Hello,

I have a chevrolet express 2500 2015 van. The RPO code I've got for the rear axle/diff is GU6 which translates to

Rear axle, 3.42 ratio

• AXLE,REAR,3.42 RATIO

I was just wondering if it's normal for it to make noises. What kind of diff usually comes on these vans? limited slip or open?

aLso when I bought the van the fluid was really low in the diff. Owners manual calls for the oil level to be level with the bottom of the filler plug. I had to add about 700 ml of fluid to get it there. I just checked again after 600 miles and the fluid level is the same. the diff appears stock because it matches the picture in the owners manual, the small pic that is there.

I am just starting to think the van I bought is a lemon because now also all tires are losing pressure (one tire lost 7 PSI in a week.) SO I am just trying to figure out if the diff is on it's way out too.

IT makes noises, but are noises normal with these vans diffs? is hesitation normal? The fluid that I found in side that diff was really clean and fresh. The back of the filler plug was covered in small shavings. nothing major though, the small shavings resembled grease. So it doesn't appear it was serviced for a while, because why else would they leave the shavings on the back of the plug? when I checked the back of my plug now, no new shavings were on it. Is it normal for diffs to get low on fluid if they are never serviced and after 160k miles and 10 years? Maybe it was drained and refilled but they never cleaned the plug and they didn't know the correct level for the fluid?

I also hear a noise coming from the passenger side front area, kind of like a bearing whining, but not sure if it's the diff or a wheel bearing. The sound does let off when the gas pedal is depressed though. only makes the sound when pressing the gas pedal. maybe some damage was done to it by having low fluid?

 

I have a 2015, 3500 with the same RPO code and I had a 14-bolt semi-floater with an open differential. G80 is the code for the limited-slip/locker. You should pull the cover off and take a look. If run low on oil it could wear out a wheel bearing. Being a semi-floater the wheel bearings ride on the axle shaft so if you suspect the wheel bearing you should replace it ASAP so that it does not destroy the axle.

 

the noise is coming from the passenger side area. I almost thought it was the wheel bearing, BUT THIS noise goes away when you let off the gas pedal. It is a very subtle noise by the way. It is very faint. I was almost thinking it could be the part that hooks into the transmission. I guess that would be the axle then and not the diff. Or the tranny could be whining itself. 160 k miles, 10 years old, and lots of city miles. Sounds like it might be getting ready to give up the ghost?

 

Have you checked your universal joints?

 

Yes, the U joints look ok. here is a strange thing though. I had it in park after reversing up the drive way. drive way is climbing uphill if you catch my drift (most driveways in surburbia, think this) I was on the incline and went underneath. I was able to rotate the drive shaft a tiny bit, not more than 4 mm. But then I went to park on flat ground and the entire drive shaft assembly had NO play. The u joints themselves ALSO had no play at all.

Also there is a loud CLUNK when you reverse sometimes. NOT SWITCHING IT REVERSE, that basically makes no noise. It's when the vehicle is under load reversing up a hill (even a small one) then "CLUNK" probably normal I know, BUT i can definitely feel vibration through the gas pedal when driving.

 

Here's one way I try to isolate driveline clunks. Find a road where you can safely drive slow and change speeds. Put it in 1st gear and take off. As you give it gas and let off it will be very responsive in switching between pulling and coasting and there will be no shifting to worry about. If there's play in your axle or rear end you'll be able to recreate the clunk every time you give it gas or let off.

 

the clunk ONLY happens when you press on the gas in reverse. There is slack in the drive shaft sometimes. A tiny little bit of slack. But once parked on flat ground, there is absolutely zero slack. The clunk Only HAPPENS when the driveshaft is under load and being accelerated backwards.

Is this excessive backlash? I am starting to think the driveshaft was serviced by a shoddy technician, and I know setting the lash is the hardest part of the job. Why else would the fluid be left so low? IT hasn't leaked at all in 600 miles of me driving it. Why was the fluid so low? It had to of been a bad tech. The history of this vehicle is dodgy and that's why I think this.

 

WEll I looked around underneath with a family member operating the vehicle. When you reverse and step on the gas it makes a "clunk noise" IT doesn't do it so badly if you ease slowly backwards. still though it's going to clunk bad if you need to make a turn around quick in the road. not good.

I checked the u joints again and the only place I can find play is where the drive axle slots into the transmission. This is a one piece drive shaft, mind you, so there are no bolts holding the drive shaft into the transmission. there are only bolts where it locks into the diff. it just slides out on the transmission side into a rubber sleeve type thing.. Is some play normal there? you can see the drive shaft moving about a 1 mm upward and downward in that little sleeve where it goes into the tranmission. all u joints look intact, and are non greaseable.

In any case the clunk noise is actually coming further forward, so I am starting to suspect transmission. The noise definitely didn't come from the drive axle.160 k is when the transmission tend to die on these things right? and why people offload em? Re manufactured tranny with a good warranty is 6k right? just because it's the 6l-90e? family member seems to think it's the suspension or something other than transmission.

I was reading the charm.li manual, it says that noise in reverse and 1 st gear could be a worn reverse clutch plate. is this possible? I see dents on the back of the van. is it possible he backed into something hard and damaged the reverse gears/ clutch?

Also there is a lot of noise coming from the diff. is that normal ? it just a noisy little case, like a sewing machine or something. when you are laying on the ground and staring at it, that's the only time you would hear all the mechanical chatter.

 

The piece that slides into the tranny is called the slide yolk.

Was the van in the air when you were under it or were the wheels on the ground? Just trying to understand the noises you were hearing.

I think 160 would be a bit early for a tranny to wear out on it's own. Different story if it was abused or run low on fluid of course.

 

The van was being driven back and forth up the drive way. I was on a creeper on the ground a couple feet away looking underneath. the noise is coming from very far forward, Honestly sounds like its coming from near very front of the vehicle, where all all the tie rods and other thing are etc. Though, you should know that the noise will be made on flat ground too, so I don't think the suspension is really getting worked here enough to make a noise. Correct me if I am wrong.

YEs abuse is probably likely. lots of city driving too. 4000 engine hours so the vehicle was run at around 40 mph on average in it's life