3.73 gear problems
04-26-2016, 11:46 AM
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3.73 gear problems I recently bought a stock 106k miles 1998 Z28 A4 car with a 2.73 rear gear. At the track I did a 13.4@103 and after a lot of reading it seemed like switching to a 3.73 gear was a good first mod. I had a reputable shop install an aftermarket 3.73 and tell me to stay off the highway for the first 200 miles. I left the shop and drove it easy for the first few miles then got into it hard to pass another vehicle. Upon decelerating I heard a loud whining noise that hadn't been there before. The noise was constantly there as I drove it back to the shop. They took the car back and called me later saying I knocked the hardness off the gear. They replaces it for free, for which I was very greatful, and told me no highway or hard acceleration or deceleration for 200 miles. I drove it like an absolute granny for the first 200+ miles. I called them this morning and asked if I needed to change the gear oil before drag racing it now that I had completed the break in. They said no so I took it on the street and did a few hard 0-60 runs then parked it for a few minutes. When I started driving again I noticed that the whine was back!!! I called the shop and they said that the 7.5" gear in these cars is very small and I probably knocked or wore the hardness off the gear again and was into the soft metal and it would get louder and louder before eventually breaking. I'm waiting to call the owner back in about an hour to see what he tells me. Am I doing something wrong? Is the shop giving me bad service and or advice about the break in? The stock 2.73 gear was taking the abuse just fine for 106k miles. I'm going nuts any advise? I already for $1060 in this dumb gear swap!
Last edited by 1st; 04-26-2016 at 11:52 AM. Reason: Grammar
04-26-2016, 03:03 PM
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Dude, I had exactly the same upgrade made to my 2002 Z28 with and A4 and 2.73 gears, so we're talking apples-to-apples at this point.
However, where one of our apples becomes an orange is the break-in time: The instructions that came with my gears, the installer himself, and numerous online articles and posts of warning on gear swaps all offered the same words of caution: Drive very gently, slowly, and avoid cruise control/maintaining consistent speeds for prolonged intervals for the first 500 miles to allow the gears to properly wear in.
Once the proper, prescribed break-in interval of 500 miles was completed, the car could be enjoyed to its fullest without need for any additional modifications to the gears or their oil.
From what you described, you were warned the first time and chose to go your own way. It's easy to do, but the end result was expected and, sadly, happened.
It sounds like you did a good job of following the guidelines the second time, but, I'm surprised that you were only advised to do so for only 200 miles, as that's quite an abridged timeline from the one that several sources recommended that I follow.
Lastly, most gears — including mine — cost in the $400 - $500 range. The shop that I went to specializes in gear swaps and had been in business for approximately 25 years when my work was completed for $300 (including fluid, seals, and bolts, so it seems that your mechanic is at the higher end of the price structure for this upgrade.
What brand of gear did you select? You may consider trying gears from a new manufacturer.
After the 500-mile break-in, I thoroughly enjoyed my 3.73 gears without any issue whatsoever.
I wish that I could recall what brand of gears I purchased, I bought them about 10 years ago. I do remember that I ordered them from Summit, based on the recommendation of one of the sales reps.
Hope this helps, at least in some small way. Best of luck to you!
However, where one of our apples becomes an orange is the break-in time: The instructions that came with my gears, the installer himself, and numerous online articles and posts of warning on gear swaps all offered the same words of caution: Drive very gently, slowly, and avoid cruise control/maintaining consistent speeds for prolonged intervals for the first 500 miles to allow the gears to properly wear in.
Once the proper, prescribed break-in interval of 500 miles was completed, the car could be enjoyed to its fullest without need for any additional modifications to the gears or their oil.
From what you described, you were warned the first time and chose to go your own way. It's easy to do, but the end result was expected and, sadly, happened.
It sounds like you did a good job of following the guidelines the second time, but, I'm surprised that you were only advised to do so for only 200 miles, as that's quite an abridged timeline from the one that several sources recommended that I follow.
Lastly, most gears — including mine — cost in the $400 - $500 range. The shop that I went to specializes in gear swaps and had been in business for approximately 25 years when my work was completed for $300 (including fluid, seals, and bolts, so it seems that your mechanic is at the higher end of the price structure for this upgrade.
What brand of gear did you select? You may consider trying gears from a new manufacturer.
After the 500-mile break-in, I thoroughly enjoyed my 3.73 gears without any issue whatsoever.
I wish that I could recall what brand of gears I purchased, I bought them about 10 years ago. I do remember that I ordered them from Summit, based on the recommendation of one of the sales reps.
Hope this helps, at least in some small way. Best of luck to you!
