Torque tube coupler question
02-16-2004, 04:01 PM
#1
Racer
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Torque tube coupler question
I am picking up a new to me 928 S4 and want to check, if their is any thrust on the flex plate before driving home. Therefore, does anyone have a list of tools needed to check the torque tube shaft coupler at the flex plate?
Also, does anyone know wether or not the exhaust system has to be dropped prior to pulling the flex plate cover. Any help with this issue would be appreciated.
Thanks in advance,
Terry
Also, does anyone know wether or not the exhaust system has to be dropped prior to pulling the flex plate cover. Any help with this issue would be appreciated.
Thanks in advance,
Terry
02-16-2004, 04:23 PM
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Can't remember the sizes need for the wrenches. You will have to drop your exhaust down a couple of inches for the back 2 bolts. It is a good idea to check your flex plate periodically. I cut the 2 back bolts down so that I could remove them without dropping the exhaust and it made check the flex plate a breeze.
Congrats on your new car!
Congrats on your new car!
02-16-2004, 05:02 PM
#3
Rennlist Member
Enjoy the new ride!!
Wish I could remember all the sizes, but..... as I recall, all 13mm for the 6 ex. header flanges: you'll need a variety of sockets/extensions/ wrenches to get at them. There's a bracket in the way, needing a 17mm 1/2' drive gear, and the gland nuts on the air pump injection line - 21/22mm, needing two wrenches to counter hold. This gets the exhaust loose - it must be supported( and it's heavy) or the O2 sensor wires will part company!
The lower bell housing is too easy - 6 13mm bolts: inside. the flex plate coupling is held by a 7 or 8mm allen head - an allen key won't do it: 3/8" drive and retorque to 65#: add torque wrench and two 11/4" adjustables.
Also, the eng has to be turned to expose the head of the coupling bolt: bump the starter, or turn the crank with a 27mm 1/2", 2" extension, and a breaker bar.
Don't forget the floor jack and jack stands - BTW, are you flying???
Hope that the seller has the space and the gear, because while it's a simple job, there's a reasonable amount of wrestling with the exhaust system, Good luck.
Wish I could remember all the sizes, but..... as I recall, all 13mm for the 6 ex. header flanges: you'll need a variety of sockets/extensions/ wrenches to get at them. There's a bracket in the way, needing a 17mm 1/2' drive gear, and the gland nuts on the air pump injection line - 21/22mm, needing two wrenches to counter hold. This gets the exhaust loose - it must be supported( and it's heavy) or the O2 sensor wires will part company!
The lower bell housing is too easy - 6 13mm bolts: inside. the flex plate coupling is held by a 7 or 8mm allen head - an allen key won't do it: 3/8" drive and retorque to 65#: add torque wrench and two 11/4" adjustables.
Also, the eng has to be turned to expose the head of the coupling bolt: bump the starter, or turn the crank with a 27mm 1/2", 2" extension, and a breaker bar.
Don't forget the floor jack and jack stands - BTW, are you flying???
Hope that the seller has the space and the gear, because while it's a simple job, there's a reasonable amount of wrestling with the exhaust system, Good luck.
02-16-2004, 05:24 PM
#4
Terry,
I have just finished checking the end thrust on the flexplate of my 1990 928 S4 Auto (15th Feb) and the following tools were required.
1 off 8mm hexigan headed by 1/2 inch drive socket to fit allen headed set screw(Porsche call it a Pan-headed screw on page 39-138 of workshop manual);
Set of socket spanners as you have to remove the flex plate cover, 6 hexigan headed set bolts, not sure of the size as not accessible now car is back back on the ground;
Torque wrench with 1/2 inch drive head.
As my car is not fitted with a catholitic converter (more BHP) I was able to remove the cover without difficulty, but not sure about USA cars;
If you have to remove exhaust in way then this can be done with a set of socket spanners (metric) and a set of open ended ring spanners (metric);
You will need to put the car up on a hoist, ramps and supports stands to raise it sufficiently high enough off the ground to gain access.
When I had removed the ring gear/flex plate cover I used a vernier caliper to measure the distance from the back end of the flex plate clamp to the machined ring on the torque tube shaft where the tapered machining from the spline to the full diameter of the shaft give a distinct circumferencial line at the diameter change thereby allowing me to make an accurate measurement.
Release the clamp bolt and you will probably see the clamp move in the aft direction. Mine had 3.08 mm movement aft or preload, where the workshop manual say 0.3 + 0.2 mm preload at installation (old recommendation and surpassed by Technical Bulletin mention below).
I then checked the thrust play on the engine by using a magnetic dial indicator which I placed its bottom magnetic "v" section on the drive shaft and put the dial indicator point onto the ring gear and set it to zero. The thrust bearing clearance was 0.20 mm or 0.008 thousands of an inch when I move the ring gear with the aid of a large screw driver.
New bearing clearances are 0.110 to 0.312 mm to a maximum clearance of 0.4 mm, so mine was in good shape and well within manufactures tolerances.
When I changed the oil I inserted a swab into the oil sump via the drain hole to check for metal pieces from a fail thrust bearing; nothing in evidence.
With reference to Porsche Technical buylletin number 9203 dated the 5th May 1992 relating to all model year 928's with automatic transmission states that after the installation of the central tube, first tighten the the six (6) drive plate attaching bolts (flex plate) then tighten the clamping screw to 54-62 ft lbs and there is no mention of any preload.
