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AWD to RWD conversion

PostPosted: September 13th 2015, 9:51am
by sadglad
I was driving down the interstate and heard a sound which quickly changed to a loud clunking and big vibration. I saw a big chunk of something fly off to the side into the weeds as I pulled over. Turns out what flew off was the inner joint of the drive axle and the output shaft from the front diff. I looked for it for 30 minutes while I waited for the tow truck but never found it. The outer joint and drive axle where left to flail around. Not sure what went wrong. Drive shafts were new, installed last March. Diff fluid was changed at the same time. I have not had time to do an autopsy on the diff yet. The outer seal and bearing are wrecked with needle bearings stuck in the grease from the inner joint which spattered everywhere.

I don't want to spend time and money right now to put this back together so I just removed the AWD drivetrain. I put the outer stubs from the drive axles in the wheel hubs to hold them together. I removed the front diff and drive shaft. This left the output shaft from the transfer case exposed. I wanted to protect it so I made an aluminum cap to cover it and a bracket to help hold it in place. It's a light hammer fit onto the nose of the transfer case and sealed up with silicone.

The front of the van looks like it might be riding slightly higher. I figure it's about 100 pounds lighter in front now.

I don't plan to pull the AWD fuse. I figure if the AWD system ever engages, the output shaft from the transfer case will just spin harmlessly inside the new cover. I rarely if ever have AWD engage anyway. I don't drive this van much in the winter and the plow crews usually have roads cleared pretty quickly anyway. It never goes off road.

With the front diff gone there is a lot of empty room. Motor mounts sure would be easier to change now. Maybe I'll get slightly better mileage with less drag on the drive train.

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Re: AWD to RWD conversion

PostPosted: September 13th 2015, 9:58am
by sadglad
Easy access to motor mounts with front diff and drive axles gone.

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Re: AWD to RWD conversion

PostPosted: September 15th 2015, 12:33am
by Astrofarian
Well, I guess whatever keeps you on the road is fair. I don't know if I would ever do this myself but ultimately it got your van back on the road so what the Hell, right?
-Mike-

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 12:55am
by markmitch
by looking at the pictures you posted I would say the motor mounts were already changed to poly mounts. Never seen red rubber motor mounts before.

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 3:39pm
by icebrrg3rd
So you pulled the whole front diff out? Do the AWDs have a crossmember or is the diff what holds the lower A-arms together? Just wondering if your subframe is weaker now w/o the diff in there.

I don't have an AWD nor do I remember what the AWD subframe looks like so I'm just commenting. Just that for RWD the motor mounts are pretty much hidden by the crossmember and the engine.

-Andrew

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 4:46pm
by Mmusicman
I would suspect with the front drive-shaft not turning (missing).. that the AWD is being told to engage. It may even be erratically engaging and disengaging. You went to a lot of trouble to pull everything else... I'd pull the fuse! Or at least the connector to the encoder.

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 7:13pm
by sadglad
Mmusicman wrote:I would suspect with the front drive-shaft not turning (missing).. that the AWD is being told to engage. It may even be erratically engaging and disengaging. You went to a lot of trouble to pull everything else... I'd pull the fuse! Or at least the connector to the encoder.


Hmm. I'm not sure why you think having the front drive shaft out would cause the AWD system to engage. Unless I'm missing something. :shrug:

My understanding is that AWD is engaged only when a difference in wheel speed between front and back is detected, wheel slip. Under normal circumstances on dry pavement the AWD system never engages since no wheel slip happens. This is 99.9% of my driving. If wheel slip is detected then the transfer is engaged but the computer has no idea the drive shaft is gone so no harm done other than maybe getting stuck in the snow. I guess I could pull the fuse just in case but I thought that would turn on a dash light. Don't want annual inspection showing a dash light.

Pulling the front diff out makes it a lot easier to work on. It's only 6 bolts holding it in so it goes pretty fast. Also the empty hole in the diff does not fill up with crud. My RPO sticker is missing so I have to count gear teeth to figure out my ratio before I could even shop for a replacement. Much easier to do that on the bench than on my back.

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 7:23pm
by sadglad
icebrrg3rd wrote:So you pulled the whole front diff out? Do the AWDs have a crossmember or is the diff what holds the lower A-arms together? Just wondering if your subframe is weaker now w/o the diff in there.

I don't have an AWD nor do I remember what the AWD subframe looks like so I'm just commenting. Just that for RWD the motor mounts are pretty much hidden by the crossmember and the engine.

-Andrew


Yes the whole diff got pulled out. Much easier to work on it that way if/when I ever get around to it. Not going to spend time or money on it right now. The A arms attach to the subframe so this has no effect on them or the subframe.

