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Roof Transmission Replacement


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Hi

Have a problem with a '97 986. It seems a typical problem but is maybe slightly different:

The transmission units started "knocking" when the clamshell closed. On inspection one of the red sockets had broken so it was replaced. Next time it was tried and the same knocking occurred - looked again and this time the V-arm had twisted!! on the same side (right), so bought a new one. Tried again and the same thing happened - another twisted V-arm. Now decided to get the big mallet out and re-shape the arm. Looked again and noticed that the 3 bolt/lugs holding the transmsision unit in place on the right were bent upwards resulting in the transmission canting over a few degrees and causing the clamshell (and roof) to be out of sync. I Persuaded the lugs back to level with a gentle tap on the wood end of a hammer and started to run the system without the push-rods in place to prevent any more disfigurement. I noticed that the left side transmission was stopping right at the end of the "roof close" but the right side continued for some reason (this being the cause of the damage). The left side seems to be disengaging the worm drive (you can see it when looking directly at the transmission that the end of the worm is pulling inside the transmission and disengaging. Microswitch on the clamshell is working OK. Transmission cables seem fine

My conclusion is that the left side transmission unit is Bu*&^$%d and so I am going to replace - unless anyone has any ideas?

The main question though is can I replace the early transmission units (with moon gears) with later units that may be more effective? And if so is there anything else than needs to be done or changed?

Cheers

Mat

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Hi

Have a problem with a '97 986. It seems a typical problem but is maybe slightly different:

The transmission units started "knocking" when the clamshell closed. On inspection one of the red sockets had broken so it was replaced. Next time it was tried and the same knocking occurred - looked again and this time the V-arm had twisted!! on the same side (right), so bought a new one. Tried again and the same thing happened - another twisted V-arm. Now decided to get the big mallet out and re-shape the arm. Looked again and noticed that the 3 bolt/lugs holding the transmsision unit in place on the right were bent upwards resulting in the transmission canting over a few degrees and causing the clamshell (and roof) to be out of sync. I Persuaded the lugs back to level with a gentle tap on the wood end of a hammer and started to run the system without the push-rods in place to prevent any more disfigurement. I noticed that the left side transmission was stopping right at the end of the "roof close" but the right side continued for some reason (this being the cause of the damage). The left side seems to be disengaging the worm drive (you can see it when looking directly at the transmission that the end of the worm is pulling inside the transmission and disengaging. Microswitch on the clamshell is working OK. Transmission cables seem fine

My conclusion is that the left side transmission unit is Bu*&^$%d and so I am going to replace - unless anyone has any ideas?

The main question though is can I replace the early transmission units (with moon gears) with later units that may be more effective? And if so is there anything else than needs to be done or changed?

Cheers

Mat

Mat:

If the transmission on only one side is "knocking" then your transmissions are not synchronized properly and must be reset. Because both transmissions are driven by only one electric motor, when the motor is spinning the cables that turn the worm gear inside the transmissions, it is doing so for both of them (unless one of your cables is frayed or broken inside the black plastic outer sheath or one of the cable is not engaging the worm gear properly).

The '97's mounting points on the rear quarter panel were not reinforced as those on later Boxsters were, but they can be welded and reinforced if necessary.

You can definitely replace the "A version" transmissions (those with the half-moon gear) with the "B Version" transmissions (Stehle Brand) but you must also replace the mounting studs with the "B Version" mounting studs. Take a look at page 21 of the Part II PDF for the difference between the two types of mounting studs, here: http://sites.google.com/site/mikefocke2/installinga'03-'04glasstopandframeona'97

After that, your transmissions will have to be synchronized. You can then operate the top with the original set up of the B-Pillar Microswitch and Black Lever Microswitch.

If you are feeling ambitious, you can also re-wire the system to eliminate those two external microswitches and make use of the two microswitches found inside the driver's side (left side) "A Version" transmission. Part III of the PDF covers the necessary electrical modifications if you feel up to it.

Regards, Maurice.

Edited by 1schoir
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Thanks Maurice

I synched the units (several times) but still one contiunued running whilst the other seemed to disengage from the worm drive.

You linked guide is fantastic - thanks very much.

