Potential Manual Transmission Failure

[TSTARKZ]

What I had hoped was just a pilot bearing/clutch assembly gone bad has seemingly presented as a much worse issue.

Quick background: I had started getting a rough "coffee beans in a can" grinding sound when driving my car. I only had about 10-12k on a new OEM clutch installed when i purchased the car one year ago. The sound progressively got worse and worse and got to the point that it was just embarrassing driving the car. The clutch engagement started getting worse so i assumed that it was an issue relating to the clutch assembly. Also started having a very strange feeling through the shifter primarily in 3rd gear. I could literally see the shifter move significantly when modulating the throttle. Note: the sound would go away once i pressed in the clutch, hence my assumption that it was clutch assembly related.

At this point, I had decided it's best to to change the entire assembly. I decided to make sure this was a "one and done" scenario and purchased the great stage 5r clutch from JHM. After having the clutch installed last night, it only seemed to relieve the problem in 4th gear and up. Still quite prevalent in gears 1-3. Currently, I'm now wondering if the gear stack is damaged (not sure how as the car has never been launched) as I can't attribute the issue to any other component.

Any thoughts or opinions?

[Thurston]

subscribed.

[raudiace4]

Stock or tuned?

[TSTARKZ]

Stock or tuned?

Tuned within the last 2k miles. Unitronics with 270mm crank pulley and all supporting mods (CPS, Exhaust, etc.)

[jonwoods]

I would frain and filter the transmission fluid. You’re looking for chunks of transmission in the fluid that shouldn’t be there. This won’t rule out a problem, but it’ll instantly tell you if something like a bearing has disintegrated.....

[sonic32]

Did you reuse TOB, clutch fork, do you have a SS clutch line? Did you reuse Slave, master?


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[sonic32]

Did you get tranny flushed? So many variables to take into consideration


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[TSTARKZ]

I would frain and filter the transmission fluid. You’re looking for chunks of transmission in the fluid that shouldn’t be there. This won’t rule out a problem, but it’ll instantly tell you if something like a bearing has disintegrated.....

I had changed the fluid not too long ago but I don't recall if i checked for shavings or anything. Can't hurt to do it again.

Did you reuse TOB, clutch fork, do you have a SS clutch line? Did you reuse Slave, master?


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Did not install the SS clutch line, new TOB and I don't recall if the JHM kit came with a new fork. New slave was installed as well.

[ellwood]

your "coffee beans in a can" sound is coming from the mismatch in speed between the locking collar and selector gear. the mismatch is supposed to be attenuated by the synchros. if the friction material on the synchros is worn, they cannot perform their job. the mismatch could also be driven by the input shaft being loaded during a gear change from a worn out pilot bearing/throwout bearing/friction disk, bent shift fork, failed slave, or maybe even damaged fingers on the diaphragm spring in the pressure plate... any of these conditions can rapidly wear out synchros

as far as the shifter moving in gear, my first guess would be motors mounts. if the engine/gearbox is moving excessively relative to the body of the car, it'll cause the shift lever to rock during load changes (on/off throttle or clutch engaged/disengaged)

like others suggested, an easy first step is to check the trans fluid for shiny metal bits or even other larger bits of metal

[TSTARKZ]

your "coffee beans in a can" sound is coming from the mismatch in speed between the locking collar and selector gear. the mismatch is supposed to be attenuated by the synchros. if the friction material on the synchros is worn, they cannot perform their job. the mismatch could also be driven by the input shaft being loaded during a gear change from a worn out pilot bearing/throwout bearing/friction disk, bent shift fork, failed slave, or maybe even damaged fingers on the diaphragm spring in the pressure plate... any of these conditions can rapidly wear out synchros

as far as the shifter moving in gear, my first guess would be motors mounts. if the engine/gearbox is moving excessively relative to the body of the car, it'll cause the shift lever to rock during load changes (on/off throttle or clutch engaged/disengaged)

like others suggested, an easy first step is to check the trans fluid for shiny metal bits or even other larger bits of metal

Thanks for your insight!

The shifter movement is odd because it only seems to be in third gear. No other movement in any of the forward or reverse gear.

Taking the potential assumption of damaged sycnros in 1, 2 and 3 gear stacks ( actually it's one stack, correct?); the next thought is if it's more cost effective to have a shop disassemble and repair or pick up a used transmission?

[sonic32]

Thanks for your insight!

The shifter movement is odd because it only seems to be in third gear. No other movement in any of the forward or reverse gear.

Taking the potential assumption of damaged sycnros in 1, 2 and 3 gear stacks ( actually it's one stack, correct?); the next thought is if it's more cost effective to have a shop disassemble and repair or pick up a used transmission?

I would look into shifter linkage first before anything since that needs to come out when trans comes out, it’s easy to put back in but if distracted tech it could be an issue


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[ellwood]

Thanks for your insight!

The shifter movement is odd because it only seems to be in third gear. No other movement in any of the forward or reverse gear.

Taking the potential assumption of damaged sycnros in 1, 2 and 3 gear stacks ( actually it's one stack, correct?); the next thought is if it's more cost effective to have a shop disassemble and repair or pick up a used transmission?

