83 3-speed Auto - Torque conv. replacement for low power
10-03-2021, 05:21 PM
#1
83 3-speed Auto - Torque conv. replacement for low power
Hi all,
I've read that the 3-speed auto was one of the slowest cars 0-60.
But I feel mine is a little extra slow and not putting all the power to the wheels.
I did the stall speed test described in the WSM and got a stall speed of about 1900rpm. WSM indicates that this result means the TC needs to be replaced.
There is also a whine coming from that part of the car when I accelerate.
I have brought the car to a vintage gearbox guy and he is dubious about the TC and thinks it is most like like the gearbox.
My current plan is the get both TC and gearbox rebuilt in one go which is going to cost a few thousand.
Does this seem like a reasonable move to improve the cars performance and to ensure the transmission is not in danger of failing anytime soon?
There is 140k on the clock,
Or does this seem like a waste of money?
The car is in very good condition in all other ways.
Anyways, would like to hear opinions of the Rennlist group.
Thanks,
Robert.
I've read that the 3-speed auto was one of the slowest cars 0-60.
But I feel mine is a little extra slow and not putting all the power to the wheels.
I did the stall speed test described in the WSM and got a stall speed of about 1900rpm. WSM indicates that this result means the TC needs to be replaced.
There is also a whine coming from that part of the car when I accelerate.
I have brought the car to a vintage gearbox guy and he is dubious about the TC and thinks it is most like like the gearbox.
My current plan is the get both TC and gearbox rebuilt in one go which is going to cost a few thousand.
Does this seem like a reasonable move to improve the cars performance and to ensure the transmission is not in danger of failing anytime soon?
There is 140k on the clock,
Or does this seem like a waste of money?
The car is in very good condition in all other ways.
Anyways, would like to hear opinions of the Rennlist group.
Thanks,
Robert.
10-03-2021, 07:32 PM
#2
Former Sponsor
Opinions are a Rennlist specialty!
Get 10 people to answer a question and you'll get a minimum of 11 answers......all from experts.
I'm not an expert, but I know enough to be dangerous....
There's something wrong with your premise about automatic transmissions and torque converters.
And your transmission guy is obviously not an expert about automatic transmissions, either.
First off, I have no idea what your noise is....that might indicate some sort of a problem.
That's a separate issue that should be traced.
However, your "lack" of stall speed is almost impossible to occur from a worn/damaged torque converter or transmission issue.
Torque converters, by design, always slip more when they are damaged.
Transmissions also always slip more, when they are damaged.
It's virtually impossible for either one of these items to "increase" their amount of resistance.
The lack of rpm tells you one thing and one thing only....the engine isn't making enough torque.
You need to fix the engine, not the transmission or the torque converter!
Let me explain more about a torque converter.
These pieces are essentially one fan turning another fan.
If the fan attached to the engine has a change in the amount of torque it can deliver, this directly affects the fan that it is turning.
If you were to double the torque of your engine...the converter would "lock up" at a much higher rpm....say 4,000 rpms.
If you were to loose torque, the converter will "lock up" at a lower rpm.
It's how torque converter work.
As far as the transmission itself having something wrong that would "absorb" 500 rpms worth of torque....there's nothing inside to do that...and last more than a quick trip down the street.
The amount of heat that would be generated would "cook" the fluid instantly.
Fix your engine power issue, then remeasure your stall speed.
Get 10 people to answer a question and you'll get a minimum of 11 answers......all from experts.
I'm not an expert, but I know enough to be dangerous....
There's something wrong with your premise about automatic transmissions and torque converters.
And your transmission guy is obviously not an expert about automatic transmissions, either.
First off, I have no idea what your noise is....that might indicate some sort of a problem.
That's a separate issue that should be traced.
However, your "lack" of stall speed is almost impossible to occur from a worn/damaged torque converter or transmission issue.
Torque converters, by design, always slip more when they are damaged.
Transmissions also always slip more, when they are damaged.