04-26-2016, 05:02 PM
#3
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Wrong break-in per the shops instructions 
https://www.ringpinion.com/Technical...r_break-in.inc
http://www.differentials.com/technic...reak-procedure
https://www.ringpinion.com/Technical...r_break-in.inc
http://www.differentials.com/technic...reak-procedure
New Ring and Pinion Break In Procedure
Because of the slight roughness of the new gear contact faces and the heavy preloads that must be applied to the new tapered roller bearings, your new rear axle will generate its maximum amount of waste heat in its first few miles. With use, bearing preloads diminish and gear surfaces become smoother. Therefore, the first few hundred miles on a new gear set are the most critical. To prevent premature (and almost immediate) failure of your new gear set, this break-in procedure must be followed:
All new gear sets require a break in period to prevent damage from overheating the gear oil. The lubrication properties of overloaded or overheated gear oil will be diminished. If the gear oil to breaks down, the end result will be catastrophic damage to the ring and pinion.
Avoid burn outs, sudden starts and heavy acceleration for the first 500 miles.
Drive the vehicle gently for 15 – 20 miles, but no longer than 25 - 30 minutes to build up the heat. Do not exceed 50 mph. Let the differential cool down for one hour. Before driving again, feel the differential with the back of your hand. The rear differential should be cool to the touch. Repeat this cycle five times.
When driving on the highway, vary your speed while avoiding heavy acceleration.
I cannot overemphasize the importance of changing the gear oil after the first 500 miles. This will remove all metal particles, black phosphoric coating and other contaminants shed by the gears during the break in period. The integrity of the gear oil is compromised as a result. The gear oil must be changed.
When a posi unit is rebuilt along with a gear change, the clutch discs will break in and settle as well. There will be additional metal particulate in the gear oil from the clutch discs. Again, it is extremely important to change the gear oil after the first 500 miles. I always recommend a good quality petroleum based 80W90 gear oil with GM Limited Slip Additive.
DO NOT use synthetic lubricants in clutch type limited slip differentials. Synthetic oil makes the clutch discs too slippery. This will not allow the clutch discs to lock up. When the clutch discs slip, one wheel spins. This defeats the purpose of using a Limited Slip differential. Using synthetic gear oil will eventually render the limited slip operation useless.
Because of the slight roughness of the new gear contact faces and the heavy preloads that must be applied to the new tapered roller bearings, your new rear axle will generate its maximum amount of waste heat in its first few miles. With use, bearing preloads diminish and gear surfaces become smoother. Therefore, the first few hundred miles on a new gear set are the most critical. To prevent premature (and almost immediate) failure of your new gear set, this break-in procedure must be followed:
All new gear sets require a break in period to prevent damage from overheating the gear oil. The lubrication properties of overloaded or overheated gear oil will be diminished. If the gear oil to breaks down, the end result will be catastrophic damage to the ring and pinion.
Avoid burn outs, sudden starts and heavy acceleration for the first 500 miles.
Drive the vehicle gently for 15 – 20 miles, but no longer than 25 - 30 minutes to build up the heat. Do not exceed 50 mph. Let the differential cool down for one hour. Before driving again, feel the differential with the back of your hand. The rear differential should be cool to the touch. Repeat this cycle five times.
When driving on the highway, vary your speed while avoiding heavy acceleration.
I cannot overemphasize the importance of changing the gear oil after the first 500 miles. This will remove all metal particles, black phosphoric coating and other contaminants shed by the gears during the break in period. The integrity of the gear oil is compromised as a result. The gear oil must be changed.
When a posi unit is rebuilt along with a gear change, the clutch discs will break in and settle as well. There will be additional metal particulate in the gear oil from the clutch discs. Again, it is extremely important to change the gear oil after the first 500 miles. I always recommend a good quality petroleum based 80W90 gear oil with GM Limited Slip Additive.
DO NOT use synthetic lubricants in clutch type limited slip differentials. Synthetic oil makes the clutch discs too slippery. This will not allow the clutch discs to lock up. When the clutch discs slip, one wheel spins. This defeats the purpose of using a Limited Slip differential. Using synthetic gear oil will eventually render the limited slip operation useless.
04-27-2016, 12:29 AM
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For that kind of cash, you could have done a top shelf 3500+ stall converter plus install, not had all these issues, and achieved about twice the acceleration gains. Gear swap would definitely not be a first mod I would recommend to an A4 LS1 owner, regardless of original factory ratio.
Sorry to hear about the troubles. Seems that the recommended break-in mileage just wasn't long enough for the application.
Sorry to hear about the troubles. Seems that the recommended break-in mileage just wasn't long enough for the application.
