A recent thread got me motivated to make a post out of this stuff. Later on I'll make it into a web page, with link in my sig. line. I hope what's here saves somebody some money.

It's rare, but your convertible top's hydraulic pump may stop working, sometimes blowing its 40 amp fuse. One solution is to send it off for a rebuild, this costing about $400.00. IMO, such an expense is seldom necessary. The problem may well be fixable at little or no cost by the car owner, or by a local shop.

What follows are suggestions on how to try for a low-cost fix. Some troubleshooting (but not much) can be done visually. More can be done with a continuity tester, but the most productive tests require a good multi-meter, one that can measure resistance as small as a fraction of 1 ohm.


First measurements (multi-meter required)

I'll assume that checks have been done to assure that voltage is really reaching the motor and that it will not run. The best first step is to open the pump's power connector and take three resistance measurements there: one between the two spades in the connector (0.4-0.6 ohms expected), and then between each spade and the motor case (open-circuit expected). This first step gives an indication of what to look for once we're inside the motor.

What we hope not to find is resistance between the spades of something close to, but outside of, the expected range of 0.4 to 0.6 omms ... say 0.2 ohms, or 1.0 ohms. This would indicate a possible short or open circuit within the armature, probably requiring a rewind. Otherwise, there's a good chance nothing serious is wrong. (For example, other than open-circuit between either spade and the motor case is probably a simple wiring fault.)


Separating motor from pump

Remove the pump from its mounting (well documented on the forum) being careful not to damage the two solenoid connectors. Remove the four fasteners which attach the pump to the motor (hex or torx depending on MY). Open the motor power connector (if it wasn't done above). Pull straight back to separate the motor from the pump. Some hydraulic fluid may escape. No hose connections need to me disturbed.

Rotate the pump (not the motor) manually. If the action is smooth, there's no reason to think anything is wrong with the pump. As far as I know no pump failures have been reported on the forum, and anyway the pump needs to run for only something like 10 hours (600 raise/lower top cycles) throughout its entire life; it should not need a rebuild. From here on, we're concerned only with the motor.


DIY or repair shop

One option is to take the motor to a local repair shop (Google "electric motor repair"). Such shops see simple motors like this one every day and with a little luck can provide a low-cost repair. Often it's just "servicing" ... cleaning, perhaps freeing a stuck brush, or repairing a solder joint. (As above, this motor needs to run for only 10 hours or so throughout its life; it should not need a new set of brushes.)

Or ... if you are comfortable poking around inside the motor, DIY is a good option to try.


DIY troubleshooting and repair

To open the motor, remove the two bolts securing the bell casing and pull it straight back. It will feel like you're pulling against a strong spring (actually it's the magnetic field created by permanent magnets in there). A quick tour inside the motor ...


The armature is the rotating shaft with 12 coils of wire around it. At one end of the armature is a split ring with 12 segments, called the commutator. There are 4 brushes in little rectangular housings that contact the commutator. Not visible here is a noise-suppression diode-pair (the only electronic bit in the whole motor).


If at any point in the following work you believe you've fixed the problem, skip the remaining steps and test the motor (see below).
To begin, we can greatly simplify things by insulating the armature from the brushes, and then testing components separately.


This shows the motor with insulators inserted between the brushes and the commutator. Whatever material you use to do this (shown are plastic collar staves) use something soft and slide them in very gently. With the components insulated in this way, perform the following tests.


Troubleshooting brush circuits (continuity tester or multi-meter):

- Check continuity between the "black wire" spade on power connector and the two brushes that are connected to black wires.
- Do the same for the "white wire" circuit.
- Check for open-circuit between the black and white spades on the connector. (Do this check a second time, swapping the test leads to reverse polarity. For all other measurements, polarity does not matter.)

There should be continuity throughout the black-wire and white-wire brush circuits. Between the connector spades should be open-circuit; otherwise, the noise-reducing diode pair has probably failed and must then be replaced.

Most faults found through these checks call for re-soldering. (It's hard to get at the underside of the component board, so solder from above. It does not have to be pretty.)