It's virtually impossible for either one of these items to "increase" their amount of resistance.
The lack of rpm tells you one thing and one thing only....the engine isn't making enough torque.
You need to fix the engine, not the transmission or the torque converter!
Let me explain more about a torque converter.
These pieces are essentially one fan turning another fan.
If the fan attached to the engine has a change in the amount of torque it can deliver, this directly affects the fan that it is turning.
If you were to double the torque of your engine...the converter would "lock up" at a much higher rpm....say 4,000 rpms.
If you were to loose torque, the converter will "lock up" at a lower rpm.
It's how torque converter work.
As far as the transmission itself having something wrong that would "absorb" 500 rpms worth of torque....there's nothing inside to do that...and last more than a quick trip down the street.
The amount of heat that would be generated would "cook" the fluid instantly.
Fix your engine power issue, then remeasure your stall speed.
10-03-2021, 08:41 PM
#3
Hi Robert,
The whine could be either low transmission fluid or the torque converter (TC) bearings at the front of the transmission.
Since it is an automatic, would check the front flex plate load and see if the front flex plate is being pushed toward the engine using a small straight edge. Loosen the front pinch bolt and see if the flex plate goes backward unto the drive shaft.
If there was front load, that load is seen by the engine's thrust bearing at the front as well as the torque tube (TT) and TC bearings at the rear. The TC bearings if loaded in this manner will start making noise, more so than the TT bearings.
While doing the check at the front flex plate would also check the crank shaft end float with a dial indicator to establish the engine thrust bearing health.
HTH.
The whine could be either low transmission fluid or the torque converter (TC) bearings at the front of the transmission.
Since it is an automatic, would check the front flex plate load and see if the front flex plate is being pushed toward the engine using a small straight edge. Loosen the front pinch bolt and see if the flex plate goes backward unto the drive shaft.
If there was front load, that load is seen by the engine's thrust bearing at the front as well as the torque tube (TT) and TC bearings at the rear. The TC bearings if loaded in this manner will start making noise, more so than the TT bearings.
While doing the check at the front flex plate would also check the crank shaft end float with a dial indicator to establish the engine thrust bearing health.
HTH.
10-04-2021, 01:29 PM
#4
Former Sponsor
Hi Robert,
The whine could be either low transmission fluid or the torque converter (TC) bearings at the front of the transmission.
Since it is an automatic, would check the front flex plate load and see if the front flex plate is being pushed toward the engine using a small straight edge. Loosen the front pinch bolt and see if the flex plate goes backward unto the drive shaft.
If there was front load, that load is seen by the engine's thrust bearing at the front as well as the torque tube (TT) and TC bearings at the rear. The TC bearings if loaded in this manner will start making noise, more so than the TT bearings.
While doing the check at the front flex plate would also check the crank shaft end float with a dial indicator to establish the engine thrust bearing health.
HTH.
The whine could be either low transmission fluid or the torque converter (TC) bearings at the front of the transmission.
Since it is an automatic, would check the front flex plate load and see if the front flex plate is being pushed toward the engine using a small straight edge. Loosen the front pinch bolt and see if the flex plate goes backward unto the drive shaft.
If there was front load, that load is seen by the engine's thrust bearing at the front as well as the torque tube (TT) and TC bearings at the rear. The TC bearings if loaded in this manner will start making noise, more so than the TT bearings.
While doing the check at the front flex plate would also check the crank shaft end float with a dial indicator to establish the engine thrust bearing health.
HTH.
Unless someone removed these pieces, this should be a non-event, but certainly worth checking.
10-04-2021, 03:09 PM
#6
Thanks Guys for the replies.
@GregBBRD I am certainly no transmission expert. The reason I focused in the the TC was because of the following line in the Porsche workshop manual......
"Condition:
Poor acceleration when moving off.
Cause/Correction:
1. Check stall speed
2. If stall speed drops below specified value by approx 400 to 700rpm, one way clutch in convertor is slipping. Replace torque convertor"
Do you think this is over simplified or am I misunderstanding?