The locking collars (and therefore synchros) are on the output shaft for 1-2 and reverse, 3-4 and 5-6 are on the input shaft. It does seem bizarre that the movement is only apparent in one gear, but perhaps its just more pronounced in 3rd. As far as rebuild vs. used, there are certainly pros and cons for each... rebuild gets you new parts, but you have to rely on the capabilities of the installer, also not sure about $$ and parts availability. buying used would be an easy like-for-like swap, but you may not have a good idea of the internal health of that transmission.

it's also probably useful to note that the center diffs changed between B8 and B8.5, not sure if this affects how each trans bolts up

[sonic32]

The locking collars (and therefore synchros) are on the output shaft for 1-2 and reverse, 3-4 and 5-6 are on the input shaft. It does seem bizarre that the movement is only apparent in one gear, but perhaps its just more pronounced in 3rd. As far as rebuild vs. used, there are certainly pros and cons for each... rebuild gets you new parts, but you have to rely on the capabilities of the installer, also not sure about $$ and parts availability. buying used would be an easy like-for-like swap, but you may not have a good idea of the internal health of that transmission.

it's also probably useful to note that the center diffs changed between B8 and B8.5, not sure if this affects how each trans bolts up

What changed on center diffs between the 2?

[ellwood]

What changed on center diffs between the 2?

B8 has torsen type center diff and the B8.5 got a crown wheel type center diff

[TSTARKZ]

Yes we did realize there was a diff difference when i started my preliminary research on used transmission prices. Thanks for confirming!

[Corradobrit]

B8 has torsen type center diff and the B8.5 got a crown wheel type center diff

Not for the 6MT versions. Only DSG got the crown center diff

[ellwood]

Not for the 6MT versions. Only DSG got the crown center diff

interesting, i've never seen it differentiated between the two transmission types. thanks for the info

[sonic32]

interesting, i've never seen it differentiated between the two transmission types. thanks for the info

makes sense its only the DSG, the 6MT stayed the same up to the B9 A4. what are pros vs cons on torsen center vs crown center.
OP where are you located?

[Oloung1]

makes sense its only the DSG, the 6MT stayed the same up to the B9 A4. what are pros vs cons on torsen center vs crown center.

i was curious myself and found half of the answer: https://www.audi-mediacenter.com/en/...from-audi-2841.

The crown-gear differential
Exactly 30 years after the debut of the first quattro, Audi introduced a new, innovative evolutionary stage of its permanent all-wheel drive system for longitudinal front-mounted engines – the quattro drive with crown-gear differential and torque vectoring.

Inside the new center differential used in the RS 5, the A7 Sportback and the new A6 are two rotating crown gears that owe their name to the crown-like design of their teeth. The rear crown gear drives the propeller shaft to the rear-axle differential while the front crown gear drives the output shaft to the front-axle differential. The crown gears mesh with four rotatable pinion gears. They are arranged at right angles to each other and are driven by the differential’s housing, i.e. by the transmission output shaft.

Under normal driving conditions, the two crown gears rotate at the same speed as the housing. Because of their special geometry, they have specifically unequal lever effects. Normally 60 percent of the engine torque goes to the rear differential and 40 percent to the front differential.

If the torques change because one axle loses grip, different speeds and axial forces occur inside the differential and the adjacent plate packages are pressed against one another. The resulting self-locking effect subsequently diverts the majority of the torque to the axle achieving better traction; up to 85 percent can flow to the rear. Conversely, if the rear axle has less grip, the opposite happens; up to 70 percent of the torque is correspondingly diverted to the front axle.

Thanks to this even wider range of torque distribution, the crown-gear differential surpasses its predecessors to facilitate even better traction. Forces and torques are redistributed utterly consistently and without delay. The mechanical operating principle guarantees maximum efficiency and instantaneous responsiveness. Other strong points of the crown gear differential are its compactness and low weight – at 4.8 kilograms (10.58 lb) it is roughly two kilograms (4.41 lb) lighter than the previous component.

Audi couples the crown-gear differential with an intelligent brake management software solution called torque vectoring. The software can act on each of the four wheels individually, and the new system makes cornering even more precise and dynamic.

When cornering at speed, the software uses the driver’s steering input and desired level of acceleration to calculate the optimal distribution of propulsive power between all four wheels. If it detects that the wheels on the inside of the curve, which are under a reduced load, will soon begin to slip, it marginally brakes these wheels – just slight application of the pads on the disks at minimal pressure is all that it takes.

This action by the differential enables the outside wheels to apply more torque to the road. This assistance is provided smoothly and continuously. The car remains neutral noticeably longer; understeer while turning and accelerating is practically eliminated. Last but not least, the ESP intervenes later and more gently – if any intervention at all is necessary.

cliffs: basically the crown type is faster, has a wider torque distribution bias, and 40% lighter than the torsen type. plus is it 10000% mated & designed for the sport diff. so IRL any or all torsen center diff cars are not fully utilizing the powers of the sport diff

gl op with the your findings!

