Broken Front Differential AWD Bravada? (Page 1/1)
IanT720 JAN 13, 02:53 PM
Hey guys bought a 2000 Bravada the other day, its basically a Jimmy but has automatic 4wd.. Its clean and I bought not running for cheap. Got her running with only a new battery but found out pretty soon the Auto 4WD isn't working. Apparently when the rear wheels slip, a motor shifts it into 4x4 then releases once you have traction. I've heard the front diff is supposed to be constantly engaged.. So far I found that it does shift into 4x4, it engages, and the front drive shaft spins... But the front wheels do not move. Further more if I hand spin the wheel, the other does not move, at all. Does this mean an axle broke internally? Diff is imploded? Or am I missing something... Fun fact, the T-Case motor was unplugged, now I believe intentionally.. And it drives great in 2WD.

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1987 Fiero GTX 3800 Turbo... My Build, ST3 Cam, Lowered, Wheels, and pics enjoy!http://www.fiero.nl/forum/Forum1/HTML/089483.html

thesameguy JAN 13, 04:20 PM
I don't know what I am talking about, but my recollection is that the AWD system on the Bravada is electronic and automatic. It won't activate on a lift as it needs feedback from a few sensors (probably VSS plus both diffs) to tell it to engage and the right combination of feedback can't happen on a lift. The hubs are permanently locked and the diff/axle is permanently engaged - the only thing that happens is a solenoid in the tranfer case couples or uncouples the driveshaft to engage or disengage AWD. So, I think what you're seeing is all normal - I don't know how to test the system other that put it on the ground, get the rear wheels on something slippery, and see if the front wheels will drag it out. There is probably a way with TECH2 to force the transfer case to engage, or maybe it can be done "manually" by energizing the solenoid... that latter approach might generate a fault code, though.

I was looking at AWD Astros for a while, and I'm pretty sure all these trucks use the same system. IIRC that front solenoid Is prone to failure. If you're sure the system isn't working, I'd start there.

[This message has been edited by thesameguy (edited 01-13-2015).]

IanT720 JAN 13, 07:20 PM
Appreciate the response! My year Bravada is not like the older constant AWD ones. It's more Automatic 4WD. So like you said the VSS's detect that the rear wheels are spinning, and the fronts are not. At this point I can look under the truck and see the T-Case motor engage the front drive shaft which should be connected to the front diff, which should be connected directly to the wheels. The Jimmys, and Blazers had a vacuum or electric or cable actuator up front but I don't think the Bravadas do. Also there is no amount of %power, I beleive it only kicks it into 4x4 when the rear spins, then disengages it. Either it is, or it isn't. that's why I'm worried something is seriously wrong in the diff. Also as I stated when I spin a front wheel, the other wheel does not spin. From what I heard, it should.. Right?

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1987 Fiero GTX 3800 Turbo... My Build, ST3 Cam, Lowered, Wheels, and pics enjoy!http://www.fiero.nl/forum/Forum1/HTML/089483.html

thesameguy JAN 14, 02:06 AM
Although the AWD system on the later cars is automatic, it's really not much different from the earlier manual cars - at least that's my recollection. What it sounds like is missing in your equation is the solenoid/actuator on the front diff. On the earlier manual cars there is a cable which engages the diff, on the later automatic cars it's electric. Without that, even if the xfer case engages, you still won't get power out of the front wheels. Google "bravada diff actuator" or "bravada diff solenoid" to see what I'm talking about, but it's this thing:
2.5 JAN 16, 01:55 PM
Yeah the S10/Bradava/etc front diffs around that era were vacuum operated. I'm not sure if 2000 changed that but some S10 folks convert it to a manual cable when the vacuum stuff fails. I did that with my 1996 Sonoma.
IanT720 JAN 21, 02:57 PM
So update! Let it be known the Bravada Diff is always connected to the wheels. There is no actuator like the Blazers. Anyhow The drivers front CV axle looked a little weird, loose almost. So I got the CV axle free and it basically fell out! I looked inside the differential and found the splines for the spider gears were completely stripped! They couldn't mesh with the axle spine at all, super loose. I've heard AWD TrailBlazers have this problem too.. Has anyone experienced this? Just buy a new whole front axle? or replace the diff innards.. Honestly I bought it to do a quick flip, it has no other problems besides this.. I'm thinking about not even bothering, its winter anyway.. aha.

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1987 Fiero GTX 3800 Turbo... My Build, ST3 Cam, Lowered, Wheels, and pics enjoy!http://www.fiero.nl/forum/Forum1/HTML/089483.html

RayOtton JAN 23, 08:07 AM
I didn't want to chime in at first because I had an '02 Bravada and I wasn't sure if they were the same.

Apparently they are since I had the same issue.

With about 120K miles on it I noticed a slight vibration in the front end over 70 MPH. This was about a month before our last cross-country trip. A balance of the tires seems to fix it but the speed Nazis over here in Virginia REALLY discourage high speed driving so I couldn't be sure until we actually started the trip.

The vibration was still there although reduced by about 50%. Since we did almost all of the traveling on secondary roads it wasn't an issue but on the way home the vibration got worse and a clicking noise started to appear. Took it to a good mechanic after getting home and sure enough, we hand the same problem you described. Once replaced, all of the vibration and noise was gone. So we went about 7500 miles with a broken front axle.

Other than that and leaking air bladders at 100K the Bravada has been trouble free.

In fact, I gave that one to my son-in-law at about 170K miles and it's still going strong. Then I went and bought a low mileage '04 that I found though an internet search.