04-27-2016, 11:39 AM
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Spoke to the owner The gear I used was an aftermarket gear and I reconfirmed with the owner that the 200 miles of easy driving I did should have been all that was needed before taking it to the drag strip (which I have yet to go to). He said the company who the gears were from would warranty the gears so just drive it and if it breaks we'll go from there, however he cannot afford to cover the cost of installation again. A friend who is an AC repair man for work but a gear head at heart said he thought the break in should be 500 miles and to double check with the installer on that 200 mile break in period. Now after ya'll responses I feel that the gear failure was a result of not doing the 5 warm up and cool down cycles as well as not completing 500 easy miles before getting on it. I'm frustrated I wasn't told this by the installer and if everyone recommends changin the gear fluid after the break in period, which my friend also said to ask them about doing, then I'm also frustrated they didn't recommend that as well. I guess the good news is if/when this gear breaks I will now know how to properly break in the next one. If the gear breaks at the track and I immediately shut it down and load it back on the trailer to tow it home will a simple gear swap again have me back up and running or is there a chance it will take out my factory limited slip? The repair shop didn't give me any warning about this when they told me to just drive it until it breaks then bring it back if it does but now I'm afraid this might be another problem I could face and wonder if I should just do another gear swap before it breaks.
Last edited by 1st; 04-27-2016 at 11:45 AM. Reason: Adding pic
04-28-2016, 06:38 PM
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OK....is this a general repair shop or a trans and rear shop ?
Call and ask a trans and rear shop the price and break-in....I would not pay another penny and IF you do, I would call my CC company and argue the charges.
Call and ask a trans and rear shop the price and break-in....I would not pay another penny and IF you do, I would call my CC company and argue the charges.
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04-30-2016, 08:30 PM
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The shop specializes in driveshaft repair, gear swaps, and axle rebuilds. I have used them 2 or 3 other times over the past 14 years with good results. I spoke to a couple friends who know the owner and they say he knows his stuff and recommended I go talk to him in person which I plan to do. My receipt says 85w-140 Lucas but I don't know if it is synthetic or not. I took the car to Palm Beach International Raceway yesterday after being told by the shop to just go ahead and run it. I trailered it up for fear that it would break but got 6 runs in and no breaking so that's a win....bad news is it somehow performed almost exactly the same with the new 3.73 gear as it did with the stock 2.73 
on the same track!
2.73 gear vs 3.73 gear w/ SLP lid & new filter
60' ... 2.073 2.021
330' ... 5.733 5.666
1/8 ... 8.745 8.579
MPH ... 82.68 82.38
1000'... 11.284 11.210
ET ... 13.440 13.369
MPH ... 103.84 104.76
This is a comparison of my best runs before and after the gear swap. The track temp was maybe in the low 60's with the 2.73 gear and probably in the low 70's with the 3.73 gear. Unless that 10 degrees (estimated) air temp is makes that much difference I am at a loss as to how a huge change from 2.73 to 3.73, as well as a new SLP lid and replacing the filter, gets me virtually no improvement! Is this normal? On the street it feels stronger and seems like it chirps the tires on the 1-2 upshift more easily then before. My wife is fussing at me that I spent $1060 and now have a whining rear end that threw off my speedometer, odometer, will get worse highway gas mileage and runs the engine RPM's up higher and got me virtually no faster or louder! She told me I should have done the long tube headers first.
on the same track!2.73 gear vs 3.73 gear w/ SLP lid & new filter
60' ... 2.073 2.021
330' ... 5.733 5.666
1/8 ... 8.745 8.579
MPH ... 82.68 82.38
1000'... 11.284 11.210
ET ... 13.440 13.369
MPH ... 103.84 104.76
This is a comparison of my best runs before and after the gear swap. The track temp was maybe in the low 60's with the 2.73 gear and probably in the low 70's with the 3.73 gear. Unless that 10 degrees (estimated) air temp is makes that much difference I am at a loss as to how a huge change from 2.73 to 3.73, as well as a new SLP lid and replacing the filter, gets me virtually no improvement! Is this normal? On the street it feels stronger and seems like it chirps the tires on the 1-2 upshift more easily then before. My wife is fussing at me that I spent $1060 and now have a whining rear end that threw off my speedometer, odometer, will get worse highway gas mileage and runs the engine RPM's up higher and got me virtually no faster or louder! She told me I should have done the long tube headers first.
05-01-2016, 06:22 AM
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The shop specializes in driveshaft repair, gear swaps, and axle rebuilds. I have used them 2 or 3 other times over the past 14 years with good results. I spoke to a couple friends who know the owner and they say he knows his stuff and recommended I go talk to him in person which I plan to do. My receipt says 85w-140 Lucas but I don't know if it is synthetic or not. I took the car to Palm Beach International Raceway yesterday after being told by the shop to just go ahead and run it. I trailered it up for fear that it would break but got 6 runs in and no breaking so that's a win....bad news is it somehow performed almost exactly the same with the new 3.73 gear as it did with the stock 2.73 on the same track!
