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weeroxy Posted - 22 Jan 2011 : 19:57:54
hi can anyone please tell me what is the differences between the jtype and the d type laycock gearboxs,every one seams to want the jtype what is the reason for this, are these gearboxs interchange able on a car, and are these gearboxs standard on rapiers and hunters,can any one please give me a breakdown on this info

13   L A T E S T    R E P L I E S    (Newest First)
turbinecol Posted - 13 Oct 2011 : 12:21:09
Yes, my Dad was the same, no spare money so the Wolseley 1500 and Humber Sceptre were mended to keep the family mobile. I wasn't interested in cars then but I know he spent a lot of unhappy winters covered in snow trying to keep the Wolseley on the road in particular. That thing had a bullet-proof engine but the sills rotted out (twice) before it finally went to the breaker's yard!
1922 Posted - 12 Oct 2011 : 20:24:50
turbinecol - pleased I can help. But sounds like you have the advantage of newer parts book, my book is a '72 and doesn't show the J type.
I drove my '73 Rapier from 1986 to about 2003 as my everyday car and much of the time on a tight budget, especially in the early days. It's surprising how much you learn when you've got to fix everything yourself

turbinecol Posted - 12 Oct 2011 : 09:02:56
Exactly Paul!, sorry I got too excited talking about the closer 1-3 ratios there, forgot about direct 4th!
Paul Posted - 11 Oct 2011 : 21:33:57
Originally posted by turbinecol
Since overall effect is taller gearing with the close ratio box, in theory higher top speed is available at the slight expense of acceleration if you look at the gearbox alone.

No. - Top speed (for the same RPM, overdrive and final drive ratios) will always be the same because top gear is direct drive and hence independent of any intermediate gearing.

By the way, John Roseby of the S.A.O.C. rebuilds these gearboxes and I'm sure he would be very happy to help Rapier owners.

My Alpine won't float! I need one which does!!
turbinecol Posted - 11 Oct 2011 : 21:14:26
Thanks 1922, great reply, really good to have your knowledge on hand! If you put 27/20 into the numbers it gives the exact ratios expected on the close ratio box (Haynes)- interesting it meshes ok, perhaps the angles are cut slightly different on the teeth? and hence the different part number on the input shaft?...more guesswork.

I checked the parts list again and the J type mainshafts are showing different part numbers for GLS/H120. Friend of mine who works in transmissions thinks it might be that the GLS/H120 shaft is physically the same dimensions, but possibly shot peened or hardened differently.

Agree about the 3/4 nuts, seems to stack up with the parts book. For the mainshaft nut, I noticed the picture in Haynes (early car I guess) was different to mine - there was no lock tab, so something changes along the years, but across the board I think.

Since overall effect is taller gearing with the close ratio box, in theory higher top speed is available at the slight expense of acceleration if you look at the gearbox alone.
1922 Posted - 09 Oct 2011 : 16:19:44
I lost track of this thread - but better late than never.

Re Volvo overdrive:
I've never seen one and just don't know. I would expect that the unit is the same apart from the adapter plate that connects it to the gearbox. I intend to replace the D type on my '68 with a newer unit so I may find out.

Re - teeth
The difference between the close ratio and standard box is just the the input shaft gear and the input gear on the layshaft. The 1st, 2nd and 3rd gears are the same as are the 1st, 2nd and 3rd gears on the mainshaft.
So turbinecol's numbers for the 1st, 2nd and 3rd gear apply to both standard and close ratio (Rapier, H120, GLS) boxes.
The different gear at the front means the layshaft spins a bit faster on the close ratio box so the car is a little quicker (for the same engine revs) in 1st, 2nd and 3rd.
On a couple of old layshafts I count 27 teeth for the input gear. But the primary I found also has 20 - though this could be a from standard box (can't remember now - they've been there twenty years).

I found a note scribbled in my parts book that says the earlier cars with a D type overdrive use different mainshaft and mainshaft 3/4 nut (the one that holds the 3rd/4th hub) for H120s.
Presumably, as turbinecol mentioned, these are a little tougher to cope with the extra power.
But for later cars with the J type overdrive there is only one type of gearbox mainshaft.
The note is in my handwriting so I must have picked up this gem of information somewhere along the way. My guess is that all cars got the H120 mainshaft - they are all interchangeable, so why have two types?

weeroxy Posted - 23 Jan 2011 : 16:56:00
thanks turbinecol i will give them a call tommorrow,can anyone recommened a suppler for a good quality clutch kit for a holbay i dont want a recon must be new, i see theres a company on ebay selling panther clutches for the holbay has anyone had any dealings with these

thanks robbie
turbinecol Posted - 23 Jan 2011 : 16:10:14
'' of Rugby should have no trouble providing you with the parts you need Robbie. Best of luck
turbinecol Posted - 23 Jan 2011 : 16:04:32
No idea if this is of any use to anyone, but I counted the teeth on my normal ratio box when I was doing the rebuild, and here were the results.

