| Author |
Message |
    
Bill Vatter
| | Posted on Thursday, 04 October, 2001 - 09:59: |    |
I have just completed renewing the clutch on my friend’s Silver Wraith. The following comments are provided referenced to applicable sections of the factory workshop manual. (Headings in all-capitals correspond to manual sub sections, and lower case roman numerals correspond to same-numbered paragraphs.) With the workshop manual to read with my notes the following comments should be easily understood. Without the manual this is probably gibberish. For those with Bentley VI and R types, this work is virtually the same, and while I have not seen the corresponding Bentley workshop manual for this job, I would assume it is very similar.
Before starting, remove the spark plugs. It will then be easy to turn the flywheel by hand while you are laying under the car.
TO EXPOSE THE GEARBOX AND CLUTCH CASING
(i) The coolant need not be drained if the standard under-seat heater is the only one fitted.
(ii) The under-seat heater need not be disturbed; however I have not seen an optional under-dash heater, which may need to have the hoses removed as stated in the manual.
(iii) The right side floorboard needs to be removed to access the gear change mechanism. The center floorboard needs to be disconnected from the firewall where it is attached by four 1/4 inch BSF screws so that the front of the floorboard may be raised sufficiently to gain access to the uppermost gearbox-to-clutch-housing nuts. Steel-body cars may have a different floorboard arrangement, but the objective is the same: Access the gear-change mechanism and raise the front of the floor about 2 inches to get at the top gearbox attachment nuts.
TO REMOVE THE GEARBOX
(i) The oil need not be drained from the gearbox unless gearbox disassembly is intended, and then only because it is easier to drain the gearbox while it is yet in the car.
(vi) After removing the seven nuts holding the torque reaction bracket to the rear of the gearbox, you will find that it won’t come out due to insufficient clearance. Leave it loose in place until the weight-holding gearbox mount is removed, and then lower the engine and attached gearbox as a unit until sufficient clearance is available to remove the torque bracket.
(xi) It is easier to remove the forward universal joint if you wait until the engine is supported on a jack and the cross-member supporting the gearbox is removed in paragraph (xvi).
(xii) (a) It is not necessary to remove the top cover from the gearbox. Incidentally, it is not possible remove said cover unless the center floor is completely removed, so not removing the top cover is preferred. There are two reasons to remove the gearbox top cover, but neither is essential: (1) see the engagement of the selector shaft with the jaws in the selector rods, and two, change in and out of gear during the procedure, which is not necessary. If you don’t remove the top cover, the gearbox must be in neutral throughout the work. This will also to allow the selector arm to be removed and replaced from/to the gearbox.
(xv) Use a good quality gear type jack such as provided with the car by the factory. A hydraulic jack will leak down over time causing problems, and you will want to be able to raise and lower the engine precisely and in small increments to remove the torque bracket and to refit the gearbox.
(xvi) Once you complete this step it is time to remove the forward universal joint. Then lower the engine and remove the torque bracket that was unfastened in step (vi). Don’t lower it more than necessary as lowering puts stress on the exhaust manifolds and forces the clutch operating levers and rods away from correct alignment.
(xvii) The easiest way to remove the top gearbox-to-clutch cover attachment bolts is while laying on your back under the gearbox, head forward and under the clutch. Reach around each side of the gearbox to work the top nuts with both hands while the floor is held up by a suitable scrap of wood. When the all nuts but one of the lower ones are all removed, support the gearbox with a transmission jack. If the gearbox falls out uncontrolled while you are under it, you will catch a good bruise and maybe break a couple of teeth. Also, the levering action of a falling gearbox on the driven disc will likely bend it beyond repair. A transmission jack cost me $75 (US) but this single use fully justified the expense. Holding the gearbox from above with ropes as described in the workshop manual is only possible if the floor is completely removed, and I can imagine this would be quite a strain on the rope-holder, especially during reassembly.
TO REMOVE THE CLUTCH FROM THE FLYWHEEL
(iv) The mentioned spacers (3) must be used, but the thickness required will vary depending on the amount of wear to the driven disc. I used 1/8 inch thick aluminum and bent it in a “U” shape to aid in inserting the spacer while removing the clutch cover bolts. (This driven disc was very worn. A less-worn disk might need 3/16 thick spacers. Anyway, if you use the thickest material that will slip into place you will be right.) 1/4 inch thick spacers were needed to reinstall the clutch with a relined driven disc. For this I used Large washers adding up to 1/4 inch and passed a string through all so that on tightening up the bolts I avoided loosing washers inside the pressure plate assembly.