@Constantine /Greg . Can the checks around the flex plate be done without dropping the transmission or TC out? If so I could tackle this myself if I can get the car high enough.
What effects would flex plate preload have on the car apart from the whining noise?
Transmission fluid level was always ok.
Many thanks again for your advice.
Robert.
@GregBBRD I am certainly no transmission expert. The reason I focused in the the TC was because of the following line in the Porsche workshop manual......
"Condition:
Poor acceleration when moving off.
Cause/Correction:
1. Check stall speed
2. If stall speed drops below specified value by approx 400 to 700rpm, one way clutch in convertor is slipping. Replace torque convertor"
Do you think this is over simplified or am I misunderstanding?
@Constantine /Greg . Can the checks around the flex plate be done without dropping the transmission or TC out? If so I could tackle this myself if I can get the car high enough.
What effects would flex plate preload have on the car apart from the whining noise?
Transmission fluid level was always ok.
Many thanks again for your advice.
Robert.
10-04-2021, 03:23 PM
#7
Rennlist Member
Thanks Guys for the replies.
@GregBBRD I am certainly no transmission expert. The reason I focused in the the TC was because of the following line in the Porsche workshop manual......
"Condition:
Poor acceleration when moving off.
Cause/Correction:
1. Check stall speed
2. If stall speed drops below specified value by approx 400 to 700rpm, one way clutch in convertor is slipping. Replace torque convertor"
Do you think this is over simplified or am I misunderstanding?
@Constantine /Greg . Can the checks around the flex plate be done without dropping the transmission or TC out? If so I could tackle this myself if I can get the car high enough.
What effects would flex plate preload have on the car apart from the whining noise?
Transmission fluid level was always ok.
Many thanks again for your advice.
Robert.
@GregBBRD I am certainly no transmission expert. The reason I focused in the the TC was because of the following line in the Porsche workshop manual......
"Condition:
Poor acceleration when moving off.
Cause/Correction:
1. Check stall speed
2. If stall speed drops below specified value by approx 400 to 700rpm, one way clutch in convertor is slipping. Replace torque convertor"
Do you think this is over simplified or am I misunderstanding?
@Constantine /Greg . Can the checks around the flex plate be done without dropping the transmission or TC out? If so I could tackle this myself if I can get the car high enough.
What effects would flex plate preload have on the car apart from the whining noise?
Transmission fluid level was always ok.
Many thanks again for your advice.
Robert.
This is in the thread..you should already be familiar with.
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10-04-2021, 04:37 PM
#8
Hi Robert,
Yes, just drop the front bell housing bottom cover (six bolts, the exhaust might have to be re-positioned to get at the two most rear ones) and inspect the front flex plate.
As Greg mentioned, given your 928 is an 1983, there should be some parts at the front of the drive shaft which will not allow the drive shaft to start a forward pre-load of the flex plate. However this possibility could be present since by this time, prior owners or mechanics could have removed them, sometimes without notification to the owner of the 928.
Besides the TT and TC bearings being loaded and making noise, most infamously the engines thrust bearing could be worn down which can ruin the 928 engine.
Bottom line, all 928 automatics should be checked for this possibility.
HTH.
Yes, just drop the front bell housing bottom cover (six bolts, the exhaust might have to be re-positioned to get at the two most rear ones) and inspect the front flex plate.
As Greg mentioned, given your 928 is an 1983, there should be some parts at the front of the drive shaft which will not allow the drive shaft to start a forward pre-load of the flex plate. However this possibility could be present since by this time, prior owners or mechanics could have removed them, sometimes without notification to the owner of the 928.
Besides the TT and TC bearings being loaded and making noise, most infamously the engines thrust bearing could be worn down which can ruin the 928 engine.
Bottom line, all 928 automatics should be checked for this possibility.
HTH.