2.73 gear vs 3.73 gear w/ SLP lid & new filter
60' ... 2.073 2.021
330' ... 5.733 5.666
1/8 ... 8.745 8.579
MPH ... 82.68 82.38
1000'... 11.284 11.210
ET ... 13.440 13.369
MPH ... 103.84 104.76
This is a comparison of my best runs before and after the gear swap. The track temp was maybe in the low 60's with the 2.73 gear and probably in the low 70's with the 3.73 gear. Unless that 10 degrees (estimated) air temp is makes that much difference I am at a loss as to how a huge change from 2.73 to 3.73, as well as a new SLP lid and replacing the filter, gets me virtually no improvement! Is this normal? On the street it feels stronger and seems like it chirps the tires on the 1-2 upshift more easily then before. My wife is fussing at me that I spent $1060 and now have a whining rear end that threw off my speedometer, odometer, will get worse highway gas mileage and runs the engine RPM's up higher and got me virtually no faster or louder! She told me I should have done the long tube headers first.
on the same track!2.73 gear vs 3.73 gear w/ SLP lid & new filter
60' ... 2.073 2.021
330' ... 5.733 5.666
1/8 ... 8.745 8.579
MPH ... 82.68 82.38
1000'... 11.284 11.210
ET ... 13.440 13.369
MPH ... 103.84 104.76
This is a comparison of my best runs before and after the gear swap. The track temp was maybe in the low 60's with the 2.73 gear and probably in the low 70's with the 3.73 gear. Unless that 10 degrees (estimated) air temp is makes that much difference I am at a loss as to how a huge change from 2.73 to 3.73, as well as a new SLP lid and replacing the filter, gets me virtually no improvement! Is this normal? On the street it feels stronger and seems like it chirps the tires on the 1-2 upshift more easily then before. My wife is fussing at me that I spent $1060 and now have a whining rear end that threw off my speedometer, odometer, will get worse highway gas mileage and runs the engine RPM's up higher and got me virtually no faster or louder! She told me I should have done the long tube headers first.
As for why you didn't see better gains with the stock stall speed still in place, traction probably wasn't ideal with the 3.73s and street tires, and shift points might not be proper either if you didn't get a retune.
LT headers (plus a tune) would have certainly done more for trap speed, but I wouldn't have touched either before doing a ~3500 stall. That is where you will see the biggest gains possible for a single mod (other than FI/N2O) on an A4 LS1.
05-01-2016, 07:10 AM
#12
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Better ET can be had with a better 60'...every .1 off your 60 can make it a .2-.3 better 1320'
Put your work in there first
I found I get my best 60's staging at 1000-1500ish (just off idle) and flashing my converter.
Put your work in there first
I found I get my best 60's staging at 1000-1500ish (just off idle) and flashing my converter.
05-01-2016, 09:25 AM
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I was hoping to do mods that make my car quicker without killing it's daily driveability so I figured I would hold off on a high stall converter. I'm having to ease into the throttle off the line to keep from spinning so maybe a set or rims with drag radials that I can swap on just for the track would help me get the most out of the 3.73 gear but with it already making noise I figure I should hold off on stickier tires until I decide if I want to replace it again before it goes or just run it until it does then drop the big money for a built 9" or 12 bolt. While I make up my mind on that I think I'm gonna do Long tube headers and a dyno tune because I for sure won't be throwing money at a part I might have to replace again soon then. Thank you all for the advice and education.
05-01-2016, 02:37 PM
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I was hoping to do mods that make my car quicker without killing it's daily driveability so I figured I would hold off on a high stall converter. I'm having to ease into the throttle off the line to keep from spinning so maybe a set or rims with drag radials that I can swap on just for the track would help me get the most out of the 3.73 gear but with it already making noise I figure I should hold off on stickier tires until I decide if I want to replace it again before it goes or just run it until it does then drop the big money for a built 9" or 12 bolt. While I make up my mind on that I think I'm gonna do Long tube headers and a dyno tune because I for sure won't be throwing money at a part I might have to replace again soon then. Thank you all for the advice and education.
I wouldn't worry too much about the rear in an A4 application. They are prone to breakage with sticky tires even at stock power levels behind and M6, but with the auto you might be surprised at how much power and traction they can handle (as long as you keep wheel hop away.) Having said that, yours is currently having issues with the noisy gear set so longevity of those gears is likely suspect, but with stock (or properly installed and broken-in) gears you don't have much to worry about with an A4 until you get well past stock-to-moderate power levels. Here's a thread regarding 7.5" durability (and just how much more durable they are with an auto) that you might find interesting:
https://ls1tech.com/forums/gears-axl...ock-7-5-a.html
