Question, I am needing to rebuild the rear differential in my '90 AWD 5spd talon. Can I drive my car with the rear differential removed, if I also remove the axles, driveshaft and transfer case with no issues?

I am having driveline vibration at speeds +60 while in 5th gear. I rebuilt the rear suspension with poly bushings, rebuilt driveshaft, solid d/s carrier mount bushings trying to fix the vibration. During the rebuild, I noticed a lot of backlash in the rear differential. Now with the poly bushings I am now hearing howling during coasting.

Also, does anyone know of a source for the differential shims? Or rebuild kits. Rather not have to send this out to be rebuilt and wait 2 weeks when I could do it myself in a day. Seems the parts available are the bearings and seals. Cant find gear sets either..

Thanks in advance.

No you cannot simply remove the rear drive parts and continue driving it as FWD only. Our transmissions have an open center differential with an external viscous coupling to handle excessive slip. If you remove the rear drive any power that reaches the front wheels will have to be transmitted by this viscous coupling. It is not designed for this and with fail very quickly leaving you with a completely open center differential and no power at all to the front wheels which equals a car that wont move.

Think of it kinda like taking a LSD rear differential and removing the axle on one side. Then trying to drive around like that expecting the LSD to put all the power to the remaining axle on the other side. Doesn't work for long.

Now if you have a welded center diff like some do then it's a completely different story. Or use a viscous coupling eliminator spline which essentially locks the center diff the way welding it does.

Thank you for that. Appreciate the detailed answer.

Guess that means one plan wont work. Any sources for rear end components?

@95REGF150 , nice explaination! Will be a handy reference for others. Thank you.
@shdwmsk, go to the Classifieds and post up a WTB ad. Surely there are some out there. I have some but I am the 90 guy and they are in cars or in inventory.
3 bolts are pretty common. 4 bolts are getting harder to find. I got 1 from Miller Import Parts a few years ago. Performance Partout is another source and a good one. If in doubt, call them. Its just hunting one down and you don't need the axles, just a rear dif.
Good luck, I think you can find one.
Marty

@1990TSIAWDTALON Ended up just buying the one that's been on ebay for a while, but thank you anyways. Finally had enough driving in 4th today on my way to work. This better fix it, only thing left would be to do a toe eliminator kit. Everything else has been done. haha

Glad you snagged a dif! I figured there had to a few out there!

shdwmsk said:

@1990TSIAWDTALON Ended up just buying the one that's been on ebay for a while, but thank you anyways. Finally had enough driving in 4th today on my way to work. This better fix it, only thing left would be to do a toe eliminator kit. Everything else has been done. haha

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Driving in 4th??? Explain. As in you can't go fast enough to warrant 5th?

Getting to speed isn't the issue, its when I'm at light throttle in 5th, there is a large driveline vibration in the rear of the car at +60mph only noticeable in 5th gear.

I can drive all day in 4th at highway speeds, 30 to 75 mph, light load and heavy load. I can use 5th gear up to about 57 mph and a drive line vibration starts and gets worse the higher mph it goes. Stops when off the gas and increases with load. Does not happen in 4th. Vibrations come from the car, not the shifter or steering wheel. Getting a whine on decel that is starting to get worse, or is now more noticeable since I replaced all bushings in rear with polyurethane.

So far I have Rebuilt driveshaft, front yoke update, solid carrier bearing mounts, poly bushings in suspension and subframe, new struts, one new rear wheel bearing (inner and outer). The toe arm bushings did not feel different side to side and I don't have weird steering issues during turns. I noticed what I thought was excessive backlash when rebuilding my rear subframe, by going off the degrees the pinion is able to rotate before the ring gear turns. So now I am replacing the rear end with a hopefully good one.