Troubleshooting the armature (multi-meter required):

- Check the resistance between any two commutator segments 180 degrees apart. Repeat for each such pair of sections working around the commutator
- Check resistance for two adjoining commutator segments. Repeat for each such pair.

The resistance values should be about the same for all 180-degree measurements and (though a different value) about the same for all adjoining-pair measurements. Don't worry about the actual values, just that they are all nearly the same for each test. If not, check for conductive dust accumulated in the slots between commutator segments, or a loose connection between a segment and coil of wire, or a dirty segment. (See cleaning technique below.)


Next, we'll check the armature and brushes as they work together. For this, remove two (one "white wire", one "black wire") of the 4 insulators that were put in place for the preceding tests.


This shows the motor with 2 of the 4 insulators (that were installed above) removed from the brushes.


Troubleshooting armature-to-brush contacts (multi-meter required):

- Connect your meter to the motor's power connector and watch the resistance readings (using lowest scale) as you slowly rotate the armature, stopping fully on each of the 12 commutator segments. All readings should be about the same.
- Repeat the measurements after replacing the two insulators which had been removed, and removing the other two.

If the resistance readings vary through the measurements, check that the brushes are able to move freely, pressing on the commutator in response to the springs pushing them inward. Gently clean (see below) around the brushes if needed to free them.

When done, remove the remaining two insulators installed above.


Testing motor operation

Replace the bell casing onto the motor. Hold on tight as you do this, since the magnetic field will pull the casing in strongly. Test the motor by applying power just for an instant to the connector. You should hear and feel it run (hold it firmly as you test). Reverse power polarity and repeat the test.


All done!

The steps given here can clear many common electric motor faults. An internet search on "how to repair electric motor" will turn up many links with more extensive troubleshooting methods.


_______________________________

A note on motor-cleaning technique:

If you've gotten the motor working without cleaning anything ... leave it alone. Otherwise, note that the brushes in electric motors create a conductive dust as they wear down. If troubleshooting indicates something needs cleaning, we want to remove the dust, being careful not to drive it into places where it can cause more trouble. Using a soft brush wetted with an agent like contact cleaner is a good approach. If you do use a spray cleaner, or compressed air, try to position things so that what comes loose will fall out of the motor, rather than disappearing into it. Holding the motor with the shaft horizontal and spraying horizontally at "low side" components is a good practice.

 

Looks like a 'HOW TO' candidate.

 

I see you've dropped a link into the "How To" sticky. Thanks, Norri

 

Greetings all. I thought I would post my issues. I bought a 2000 XK8, and it had some issues. The top worked at the dealer and went up and down a few times, then it only just closed. I got it home and went to check out the problem. I saw the motor under rear right fender through the trunk. I took off the bolts holding it in place and started to remove it. I did not see the wire connecting to the solenoids on top and damaged the connection to solenoid. I took it to ever shop in town and NOBODY could fix it. I looked into the solenoid RaPa and found nothing. It is a German company Rausch Pausch, that s even opening a plant in Auburn, AL. No contact info. The dealership would replace the whole motor for only $4500. I tried a lot of ways to contact RaPa, nothing worked! I was able to locate a used pump for around $200. The real problem was a leaking cylinder that slowly deposited the fluid under the rear seat. That is now fixed also. Now I am waiting for warm days to run the top down. What I learned: be very careful with the wires!!! Some parts are impossible to find so be careful. The dealership has the parts, and god bless them for that, but if its my money involved I will find used parts. So if anyone has a solenoid the want to sell me or buy a motor with a broken solenoid, let me know. Also switch the fluid to the green CHF, its better.

 

This one's for Norri, I guess.

So I sent someone to the "how to" sticky, but the link you placed there has been moved or removed. Unless I missed something.

Seems odd. How come?

 

Dennis, there was a bit of a glitch with the sticky, as a result it's been rolled back to an earlier saved copy.
I'll get it updated again.

 

Thanks for the great info. in this post.

Have recently purchased an XK8 in very good condition, however the major problem (I did know before the sale) was that the roof was inoperative due to the failed roof motor.

I am going to attempt the fix myself but after many forum searches I can't find the instructions / posts that you reference ("Remove the pump from its mounting (well documented on the forum) ).

Any pointers to this ?

