Was driving and heard a very loud "boom". Nothing leaking but I had no forward gears, only reverse would work. I am assuming the trans broke but is it possible for a differential to fail and only work in reverse?

It's a Chevy 12 Bolt posi rear end.

 

Seriously doubt it. Does the engine load down at all in the forward gears, or act like extra neutrals? If you feel no torque being applied to the drivetrain, and only free revving of the engine, the transmission is toast.

Either way, sorry to hear that.

 

There is no possible way the rear diff can only go in reverse. Your issue is in the transmission.

 

I disagree, I can imagine a scenario where the ring and pinion gears would engage in one direction but not in the other. If one end of a gear tooth (or multiple teeth) is (are) broken off, the teeth could engage from the opposite end but not from the broken end.

I'm not saying this is what happened or is even likely, just that it may be possible.

 

Stator broke in trans .

 

I jacked up the rear differential and and put the trans in neutral and then drive (car was off). I was able to grab the driveshaft and turn the differential and both rear tires rotated forward and back by turning the driveshaft. Both rear tires would rotate with the driveshaft being turned.

I assume that test proves the differential is OK and it's the trans that is broken?

The loud "boom" I heard, is that possible for a transmission stator to be that loud when they fail?

 

All forward gears act like neutral. Only neutral engages and works.

 

Is the fluid level full with the engine running and is it a nice red color?

 

Yes, trans fluid is clear and full

 

Was driving and heard a very loud "boom". Nothing leaking but I had no forward gears, only reverse would work. I am assuming the trans broke but is it possible for a differential to fail and only work in reverse?

It's a Chevy 12 Bolt posi rear end.

I jacked up the rear differential and and put the trans in neutral and then drive (car was off). I was able to grab the driveshaft and turn the differential and both rear tires rotated forward and back by turning the driveshaft. Both rear tires would rotate with the driveshaft being turned.

I assume that test proves the differential is OK and it's the trans that is broken?

 

I merged your question into your last thread on the same subject. There is no need to start multiple threads for the same issue.

Your assumption is correct, your problem is in the transmission.

 

You didn’t say what transmission, but if it’s a TH350 I bet you find the low roller clutch exploded. It’s designed to lock in forward gears, and freewheel in reverse.

Has your son borrowed the car without your knowledge?? I only mention that because when I was a young 16 year old, moms 83 98 suffered the same issue. Neutral drops were the only way to burn the tire (one wheel peel!) with the mighty 307. Dad was NOT happy with me.

This is also a common failure in trucks, or rocking a car when stuck in snow.

 

Its actually a 2004R transmission. It has all the billet parts and is rated for 900 HP but apparently something went wrong.

 

The 2004R also has a low/reverse roller clutch, serves the same purpose. Unfortunately, transmission removal and a autopsy will be required.

 

Putting the trans into any gear with the engine off is just neutral. Unless the torque converter is spinning the pump, there will be no fluid pressure to engage any gear.

 

I jacked up the rear, started the motor, and put it into gear. Driveshaft does NOT spin. Trans is shot. Pulled trans out and shop will be tearing it down to see what happened.

 

UPDATE -

The forward planetary gear spline shaft is what broke in the trans. Pretty rare to break that so maybe it was a casting flaw when it was made 30+ years ago and it eventually failed.

 

I dropped the ball on that one! When you did you had nothing forward, and 2004r, the forward hub should have been my first guess
This is some of the parts on display on my Wall of Shame. If you look closely at the forward clutch housing, you wil see the splines are twisted. That tens was in my 87 Cutlass, with a 68 Toronado 455 engine. I built the trans with a CK Performance shift kit, servo, governor, good band, etc and used a friends factory D5 Grand National converter. Trans worked perfectly for 2 years I bought a 10 inch converter, i decided to open up the trans to see how things looked. I could not pull the hub off the shaft! The splines had twisted inside, and wouldn’t have taken much longer to snap off.

When I started to build the 87 Cutlass, I told my wife it was going to be a cheap car, using whatever leftover/spare parts I had. For the most part, I did. She wasn’t happy when I bought the converter. She was pissed when I told her I needed to spend another 500 buck on the hardened hub to fix a car that drove into the garage just fine. Women!

 

Matt, your wall of shame sure has some fateful items! My wall of shame only has a stripped out harmonic balancer bolt on it. ( I was on the way to ruining the crankshaft trying to use a impact to pull on balancer.... made a believer out of me to use a installer... Pettix I hope your trans isn't too costly to fix...

 

Trans is under a 2 year warranty so it was repaired and rebuilt free of charge. Everything else looked great in the trans, the clutches, the band, etc were in like new condition.

Just a fluke to break the forward planetary spline shaft. A very rare break. Builder claims its the 1st time he seen it shear at the splines. He has been building transmissions for 20+ years and did 1,000s of 2004Rs and never seen anything like this. They can break the actual forward planetary gears but not the splines. Proves that anything mechanical can break.

 

The connecting rod came from the same Cutlass that I swapped the 455/2004R trans. I bought the car with a knocking 307. Before I swapped in the 455, I decided to send the 307 to that big Scrapyard in the Sky. Foot to the floor, 2 minutes later it chucked the rod and piston out. When I cooled down, I turned the key to see if it would crank or locked up completely. It not only cranked, it started back up!! No oil, a hole in the pan big enough to reach in and touch the other side of the oil pan, and still running! I have a video of this, it was recorded on a camcorder, a friend transferred it to a DVD. I’d love to share the childish fun.

The bricks are from the Olds assembly plant in Lansing. We took a family vacation years years ago all thru Michigan, I insisted on making a detour to see the plant, unfortunately it was being knocked down. 😟.

Maybe I’ll start a thread asking people to post stuff on their Wall of Shame?

 

So the shaft didn’t snap off the forward clutch housing? The splines stripping out of that carrier is a unusual failure. I have heard of the overdrive carrier breaking, I think when that one goes the trans won’t move at all. It’s been awhile since I messed with a 2004R, if I remember correctly the carrier you posted is in the back of the trans, inside the sun gear shell?