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F0355
South Africa
298 Posts |
 Posted - 05/12/2006 : 14:24:48
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Although a purist when it comes to my own cars, an article read some years back in the Octagon Car Club magazine talked of someone who had fitted (or was about to fit?) an overdrive to a P-Type gearbox which intrigued me somewhat - seemed like a good idea as we are not blessed with the beautiful and picturesque country lanes this side and speeds are of a slightly higher tempo as a result.
Any news welcome, thanks.
Peter Steyn
Johannesburg, RSA
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talbot
United Kingdom
718 Posts |
Posted - 05/12/2006 : 17:06:06
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There was a converted 'box with overdrive for sale on ebay a few months ago. I think Andy King at mgsparesandrestorations.com was selling it. Even if he wasn't it's worth contacting him - I've had excellent service and advice from him.
Jan T |
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mgptype
United Kingdom
709 Posts |
Posted - 05/12/2006 : 17:27:46
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Peter, Jan.
It was Andy King that was selling it on ebay, I think it was a J2 box and I have kept a picture of it as I was also intrigued with it.
Fred... |
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George Eagle
United Kingdom
3240 Posts |
Posted - 05/12/2006 : 18:15:13
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| There are several cars fitted with the overdrive units which I believe are the same as that fitted to the MGB's; one is the PB owned by John James. There is also one N type with overdrive, at the moment I cannot recall the name of the owner who installed it himself but no doubt it will come to mind the moment I log off! |
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Bob Stringfield
United Kingdom
854 Posts |
Posted - 05/12/2006 : 19:25:40
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Barrie Dean,143 St. Alban's Rd., Arnold, Notts.,NG5 6GT 0115 9208416. does MGB- type reversible overdrive conversions for the PA from ú450 - 950.
Has anyone driven an overdrive car?
One acknowledged practitioner told me that the PA doesn't have sufficient torque to pull a higher gear, but Barrie reckons to have happy customers. |
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George Eagle
United Kingdom
3240 Posts |
Posted - 05/12/2006 : 20:24:00
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| Thanks Bob - Barrie Dean is the man for overdrives! |
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F0355
South Africa
298 Posts |
Posted - 06/12/2006 : 09:32:45
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Thanks to all for the useful info, the mention of John James rings a bell and it was his conversion that was featured in the magazine if my memory is not failing me, I stand corrected of course.
As Bob asks, has anyone in this forum driven an overdrive conversion?
Peter Steyn
Johannesburg, RSA
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Bob L
Sweden
50 Posts |
Posted - 10/12/2006 : 23:02:17
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Purist or not, being a practical man I fitted an overdrive to my PA407 about 3 years ago. It made a big difference to motorway driving. I designed the installation, made the foundry models and did the machining. It is a bit tricky to incorporate the reverse gear shaft into the adaption unit and also to make it so that you can remove the overdrive without having to dismantle the complete box, but it is possible.
You should use the Laycock model LH (22%) as fitted to MGBs since there is not much space and that model has an inbuilt solonoid. The handbrake lever has to be moved 25mm along its shaft. I also used an MGB tail shaft (shortened) and I built in an interlock so that the overdrive can only be used in 3rd and 4th gears which gives the car a "6 speed box" with rather nice spacing between the gears. 100 km/h is now about 3100 rpm.
My PA is supercharged which is a necessity if you are to get full benifit of the overdrive.
This is not a project for the faint hearted but well worth it. |
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DickMorbey
United Kingdom
3677 Posts |
Posted - 11/12/2006 : 06:29:08
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Bob,
This must have been an interesting project! Have you considered writing up the steps you took and publishing them - maybe in the Triple-M yearbook, or the Bulletin? I am sure many members would be fascinated to hear how you carried out the conversion.
Regards
Dick Morbey, PA/B 0743 |
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Bill Putnam
USA
64 Posts |
Posted - 11/12/2006 : 15:16:46
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I'm curious why people feel it's worth the effort to fit an overdrive rather than install a taller diff ratio. If you have a blown engine, the taller diff can be handled quite easily with the added torque available, and typically the bottom gears with a stock diff ratio are quite low, so with a taller diff first gear can actually be of some use.
I'm not saying there's a wrong or right way to go about more comfortable high speed cruising, just curious why people consider it worth the effort. It would be interesting to see one fitted, there isn't much space in a J or P type cockpit even without an o/d unit.
Respectfully Curious,
Bill Putnam
J3488
bputnam@cityofmadison.com |
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F0355
South Africa
298 Posts |
Posted - 11/12/2006 : 20:06:55
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Thanks Bob L, as Dick suggests, it would make a great article.