Hope that helps explain why I drive it in 4th. If you have another idea, let me know. Only thing left would be installing a toe eliminator kit and maybe transfer case? I did not feel any backlash on it when I did the driveshaft though. I did clean and re-grease the lobrow joint in the drive shaft but can not guarantee the balls went back into the same "slot". It articulates freely, but full disclosure.

shdwmsk said:

Getting to speed isn't the issue, its when I'm at light throttle in 5th, there is a large driveline vibration in the rear of the car at +60mph only noticeable in 5th gear.

I can drive all day in 4th at highway speeds, 30 to 75 mph, light load and heavy load. I can use 5th gear up to about 57 mph and a drive line vibration starts and gets worse the higher mph it goes. Stops when off the gas and increases with load. Does not happen in 4th. Vibrations come from the car, not the shifter or steering wheel. Getting a whine on decel that is starting to get worse, or is now more noticeable since I replaced all bushings in rear with polyurethane.

So far I have Rebuilt driveshaft, front yoke update, solid carrier bearing mounts, poly bushings in suspension and subframe, new struts, one new rear wheel bearing (inner and outer). The toe arm bushings did not feel different side to side and I don't have weird steering issues during turns. I noticed what I thought was excessive backlash when rebuilding my rear subframe, by going off the degrees the pinion is able to rotate before the ring gear turns. So now I am replacing the rear end with a hopefully good one.

Hope that helps explain why I drive it in 4th. If you have another idea, let me know. Only thing left would be installing a toe eliminator kit and maybe transfer case? I did not feel any backlash on it when I did the driveshaft though. I did clean and re-grease the lobrow joint in the drive shaft but can not guarantee the balls went back into the same "slot". It articulates freely, but full disclosure.

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If it only does it in a specific gear it can't be in the rear end. I would be looking at your transmission.

I am on board with it being the transmission about 75-80%. The only things that makes me question it is that the vibration and gear whine both feel and sound like it is in the back half of the car. If anything more passenger rear vibration, centered rear gear whine. Shifter handle does not vibrate with the car either, shifter is fully rebuilt, not all sloppy.

But, I could also be making the gear whine noise transfer to the body with the poly suspension bushings and solid ds mount bushings. Then a bad 5th gear or bearing could make the driveline vibrate.

If replacing the rear diff does not fix this, I will be rebuilding the transmission in a month or so. It will be getting rebuilt next spring/summer anyways due to crappy 1st gear synchro. Also the rear diff I bought is supposed to be a B17 with the viscous LSD. Pretty sure mine is an open diff. So its not a total waste of time.


Vibration reminds me of driving with a bad strut and tire, but gets worse with load (in a certain gear) like a bad U joint. Really wish you could drive it to feel it.

UPDATE:

While I had the car on the lift to replace the rear differential, I decided to inspect 5th gear after reading that it can be accessed with the trans in the car. Upon disassembly I found that the 5th gear needle bearings all had flat spots on them. The main shaft splines are chewed up along with scratches on the case by the lower gear shaft and a chewed up 5th gear synchro.

The owner that I bought this car from stated that they retorqued the 2 shaft nuts due to 5th gear popping out. Looks like they torqued the nuts by jamming a screwdriver between the case and the gear. Scratching the case and deforming the needle bearings. Vibration was barely noticeably when I bought the car, and got worse until 5th was almost unusable in 1 year. Mainly drove in 1-4 last 3 months of that 1 year.

I replaced the needle bearing assembly and the lock nut. Synchro worked ok before so it went back in as ugly as it is. Works fine still. The main gear assembly bearing surfaces did not show any signs of deformation from the needle bearings so they were reused.

I have been driving it since I replaced this in December and the vibration in 5th is fixed. There is a slight gear whine while coasting, either the 5th gears set teeth are slightly worn from this, or its just because of the solid drive shaft mount washers and poly subframe mounts.

@pauleyman Thanks for pushing me to look into the transmission.

shdwmsk said:

UPDATE:

While I had the car on the lift to replace the rear differential, I decided to inspect 5th gear after reading that it can be accessed with the trans in the car. Upon disassembly I found that the 5th gear needle bearings all had flat spots on them. The main shaft splines are chewed up along with scratches on the case by the lower gear shaft and a chewed up 5th gear synchro.

