ausername
ausername New Reader
1/23/21 6:34 p.m.

Hello I am new here and hope this is the right section to post this. I am after some advice. I have a 2000 Ford Mustang GT with a 5 speed manual transmission with 127,000 miles. The car is jerky when using just the clutch to move it without throttle. I dont know if this is a characteristic of this car but with previous manual cars I have had, I have been able to move them smoothly with just slipping the clutch at low speed e.g. traffic jam or parking lots. Another thing is after a 20-30 mile drive when everything is warm, I hear a low pitched moaning/whinning sort of noise from the rear when turning the car at low speeds in a parking lot. Its hard to pinpoint this noise when driving the car but I feel like it is coming from the rear.

I took it to a mechanic who told me there is huge rotational play when moving the driveshaft by hand and the whole rear end needs to be replaced. So I jacked up the car and I can feel a very minor rotational play when trying to rotate the driveshaft by hand. I am not a mechanic but have been working on my cars for a fairly long time, in my opinion the play just does not seem even close to what the mechanic said. Also cannot feel any back and forth or side to side play in the driveshaft which I'd expect to be present if the rear gears were so worn out. So my question is what can I do to make sure if the differential is bad or what the issue is before spending money on a differential rebuild?

The reason I dont think this is the clutch is because the clutch feels strong and there is no noise with the car stationary and the clutch engaged (in neutral) or disengaged indicating the throw out bearing is not defective.

Do you guys have any advice? Thank you.

Mr_Asa
Mr_Asa UltraDork
1/23/21 6:39 p.m.

I'd probably start by pulling the cover off the rear end and inspecting it directly.  The fluid probably needs to be changed anyways, so you might as well.

ausername
ausername New Reader
1/23/21 6:40 p.m.
Mr_Asa said:

I'd probably start by pulling the cover off the rear end and inspecting it directly.  The fluid probably needs to be changed anyways, so you might as well.

I will be doing a fluid change. What should I be looking for? Metal shavings? Is there a way to tell if the bearings inside are bad? The pinion is behind the carrier so its hard to see if the pinion is the problem. If it was the clutch or flywheel was warped it would explain the jerkiness when moving the car at idle but does not explain the noise when turning the car at slow speed. 

Mr_Asa
Mr_Asa UltraDork
1/23/21 6:51 p.m.

Yeah, check for sparklies in the oil, clean everything off with brake clean or whatnot and then check the gears.  You will be able to look at the pinion gear and ring gear engagement and you can twist them back and forth to see the amount of play.  For the bearings I don't have any suggestions other than just checking the play.

There is a bit of clearance in every part of the rear end, the gears, the meshing of the axles, etc, so expect some play.  

ausername
ausername New Reader
1/23/21 7:02 p.m.
Mr_Asa said:

Yeah, check for sparklies in the oil, clean everything off with brake clean or whatnot and then check the gears.  You will be able to look at the pinion gear and ring gear engagement and you can twist them back and forth to see the amount of play.  For the bearings I don't have any suggestions other than just checking the play.

There is a bit of clearance in every part of the rear end, the gears, the meshing of the axles, etc, so expect some play.  

Ok thank you. And yes I'd expect some minor play which is why I want to make sure differential is actually bad.

TurnerX19
TurnerX19 SuperDork
1/23/21 7:41 p.m.

There will not be any side to side play from worn pinion bearings until they are minutes from total disasterous failure. Your jerky start ups could be as simple as bad bushings in control arms or bad engine/gearbox mounts. The play does not need to be in the gears themselves. Do the cover off inspection anyway it can't hurt.

Streetwiseguy
Streetwiseguy MegaDork
1/24/21 12:16 p.m.

I read two problems.  The roughness pulling away is a bit ilof a clutch shudder, which you can either live with, learn to drive around, or replace the clutch.

The low speed moaning from the rear is the lsd clutches.  Add some friction modifier, rebuild the lsd, or live with it.  If you want to feel better about yours, come for a ride in my Camaro.

ausername
ausername New Reader
1/30/21 2:50 p.m.

I did a fluid change and took some pictures. I did not see any sparkly bits or metal in the oil but under flash it looks like there are some present? Also used some gear compounds to see the contact pattern. I am not sure if this is good or bad? Does it look like this differential is going to explode at anytime or soon? Another thing I noticed was when moving a wheel there was a noise that sounded like backlash or 'deadzone' if that makes sense but the pinion gear moved as soon as I moved the wheel. I have a video will try to upload later. There was also dirt inside the differential. The little pieces you see on the gears is dirt.

ausername
ausername New Reader
1/30/21 3:44 p.m.

In reply to Streetwiseguy :

I added some ford friction modifier with the fluid

ausername
ausername New Reader
1/31/21 12:34 p.m.

Here is a video of the differential moving using the tire. There doesnt seem to be much backlash between the pinion and ring gear but it makes a clunking noise. Any idea what this clunking noise is?

 

https://youtu.be/gTW8x4mj0t0

ausername
ausername New Reader
2/1/21 5:59 p.m.

Anyone?

eastsideTim
eastsideTim PowerDork
2/1/21 6:05 p.m.

