:36 PM
 
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Re: Buzzing from front axle/diff \'95 Tahoe

To verify that ur front diff isn't disengaging, do this: Put it in 2 hi, duct tape a piece of cardboard to the front driveshaft so that it contacts something when it rotates, and go for a drive. In 2hi, the front dshaft will only rotate if ur front end is still engaged.

Instead of the electric actuator from gm, for a little more money you can buy a cable actuated "Posi-Lock" where you just pull a cable to engage. I think this would be more dependable than even the electric one.
http://www.4x4posi-lok.com/chevy_page.html

Plus, with the posi lock, you can use 2 lo by putting the transfer case in 4lo and disengaging the front diff.
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post #3 of (permalink) Old 12-11-2003, 01:04 PM
jzack
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Re: Buzzing from front axle/diff \'95 Tahoe

Thanks for that link, dhcomp -- helps me see how it's built.

To be clear on the problem, the buzzing sounds like the disengage spring is weak or the internal locking machinary is sticking. That post I quoted (and the photo on your link of the OEM unit) makes is seem like the original design is to run current through some dohicky (gas piston?) which then somehow pushes on the guts. So it's these guts that aren't engaged, but they're also not pulled away from hitting the tops of the gears/teeth/pins/etc., thus the buzzing noise like somebody is lightly grinding gears.

So I guess what I'm asking is do the OEM soleniod, posi-lok, or whatever, only push on the lock, and not pull? Does it rely on a pull off spring, that in my case may be weak?

If you have any more links on the subject then please post em!

Thanks!
-Jay-
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post #4 of (permalink) Old 12-11-2003, 02:09 PM
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Re: Buzzing from front axle/diff \'95 Tahoe

whoa....i'm getting all confused with such fancy and detailed descriptions of....the front diff [img]images/graemlins/smirk.gif[/img]

anyway, your 95 actuator is more than likely thermal. so, when you engage 4wd, it sends the signal to the actuator, which heats the goo inside and extends the rod. (if i remember correctly) that rod presses on a sprocket in the diff, that engages the axle shafts.

another way to see if your actuator works is, unscrew it, engage 4wd, then look at it again and see if the rod extended. if it did, the actuator is not the problem.

another thing i suggest you take a look at is the tcase switch. look on the front diff, right behind the actuator, theres another little screw in thingy. unscrew that and make sure the little rod and spring in that are working correctlt and are not jammed. mine was jammed and it would not let the sprocket/gear thing in the diff to completely disengage. if its not working, replace it. $16 part. you dont need it though. all it does is control the lights on the floor shifter to let you know whats on.
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post #5 of (permalink) Old 12-12-2003, 10:06 AM
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Re: Buzzing from front axle/diff \'95 Tahoe



Okay, I just removed the switch that for you was jammed. Sorry (for me) to report that it's fine.

Is it possible that the original actuator is jammed? I could buy the replacment elctrical (non-goo) actuator locally, but it's going to cost me ALOT more than if I mail order (which would render me immobile for the weekend).

Again, i get the feeling from the post I've read that a bad actuator shows symptoms of not-engaging, not not-disengaging. Is there a positive /pull/ from the actuator when disengaged, or does it only push to engage?

Well, at any rate I guess it's time to pull and inspect.

-JAZ-
post #6 of (permalink) Old 12-12-2003, 10:53 AM
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Re: Buzzing from front axle/diff \'95 Tahoe

I just got of the phone with a a guy from posi-lok -- I fugured they would be authorities on the subject, and from our conversation I believe they are. He thinks it's a good chance that it's the transfer case. <sigh> [img]images/graemlins/frown.gif[/img]

As a sanity check I picked up each of the front wheels (separately) and they spin freely. (oops -- NOT free when it's warm -- see below)

Okay, can anybody tell me how to check if transfer case is messed (re buzzing sound) aside from clinging to the underside of the truck while someone else drives it [img]images/graemlins/wink.gif[/img]

If it is the transfer case, then is there an adjustment, or am SOL and need a rebuild?

-JAZ-

----------------
Okay here's more (I edited this post so anybody who finds only this post won't be thrown off)

I think it's the stupid 4x4 actuator. I just drove 20 miles to warm it up -- seems the buzzing sound isn't present when it's cold, and begins when the front diff warms up.

So with the buzzing happening, I parked the truck and lifted the front. Turn either wheel makes the buzz -- it comes from the front right in the vacinity of the 4x4 lock ring. So i'm off to get a better actuator. I'll report back once I've changed it.

Thanks everybody! [img]images/graemlins/40BEER.gif[/img]
-JAZ-
post #7 of (permalink) Old 12-12-2003, 11:21 AM
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Re: Buzzing from front axle/diff \'95 Tahoe

</font><blockquote><font class="small">In reply to:</font><hr />
Well, at any rate I guess it's time to pull and inspect.

[/ QUOTE ]

yeah, that would have been my first move [img]images/graemlins/grin.gif[/img]

ok, if its just a bad actuator, verify by testing, then replace it. dead...done.

as for posilok, search the forum here, several gyus installed it on their trucks and put up pics.
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post #8 of (permalink) Old 12-12-2003, 11:24 AM
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Re: Buzzing from front axle/diff \'95 Tahoe

i just thought to ask, but, are you sure the buzzing is not from the fuel pump?
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post #9 of (permalink) Old 12-12-2003, 12:34 PM
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Re: Buzzing from front axle/diff \'95 Tahoe



Okay here's more...

I think it's the stupid 4x4 actuator. I just drove 20 miles to warm it up -- seems the buzzing sound isn't present when it's cold, and begins when the front diff warms up. It's about 30 degrees out now, and after a drive the diff feels like about 90 degrees. I hope that doesn't signify excessive wear -- but I can see that the rubbing from the lock ring could warm it up, or perhaps the actuator is warmed by surrounding casting (hmmm... Chicken or Egg?)

So with the buzzing happening, I parked the truck and lifted the front. Turn either wheel makes the buzz -- it comes from the front right in the vacinity of the 4x4 lock ring. So i'm off to get the new electo-solenoid actuator. I'll report back once I've changed it.

Thanks everybody! [img]images/graemlins/40BEER.gif[/img]
-JAZ-
post #10 of (permalink) Old 12-12-2003, 05:19 PM
jzack
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Re: Buzzing from front axle/diff \'95 Tahoe


Sho nuff! Buzz is gone!

My driveway slopes, so I parked with the right side uphill so it would ooz gear oil. The boot on the old unit was balloned out like a swollen gall bladder. I didn't bother with the harness 'cause it was late and cold... I'll get to that tomorrow. Luckily I found the right dealer who sold it to me wholesale. [img]images/graemlins/cool.gif[/img]

But what's up with the plastic actuator?! [img]images/graemlins/lame.jpg[/img] Hello GM? Who the heck's at the helm of the parts division? If I weren't in such a hurry to fix I definately would've gone for a posi-lok.

Thanks for all your help -- you guys ROCK!

Now it's Miller time [img]images/graemlins/givemebeer.gif[/img]

-JAZ-
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