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93 suburban 4 wheel drive issue
12-04-2013, 08:34 AM
Post: #1
93 suburban 4 wheel drive issue
ok well here we go again it is a 93 gmc suburban K2500 4x4 7.4L I was on my way to work the road was icy so I had it in 4 wheel it seemed to work fine but noticed a little whine, I left the truck run when I went in to one building and when I came out to leave the 4 wheel did not seem to be engaged and have not been able to get it to engage since any ideas on where to start. oh when I put it in 4 high just the back wheels turn and when I put it in 4 low I get the gear reduction but only to the rear wheels no drive power to the front wheels.

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12-04-2013, 10:53 AM
Post: #2
RE: 93 suburban 4 wheel drive issue
I am just guessing that; being a 93, it would have a vacuum switch on the transfer case that engages the front axle. It was common for the switch to fail as well as for the vacuum lines to get holes in them or break. I usually check at the switch to see if it is getting vacuum. If it is, see if the switch opens when it is in 4WD. If it does, follow the line to the axle and see if it has vacuum there. If it does then we have to look at something else.

You also didn’t mention if it has manual hubs. Could it be something as simple as someone fooling with you when you went in the building? They only have to unlock one hub and your 4WD no longer works. A malfunctioning hub will do the same thing.

When it is in 4WD, does the front drive shaft turn?

Please let us know what you find.

Thanks for using the forum,
Garner

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12-21-2013, 06:09 PM (This post was last modified: 12-21-2013 06:10 PM by tommyboy.)
Post: #3
RE: 93 suburban 4 wheel drive issue
ok, as for manual hubs no it does not have lockouts it has the independent front suspension and after looking I find that it blew a fuse, so I put a new one in and it blew moments later, I tried it a few more times just to be sure, and sure enough it blew them also so I am thinking the actuator, but could it be as simple as low on differential fluid.

and with the icy weather it would be nice to have.

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12-21-2013, 08:18 PM
Post: #4
RE: 93 suburban 4 wheel drive issue
I really doubt that the fluid level would do that, but it couldn’t hurt to check it if you haven’t done it in a while.

I would guess that it will be the actuator, but here again, I would check things out before spending money. It could just be a wire rubbed through or burnt on the exhaust. I don’t know how that system works but I have seen some Fords that have a separate control module for the 4WD. It was real common for them to short out. I don’t know if the GM has anything like that? I just wouldn’t want to pay for an actuator and find out that it was something else.

You may be able to test things out by unplugging the actuator motor and trying to put it in 4WD. If the fuse doesn’t blow it would point to the actuator being the culprit. At that point I would probably unbolt the actuator, plug it in, and try it again. If it didn’t blow the fuse and the actuator moved it would point to something it the transfer case being bound up.

Rupe has a whole fleet of GM’s so if I’m telling you something wrong or omitting something I hope he’ll jump in and correct me.

Thanks for using the forum,
Garner

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12-21-2013, 08:29 PM
Post: #5
RE: 93 suburban 4 wheel drive issue
ok I will check that out when I can get it on dry ground. and I forgot to met mention it was going into 4-wheel for a short time before the fuse blew but was hearing a whining noise from the front end. not real loud but with the heat and radio off I could hear it. and need to change the universal joints in the front end only got to the rear before bad weather. and I am new to the whole 4 wheel drive experience.

thanks

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12-21-2013, 09:12 PM
Post: #6
RE: 93 suburban 4 wheel drive issue
It is near impossible for me to advise you on a noise. About all I can tell you is that most 4WD’s will have a different sound from 2WD when they are in 4WD simply because of all the extra iron spinning around. You will have extra parts in the transfer case, front drive shaft, front diff., and front axles all spinning. Even in a new system most mechanics can hear those extra parts turning. At 20 years old I would guess that it’s going to be a bit noisier, but I can’t guess from here if what you are hearing is normal??? Your best bet would probably be to check the fluid in the front diff. and transfer case as preventative maintenance. You’re going to be under there anyway.

Please let us know what you find.

Thanks for using the forum,
Garner

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12-22-2013, 01:35 AM
Post: #7
RE: 93 suburban 4 wheel drive issue
My fleet is all wheel drive so quite different than 4wd for the most part.

That said, if the fuses are blowing then it's time to get the vehicle where you can both see and think rather than out in the cold and dark. The actuator (as I recall) is vac operated but that's fed from an electrical source. If it's the system I am thinking of there's a module and a dash switch rather than a floor mounted manual shifter. Obviously what Garner mentioned avout wires and vac lines applies. It's 20 years old and things are bound to be ready for attention. Recalling Blazers in that era had issues with the vac line that went from the rear of the engine to feed the actuator on top of the front dif. Certainly worth a look for cracks / splits while in there.
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12-23-2013, 07:24 AM (This post was last modified: 12-23-2013 07:25 AM by tommyboy.)
Post: #8
RE: 93 suburban 4 wheel drive issue
thanks guys you are being very helpful and patient with me, Ok had it pulled in a garage, got under it and looked at the wires up as far as I could see, and checked for ,splits, cracks, and etc... all looked good, so I went to the top side, and from what I could follow, looked fine also. so I went back under and pulled out what I believe is the actuator 2 wires, threaded into the front diff. , when I got it out there was a rubber boot on the end of it that was a little torn on the end, could this be my problem, and where it is shorting out due to fluid getting in side the actuator.

Rupe it has the manual shift on the floor. but I think it operates in the same aspect as the switch on the dash minus the shift solenoid instead of a linkage.

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12-23-2013, 10:46 AM
Post: #9
RE: 93 suburban 4 wheel drive issue
Ok, I follow you here. There were so many variations over the years it's hard to keep track of when things changed.

That actuator is what engages the front wheels. The wires operate a little motor that moves a linkage in the diff. It doesn't need to be shorted, just higher than normal draw can blow a fuse. A tear in the outside boot / seal can allow water in and cause it to fail.... or the wire could have a chafe somewhere. Now that you have it out of the circuit maybe install a new fuse and see if it still blows. If that's the case then you have more detective work ahead.
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