| Author |
 Topic  |
|
Hornet
United Kingdom
382 Posts |
 Posted - 10/05/2014 : 23:07:25
|
| first gear would have to remain 15/38 as the reverse gear has also to mesh . the constant of the set of gears is 53. the spur gears are 10 dp . the only ratio you can change is second gear ,unless you change the constant mesh third as a pair . the teeth on second gear are machined to form dogs to lock to third to drive it ( second gear in the photo has 21 teeth and 21 dogs ) . on some boxes these are different number of teeth to the number of drive dogs . |
 |
|
|
Oz34
United Kingdom
2542 Posts |
Posted - 10/05/2014 : 23:29:49
|
Are you aware Neil that Mike did do a batch of close ratio gear sets some years ago so basically it should only (lovely word that!) be a question of another batch, He says hopefully.
Dave |
|
|
|
John Reid
United Kingdom
704 Posts |
Posted - 11/05/2014 : 01:15:03
|
The batches of close ratio gears which Sports and Vintage produced have teeth numbers:
Input: 24 28 32 38
Layshaft: 29 25 21 15
The spur gears are the same as PB.
This gives ratios of 3.08 1.84 1.35 1
Bill Bennett also arranged a small batch of new spur gears to PB ratio, with the layshaft modified to take metric roller bearings.
I seem to remember there is an article somewhere (Yearbook?) about the various gear ratios used over the years , with their respective merits.
John R
|
|
|
|
BobRichards RIP
United Kingdom
238 Posts |
Posted - 11/05/2014 : 09:02:27
|
I think the article that John Reid mentions is 'Gear Ratios - A Study in Steps' by Mike Allison.
You can find it in the 1998 Yearbook or as reproduced in the Bulletin for June 2013 (on this website, see Home Page/Bulletin/On the Web).
Bob Richards
Bulletin Editor
(PA 1052) |
|
|
|
Andrew Fock
Australia
374 Posts |
Posted - 11/05/2014 : 10:34:51
|
Hi Dave and George,
Malcom Greens book (4 cylinder) discusses the differences The enlarged 3rd gear in the PB box necessitates a new selector and a new (?) caged pinion bearing is required as well I think.
So in the PB box the constant mesh ratio is changed which then requires the third gear to be altered to keep the 3rd to top gap at 1.35 and then the change in CM brings 1st and second up closer to third eliminating that nasty gap.
Otherwise the PB box pretty much the same as the PA / NA.
Andrew
|
|
|
|
Andrew Fock
Australia
374 Posts |
Posted - 11/05/2014 : 11:51:52
|
Should have added in the last post.... I was also under the impression from the 'gearbox articles' that in the original PB box the top gear dogs are reversed with the male being on the output shaft gear......(?)
The 1982 yearbook has a discussion on this.
Andrew
|
|
|
|
Bob L
Sweden
50 Posts |
Posted - 11/05/2014 : 22:45:53
|
When I rebuilt the gear box on my PA about 15 years ago. I purchased gears from:
John Needham
Gear Spec Pty Ltd
Moorabbin
Victoria
Australia
Tel +61 3 9553 3203
He does a few tricks with the gear module on 1st and 2nd to give the following results:
Modifying a PA box gives the ratios 3.96 2.18 1.36 1.0
Modifying a PB box gives the ratios 3.38 2.01 1.36 1.0
I managed to get the innards of a PB box to start with and am pleased with the results.
Bob
|
|
|
|
Andrew Fock
Australia
374 Posts |
Posted - 12/05/2014 : 11:51:47
|
The 'Needham' fix involves doing a 'dodge' to alter the number of teeth on the first gear. The CM and third are left alone. A few people have these and apparently they work OK.
One issue with arranging a new set of gears is selecting the ratios you want. I was led to believe that the last set of close ratio gears that were made were basically a racing set and not necessarily all that good for road use (?)