It is wise to resurface the friction plate that is bolted to the flywheel, as well as the pressure plate. A reputable clutch shop can reline the driven disc and resurface the steel plates. The shop I went to said the clutch is rather like a Ford, and they had no problem fitting new lining from materials on hand. Altogether it was $50 (US) for relining the driven disc and resurfacing the pressure plate and friction disc. This is far less than buying replacement components from Rolls-Royce.
TO REASSEMBLE THE CLUTCH TO THE FLYWHEEL AND CHECKING THE OIL FEED TO THE CLUTCH RELEASE BEARING
(iv) I used washers held together by string for spacers. The 1/4 inch thickness is rather critical. Anything less and you won’t get the clutch assembly in, and much more and you will have difficulty getting the spacers out after bolting the pressure plate to the flywheel.
(v) No doubt you won’t have the referenced splined aligning tool. The tool is helpful, but splines are unnecessary. I made my own tool by selecting sockets from my toolbox that matched the inside diameter of the spigot bearing and the inside diameter of the driven disc. I held them together in concentric manner using a 3/8 inch carriage bolt. I have heard that a dowel turned on a lathe will also work well.
TO REFIT THE GEARBOX
(ii) There is no need to put the gearbox into gear. Leave it in neutral, and align the splines by turning the flywheel. It is possible to peer into the clutch from below to see the spline engagement while you move the flywheel to effect proper alignment.
(iii) Forget the rope; use your transmission jack. After maneuvering the first motion shaft through the release bearing, the first engagement is splined shaft to the driven disc. Look up from below to see the engagement and adjust the position of the gearbox with the transmission jack. The second engagement is clutch cover studs through the stud holes in the gerabox front. The third engagement is the pilot shaft to the spigot bearing. This cannot be seen, only felt, and it is difficult to feel while pushing on this 100 lb. gearbox, (which is beginning to feel like 500 lbs about now if you didn’t get a transmission jack). I had some difficulty getting the pilot shaft to go into the spigot bearing. To help, I backed out a stud from the clutch cover about 1/4 inch. (You can grab the stud to turn it with your needle-nosed vice-grip pliers.) It then protruded through the gearbox hole sufficient to get a nut started. After snugging up a nut on this stud, I jiggled the gearbox from behind until the pilot shaft popped into the spigot bearing. Then before pushing it home, use your vise grips to return the stud to its proper location. Actually it is easiest to push the gearbox home by tightening a couple of nuts evenly on opposite studs.
(iv) First get the torque bracket in position above the rear of the gearbox. You will need to lower the engine to get it up there, just like when you removed it. Then, raise the engine back up to correct position, insert the torque reaction rubbers and bolt the torque bracket to the back of the gearbox. (If you don’t put the rubbers in before you bolt up the bracket, you may have trouble getting them in later.) Finally, connect the front universal joint before you put the cross member in place so as to have more room to work on the universal joint.
(vii) No need to put the gearbox back in neutral as it never left neutral.
(viii) You can’t see the engagement of the selector shaft with the selector rod jaws, so you have to feel it. For reference, when properly engaged, the dogs on the right end of the shaft are virtually vertical, corresponding to neutral on the gear-change gate. Move it in and out through the three positions (R, 1-2, and 3-4) and noting that rotation is resisted in both directions by engagement with the selector rod jaws, and you will be confident you have got it properly engaged. Anyway, it won’t go together wrong and still line up with the gear change selector in neutral, so that is your final test of this step.
(xx) Don’t forget to adjust the clutch before refitting the undershields or before fitting the right floor board. It can be adjusted from below or above but it is easier to get at from above.
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Overall comment:
Marty said he was charged four hours labor to remove the gearbox from his Mk VI Bentley. As he said, that was a very fair price. A reputable shop in the US that specializes in the early post-war cars quoted an aproximate labor charge of 12 hours for this job. This clutch job took me about eight hours apart and eight back together. This was slower than a professional shop because I took time to make sure it was going right, time to tell stories with the car owner, and some friendly visiting with the car owners wife, all of which are essential to a job well done when it is being done among friends. |
Martin Cutler
| | Posted on Friday, 05 October, 2001 - 11:54: | |
Bravo Bill! Well done. |
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