The owner that I bought this car from stated that they retorqued the 2 shaft nuts due to 5th gear popping out. Looks like they torqued the nuts by jamming a screwdriver between the case and the gear. Scratching the case and deforming the needle bearings. Vibration was barely noticeably when I bought the car, and got worse until 5th was almost unusable in 1 year. Mainly drove in 1-4 last 3 months of that 1 year.

I replaced the needle bearing assembly and the lock nut. Synchro worked ok before so it went back in as ugly as it is. Works fine still. The main gear assembly bearing surfaces did not show any signs of deformation from the needle bearings so they were reused.

I have been driving it since I replaced this in December and the vibration in 5th is fixed. There is a slight gear whine while coasting, either the 5th gears set teeth are slightly worn from this, or its just because of the solid drive shaft mount washers and poly subframe mounts.

@pauleyman Thanks for pushing me to look into the transmission.

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Hold up. Some things don't look right. Nothing touches those shaft splines so how did they get chewed up? You can see the input shaft bearing through the case. That doesn't look right to me either. It looks like something wasn't assembled correctly. Deserves further inspection and review.

pauleyman said:

Hold up. Some things don't look right. Nothing touches those shaft splines so how did they get chewed up? You can see the input shaft bearing through the case. That doesn't look right to me either. It looks like something wasn't assembled correctly. Deserves further inspection and review.

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Splines: Doesn't the 5th gear synchro assembly mate with those splines? It was there, just not in that picture. I removed it, saw the splines, then took the picture. Could that nut have backed off enough, before the last owner retorqued that nut, to chew up those teeth? I was popping out of 5th, no idea how violent or long it was occurring. Works fine now, though I am planning on replacing the input shaft when I rebuild it.

Input shaft bearing showing. Can you elaborate? I am looking through the FSM and the transmission and I don't see anything glaringly obvious that is missing.

shdwmsk said:

Splines: Doesn't the 5th gear synchro assembly mate with those splines? It was there, just not in that picture. I removed it, saw the splines, then took the picture. Could that nut have backed off enough, before the last owner retorqued that nut, to chew up those teeth? I was popping out of 5th, no idea how violent or long it was occurring. Works fine now, though I am planning on replacing the input shaft when I rebuild it.

Input shaft bearing showing. Can you elaborate? I am looking through the FSM and the transmission and I don't see anything glaringly obvious that is missing.

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Maybe it's an illusion. The splines just look chewed up. As for the bearing when the 5th gear is off. It just didn't look right to me. Also wondering how the sleeve got so chewed up. Very odd wear. Even if the nut were loose the 5th gear presses against the sleeve and sits flat.

pauleyman said:

Maybe it's an illusion. The splines just look chewed up. As for the bearing when the 5th gear is off. It just didn't look right to me. Also wondering how the sleeve got so chewed up. Very odd wear. Even if the nut were loose the 5th gear presses against the sleeve and sits flat.

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No illusion, they are messed up. I don't have a picture of the inner teeth on the synchro assembly, so they must not have been bad.

Maybe a vibration from the bad needle bearings was making 5th gear synchro assembly eat the splines on the input shaft? Weird marks for sure. That outer synchro ring is also messed up. The splines are still crappy. Shift fine now though. All I know is that the vibration went away with the new needle bearings. Vibration was pretty bad too. Like a really blown right rear strut.

Thanks

That happens when shaft nuts get loosened. Input shaft, 5th gearset (including hub and slider) and needle bearing all take damage when that happens for a long time.

Tim,
Thank for that information. I was hopping that you would get a chance to look at these pictures.

The transmission should be a 1990 transmission, I'm guessing that the 5th gearset assembly is going to be a hard find, I remember the synchro is impossible to find new. Is the input shaft the same as other years transmissions and still available, or is it 1990 model year specific also?

Thanks