Bellhousing alignment - Is it even helpful?
Thread Starter
Launching!
Joined: Jun 2016
Posts: 285
Likes: 54
Bellhousing alignment - Is it even helpful? People seem to be split on this one. But those in favor will tell you that a failure to do a bellhousing alignment will result in bad shifts at best and transmission failure at worst. However, when I think of the following things, I don’t really see how it could be very helpful.
1. Even if done with 100% accuracy, it completely ignores any misalignment between the bellhousing and transmission. If we are going to worry about the inaccuracies associated with the dowel pins between the block and bellhousing, why would we expect those between the transmission and bellhousing to be any better?
2. Because the T56 bellhousing does not have a circular aperture for the input shaft, doing a bellhousing alignment on a T56 bellhousing requires that a plate be bolted to the bellhousing. The issues here echo those above. And because the plate could be off, a ‘perfect’ alignment with the plate might be more ‘off’ than what you would have with the stock dowel pins if you did nothing.
3. How accurately can the average person actually do the alignment? And given the inaccuracies of doing the alignment, is the end result TRULY better than just leaving things be?
4. Although alignment issues may have been a problem in the past, are they REALLY an issue with the more accurate manufacturing today?
5. Given that GM uses a standard dowel pin and is out to save money, you can bet your bottom dollar they DON’T do a bellhousing alignment on their cars. Yet they generally run fine for hundreds of thousands of miles with no resulting issues.
What do you think? Am I missing something here?
1. Even if done with 100% accuracy, it completely ignores any misalignment between the bellhousing and transmission. If we are going to worry about the inaccuracies associated with the dowel pins between the block and bellhousing, why would we expect those between the transmission and bellhousing to be any better?
2. Because the T56 bellhousing does not have a circular aperture for the input shaft, doing a bellhousing alignment on a T56 bellhousing requires that a plate be bolted to the bellhousing. The issues here echo those above. And because the plate could be off, a ‘perfect’ alignment with the plate might be more ‘off’ than what you would have with the stock dowel pins if you did nothing.
3. How accurately can the average person actually do the alignment? And given the inaccuracies of doing the alignment, is the end result TRULY better than just leaving things be?
4. Although alignment issues may have been a problem in the past, are they REALLY an issue with the more accurate manufacturing today?
5. Given that GM uses a standard dowel pin and is out to save money, you can bet your bottom dollar they DON’T do a bellhousing alignment on their cars. Yet they generally run fine for hundreds of thousands of miles with no resulting issues.
What do you think? Am I missing something here?
Last edited by StorminMatt; Feb 13, 2021 at 08:36 PM.
TECH Apprentice
Joined: Sep 2014
Posts: 362
Likes: 23
From: Merica
People seem to be split on this one. But those in favor will tell you that a failure to do a bellhousing alignment will result in bad shifts at best and transmission failure at worst. However, when I think of the following things, I don’t really see how it could be very helpful.
1. Even if done with 100% accuracy, it completely ignores any misalignment between the bellhousing and transmission. If we are going to worry about the inaccuracies associated with the dowel pins between the block and bellhousing, why would we expect those between the transmission and bellhousing to be any better?
2. Because the T56 bellhousing does not have a circular aperture for the input shaft, doing a bellhousing alignment on a T56 bellhousing requires that a plate be bolted to the bellhousing. The issues here echo those above. And because the plate could be off, a ‘perfect’ alignment with the plate might be more ‘off’ than what you would have with the stock dowel pins if you did nothing.
3. How accurately can the average person actually do the alignment? And given the inaccuracies of doing the alignment, is the end result TRULY better than just leaving things be?
4. Although alignment issues may have been a problem in the past, are they REALLY an issue with the more accurate manufacturing today?
5. Given that GM uses a standard dowel pin and is out to save money, you can bet your bottom dollar they DON’T do a bellhousing alignment on their cars. Yet they generally run fine for hundreds of thousands of miles with no resulting issues.
What do you think? Am I missing something here?
1. Even if done with 100% accuracy, it completely ignores any misalignment between the bellhousing and transmission. If we are going to worry about the inaccuracies associated with the dowel pins between the block and bellhousing, why would we expect those between the transmission and bellhousing to be any better?
