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AudiB5owner
02-09-2014, 07:12 PM
Hey All,

Drove my car for the first time on the highway today since I got my new front drive axle installed a few weeks ago. I was going around 75 and peeked at my speedometer to see something odd.

Readings were dipping going over 10 MPH the actual speed I was travelling. When I accelerated it got worse and jumped even harder, dipping once all the way to 40 MPH.

I was going 65 and put the car on cruise control. The car was going fine then out of nowhere the speedometer dipped and the car started to gun it, literally. But the thing is I wasn't slowing down and the car accelerated way past 65 thinking I was going slower.

Just once I was able to reproduce this crazy speedometer stuff at lower speeds. I accelerated onto the freeway and the speedometer jumped from 1, 20, to 40, and went crazy until 60. Then it kind of settled down but the bouncing occurred over 60MPH.

No codes no nada. Classic sign of a bad output speed sensor? Do you think the shop could have done something wrong? Every past post states how bad speed sensors do not allow the speedometer to work at all along with CEL. Any help would be great [:D]

BaseDrifter
02-09-2014, 07:13 PM
Does the needle jump around or move smoothly? It could be a bad stepper motor in the cluster.

AudiB5owner
02-09-2014, 07:21 PM
It moves smoothly while accelerating under 60 MPH. When I am holding 65 MPH it starts jumping around. As I increase speed 65+ it starts jumping more, not displaying any concrete speed reading. Do you think that since it starts going crazy fast in cruise control indicates that the stepper motor is okay? I assume the ECU sends a signal to the stepper motor based off the speed sensor, so the actual jumping of the needle would be merely indicating something's wrong with a sensor.

But then again I have no clue. I'll look into the stepper motor. Hope this isn't an expensive fix [:|]

BaseDrifter
02-09-2014, 07:24 PM
It could be the speed sensor, you usually get an implausible signal code when they go bad. I have a known to be working one laying around if you want to try and test it.

AudiB5owner
02-09-2014, 07:31 PM
That's what I though too. Maybe my speed sensor's connection is messed up so it is making the speeds jump. I plan on taking it to the mechanic tomorrow because he literally just worked on that part. From the diagrams on ELSAWIN the drive axle spins the sensor to get a reading. Thank you for offering the part, I will have to see what the mechanic says. Doesn't look too hard to swap out though.

audinutt
02-10-2014, 08:37 AM
Sounds exactly like when my magnet for the speed sensor needed to be replaced. This isn't a horrible job but I recommend replacing the bearing and seal at the same time.

Sent from my SCH-I605 using Tapatalk 4

AudiB5owner
02-10-2014, 09:16 AM
Sounds exactly like when my magnet for the speed sensor needed to be replaced. This isn't a horrible job but I recommend replacing the bearing and seal at the same time.

Sent from my SCH-I605 using Tapatalk 4

The magnet as in the whole sensor itself? Looks like it just slides into a hole that seats the sensor so it touches the drive axle. I just got the whole axle and seal replaced and had this issue after the work so I assume the shop did something wrong. Thanks for the input everyone [up] I appreciate it!

audinutt
02-10-2014, 09:33 AM
The magnet is behind the seal inside the diff behind the cover.

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AudiB5owner
02-10-2014, 10:02 AM
From the diagram, it looks like that magnetic ring is where the tranny oil seal sits into, or at least they are next to each other in the assembly. Looks like the only way to access it is to remove the drive axle. Didn't realize the speed sensor was magnet driven. The mechanic must have had to do something to mess up the system, no way this is a random occurrence.

BaseDrifter
02-10-2014, 10:51 AM
I would highly recommend starting with a new OEM (and known to be working) sensor first before tackling the magnetic ring. When my speedometer died I tried replacing the sensor with a Meyle replacement and it didn't fix the problem, so I went in and pulled the drive flange and side cover to replace the ring and it still didn't fix my problem. Turned out that I had a bent and shorted VSS pin on my instrument cluster, after fixing that the Meyle unit still didn't work, but an OEM VSS did.

Long story short, I would try a different OEM VSS first.