Cheers,

john

 

John,

There is updated info on trouble-shooting the motor in the "motor repair" link below. Having been involved in a half-dozen or so of these I can report that the transient voltage suppressor discussed there should be viewed as the primary suspect, if the pump blows fuses and will not run.

Removing the pump from its mounting calls for removing two Torx fasteners and three electrical connectors and then sort of wiggling the pump forward until it clears the pedestal it had been mounted on. Be especially careful with the two electrical connectors on the solenoid valves (the cylindrical cans on top of the pump) as these are easy to damage if not treated with care.

 

Put another one down to a failed transient voltage suppressor (TVS).

The pump motor was blowing the 40 Amp fuse, and sure enough after removing the failed TVS, and connecting a new one, it was all working again ! Great idea to connect the TVS external to the motor, made the job a lot easier.

Thanks to the great advise, have managed to fix my major problem for $1 (well $10, min qty was 10). I still have 9 spare, PM me if you are in Australia and need one.

A couple of notes from my install.
- The MY 2003 I have, only has 2 power connectors to the pump unit (rather than 3 above). One for the motor, the other connects to both the solenoids.
- To remove the unit, undo the two Torx screws at front, but then you need to pull up with some force at the back, to remove the unit as it is connected with two cone shaped rubber connectors. Was paranoid about breaking the solenoids, so had my other hand protecting these
- wasn't sure how to test the motor. A 12V 2 Amp transformer wouldn't drive it. Ended up connecting some leads to a car battery briefly (< 1 sec)

Thanks again

 

Dennis, Thank you for the post. I have a 2000 and the motor stopped working while closing with the top almost latched. The 40 amp fuse is good and I can hear both relays clicking using the center console switch. I pulled the motor power connector and I get no voltage using the console switch in open or close. Any suggestions would be appreciated. As a note, I recently had the latch hydraulic hoses replaced by a local garage. The top has been working fine until today. Thanks, Harry

 

Hi, Harry

A couple of preliminary checks please:
- open the motor's power connector. Apply battery power directly to the motor just for an instant using test leads. Test both polarities. Does the motor run?
- open the connector for the two solenoids and measure the resistance of each solenoid. What are the measured values?

Since there has been work done in there recently, let's check that the connectors are seating fully, and inspect the wiring integrity at the top of each solenoid.

 

Hi Dennis, The motor does run on both polarities. The yellow solenoid connector has three female pins. They measure no resistance between them. My meter is not that accurate. It would not measure less than an ohm. The connectors on the solenoid appear fastened properly. And, thank you for your help... H

 

The solenoid connector ...
One of the pins connects to a black wire (ground). Between either of the other two pins and the ground pin we should see something on the order of 11 ohms. We don't need precision here; just want to be sure neither pin reads short or open circuit.

I want to be sure we have good components there before looking further. The fact that you had work done in there recently still seems like too much of a coincidence.

What position is the top in currently? Do you know about the procedure to close it manually if needed?

Sorry for the slow responses. Will be able to do better in a couple of days if you're still in trouble.

 

Thanks Dennis, All three pins read a short to each other, but not to ground. I am assuming the negative battery terminal is ground. I visually inspected the cable to the solenoids and it isn't pinched or damaged. I can't reach the top of the solenoids to disconnect the cable at that point. I have manually latched the top, but the rear windows are still down. H

 

Dennis, Got it! I saw from the wiring diagram that the Body Processor and Security module were involved in the operation, so I rebooted by removing the negative battery lead for several minutes. That got everything working again. Thank you again for all your support. H

 

Well done, Harry! You encountered the case where the system gets "confused". Not uncommon.

I was beginning to fear that one or more of the micro-switches in the latch area had been disturbed during the hose replacement. Glad we don't have to go there.


(BTW, on the solenoid measurement ... with the connector open everything is floating, so open-circuit to chassis ground is expected on all pins. I think your meter may have prevented you from seeing the true resistance of the solenoids, about 11 ohms.)

 

hi killa,
can the TVS be purchased from jaycar or any other MELBOURNE stores?
im in Melbourne, Australia.
desperately keen to resolve my motor problem. Thanks!