10-04-2021, 06:09 PM
#9
Former Sponsor
Hi Robert,
Yes, just drop the front bell housing bottom cover (six bolts, the exhaust might have to be re-positioned to get at the two most rear ones) and inspect the front flex plate.
As Greg mentioned, given your 928 is an 1983, there should be some parts at the front of the drive shaft which will not allow the drive shaft to start a forward pre-load of the flex plate. However this possibility could be present since by this time, prior owners or mechanics could have removed them, sometimes without notification to the owner of the 928.
Besides the TT and TC bearings being loaded and making noise, most infamously the engines thrust bearing could be worn down which can ruin the 928 engine.
Bottom line, all 928 automatics should be checked for this possibility.
HTH.
Yes, just drop the front bell housing bottom cover (six bolts, the exhaust might have to be re-positioned to get at the two most rear ones) and inspect the front flex plate.
As Greg mentioned, given your 928 is an 1983, there should be some parts at the front of the drive shaft which will not allow the drive shaft to start a forward pre-load of the flex plate. However this possibility could be present since by this time, prior owners or mechanics could have removed them, sometimes without notification to the owner of the 928.
Besides the TT and TC bearings being loaded and making noise, most infamously the engines thrust bearing could be worn down which can ruin the 928 engine.
Bottom line, all 928 automatics should be checked for this possibility.
HTH.
Previous "mechanics" can do almost anything.
The shop took apart an '83 recently, which had a 28mm shaft, without the longer shaft and circlip groove.
The flexplate was crushed into the flywheel, but had not destroyed the thrust bearing, yet.
I never thought that an '83 engine could develop enough torque to cause this to occur.
.....Of course, Porsche obviously knew that the entire flexplate movement could/would occur...since they added the shim, thrust washer on circlip on all the early models.
The only real mystery is what idiot engineer signed off on the removal of these pieces on the 4 speed models, resulting in hundreds of thousands of dollars worth of engine failures.
10-05-2021, 02:15 PM
#10
This flex plate definitely seems like something to be checked regardless of any TC / acceleration issues.
I'll get the car in the air this weekend and have a go.
Back to my original issue, I'm not finding any evidence from Rennlist or elsewhere to suggest that rebuilding the TC will improve acceleration from standstill - despite the text in the WSM suggesting it would.
€5k is a lot to spend on something that may not change anything apart from giving some peace of mind that the transmission and TC are at their best.
Unless any other wise Rennlister says other wise I might hold fire on that move for now.
Robert.
I'll get the car in the air this weekend and have a go.
Back to my original issue, I'm not finding any evidence from Rennlist or elsewhere to suggest that rebuilding the TC will improve acceleration from standstill - despite the text in the WSM suggesting it would.
€5k is a lot to spend on something that may not change anything apart from giving some peace of mind that the transmission and TC are at their best.
Unless any other wise Rennlister says other wise I might hold fire on that move for now.
Robert.
10-05-2021, 07:56 PM
#11
Hi Robert,
You can bank on what Greg has said about this situation concerning the TC and transmission not being your issue. Very few have his decades of knowledge about all things 928.
The main issue is for you to find a comparable tech shop that is truly focused on 928s. The 928 has a lot of quirks and the many changes made to it by Porsche through its lifespan really ratchets up the difficulty in figuring out what is wrong according to the model year.
Passing knowledge on 928s can do more harm than good in many instances.
Good luck with you problem and please let us know what you find out. This might help another 928er sometime in the future.
Cheers,
Constantine
You can bank on what Greg has said about this situation concerning the TC and transmission not being your issue. Very few have his decades of knowledge about all things 928.
The main issue is for you to find a comparable tech shop that is truly focused on 928s. The 928 has a lot of quirks and the many changes made to it by Porsche through its lifespan really ratchets up the difficulty in figuring out what is wrong according to the model year.
Passing knowledge on 928s can do more harm than good in many instances.
Good luck with you problem and please let us know what you find out. This might help another 928er sometime in the future.
Cheers,
Constantine