Awinn11
02-11-2014, 07:50 PM
I broke my oem VSS changing that axle. Replaced it with meyle. it worked for a week, then started doing what the op described. after a while it started coming in and out, now it doesn't work at all. The inner boot is now torn on that same axle, so i have to get back in there. Is it worth changing the ring if I'm that far in already? or should i put off the axle and change to an oem VSS first?

AudiB5owner
02-11-2014, 08:12 PM
Hey how did you end up breaking it by changing the axle? My mechanic doesn't believe he caused the damage. Mechanic says that the ring is probably not the problem with these symptoms, as if the ring was faulty, the speedometer bounce would occur across all speeds. For me, it is getting worse everyday, before it was only at high speeds but it now happens around 40 mph. The faster the axle moves, the faster the VSS has to pickup the magnetic signals, which a bad sensor cannot do so well. Tomorrow the mech is putting in a new OEM VSS to see if that solves the problem *finger crossed*.

I'd try a new sensor first and if you happen to change out the axle, I guess it wouldn't hurt to look at the ring. I'll report back on what happens.

ianwpb
02-11-2014, 08:53 PM
I had the same issue with an erratic speedometer. It didn't happen all of the time though. It was off and on. When it started acting up the fuel gauge would move and I wouldn't be able to rev over like 5200 or something in that range. I replaced my VSS, that didn't fix it. So I opened up the diff case to change the magnetic ring. Visually, the ring looked fine, but changing it fixed my problem.

That job was a pain. I hope I don't have to do it again. I had a bunch of stripped bolts.



I'd try a new sensor first and if you happen to change out the axle, I guess it wouldn't hurt to look at the ring. I'll report back on what happens.

Unfortunately, it's not as easy as just "looking" at the ring. You have to drain the transmission fluid, pull the axle flange out (PITA), unbolt the 10(?) T45 bolts for the diff cover (3 were stripped, they're really in there...), pull the diff cover off, then you'll be able to see the ring sitting on the side of the diff. IIRC, it just pops off. Basically, the only way you're going to see it is if you are going to change it. If it all goes perfectly and you don't strip anything, I could see it taking 2 hours at best.

BaseDrifter
02-11-2014, 09:32 PM
That job was a pain. I hope I don't have to do it again. I had a bunch of stripped bolts.

Pretty much this.



Unfortunately, it's not as easy as just "looking" at the ring. You have to drain the transmission fluid, pull the axle flange out (PITA), unbolt the 10(?) T45 bolts for the diff cover (3 were stripped, they're really in there...), pull the diff cover off, then you'll be able to see the ring sitting on the side of the diff. IIRC, it just pops off. Basically, the only way you're going to see it is if you are going to change it. If it all goes perfectly and you don't strip anything, I could see it taking 2 hours at best.

Took me a lot longer than 2 hours and none of my bolts were stripped. Getting the axle flange in and out was the worst, royal pain in the ass. The ring does just pop off, and as you said, if you're going in there you might as well replace it anyways.

ianwpb
02-11-2014, 09:52 PM
Pretty much this.




Took me a lot longer than 2 hours and none of my bolts were stripped. Getting the axle flange in and out was the worst, royal pain in the ass. The ring does just pop off, and as you said, if you're going in there you might as well replace it anyways.

Yeah, when I did it, it ended up taking probably 10 hours over 2 days.

Getting the flange out was tedious. I used two really long axle flange bolts, M8x100 or something like that, tightening back and forth until it finally popped out. Putting it back in was pretty simple once I figured out a good way to do it. I lined it up and tapped it with a rubber mallet to make sure it was in the splines, then I took the whole 4ft jack handle with a rag on the end, put it up against the flange and hammered away with a mallet. Much quicker that way.

Proper preparation is key. Even then, it's annoying.

BaseDrifter
02-11-2014, 10:01 PM
Yeah, when I did it, it ended up taking probably 10 hours over 2 days.

Getting the flange out was tedious. I used two really long axle flange bolts, M8x100 or something like that, tightening back and forth until it finally popped out. Putting it back in was pretty simple once I figured out a good way to do it. I lined it up and tapped it with a rubber mallet to make sure it was in the splines, then I took the whole 4ft jack handle with a rag on the end, put it up against the flange and hammered away with a mallet. Much quicker that way.

Proper preparation is key. Even then, it's annoying.