Bill raises an interesting view. It would be interesting to see a comparison in ratios between the 2 schools of thought, and what rpm are being recorded against the varying ratios.
Thanks again.
Peter Steyn
Johannesburg, RSA
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George Eagle
United Kingdom
3240 Posts |
Posted - 11/12/2006 : 21:19:54
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I am with Bill on this one!
I use an 8:39 diff and slightly larger tyres on my blown NB resulting in about 19mph per 1000 revs in top. The car pulls very well on this ratio although I do have to use third more in slower traffic where there is a 30mph speed limit.
The supercharger allied to the extra torque of the 6 cyclinder makes for a very nice car to drive, cruising at the legal limit of 60mph is more relaxing.
I have looked briefly at a car with the overdrive fitted and from what I recall the unit does protrude into the passenger area with modifications required to shorten the transmission tunnel.
The T type owners appear to prefer fitting a modified Ford Sierra 5 speed box. Now would that fit into a Triple-M!!
George Eagle.
NA0960 |
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Bob L
Sweden
50 Posts |
Posted - 11/12/2006 : 22:31:07
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Perhaps I should explain that my PA project has been a development project over about 10 years. Prior to getting the idea of fitting an overdrive to the car I closed up the gear ratios in the original box as I found 1st and 2nd gears too low. The result was a PA box with ratios 3.38/1 2.01/1 1.36/1 and 1/1. To do this is another story in which I had to get a few gears cut but the result gave a car with a 2nd gear which gives good acceleration within the city limits.
Then I desired better highway cruising so I wrote a computer program to simulate the car. The resulting model had all the variables such as gear ratios, diff ratio, supercharging etc. I could then try all variations on the model. I found that changing the diff ratio would reasonably easily improve highway driving however since I had already raised 1st gear I was afraid it may be too high with an 8/39 diff. I also found that a number of closer ratios at the top end improved the performance because the torque to overcome the wind resistance increases with the square of the speed. Hence I started on the overdrive project. I have found that after fitting the overdrive the car performance agrees with the results from my computer simulation.
The ratios are now 3.38/1 2.01/1 1.36/1 1.115/1 1/1 0.82/1
I use my car in trials and competition rallies and I find 3rd (1.36/1) and 3rd overdrive (1.115/1) are good on narrow undulating roads as it is only a flick of the switch to change between them, you don't even have to declutch.
Changing the diff ratio is much simpler and would give improved highway driving.
The space the LH overdrive take up does not inconvenience me so much as it extends partly into the tunnel between the seats.
No promises however some day I might write about my PA project.
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John Reid
United Kingdom
704 Posts |
Posted - 12/12/2006 : 00:04:11
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Bob,
With my Yearbook Editor's hat on, I would be most interested in an article on your overdrive project and the theory behind it. No pressure!
Best wishes
John Reid |
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Bob Stringfield
United Kingdom
854 Posts |
Posted - 12/12/2006 : 10:35:54
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A good start might be articles which deal carefully with what alternative gearbox internals and diff. ratios are available at present, how useful they are, what they cost and who makes them.
Likewise a summary on this site of available historical sources on the cars.
There is a tendency for the technically switched - on / long-established member factions of an organisation to assume that such material is common knowledge, to the bewilderment of members who are neither of these. It might also avoid the irritation of trying to obtain information from the, happily few, established experts who aren't good at being contacted or replying.
The Pre-War Austin Seven Club has, very wisely, started a series of modern book-reviews of the older or 'standard' books on the cars, for the benefit of members who may not know them. We tend to talk blithely of 'Blower' 'Smith' or 'Green' for instance, and an up-to-date eye might give a better insight into their strengths and the deficiencies which have become apparent since their 'new-book' reviews, again in order to help a potential, present-day purchaser.
All of this might encourage new participants in the MMM movement, a policy being actively pursued by the VSCC, Veteran-Cycle and PWA7C, for instance, The MGCC might well be seen to be concentrating on moderns, judging by its publications.
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Peter Scott
United Kingdom
1240 Posts |
Posted - 12/12/2006 : 10:48:08
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quote:
Originally posted by Bob Stringfield
A good start might be articles which deal carefully with what alternative gearbox internals and diff. ratios are available at present, how useful they are, what they cost and who makes them.
Here here. As a newcomer to the world of Triple M I would love to see an article on gearbox ratios, diff ratios, how appropriate they are and in particular what gears are available and where from.
Peter, screaming second-gear, Scott |
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