|Posted on Tuesday, 07 August, 2001 - 11:40: |
Had the misfortune to blow up the gearbox on the MK VI last night. During a hill start, a large bang occured, and the forward motion abruptly stopped. I got the car moving again, however, the gearbox kept jamming. I can get all gears except for 3rd.
I have not had a chance to take the inspection covers off yet, but I fear the worst. My mate Rob Hurren has a spare manual gearbox out of an R Type, are they the same? This gearbox is down at John Vawsers, so I need to get down and see John and pick it up asap. I have heard that the splines can give out? Any info appreciated before I try and drop this box out over the weekend. I don't think I have stripped teeth off first, as this box was nice and quiet in first, and I can still drive the car in 1st, just not 3rd.
Please, oh please tell me this is a one in a million thing!
|Posted on Wednesday, 15 August, 2001 - 12:21: |
First I would drain off the oil and see what comes out. If a lot of small pieces, acquire the R-type gear box asap as yours is toast. If no parts come out, perhaps you have a problem with adjustment of the shifting mechanism, i.e., not properly engaging the gears. When youran it after the "failure" did it make terrible noises or was it as quiet as before? I would not move it at all until the nature of the failure is determined. This gearbox is a very sturdy unit, and a failure like you describe seems unusual to me.
|Posted on Saturday, 18 August, 2001 - 20:44: |
Hi guys and girls,
Ok, the gearbox is out and in pieces. The spacer shim behind the 3rd gear syncro broke. As it failed, a part of it fell down and jammed the gears. Apart from the broken shim, there is no other damage. One of the 4th gear teeth has a large chip but by the looks of it that has been there for a long time. I will not worry about this. The first gear is in surprisingly good condition. I have seen some boxes where half the teeth where damaged/missing. This box was always quiet in first, which seemed to say the original owner had used the second gear synchro when going into first, instead of shoving it in from neutral. In this case, thank goodness for the dreaded previous owner!
I have done a bit of research. The shim that broke went through a few changes in the production life of this gearbox. First change was to increase it's thickness by 50 thou, and chamfer the splines on the shaft. The second change was to increase its thickness by ANOTHER 50 thou, which took in machining a wider groove in the shaft, and also modifying the 3rd gear syncho. Obviously this was seen as a weakness in the box!!!!
I am now in a quandry. The car has done 106,000 miles, (6000 miles under my ownership). The book says the end float on the shaft should be 2 thou. Mine was 12 thou. The extra 10 thou is waht would have loaded up on the shim. I will rectify the end float, but am unsure whether to upgrade the recalcitrant shim or not. Replacing it with the same shim means no machining to the shaft, and it will probably last another 50 years and 100,000 miles. Going to the second modification on the shim means machining the shaft, which may introduce stresses to the shaft. At this time I am leaning towards going with the original setup, whilst retifying the end float and replacing the bearings.
Any thoughts on this course of action would be greatly accepted.
My MG Magnette has now done in excess of 200,000 miles, and when I rebuilt the engine recently, I pulled the gearbox apart just out of curiosity. The thing was perfect! Put the covers back on and left it alone. Has done another 8000 miles since then! Pity the diff isn't as quiet!
|Posted on Saturday, 18 August, 2001 - 20:47: |
Just to answer your questions, I retrieved the R type box from John Vawser, so will return this to it's rightful owner. The box was still quiet to drive after the mishap, just no 3rd, and nothing came out with the oil. The chunk of shim was too heavy to move from the bottom of the box.
|Posted on Monday, 27 August, 2001 - 17:23: |
I have gone with the original width spacer, as this involved no machining work on the shaft. I have replaced the bearings and eliminated the end float on the shaft, and the gearbox feels fine. I will take it for a good run before the weekend, as I have 2 weddings to do this weekend. Lets hope I never have to see the inside of my gearbox again!
|Posted on Friday, 31 August, 2001 - 19:59: |
Martin, can you provide us all some comments from your experience at removing/replacing the gearbox? For example, what steps were difficult and how did you deal with that? or what did the factory forget to tell us in the service instructions?
|Posted on Monday, 03 September, 2001 - 10:55: |
Have to admit I piked out on this, and got somebody to do it for me. I have had a go at it before, and got all the servo gear disconnected, etc. The guy who did the work charged me 4 hours labour to remove the box, which is pretty good in my opinion. I had a deadline to meet as I did 2 weddings on the weekend. If it wasn't for the weddings, I would have done it myself. As for disassembling the gearbox, that is way past my DIY skills! I suppose you get used to it. I can pull an MG Magnette motor and gearbox out in a day now, and splitting the cases on my 750 Laverda is like second nature, but the Bentley was a bit daunting. Added to the problem was you can get the engine /gearbox out in one piece from above with a gantry and block and tackle on the MG, but with the Bentley, the gearbox needs to come out from underneath, so you really need a hoist. The gearbox itself looks fairly straight forward, but I hope not to see the inside again!
When I put the car together, the body was off the chassis, so a lot easier to put the gearbox in place when you can get to everything from above. Without access to a hoist, I would get somebody else to do it for you. If they charge you more than 4 hours they don't know what they are doing.
|Posted on Tuesday, 04 September, 2001 - 23:30: |
Mk VI-R-Type Master Cylinder and Brushes.
The generator brushes for your car are Lucas USB105, available from any autoelectrician for a trivial price. Try Lucas in Falcon St at Crows Nest, Sydney.
The brake master cylinder overhaul kit is a Repco PBR K4 (including a new piston) or K4X without piston. This are the same kits as for a fork lift truck !! and they are available at any brake specialist, like Better Brakes.
I hope this is useful.
|Posted on Thursday, 06 September, 2001 - 12:29: |