Jack knight gears

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mtnbikepoacher
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Jack knight gears

Post by mtnbikepoacher » Mon Apr 18, 2005 1:43 pm

Hey all,
We made it through the weekend without any mechanicals. Pretty good considering the cars had never been really sorted out. Jonathans had only been driven on the trailer prior to being driven opn the track!
His Imp beat the G15 that was out there running a 998. We're fairly surer it was due to the Jack knight box being in it.
Which brings me to my question. How many ratios are out there, and how rare are they?
What parts to you have to replade in the trans to convert it to a J/K box?
Is the 5th gear Mod available still?

I had never drove with one before. Very Impressive! It was like shifting from second into second again.

With the ratio he had, he was hitting 9500 on the straights in 4th and could have kept going, but had taken it past the limit I wanted them to push the engines as it was. He needed a 5th or a greater spread of gearing.

I think that this ratio will be really useful at the Mission BC track in late may.

Cheers
Al
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Post by TommyDeVito » Mon Apr 18, 2005 1:47 pm

Sounds like you had a laugh, man.

I've often had this same problem in road conditions - it's always bugged me that the engine screams away and I (personally) have always felt a 5th gear would help.

Jack-Knight are still around and they have told me that although they don't keep any Imp parts on the shelf, then can still make them. I have the attachment they sent me somewhere. I'll dig it out.

Cheers.
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Post by aldrin » Mon Apr 18, 2005 3:28 pm

TommyDeVito wrote:Sounds like you had a laugh, man.

I've often had this same problem in road conditions - it's always bugged me that the engine screams away and I (personally) have always felt a 5th gear would help.

Jack-Knight are still around and they have told me that although they don't keep any Imp parts on the shelf, then can still make them. I have the attachment they sent me somewhere. I'll dig it out.

Cheers.
Hi
Dennis Alt of transip keeps alot of Jack Knight stuff and regularly gets new batches from them.
Many of the other imp race engine builder do as well.

Aldrin
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Post by mtnbikepoacher » Tue Apr 19, 2005 2:36 pm

Does Dennis Alt have a website?
I still haven't spoken with him over the phone...

Anyone know off hand what the available ratios are?

It seems I may have confused the tranny with a JK as it has syncro gears, and I'm told JK's don't.
What exactly are "dog" gears?

Alan
SMSport

Post by SMSport » Tue Apr 19, 2005 4:58 pm

Gearboxes and gearchange types - very confusing and uses some odd language.

Lets try to explain some of the basics.

The function of any transmission is transferring engine power to the driveshaft and rear wheels (or axle halfshafts and front wheels in a front-wheel-drive vehicle). Gears inside the transmission change the vehicle's drive-wheel speed and torque in relation to engine speed and torque. Lower (numerically higher) gear ratios serve as torque multipliers and help the engine to develop enough power to accelerate the car from a standstill.

Initially, power and torque from the engine comes into the front of the transmission and rotates the main drive gear (or input shaft), which meshes with the layshaft gear -- a series of gears forged into one piece that resembles a cluster of gears. This-gear assembly rotates any time the clutch is engaged to a running engine, whether or not the transmission is in gear or in neutral.

There are two basic types of manual transmissions. The sliding-gear type and the constant-mesh design.

With the now obsolete -- sliding-gear type, nothing is turning inside the transmission case except the main drive gear and cluster gear when the transmission is in neutral. In order to mesh the gears and apply engine power to move the vehicle, the driver presses the clutch pedal and moves the shifter handle, which in turn moves the shift linkage and forks to slide a gear along the mainshaft, which is mounted directly above the cluster. Once the gears are meshed, the clutch pedal is released and the engine's power is sent to the drive wheels. There can be several gears on the mainshaft of different diameters and tooth counts, and the transmission shift linkage is designed so the driver has to unmesh one gear before being able to mesh another. With these sliding mesh transmissions, gear clash is a problem because the gears are all rotating at different speeds, which is why they are genrally known as “crash” boxes and need double de-clutching to change gear quickly without damage.

