Dear Unregistered, the permission changes should be complete, if you notice any issues with your access on the site please let us know and we will check into it.
Hey Unregistered it seems that you haven't posted a message in our forums yet. Please join in on the fun and post a message!
Dear Unregistered,
We've noticed that you are not yet a member of our Cayman Insiders group. This group provides a number of additional value-add services via this website for a very low annual fee. You can find out more about this group here:
Insider Announcement
You can join the Cayman Insiders Group here:
Insider Enrollment Form
We hope to see you "Inside" soon!
Your Donation Will Be Used To Pay For our ever increasing bandwidth costs, our hosting Service, domain registration, software licensing fees, maintenance costs and product evaluations Only!
Please enter your donation amount above, and then click on the donate button below.
Can someone explain preload & backlash? How is it measured?
I am hoping to install a TBD myself this summer. I see a lot of talk about preload and backlash; however, it is not covered hardly at all in the article section. Could we make this a thread about specifically what preload and backlash are along with how to measure for them and adjust to factory spec? I would really appreciate this information, as Im sure others would too. Thanks.
LSD - Limited Slip Differential
A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.
To see the installation of a LSD style unit Click Here -> Article Forthcoming Stay Tuned
__________________
06 Cayman S
Seal Gray, Black Full Leather, Sport seats heated, Sport wheel, Sport tips, Bose surround, V1, K40 laser jammer, 18% tint, 19" Carrera S wheels.
Other notables of the family: 996 GT3, '71 914, '73 914, '71 914-6 2.7L, 955S, (3)993's, 964, 944, 356, 06 Elise, E46 M3, 04 S4, 04 Mini CS, 06 A8, 02 GTi 337 Stg 3+, 02 TT, various race cars.
The Porsche Service Manual devotes 17 pages to this topic (Section 39 08 15 Adjusting the drive set). I'm not going to transcribe it here. I suggest you get a copy of the Service Manual and study it before you tackle this job.
The procedure uses 12 special tools. Some of these are common, like a dial gauge holder, but others are special precision tools that may be hard to obtain.
Hmm, in other words this really is not a DIY application like the article section teases. We know our way around the garage...and my dad has been tearing apart and rebuilding Porsche's since the 70's, but this sounds more difficult than the TBD article suggests.
LSD - Limited Slip Differential
A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.
To see the installation of a LSD style unit Click Here -> Article Forthcoming Stay Tuned
__________________
06 Cayman S
Seal Gray, Black Full Leather, Sport seats heated, Sport wheel, Sport tips, Bose surround, V1, K40 laser jammer, 18% tint, 19" Carrera S wheels.
Other notables of the family: 996 GT3, '71 914, '73 914, '71 914-6 2.7L, 955S, (3)993's, 964, 944, 356, 06 Elise, E46 M3, 04 S4, 04 Mini CS, 06 A8, 02 GTi 337 Stg 3+, 02 TT, various race cars.
The Porsche procedure may be overkill, someone who is a competant Porsche mechanic posted some pics of his method of doing the job in the topic thread about the TBD article several months back as I recall, you might check those out. I don't recall his procedures being that complicated that it required so many specialized tools.
LSD - Limited Slip Differential
A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.
To see the installation of a LSD style unit Click Here -> Article Forthcoming Stay Tuned
I am hoping to install a TBD myself this summer. I see a lot of talk about preload and backlash; however, it is not covered hardly at all in the article section. Could we make this a thread about specifically what preload and backlash are along with how to measure for them and adjust to factory spec? I would really appreciate this information, as Im sure others would too. Thanks.
Preload is the amount of force pressing the tapered roller bearings, mounted on the ends of the differential, together. Preload is used to pre-compensate for wear in the bearings (prevents the bearings from getting loose as they wear), and is defined as the amount of rotational drag induced by the load on the bearings. It is measured as the amount of torque required to turn the diff slowly. For best results, preload should be measured without the seals, and either before the pinion is installed or before the ring gear is installed on the differential.