[sonic32]

i was curious myself and found half of the answer: https://www.audi-mediacenter.com/en/...from-audi-2841.



cliffs: basically the crown type is faster, has a wider torque distribution bias, and 40% lighter than the torsen type. plus is it 10000% mated & designed for the sport diff. so IRL any or all torsen center diff cars are not fully utilizing the powers of the sport diff

gl op with the your findings!

Yeah but none of those cars mentioned are manual. I guess us manual guys got shafted on something else besides shitty clutches lol


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[timzcat]

Coffee beans in a can when during the drive, all the time? That is not synchro issue in any case. I'd still question the clutch install, to bearing, pilot bearing, bent fork, etc. The noise you describe is typically the TO bearing. Basically, no noise when the pedal is depressed regardless of gear, movement or neutral but noise if pedal release in neutral or any gear then that is typical throw out bearing noise. The other trick is to apply slight pressure to the pedal to see if it quiets down. If its a new bearing then something else is causing to misaligh on the clutch fingers adn rattle.
I agree with the motor mount comment. I don't know the overall design of the shift linkage but once in gear the shifter will not move on load caused by transmission but certainly can for a bad mount. If it did the transmission would be really obviously destroyed and you have much bigger issues. If it's not any of the clutch related parts then the only other possibiliy is the input shaft bearing is going bad, likely due to other clutch issues causing excessive wear.
If you were further south in NJ I'd love to hear the noise. I used to be an auto technician ib a prior life and was the go to for diagnosing issues no one else could fix.

[TSTARKZ]

makes sense its only the DSG, the 6MT stayed the same up to the B9 A4. what are pros vs cons on torsen center vs crown center.
OP where are you located?

I'm on long island in NY


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[sonic32]

I'm on long island in NY


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Shoot me a PM. I’m in queens we can meet up I’m curious to see what it sounds like I might be able to help


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[ellwood]

Coffee beans in a can when during the drive, all the time? That is not synchro issue in any case. I'd still question the clutch install, to bearing, pilot bearing, bent fork, etc. The noise you describe is typically the TO bearing. Basically, no noise when the pedal is depressed regardless of gear, movement or neutral but noise if pedal release in neutral or any gear then that is typical throw out bearing noise. The other trick is to apply slight pressure to the pedal to see if it quiets down. If its a new bearing then something else is causing to misaligh on the clutch fingers adn rattle.
I agree with the motor mount comment. I don't know the overall design of the shift linkage but once in gear the shifter will not move on load caused by transmission but certainly can for a bad mount. If it did the transmission would be really obviously destroyed and you have much bigger issues. If it's not any of the clutch related parts then the only other possibiliy is the input shaft bearing is going bad, likely due to other clutch issues causing excessive wear.
If you were further south in NJ I'd love to hear the noise. I used to be an auto technician ib a prior life and was the go to for diagnosing issues no one else could fix.

you make a good point about if the noise is present all the time, i just assumed this occurred while changing gears... if the noise occurs while driving in gear, you're looking other problems... maybe something with the input/output shaft bearings

[ellwood]

Not for the 6MT versions. Only DSG got the crown center diff

for what it's worth, post #187 in the following build thread from member Lensch09 indicates that his 2016 6MT had the crown wheel differential... unfortunately all the photobucket links are broken

http://www.audizine.com/forum/showth...ld-(6MT)/page5

[grovlet]

for what it's worth, post #187 in the following build thread from member Lensch09 indicates that his 2016 6MT had the crown wheel differential... unfortunately all the photobucket links are broken

http://www.audizine.com/forum/showth...ld-(6MT)/page5

Psst - you can enable an extension in Google Chrome that turns them back on!!

[TSTARKZ]

Coffee beans in a can when during the drive, all the time? That is not synchro issue in any case. I'd still question the clutch install, to bearing, pilot bearing, bent fork, etc. The noise you describe is typically the TO bearing. Basically, no noise when the pedal is depressed regardless of gear, movement or neutral but noise if pedal release in neutral or any gear then that is typical throw out bearing noise. The other trick is to apply slight pressure to the pedal to see if it quiets down. If its a new bearing then something else is causing to misaligh on the clutch fingers adn rattle.
I agree with the motor mount comment. I don't know the overall design of the shift linkage but once in gear the shifter will not move on load caused by transmission but certainly can for a bad mount. If it did the transmission would be really obviously destroyed and you have much bigger issues. If it's not any of the clutch related parts then the only other possibiliy is the input shaft bearing is going bad, likely due to other clutch issues causing excessive wear.
If you were further south in NJ I'd love to hear the noise. I used to be an auto technician ib a prior life and was the go to for diagnosing issues no one else could fix.

Some great insights here. As of right now, I'm waiting for the shop to change fluid so we can inspect. I'll note your points to them as well. Thanks!


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[Corradobrit]

for what it's worth, post #187 in the following build thread from member Lensch09 indicates that his 2016 6MT had the crown wheel differential... unfortunately all the photobucket links are broken

http://www.audizine.com/forum/showth...ld-(6MT)/page5

Everything I've read and heard says that's not the case. The 6MT got the Torsen system. Perhaps there was a redesign for the 2016 MY.
https://www.youtube.com/watch?v=nBbKLIjrUSg