Yeah, I think I was close to 6 hours in one evening.

I did it exactly the same way. I used two long bolts with two pieces of 1/8" aluminum plate to back the bolts against the flange cover. What made it super annoying was that as I tightened one bolt, the backing plate behind the other would slip out of place. To get it back in I used a long piece of wood to reach the flange while I hammered it in from the side of the car. No way it was going to get seated without using an extension, no room to swing a sledgehammer under the car. I was super worried about getting the splines seated correctly but all went well. Still never want to do it again.

AudiB5owner
02-11-2014, 10:24 PM
Wow guys that sounds like a tedious mechanic operation. The diagram I was looking at to service the drive wheel magnet made it seem a lot more simple. Didn't realize you have to drain the transmission fluid, it would obviously flow out with the output flange removed. Sorry I couldn't crop the screenshot:
http://oi62.tinypic.com/11blqm8.jpg

I literally just had my output shaft seal replaced, and according to this diagram, they fit over one another. I sure do hope a new VSS is the fix! Otherwise I'd suspect something fishy with my mech shop's work.

BaseDrifter
02-11-2014, 10:34 PM
That's interesting, but I did not see how it would be possible without removing the side cover. Here are some pictures from when I did it. Unfortunately I don't have a picture with the flange removed but cover still on. I also didn't replace the output shaft seal (luckily it hasn't leaked.)

Axle removed.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04964_zps2c841647.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04964_zps2c841647.jpg.html)

Bolts/plates to remove flange.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04966_zps47840fb4.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04966_zps47840fb4.jpg.html)

Flange removed.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04967_zpscb5c2f94.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04967_zpscb5c2f94.jpg.html)

New magnetic ring.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04968_zps935ac82c.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04968_zps935ac82c.jpg.html)

New vs old.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04969_zps340323af.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04969_zps340323af.jpg.html)

The ring sits just in front of the bearings.

http://i346.photobucket.com/albums/p439/blkA4alb-3/A4%20B5/DSC04970_zps67b7f12c.jpg (http://s346.photobucket.com/user/blkA4alb-3/media/A4%20B5/DSC04970_zps67b7f12c.jpg.html)

AudiB5owner
02-11-2014, 10:41 PM
That's actually really cool, I had no idea what the axle shaft looked like inside the diff. Thanks a ton for posting the pics. Being prepared for this type of job looks absolutely necessary, just time consuming. If that magnetic ring is actually faulty in my car, I don't think I'll be too happy with my shop based on pure coincidence between the problem and recent work I had done.

BaseDrifter
02-11-2014, 10:51 PM
I thought it was all pretty cool too as I was disassembling it. I love seeing how these things work, but it was still a royal pain. Avoid if possible! Don't make the mistake I did and replace the ring when it was the sensor all along...

AudiB5owner
02-12-2014, 01:36 PM
Went to my mechanic today, the new VSS speed sensor did not fix the problem. My speedometer wasn't even working after 5 minutes of driving. Decided it must be the magnetic ring. It's going to be installed tomorrow and it will be decided whether it failed due to wear and tear or improper installation when the new axle seal was installed. Good thing I have such a great shop near me though, the owner is great! He quoted it being a 2 hour job if wear and tear which I guess is around $200 plus parts. Maybe it should be recommended that this magnetic ring to always be replaced when servicing the output shaft seal. It'd save another trip to the mechanic. Seems like a part that is prone to fail.

BaseDrifter
02-13-2014, 01:04 AM
Went to my mechanic today, the new VSS speed sensor did not fix the problem. My speedometer wasn't even working after 5 minutes of driving. Decided it must be the magnetic ring. It's going to be installed tomorrow and it will be decided whether it failed due to wear and tear or improper installation when the new axle seal was installed. Good thing I have such a great shop near me though, the owner is great! He quoted it being a 2 hour job if wear and tear which I guess is around $200 plus parts. Maybe it should be recommended that this magnetic ring to always be replaced when servicing the output shaft seal. It'd save another trip to the mechanic. Seems like a part that is prone to fail.

Glad to hear you're getting it sorted, hope that fixes your speedo.

I'm wondering if the ring placement is different because you're FWD, didn't think about that until now.