Standard PA: (gap)
4.18 (1.8) 2.32 (1.71) 1.36 (1.36) 1:1
Needham
3.96 (1.81) 2.18 (1.6) 1.36 (1.36) 1:1
Standard PB
3.58 (1.67) 2.14 (1.57) 1.36 (1.36) 1:1
R type
3.097 (1.68) 1.84 (1.4) 1.31 (1.31) 1:1
1275 Midget (for comparison)
3.2 (1.67) 1.916 (1.41) 1.36 (1.36) 1:1
TC (for comparison)
3.38 (1.73) 1.95 (1.43) 1.36 (1.36) 1:1
The 1275 Midget / R type ratios are lovely to use but the 1275 Midget has a much better P/W ratio than a standard PA. I suspect they would be fine for an N type or a supercharged P. The Needham mod still leave a big gap between first and second but is better once moving.
The ENV 75 high ratio set might make a good compromise for general use?
ENV 75 High
3.4 (1.7) 2 (1.47) 1.36 (1.36) 1:1
I have the standard ENV ratios in my P type (S/C, P/S). First is rather too low @ 3.9 but the progression in the other gears is good with no large gaps and it is easy to beep the car in the power band...... but then is is not a standard car.
ENV 75 Standard
3.9 (1.75) 2.23 (1.54) 1.45 (1.45) 1:1
Andrew
|
|
|
|
mgmike
New Zealand
39 Posts |
Posted - 14/05/2014 : 03:12:14
|
| I would also be interested in this subject to knowing pricing, thanks. |
|
|
|
cryrnr
United Kingdom
214 Posts |
Posted - 14/05/2014 : 17:53:20
|
| Thanks to all for the interest and very helpful information/discussion. Mike Dowley tells me that he will get up to date prices from his gear cutter and then post details. Can't imagine it will be cheap but from everything that's been said it sounds like a really worthwhile conversion and with the addition of bearings the result would be a virtually new gearbox. At least that's how I intend to justify the expenditure! Do hope demand will be sufficient for a new production run to prove viable. Neil |
|
|
|
MaGic_GV
United Kingdom
868 Posts |
Posted - 16/05/2014 : 08:51:52
|
To encourage folk further, I can relate that my original PA box had a horrendous whine in second, which I think is not uncommon. on inspecting the gears they were almost worn away by fifty plus years of clashing - so if your whine is as piercing as mine was, it will be worth your while biting the bullet if the gears become available!
Regards,
Graham
|
|
|
|
Colin Butchers
United Kingdom
1487 Posts |
Posted - 17/05/2014 : 10:13:48
|
Graham, If anyone is prepared to spend several hundreds of pounds on a new close ratio gear cluster simply to reduce the whine of the second speed gear, I think they will be disappointed. The reason for the whine is the fact that the first and second speed gears are straight cut (lower production cost plus added tooth strength.) as opposed to spiral bevel or double helical gears). Logically, if yours produced a loud whine with only two-thirds of the teeth left, the whine could even increase with a new set of full width teeth !
Admittedly it related to the crown wheel and pinion rather than the gearbox, but in "Wheelspin", Austen May mentioned that when he bought his Cream Cracker, JB7521 from Abingdon, the noise from the straight-cut gears in the back axle was so loud that his fiancee was reluctant to ride in the car. I am afraid that a screeching second gear is something we should get used to - although my friends in the second-hand car trade swear that a couple of handfuls of saw-dust in the oil works wonders.
Colin B. |
|
|
|
kimber
United Kingdom
1529 Posts |
Posted - 17/05/2014 : 10:32:52
|
To be fair, Colin, there are good and bad ones.
My old J2 was terrible in 2nd although the internals looked reasonable. My current PA is pretty quiet in second (about 50% of tooth width worn away) and the PB box in the Moore car recreation was the best I have ever had - really quiet, even when thrashed.
But, as you say, 1st, 2nd (and reverse) will always be noisier that 3rd or top. I think it was sometimes referred to as a 'silent third' box, wasn't it? |
|
|
|
Nick Feakes
USA
3376 Posts |
Posted - 18/05/2014 : 13:25:56
|
Andrew, Dave
I have tidied up the duplicate post and the consequent posts.
Nick
Webmaster |
|
|
|
MaGic_GV
United Kingdom
868 Posts |
Posted - 18/05/2014 : 19:24:18
|
Just had a nasty moment as I struggled to remember my new password!
My comment re the gear whine was really an aside, it is the driveability that matters. But the whine was loud enough to drown out any whines coming from the passenger side - it really was loud! The replacement box is somewhat more tolerable.
Regards,
Graham
|
|
|
|
Topic |
|
Forum Locked
Topic Locked