Backlash is the amount of space between the teeth of the pinion gear and the ring gear. Measured as the amount of rotation of the differential, forward and backward, with the pinion locked in place. In actuality, this is really an angular measurement, but everyone "converts" it (knowingly or not) into a linear measurement by measuring the amount of distance a specified-length pointer will move (angle x radius = circumferential distance, but since the distances are small relative the pointer length, it is simply treated as tangential distance).
They can both be measured with the tranny in the car, but it would take a different setup and technique than specified in the workshop manual, which was written expecting the tranny to be on a bench. Also, preload and backlash are adjusted by changing the shims that space the outer roller bearing races that are fitted to the tranny housing and diff cover.
Preload is the amount of force pressing the tapered roller bearings, mounted on the ends of the differential, together. Preload is used to pre-compensate for wear in the bearings (prevents the bearings from getting loose as they wear), and is defined as the amount of rotational drag induced by the load on the bearings.
Bill - slight clarification. Preload is used to *prevent* wear, rather than just compensate for it - which it does as well. At the same time, it helps solidify the assembly of which the bearing(s) is part of. Too tight will wear the bearing too fast, as well as increase drag. Too loose will also wear the bearing too fast and may decrease drag at first until the bearing goes 'kaplooie'.
Preload is the amount of force pressing the tapered roller bearings, mounted on the ends of the differential, together. Preload is used to pre-compensate for wear in the bearings (prevents the bearings from getting loose as they wear), and is defined as the amount of rotational drag induced by the load on the bearings. It is measured as the amount of torque required to turn the diff slowly. For best results, preload should be measured without the seals, and either before the pinion is installed or before the ring gear is installed on the differential.
Backlash is the amount of space between the teeth of the pinion gear and the ring gear. Measured as the amount of rotation of the differential, forward and backward, with the pinion locked in place. In actuality, this is really an angular measurement, but everyone "converts" it (knowingly or not) into a linear measurement by measuring the amount of distance a specified-length pointer will move (angle x radius = circumferential distance, but since the distances are small relative the pointer length, it is simply treated as tangential distance).
They can both be measured with the tranny in the car, but it would take a different setup and technique than specified in the workshop manual, which was written expecting the tranny to be on a bench. Also, preload and backlash are adjusted by changing the shims that space the outer roller bearing races that are fitted to the tranny housing and diff cover.
So, if someone told you, "I will install your TBD and make sure the preload and backlash are properly set for around $400. You don't need to pull the tranny and pay $1500 to do this correctly. That is just the way the manual says to do it because they are not as concerned about how much it costs you. There is no benefit to pulling the tranny in terms of long term reliability."
What would you think?
LSD - Limited Slip Differential
A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.
To see the installation of a LSD style unit Click Here -> Article Forthcoming Stay Tuned
The Porsche procedure may be overkill, someone who is a competant Porsche mechanic posted some pics of his method of doing the job in the topic thread about the TBD article several months back as I recall, you might check those out. I don't recall his procedures being that complicated that it required so many specialized tools.
I have looked thru the articles several times and could not find something directly addressing how to go about measuring preload/backlash with the tranny in the car. Obviously, I see that it can be done without removing the transmission, but I just want to see the steps and make sure I know what I'm even looking for w/ regards to preload/backlash.
Do you have the link to the thread and pictures you are talking about?
ARTICLES
__________________
06 Cayman S
Seal Gray, Black Full Leather, Sport seats heated, Sport wheel, Sport tips, Bose surround, V1, K40 laser jammer, 18% tint, 19" Carrera S wheels.
Other notables of the family: 996 GT3, '71 914, '73 914, '71 914-6 2.7L, 955S, (3)993's, 964, 944, 356, 06 Elise, E46 M3, 04 S4, 04 Mini CS, 06 A8, 02 GTi 337 Stg 3+, 02 TT, various race cars.
