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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / April 20062000 Bravada reverse question
We bought this car with 90000 miles on it about a year ago. From the very beginning we started to notice a slight shudder when backing up. We took the car in to a friends place and he changed the blue fluid in the transfer case. He said that there was a problem with the All Wheel Drive function which affects the transfer cases on these and said "lets try the fluid change first and see if it helps". After doing the change there seemed to be little difference but eventually the problem seemed to all but dissappear. We were very encouraged. The car had been fine until recently when this transmission had lost reverse, which I am told is apparently a typical and unrelated problem with these. We had the trans rebuilt and it seems to be OK except for the fact that the slight shuddering problem in the drive train is now occurring again sporadically only in reverse, but not all the time when backing up. When it happens it seems to be worse if the wheels are turned but it it so intermittent that it is hard to say if the problem only occurrs when turning or it may occur when backing up in general. Like I said sometimes it doesn't happen at all. So far I have just never noticed it when straight backing up. So my questions are: 1. What is happening here? 2. Did the original problem ruin reverse on the transmission and could this occurr again? 3. We don't really use 4WD. Can it be disabled thereby saving us a possible costly future repair again? 4. Might changing the blue fluid help again? 5. Is there a solution that will really "fix" this problem or is this just a poor design. Please don't worry about providing as much technical information as possible. I really want to understand this problem and will sincerely appreciate it all. Thanks, Lenny Stein. Thewre were issues with the awd transfer case, there are tsb's relating to this condition that can require replacing the encoder and/or reprogramming the pcm. The truck is in awd all the time remember. It is also possible the locking diff is is binding , an experienced GM tech needs to feel this happening for an accurate diagnosis. > We bought this car with 90000 miles on it about a year ago. From the > very beginning we started to notice a slight shudder when backing up. [quoted text clipped - 26 lines] > possible. I really want to understand this problem and will sincerely > appreciate it all. Thanks, Lenny Stein. > We bought this car with 90000 miles on it about a year ago. From the > very beginning we started to notice a slight shudder when backing up. [quoted text clipped - 26 lines] > possible. I really want to understand this problem and will sincerely > appreciate it all. Thanks, Lenny Stein. ========= ========= "If", as yer post inplies, the symptom was not there before the tranny rebuild.......... Be sure the tranny shop put "AutoTrac" fluid back in the T-case and not regular Dextron 3. Also.... I would ask them if they applied grease to the splines on the driveshafts. One of the shafts "may" be binding under torque. jest a thought. ~:~ MarshMonster ~:~ Is auto trak fluid something you add to and use in conjunction with Dextron 3 (like the additive you use in a LSD or posi rear with 90W), or is it something you use completely in place of Dextron 3. ? > Is auto trak fluid something you add to and use in conjunction with > Dextron 3 (like the additive you use in a LSD or posi rear with 90W), > or is it something you use completely in place of Dextron 3. ? ========= ========= It's GMs designated lubricant for it's "clutch" driven trasnsfer case. so....it's not used in conjunction with Dextron 3. and...it's not used in place of Dextron 3. It's used because it's the designated lubricant for the application. ~:~ MarshMonster ~:~ I asked him about that and he never touched the fluid in the Tcase. He only rebuilt the transmission. > I asked him about that and he never touched the fluid in the Tcase. He > only rebuilt the transmission. ======== ======== Then you can tell him I said he was a half-assed tranny tech. respectfully submitted to address inferior workmanship ~:~ marshmonster ~wonders if that mechanic changes sparkplug wires but never looks at the plugs~ > Then you can tell him I said he was a half-assed tranny tech. Why? Ian > > Then you can tell him I said he was a half-assed tranny tech. > > Why? > > Ian ========= ========= How did he know the fluid was good, or that it wasn't low, or that it was the right type? if he didn't mess with it....a little bit? ~:~ marsh > How did he know the fluid was good, or that it wasn't low, or that it > was the right type? > > if he didn't mess with it....a little bit? I