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MG MGB Technical - Banjo axle with 4 syncro box
|I am planning to fit a banjo axle with a 4 syncro overdrive box. This is a combination the factory never fitted.|
Due to the different combinations fitted by the factory there were 3 different lengths of prop shaft used. The tube axle with 4 syncro box (with and without OD) used a 78.9mm prop shaft This is what my car has at the moment. Working from the other combinations it seems that the when I change to a banjo axle I should be using a 76.2mm prop shaft. These were used on the cars that had a banjo axle with a 3 syncro non overdrive box.
It strikes me that the difference of 2.7mm is not alot given that the propshafts have a sliding joint to take up the length change as the axle rises and falls relative to the car.
Does anyone have any helpful comments on this or any relevant experience?
|*Centi*metres!! Unless you working on a Corgi or Dinky ...|
2.7cm is over an inch, which is quite a lot. My old V8 shaft has 2" of movement available whilst keeping the splines fully engaged, i.e. an inch either side of a notional central point. It all depends on where in that range the splines are when installed, and as you are using a longer shaft you have to be careful it doesn't 'bottom'. In theory your shaft is going to be at or near the most it can compress when installed with that combination, which isn't going to give much leeway for axle and engine/gearbox movement when under way, the axle in particular being not particularly well located in any direction unless you have the later factory anti-roll bar or trailing links.
|I did draw up a table of all the combinations of gearbox and axle...all I need to do is find it.|
I have a 4-sync 'box with a banjo axle in my car.
|Dave O'Neill 2|
|Paul, thanks for pointing that out. It does make rather a big difference!!|
Clearly I will not get away with 2.7cm.
Dave, I have such a table. If I had had my head in gear and realised it was cm not mm I would not have asked the question.
|I did this to my '67B. The stock driveshaft worked, but it was in its collapsed position all of the time. This put a load on the trans and rear. I finally bought a new driveshaft that was about 2" shorter and it works perfectly. RAY|
|One of the issues is the screw cap that goes from the drive shaft to the transmission flange. I added an L OD to my 67 GT and was told the later model drive shaft would work. Fount that I could only get about two threads on the cap. It keeps coming off. |
Found the correct one and the cap went on fine.
|I was just going through my records and when I replaced the driveshaft in'91 it was 30" long. RAY|
|30" is 76.2cm.|
|Thank you Paul, I didn't think of converting inches to metric when I posted. Having to work with both systems on a daily basis, I should have known better. RAY|
|Just to throw a spanner in the works here, where exactly, and how does one measure the propshaft length, open or closed?|
In the current Moss catalogue they show this:
AHH7488 is listed 3 sync, non o/d, banjo 28in
AHH7487 is listed 3 sync, o/d, banjo 29in
and 3 sync, non o/d, tube 29in
and all 4 sync, tube 31 1/8in
AHH7486 is listed 3 sync, o/d, tube 32in
So something wrong here as they list 7487 with 2 different lengths.
But in my very old MG International it shows:
AHH7488 is listed 3 sync, non o/d, banjo 30in
AHH7487 is listed 3 sync, o/d, banjo 31 1/8in
and 3 sync, non o/d, tube 31 1/8in
and all 4 sync, tube 31 1/8in
AHH7486 is listed for 3 sync, o/d, tube 32in
So again inconsistancy.
I also, like David need a prop for 4 synchro to banjo. So what length???
The lengths on the Brown & Gammons website, while in metric, match the MG International ones.
|Apart from the Moss figures they all seem to be fitted lengths. I've compared Hardy Spicer data, the Leyland Parts Catalogue and my V8 fitted and they all tie up.|
3-synch no OD, Banjo AHH 7488 30" (76.2cm)
3-synch OD, Banjo AHH 7487 31.125" (78.9cm)
3-synch no OD, Salisbury AHH 7487 31.125" (78.9cm)
3-synch OD, Salisbury AHH 7486 32" (81.3cm)
4-synch all, Salisbury, not V8 AHH 7487 31.125" (78.9cm)
The Moss figures seem to be a mixture of both, compressed for the 7488, fitted for the 7486, and two compressed and one fitted for the 7487!
Some listings have 'FFC' or 'Flange to Flange Closed' dimensions, but even that isn't clear, a drawing I have shows that as being the overall length of the prop-shaft when fully closed, but a friend who worked at Hardy Spicer on prop-shafts said that is incorrect, it is taken from the machined faces of the flange, not the rougher central section which stands proud of it, i.e. FFC2 in red below and not FFC as on the original. Certainly makes more sense.
For the V8 it's the same fitted length as the 4-synch Salisbury i.e. 31.125" but additionally that is quoted as 29.75" FFC.
From the published figures comparing Banjo and Salisbury for 3-synch boxes the Salisbury flange is obviously further back in the car. OTOH comparing 3-synch non-OD and 3-synch OD with the banjo, the flange on the latter seems to be further forward in the car. Comparing 3 synch non-OD, 3-synch OD, and 4-synch with the Salisbury, because the 3-synch non-OD, and 4-synch OD/non-OD have the same prop-shaft, it seems to me the flanges must be in much the same place on the car. Therefore to mate a 4-synch box to a banjo you need the shortest prop-shaft i.e. the 3-synch non-OD to Banjo shaft 7488. I think.
|I agree with Paul. I tried a 3 synchro non/od tube axle driveshaft, but I could barely get it in place. I purchased a new driveshaft, for a 3 synchro non/od trans and it fit perfectly between the banjo axle and 4 synchro trans. The original BMC part # is AHH 6481. This is from a dealer parts book circa 1965. RAY|
|Just out of interest I measured some gearboxes today. 4 syncro with O/D 32.5in, 4 synchro without overdrive 33ins, and 3 synchro without o/d 33.25, all approx.|
|Between where and where?|
|Bellhousing face to end of flange!|
This thread was discussed between 03/08/2010 and 12/08/2010
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