1st gear 37, layshaft 16
2nd gear 31, layshaft 21
3rd gear 24, layshaft 25
input/4th gear 20, layshaft 29

To work out ratios, remember the drive passes through the input gear/layshaft mesh first, so 1st gear is 37/16*29/20 = 3.353:1

The actual ratios are all quoted in the various manuals like Haynes, but they don't usually mention the teeth numbers. If anyone can add the close ratio ones for completeness, that would be great!
turbinecol Posted - 23 Jan 2011 : 15:48:32
Good topic!

Just finished rebuilding a gearbox with J type overdrive. I counted the teeth and established I had a normal ratio gearbox. Hmm. This means that the box (we didn't know its provenance) came either from a Hunter or Alpine with optional overdrive, or possibly from a Sceptre Estate as it kept the lower ratios when introduced at L5 series (not sure if that situation ever changed).

From what I can establish, all other Sceptres, Rapiers, GT's, GLS's and H120's with J type would have had close ratio, since close ratio came in on LH models (1972) and J type followed on L3 chassis (1973).

The parts list does indicate different overdrive mainshafts in the gearboxes specifically for H120 and GLS Holbay powered cars. I presume these mainshafts are slightly more durable, or perhaps specially sorted/measured ones to ensure they were best spec for these engines. I am guessing though.

Meanwhile, I have a low mileage non-Holbay car with a D type and the change is pretty instantaneous comparing very similarly to a good J type I have tried on a friend's car, but the difference I do notice is more drivetrain clonk when coming back to direct drive on the D type. This is a one off sample of course, but the chap I bought the box off in the first place also had this opinion from his experience. My Dad's old J type's Sceptre we grew up with was very very slow to engage, but I recall cleaning the filter largely cured that.
weeroxy Posted - 23 Jan 2011 : 15:12:20
hi derek, thanks for the info thats exactly what i was looking for ive got a oil leak from the speedo drive only seems to leak after been sitting for a few days on a j type gear box,ive had a look at the manual it lists a o ring and a oil seal in the drive so i try get them (do you any where i can get them) ive also got a d type gear box which is low miles from a 68-69 humber sceptre which is clean and dry at least i know now if i cant get the j type sealed then i can swap the dtype overdrive from it
thanks again robbie
arrocuda Posted - 23 Jan 2011 : 13:21:22
Derek.... is there any interchangeability between the Volvo J type and the Rapier gearbox or is it enclosed in a whole different set up? Only reason I'm asking is cos usually when they do that the model identifier changes as well.... so the J type becomes a K type when it's in a Volvo..... if you follow me.

Building the 'Mark II' fastback Rapier ('Arrocuda').
1922 Posted - 23 Jan 2011 : 11:52:00
Hi Weeroxy,
The J type is a little newer. I'm not sure when they replaced the D type - probably around '72 as only the J is listed for the GLS.

In my experience the J type engages more quickly, less than a second. My 'D' type would usually take 1 to 3 seconds - it got faster as it warmed up.

When used on the Holbay engined cars (H120 & GLS) the D type was run at a slightly higher hydraulic pressure (510-530psi) than on the standard cars (480-500psi). But the J runs at 340-370psi on all models.

The J type overdrives a little more than the D, it's 25.4% instead of 24.67% - I doubt you'd notice the difference.

The J went on for years and was fitted to Volvos into the eighties (maybe longer).

I don't there's anything thing wrong with the D - the J is just faster and perhaps stronger.

Overdrive was standard on Rapiers and H120s. Optional on Alpines. Pretty certain also standard on manual Humber Sceptres and optional on Hunters (probably only on the 1725 ones).

The overdrives are interchangeable (I've done this several times) - you can swap D to J or J to D.

For the gearboxes there are only 2 differences.

1 - Overdrive or non-overdrive. This affects only the gearbox mainshaft which is shorter if an overdrive is used.

2 - Close or standard ratio. This is just a change to the input shaft and layshaft (different number of teeth). The close ratio box has gears 1 - 3 closer to 4th but doesn't change them relative to each other. It's difficult to tell one box from another and they are interchangeable.
The close ratio was fitted to Rapier and H120 but I'm not sure what else without checking the parts book.

Any gearbox from the 66 onwards 'Arrow' (Hunter, Sceptre, Alpine, Rapier, H120, Minx, Gazelle, Vogue) range of cars will fit any other 'Arrow' car - the only real problem is matching the speedo drive gear to the combination of back-axle and speedo that you have. You don't even have to change the prop-shaft.
With care it is even possible to swap bits with the earlier 'Series' cars gearboxes.

Back axles vary. For manual non-overdrive 1725cc cars you will generally find a 3.7:1. For overdrive cars: Rapier is 4.22:1 but Alpine, H120 and the saloons are 3.89:1. Automatics are usually 3.7:1.

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