All modern transmissions are of the constant-mesh type, which still uses a similar gear arrangement as the sliding-gear type. However, all the mainshaft gears are in constant mesh with the cluster gears. This is possible because the gears on the mainshaft are not splined to the shaft, but are free to rotate on it. With a constant-mesh gearbox, the main drive gear, cluster gear and all the mainshaft gears are always turning, even when the transmission is in neutral.

Alongside each gear on the mainshaft is a dog clutch, with a hub that's positively splined to the shaft and an outer ring that can slide over against each gear. Both the mainshaft gear and the ring of the dog clutch have a row of teeth. Moving the shift linkage moves the dog clutch against the adjacent mainshaft gear, causing the teeth to interlock and solidly lock the gear to the mainshaft.

Constant mesh gives the advantage that helically cut gears can be used with this configuration of gearbox. Helical gears are stronger and quieter in operation than straight cut or spur gears. The use of helical gears does , however, create axial thrust and thrust bearings need to be used in the gearbox. ( Citroen did eliminate axial thrust using a double helical gear and this is still reflected in the double chevron logo)

Even with this arrangement there can still be a “crunch” when gears are engaged and double de-clutching is still needed to make sure that all of the gears run at the same speed and this still caused a problem for a number of drivers.

To prevent gears from grinding or clashing during engagement, a constant-mesh, fully "synchronized" manual transmission is equipped with a synchromesh. The basic gearbox is laid out in the same manner as the constant mesh, but with the addition of a cone clutch fitted between the dog and gear components. The male clutch member is on the gear and the female on the dog clutch hub, which has a splined outer sleeve located by a series of balls and springs. Movement of the selector moves the whole dog clutch until the cones make contact, when the friction brings them both to the same speed

Continued movement of the selector causes the spring-loaded balls to be overridden and the internal splines of the outer sleeve engage with the dog teeth on the gear. However, the change must not be rushed as it takes time for the friction at the cones to bring the rotating gears to the same speed. Change gear too quickly and there may still be some noise.

To overcome this disadvantage, the Baulk or Blocker Ring System was introduced, radial movement of this additional ring is limited to half a spline width, which prevents the dog teeth from engaging until the speeds of the two members are equal.

If your car has a synchromesh gearbox it is best not double-de-clutch as this can cause undue wear on the synchro rings.

A synchro typically consists of an inner-splined hub, an outer sleeve, shifter plates, lock rings (or springs) and blocking rings. The hub is splined onto the mainshaft between a pair of main drive gears. Held in place by the lock rings, the shifter plates position the sleeve over the hub while also holding the floating blocking rings in proper alignment.

A synchro's inner hub and sleeve are made of steel, but the blocking ring -- the part of the synchro that rubs on the gear to change its speed -- is usually made of a softer material, such as brass. The blocking ring has teeth that match the teeth on the dog clutch. Most synchros perform double duty -- they push the synchro in one direction and lock one gear to the mainshaft. Push the synchro the other way and it disengages from the first gear, passes through a neutral position, and engages a gear on the other side.

I think that this design was originally patented by Porsche.

A normal synchromesh gearbox works well enough for normal driving on normal roads a good competition box, ho replaces the cone synchros, with a simple “dog” tab that locks into the next gear like the treads on your tyres lock into the mud. It is this design taht is ususally called a DOG box because the synchromesh has been eliminated.

There is absolutely no resistance to shifting – not only can you click from gear to gear in no time at all, but you don’t even need to use the clutch. This is a great advantage when left-foot braking into difficult corners, as you can just run down through the gears while keeping your left foot on the brake and rev-matching with your right foot. But the downside is that you can’t be at all slow on the shift or the shafts will begin to idle and you’ll have to crash it into gear. Also, if you’re idling on the start line (or anywhere) with your foot off the clutch and you happen to bump the gear lever, there’s nothing stopping the gearbox from engaging and you’ll soon have a stalled engine and perhaps a broken gearbox.

Dog rings, by their nature, engage by wearing, and so you will have to rebuild the box quite frequently.

“Dog” ‘boxes also generally use straight-cut gears which are noisier but cheaper to manufacture than helical gear.


So where does that take us:

The use of a standard synchromesh box on Imps is quite common as the basic design of the unit is excellent and allows quite fast gearchanges.

The problem is that the gap between second and third is too great for highly tuned engines and the final drive ratio is too high depending on tyre size.