I think that as the car is now 13yrs old (wow that went fast) I should really update the old units for newer and more relaible units and so I intend to follow your lead and install B units plus a glass roof. I'll start to collect the bits over the next few weeks and keep you updated.

Is there anything you recall that isnt in the guide that would help? I cant see there is as the guide is pretty comprehensive but htought I'd ask away :)

Cheers

Mat

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Thanks Maurice

I synched the units (several times) but still one contiunued running whilst the other seemed to disengage from the worm drive.

You linked guide is fantastic - thanks very much.

I think that as the car is now 13yrs old (wow that went fast) I should really update the old units for newer and more relaible units and so I intend to follow your lead and install B units plus a glass roof. I'll start to collect the bits over the next few weeks and keep you updated.

Is there anything you recall that isnt in the guide that would help? I cant see there is as the guide is pretty comprehensive but htought I'd ask away :)

Cheers

Mat

Mat:

Definitely a good idea to replace the old transmissions with B Version transmissions as they are more reliable and less prone to act up. The A Version system can be reliable but requires more attention and has more parts that can be troublesome. For example, the 360 degree gear in the B Version never goes past the last tooth.

If you still have the original cables installed you may be having the most common problem that the early Boxsters' tops suffer from. The inner (speedometer type) cable may be effectively "retracting" inside the vinyl outer cable (on the side that is not driving the worm gear) and thereby not engaging in the square female drive that is on the side of the electric motor. The outer vinyl sheath has a tendency to stretch on the early cables and cause the problem. If your cables have a smooth surface, you have the old style units. If there is a type of a crosshatch pattern on them, you have the new cables and that is much less likely to be the problem.

To double check the operation on that end (the electric motor end), pull out the cable from the side of the electric motor and see if you have about 3/4 of an inch of the inner steel cable protruding. If it's not, you will have to cut away a small length of the outer cable after removing the metal ferrule that is on the end such that you end up with 3/4 of an inch.

Another area to check in your case is the area where the cable drives the worm gear. Check to make sure that the flat black plate that covers the underside of the transmission is fastened securely around the perimeter of the transmission, especially in that little area around the worm gear. If that little area flexes or is cracked, it will end up not driving the worm gear, etc...

Here is a photo of the area, with the red arrows pointing to the screws to be tightened. The white arrow shows a BMW emblem on that part for some reason.smile.gif

post-6627-057985500 1278426405_thumb.jpg

Regards, Maurice.

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Hi Maurice

Well it WAS the screws holding the plastic rear in place that was making the worm disengage as you pointed out. I have tightened everything up now but as I had already bought a new B version transmission, I installed those as per your pdf inlcuding the rewire.

Upon trialling, the hood, it moved in one direction (cant remember which way - no roof installed yet) but after travelling to it's end stop (microswitch must have worked) it will not now operate in either direction. Any ideas muchly appreciated. Best regards Mat

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Hi Maurice

Well it WAS the screws holding the plastic rear in place that was making the worm disengage as you pointed out. I have tightened everything up now but as I had already bought a new B version transmission, I installed those as per your pdf inlcuding the rewire.

Upon trialling, the hood, it moved in one direction (cant remember which way - no roof installed yet) but after travelling to it's end stop (microswitch must have worked) it will not now operate in either direction. Any ideas muchly appreciated. Best regards Mat

Mat:

Did you replace the convertible top module (double relay) with the B Version double relay?

If not, the old relay is looking for the signal from the B-Pillar microswitch to reverse direction and if you have re-wired everything, it won't find that signal.

Also, make sure you double check the two fuses in the fuse panel that supply power to the electric motor and to the double relay.

Regards, Maurice.

Edited by 1schoir
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Hi

I did find one problem - I wired the connector to the transmission incorrectly - I followed the colours (brown and brown/red) from the original setup rather than following the instructions! Anyway, having rectified that, the issue is that the units work only on the OPEN roof operation. When the microswitch engages in the transmission, the motor switches off. However, once opened (I have no roof installed so am assuming it is open based on the microswitch) the close button then will not operate the motor (the close button also does nothing before the microswitch turns the motor off). Any ideas welcome. Cheers Mat

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