2. Because the T56 bellhousing does not have a circular aperture for the input shaft, doing a bellhousing alignment on a T56 bellhousing requires that a plate be bolted to the bellhousing. The issues here echo those above. And because the plate could be off, a ‘perfect’ alignment with the plate might be more ‘off’ than what you would have with the stock dowel pins if you did nothing.
3. How accurately can the average person actually do the alignment? And given the inaccuracies of doing the alignment, is the end result TRULY better than just leaving things be?
4. Although alignment issues may have been a problem in the past, are they REALLY an issue with the more accurate manufacturing today?
5. Given that GM uses a standard dowel pin and is out to save money, you can bet your bottom dollar they DON’T do a bellhousing alignment on their cars. Yet they generally run fine for hundreds of thousands of miles with no resulting issues.
What do you think? Am I missing something here?
Both are well within the acceptable range and will work out just fine. As for the QT SFI units, I have heard those usually need to be indexed and off set dowels are required to correct the runout.
Staging Lane
Joined: Dec 2020
Posts: 60
Likes: 6
I can tell you this much, on the factory 1386-212-005 we tested to compare it with our T56LSBH, the factory bell housing was about .005-008" out compared to ours which was roughly .002" out at the high end.
Both are well within the acceptable range and will work out just fine. As for the QT SFI units, I have heard those usually need to be indexed and off set dowels are required to correct the runout.
Both are well within the acceptable range and will work out just fine. As for the QT SFI units, I have heard those usually need to be indexed and off set dowels are required to correct the runout.
Thread Starter
Launching!
Joined: Jun 2016
Posts: 285
Likes: 54
Then virtually every car is coming out of the factory out of spec.
TECH Apprentice
Joined: Sep 2014
Posts: 362
Likes: 23
From: Merica
Anything .010" or more from exact centerline of the crank shaft would need to be addressed with offset dowel pins. I have seen numerous big name automatic bell housings as much as .018-.020" out and customers had no issues to report. Ideally you want it as close to .000 as possible but when you actually look at what .005" is in relation to roughly 8" distance from pilot bearing to input shaft bearing on the transmission, its not very much at all.
TECH Resident
Joined: Apr 2007
Posts: 866
Likes: 218
From: Montgomery (Lake Conroe,) TX north of Houston
AMP-D is correct on the .010" specification limit. I aligned my stock type, aluminum Tremec bellhousing. I had to buy an indexing plate and I purchased this one: Bellhousing Dial Indicator Plate for Tremec T56
I have the instructions included with the Bowler plate and they say that your final numbers should be within .010" total indicator reading. If you're planning on high performance shifting at 7500+rpm, then the total indicator reading should be within .005"
Mine required .007 offset dowels from RobbMC and I was able to get my Tremec bellhousing to .006" and called it a day.
I have the instructions included with the Bowler plate and they say that your final numbers should be within .010" total indicator reading. If you're planning on high performance shifting at 7500+rpm, then the total indicator reading should be within .005"
Mine required .007 offset dowels from RobbMC and I was able to get my Tremec bellhousing to .006" and called it a day.
TECH Apprentice
Joined: Sep 2014
Posts: 362
Likes: 23
From: Merica
AMP-D is correct on the .010" specification limit. I aligned my stock type, aluminum Tremec bellhousing. I had to buy an indexing plate and I purchased this one: Bellhousing Dial Indicator Plate for Tremec T56
I have the instructions included with the Bowler plate and they say that your final numbers should be within .010" total indicator reading. If you're planning on high performance shifting at 7500+rpm, then the total indicator reading should be within .005"
Mine required .007 offset dowels from RobbMC and I was able to get my Tremec bellhousing to .006" and called it a day.
I have the instructions included with the Bowler plate and they say that your final numbers should be within .010" total indicator reading. If you're planning on high performance shifting at 7500+rpm, then the total indicator reading should be within .005"
Mine required .007 offset dowels from RobbMC and I was able to get my Tremec bellhousing to .006" and called it a day.