As my unit was fully assembled I undertook the following procedure:
After extensive reading of posts to various bulletin board including Rennlist, I left my crankshaft in the aft position with its thrust flange butting up on the thrust bearing and then clamped up the clamping screw to the 62 ft lbs with no preload.
This will allow for an 0.008 thousands of an inch forward movement of the touque shaft before the engine thrust bearing takes any preload.
There has been reports that Porsche has verbally recommended to add 10% extra torque on the clamp screw to stop the clamp migration and other 928 Porsche owners have torqued up to say 64 ft lbs and added locktight to splines and clamp screw/bolt to halt this preload migration.
I did not do any locktight installation, however, I did spray the area with silver paint so that if the clamp migrates along the shaft in service I will be able to see (by seeing the dark ring between the clamp and my paint.
I will undertake a preload migration by looking through the plug hole at the bottom of the housing. This by inserting a small12 volt light soldered onto some cable (suitable insulated) and powered by the car battery or a spare battery and this will to allow me to push the light inside to illuminate the area (Previous suggestion of a 928 owner).
I propose to check for migration at each oil chance, however I will carry out more frequent inspection to see how all is going after this reset.
A full description of disassembling and assembling central tube is give in the workshop manual section 39 pages 137-143 which is to the initial preload of 0.3mm + 0.2mm.
I hope this is helpful and I believe that the above should be done as you will have to loosen off the clamp screw if you are to check the preload, so you should check all as above and re-clamp to be sure as some people have purchase 928 autos after a torque assembley rebuild and have sufferec failures.
Tails 1990 928 S4 Auto. Its a worry until you check the preload!
I have just finished checking the end thrust on the flexplate of my 1990 928 S4 Auto (15th Feb) and the following tools were required.
1 off 8mm hexigan headed by 1/2 inch drive socket to fit allen headed set screw(Porsche call it a Pan-headed screw on page 39-138 of workshop manual);
Set of socket spanners as you have to remove the flex plate cover, 6 hexigan headed set bolts, not sure of the size as not accessible now car is back back on the ground;
Torque wrench with 1/2 inch drive head.
As my car is not fitted with a catholitic converter (more BHP) I was able to remove the cover without difficulty, but not sure about USA cars;
If you have to remove exhaust in way then this can be done with a set of socket spanners (metric) and a set of open ended ring spanners (metric);
You will need to put the car up on a hoist, ramps and supports stands to raise it sufficiently high enough off the ground to gain access.
When I had removed the ring gear/flex plate cover I used a vernier caliper to measure the distance from the back end of the flex plate clamp to the machined ring on the torque tube shaft where the tapered machining from the spline to the full diameter of the shaft give a distinct circumferencial line at the diameter change thereby allowing me to make an accurate measurement.
Release the clamp bolt and you will probably see the clamp move in the aft direction. Mine had 3.08 mm movement aft or preload, where the workshop manual say 0.3 + 0.2 mm preload at installation (old recommendation and surpassed by Technical Bulletin mention below).
I then checked the thrust play on the engine by using a magnetic dial indicator which I placed its bottom magnetic "v" section on the drive shaft and put the dial indicator point onto the ring gear and set it to zero. The thrust bearing clearance was 0.20 mm or 0.008 thousands of an inch when I move the ring gear with the aid of a large screw driver.
New bearing clearances are 0.110 to 0.312 mm to a maximum clearance of 0.4 mm, so mine was in good shape and well within manufactures tolerances.
When I changed the oil I inserted a swab into the oil sump via the drain hole to check for metal pieces from a fail thrust bearing; nothing in evidence.
With reference to Porsche Technical buylletin number 9203 dated the 5th May 1992 relating to all model year 928's with automatic transmission states that after the installation of the central tube, first tighten the the six (6) drive plate attaching bolts (flex plate) then tighten the clamping screw to 54-62 ft lbs and there is no mention of any preload.
As my unit was fully assembled I undertook the following procedure:
After extensive reading of posts to various bulletin board including Rennlist, I left my crankshaft in the aft position with its thrust flange butting up on the thrust bearing and then clamped up the clamping screw to the 62 ft lbs with no preload.
This will allow for an 0.008 thousands of an inch forward movement of the touque shaft before the engine thrust bearing takes any preload.
There has been reports that Porsche has verbally recommended to add 10% extra torque on the clamp screw to stop the clamp migration and other 928 Porsche owners have torqued up to say 64 ft lbs and added locktight to splines and clamp screw/bolt to halt this preload migration.
I did not do any locktight installation, however, I did spray the area with silver paint so that if the clamp migrates along the shaft in service I will be able to see (by seeing the dark ring between the clamp and my paint.
I will undertake a preload migration by looking through the plug hole at the bottom of the housing. This by inserting a small12 volt light soldered onto some cable (suitable insulated) and powered by the car battery or a spare battery and this will to allow me to push the light inside to illuminate the area (Previous suggestion of a 928 owner).
I propose to check for migration at each oil chance, however I will carry out more frequent inspection to see how all is going after this reset.
A full description of disassembling and assembling central tube is give in the workshop manual section 39 pages 137-143 which is to the initial preload of 0.3mm + 0.2mm.
I hope this is helpful and I believe that the above should be done as you will have to loosen off the clamp screw if you are to check the preload, so you should check all as above and re-clamp to be sure as some people have purchase 928 autos after a torque assembley rebuild and have sufferec failures.
Tails 1990 928 S4 Auto. Its a worry until you check the preload!