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 7:28pm
by sadglad
markmitch wrote:by looking at the pictures you posted I would say the motor mounts were already changed to poly mounts. Never seen red rubber motor mounts before.


Yes, the poly mounts went in while I had the subframe out earlier, easy. My first Astro had the mounts replaced the hard way which made me wish I access this easy back then.

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 8:51pm
by Mmusicman
sadglad wrote:My understanding is that AWD is engaged only when a difference in wheel speed between front and back is detected, wheel slip...

My understanding is that the sensors measure "drive-shaft differences"... not wheel differences. I don't know where the sensors are, but I assumed they might be in the transfer case? I've also heard someone say they use the ABS sensors in the wheels... but my AWD van doesn't have ABS. Not sure... but I am sure someone will chime in.

The schematic I found shows two (actually three) speed sensors (#412) in the electronically controlled transfer-case... one on each drive-shaft. (click to zoom)

np136_parts_illust.jpg


None the less, how hard is it to pull a fuse or a connector? Especially after pulling an entire front-wheel drive differential system! :o

Re: AWD to RWD conversion

PostPosted: September 15th 2015, 9:24pm
by sadglad
Mmusicman wrote:
sadglad wrote:My understanding is that AWD is engaged only when a difference in wheel speed between front and back is detected, wheel slip...

My understanding is that the sensors measure "drive-shaft differences"... not wheel differences. I don't know where the sensors are, but I assumed they might be in the transfer case? I've also heard someone say they use the ABS sensors in the wheels... but my AWD van doesn't have ABS. Not sure... but I am sure someone will chime in.

None the less, how hard is it to pull a fuse or a connector? Especially after pulling an entire front-wheel drive differential system! :o


The front diff has a hole in it where an output shaft used to be. I don't want that filling up with road crud so off it comes. I would rather work on the diff with it sitting on a bench anyway. Gotta open it up to figure out the ratio anyway. I can drive the van while working on the diff.

There isn't really all that much to the front drive train. Front drive shaft is 4 bolts, 5 minutes. Diff is 6 bolts, easy. 95% of the work is the drive axles and one of mine was already half gone so I only had to do one side.

I would have to do more research on your diagram. Maybe I got it wrong. Either way, van is drive able while I work on the diff, if I ever do.

Re: AWD to RWD conversion

PostPosted: September 16th 2015, 5:34pm
by icebrrg3rd
sadglad wrote:
icebrrg3rd wrote:So you pulled the whole front diff out? Do the AWDs have a crossmember or is the diff what holds the lower A-arms together? Just wondering if your subframe is weaker now w/o the diff in there.

I don't have an AWD nor do I remember what the AWD subframe looks like so I'm just commenting. Just that for RWD the motor mounts are pretty much hidden by the crossmember and the engine.

-Andrew


Yes the whole diff got pulled out. Much easier to work on it that way if/when I ever get around to it. Not going to spend time or money on it right now. The A arms attach to the subframe so this has no effect on them or the subframe.


I know the A arms attach to the subframe, but is the left rail connected to the right rail by something? Is there some solid connection like in this pic (red circle) that holds the left to the right? Not a bolt-on like the trans mount or the bumper mounts (blue circles). That's all I was wondering, is the diff replacing that part for an AWD vs the RWD crossmember?

Subframe1.jpg


This is just to satisfy my own curiousity, as I am not familiar with AWD subframes.

-Andrew

Re: AWD to RWD conversion

PostPosted: September 16th 2015, 11:56pm
by sadglad
icebrrg3rd wrote:....Is there some solid connection like in this pic (red circle) that holds the left to the right?....
-Andrew


Yes, the AWD subframe has a large crossmember right at the very front that the RWD frame does not have. I can't find a good pic at the moment but it's very beefy. The AWD design does not rely on the differential for any kind of structural support.

Re: AWD to RWD conversion

PostPosted: September 17th 2015, 8:49pm
by icebrrg3rd
sadglad wrote:
icebrrg3rd wrote:....Is there some solid connection like in this pic (red circle) that holds the left to the right?....
-Andrew


Yes, the AWD subframe has a large crossmember right at the very front that the RWD frame does not have. I can't find a good pic at the moment but it's very beefy. The AWD design does not rely on the differential for any kind of structural support.


That's all that I was wondering about. Didn't want the frame crumpling up on you. It's great that you found a way to keep on rolling yet you can fix it on your time to restore it back to AWD. I try and do stuff like that all the time, sometimes it works, other times it bites me in the backside.

It's also great that you post your fix, so others can benefit from your experiences, either good or bad.

-Andrew