thought the OP said the tech said he didn't touch the t/case fluid. Which is quite possible, if you use something in place of the rear driveshaft to keep the fluid from leaking out while removing the t/case. It's not necessary to drain and fill the t/case when removing it to get at the trans. I know that I certainly wouldn't be fooling around with the t/case if I was repairing the transmission for no reverse. Pull the t/case out, put it to the side and get on with repairing the trans. I would check the t/case fluid level when re-installing, that would be only prudent. As another poster mentioned, there are bulletins out that deal with the crowhopping issue. Replacing a sensor in the encoder motor usually fixes the problem on the AWD models. Ian Ian, Is there any way possible for me to obtain any pertinent bulletins petaining to this problem. My friend is willing to help me with this if we can just locate the required information. Thanks, Lenny. > Ian, Is there any way possible for me to obtain any pertinent > bulletins petaining to this problem. My friend is willing to help me > with this if we can just locate the required information. Thanks, I had a look, for your year of vehicle, the only bulletin or fix is changing the t/case fluid. My mistake....I was thinking of the later model Bravada. So you'll have to pursue another avenue I think. If you get the shudder even without the wheels turned...I'd say that rules out any problem with the t/case. Ian > > How did he know the fluid was good, or that it wasn't low, or that it > > was the right type? [quoted text clipped - 23 lines] > > Ian ========== ========== But you would at least check it? to ensure it had the proper fill? the proper type of fluid? ~:~ marsh ~:~ > We bought this car with 90000 miles on it about a year ago. From the > very beginning we started to notice a slight shudder when backing up. [quoted text clipped - 26 lines] > possible. I really want to understand this problem and will sincerely > appreciate it all. Thanks, Lenny Stein. ============== ============== Lenny, I have seen 1st gear shudders on these units when erratic pump volume is an issue. I would suggest 2 things, first see if maybe you feel ANY shudder/washboarding on very light throttle when pulling off from a stop in Drive. Second, if you purchased this thing with 90,000 miles on it, it's very possible the unit had been rebuilt already. Not a fact, just a possibility. (my experience with the unit and the mileage you posted) Any whoo......Being as you stated that the symptom had occured before, it's possible. I would suggest having the line pressure checked with a gauge (just like checking eng. oil pres.) and seeing if the pres. is stable, good, and most importantly...NOT FLUCTUATING. You "may" see the pres. gauges needle rapidly bouncing and not being steady. This is a big indication of a pump volume problem. Again, i've seen this symptom on foward movement because of pump volume. now with that said............. SEE BELOW, (TSB) The purpose of this bulletin is to identify the correct oil pump rotor (212) and slide (203) usage for the two different transmission oil pump designs. Manufacturing of the first design oil pump rotor (212) and slide (203) ended November 30, 2000. Manufacturing of the second design oil pump rotor (212) and slide (203) began December 1, 2000. Important: It is critical that the first and second design oil pump rotors and slides do not become intermixed. Do not use first design pump components with second design pump components. If the pump components from either design are intermixed, pump efficiency will be affected resulting in less than optimal pump performance. The first design oil pump rotor (212) and slide (203) DO NOT have any identification markings. The second design oil pump rotor (212) and slide (203) are identified with dimples (circular depression) as shown above. The rotor (212) has two dimples adjacent to the rotor drive tangs (1). The slide (203) has one dimple located on the spring tab (2). Disclaimer jest a thought ~:~ marshmonster ~:~ I had the occaision to go somewhere today with my wife in this car. She drove and I observed, (usually a recipe for disaster, but it all worked out). Anyway, I noticed that when pulling into a parking space while making a tight turn in drive at low speed there was a noticeable shudder. It doesn't seem to happen when driving straight at low speed though . The same thing seems to occur in reverse. I'm not certain about this but it really appears that having the wheels turned has some bearing on this. I need to drive this thing some more to further evaluate the problem. Thanks to everyone for all your responses. I will keep you aprised. Lenny |
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