Any idea of where in general the noise is coming from?  Could the u-joints be bad?  Or could it just be driveline slack being taken up?  I think my Impala makes a similar noise when I rotate a wheel, but I can't remember for certain.

Edit:  I think I remember what it was in my case - may have just been a little slack, and the clunk was when I hit resistance from the opposite side axle.

Stampie (FS)
Stampie (FS) MegaDork
2/1/21 6:35 p.m.

How about disconnect the drive shaft from the rear and rotate the rear at the flange?  That'll tell you if it's the rear or the forward of that.  Next I guess is remove the drive shaft from the trans and watch all your trans fluid pour out as you test the u joints for play.

ausername
ausername New Reader
2/1/21 6:49 p.m.
eastsideTim said:

Any idea of where in general the noise is coming from?  Could the u-joints be bad?  Or could it just be driveline slack being taken up?  I think my Impala makes a similar noise when I rotate a wheel, but I can't remember for certain.

Edit:  I think I remember what it was in my case - may have just been a little slack, and the clunk was when I hit resistance from the opposite side axle.

Do you mean the clunking noise in the video? If so I am not sure, like you said it could be resistance from the opposite axle. The ring and pinion gear doesnt look like it has excessive backlash does it? They move together.

ausername
ausername New Reader
2/1/21 6:50 p.m.
Stampie (FS) said:

How about disconnect the drive shaft from the rear and rotate the rear at the flange?  That'll tell you if it's the rear or the forward of that.  Next I guess is remove the drive shaft from the trans and watch all your trans fluid pour out as you test the u joints for play.

I will try that at some point. Do you think the differential behaves ok?

Stampie (FS)
Stampie (FS) MegaDork
2/1/21 6:53 p.m.

In reply to ausername :

I don't see any play but I'm more of a tactile feel guy vs a visual guy.

ausername
ausername New Reader
2/1/21 7:05 p.m.
Stampie (FS) said:

In reply to ausername :

I don't see any play but I'm more of a tactile feel guy vs a visual guy.

I should have tried to move the whole diff using the ring gear but I didnt. I did push the ring gear up and down a little and felt no play. Dont want to have the diff rebuilt if it is ok for a few thousand miles. Does the wear on the gears look excessive?

Stampie (FS)
Stampie (FS) MegaDork
2/1/21 8:24 p.m.

In reply to ausername :

Let me tell you a story.  My favorite nephew called me this evening.  He was driving his new to him truck that I had given advice on buying up north.  Said all of a sudden he lost power in 5th gear so he down shifted to 4th and still didn't have power.  So he slowed down to 40mph and pulled off at an exit and was at a gas station trying to figure out what was wrong.  I was heading home from work and had to pee like a mofo.  Maybe I wasn't thinking all straight but I thought about the symptoms and my brain said eliminate the MAF first.  Told him to unplug it and I'd call him back after I relived my bladder.  As I was doing so I was thinking it through and I thought well maybe he has a fuel issue.  Maybe his pump is weak or maybe a pin hole in the pickup hose and after it gets low he is sucking air.  So I called him back and asked what the fuel gauge read.  He said half a tank.  Hmmm ok so not too low then he said he'd been driving 7 hours since that morning and it was fine.  Ok how many times did you fill up?  Oh I haven't needed too because I have half a tank still.  Well let's do the math, 7 hours driving at 70 mph means you've done 490 miles on a tank of gas.  I think you're empty.  Sure enough he puts $20 of gas in the truck and it runs fine.  Moral of the story is don't overthink the problem look at the simple solutions first.

ausername
ausername New Reader
2/3/21 8:08 a.m.
Stampie (FS) said:

In reply to ausername :

Let me tell you a story.  My favorite nephew called me this evening.  He was driving his new to him truck that I had given advice on buying up north.  Said all of a sudden he lost power in 5th gear so he down shifted to 4th and still didn't have power.  So he slowed down to 40mph and pulled off at an exit and was at a gas station trying to figure out what was wrong.  I was heading home from work and had to pee like a mofo.  Maybe I wasn't thinking all straight but I thought about the symptoms and my brain said eliminate the MAF first.  Told him to unplug it and I'd call him back after I relived my bladder.  As I was doing so I was thinking it through and I thought well maybe he has a fuel issue.  Maybe his pump is weak or maybe a pin hole in the pickup hose and after it gets low he is sucking air.  So I called him back and asked what the fuel gauge read.  He said half a tank.  Hmmm ok so not too low then he said he'd been driving 7 hours since that morning and it was fine.  Ok how many times did you fill up?  Oh I haven't needed too because I have half a tank still.  Well let's do the math, 7 hours driving at 70 mph means you've done 490 miles on a tank of gas.  I think you're empty.  Sure enough he puts $20 of gas in the truck and it runs fine.  Moral of the story is don't overthink the problem look at the simple solutions first.

Thanks I’ll try the driveshaft tests you suggested. After adding the friction modifier the groan has mostly gone. I only heard it twice when turning. I havnt done a long drive yet though. I’m hoping as the friction modifier works it’s way between the clutches the groan goes away completely. 

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