We use a synchromesh transmission fitted with a Jack Knight lowered 3rd and 4th straight cut gear set on our Historic rally car.

with 165x 70 x 13 tyres first gear (16:1 overall) is ideal and top runs out at about 105 mph at 9000 in top and is a good cost effective compromise.

The traditional Jack Knight Dog box allows all four gears to be changed independently and I have seen first gears with overall ratio's of 12:1.

They are excellent for race applications and allow gearing to be matched for individual circuits.

5 speed boxes are quite rare and use the reverse gear selector to select either first or fifth gear (I am not sure which) and so reverse has to be slected using a cable from outside the box often connected iwith the choke lever at the base of the gearstick. Great box and well worth the money on race cars.
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Post by mtnbikepoacher » Tue Apr 19, 2005 5:10 pm

Thanks for the well written reply!
I knew most of the first half, but am still trying to visualize the "dog".
So if I have read correctly, I probably am dealing with a gearbox that has the lowered 3-4 gears made by Jack Knight.

One the five speed, is it just the last case casting that is replaced to fit the 5th gears?
Really, this car doesn't need a reverse, and it's not functioning right now as it is (I need the excersize :lol: ).

We'll probably just stick with the normal setup. We do need a taller 4th at least though.
Thanks
Al
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Post by aldrin » Tue Apr 19, 2005 5:16 pm

mtnbikepoacher wrote:Does Dennis Alt have a website?
I still haven't spoken with him over the phone...
I don't think he does, always seems to have plenty of work on , he does have e-mail I will see if I can dig it out.

Aldrin
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Post by rootes » Tue Apr 19, 2005 8:27 pm

aldrin wrote:
mtnbikepoacher wrote:Does Dennis Alt have a website?
I still haven't spoken with him over the phone...
I don't think he does, always seems to have plenty of work on , he does have e-mail I will see if I can dig it out.

Aldrin
his details are on the spares pages under spares panel...

though think the email quoted is wrong should be:

transimp@ntlworld.com

Si
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Post by imull » Sat Apr 23, 2005 1:07 pm

I spoke to JK a while ago when trying to research a gearbox I had. As you do, we got talking about the imp stuff in general and they said that there was effectively an infinite number of ratios.

They dont really sell gear kits, you specify what ratios you are after or what conditions your car will be used under and they will specify a set to suit. At the time, they had had someone with a car that was only used at Lydden Hill who gave them a copy of his data logging stuff and from that tehy specified ratios for him...

I think they said that there is onyl 1 diff ratio available from memory.

How reliable is the 5 speed box and its reverse gear? Is it really only for emergency use on a race circuit, or could it concievably be used on a more regular basis?

JK also are interested in taking on batch production stuff for machining and fabrication. There was an article a while ago saying that they were looking for project to take on with owners clubs to further the engineering side now that the company has been relaunched again
SMSport

Post by SMSport » Mon Apr 25, 2005 9:56 am

I would think that the only problem with having gear sets made for specific applications is the design/drawing costs.

With modern wirecutting techniques tooling costs are less of an issue but it must making small batches of specific gears must be more cost effective than one-offs.

I think that the main problem with the 5 speed box for a rally car is more concerned with gear selection rather than strength.

I condsidered fitting a five speed into our rally car but the reverse selection worried me.

I believe that it is possible to select two gears at the same time with the system as supplied.

If you spin the car on a hairpin you must take it out of gear and select neutral before trying to find reverse, if you don't and manage to select two gears at the same time the results could be fairly dramatic.

I realise that you could fit a simple mechanical gate lock to prevent reverse bieng selected but just think of the sequence.

Spin or overshoot
Select neutral
operate gate lock
select reverse
select neutral
operate gate lock
select forward gear

Real pain in a rally car and quite slow.

I would imagine its not too much problem, in a hillclimber or sprint car.

There was also a "dogbox" manaufactured by Tran-X in the seventies and this differed from th JK box as I think it used radial dogs rather than face dogs, which I am told gives better reliability and less wear. I have tried without any success to interest Tran-X in producing some more of these gearboxes but without any success.

I would ceratinly be interested in a couple of Tran-X style gearkits.

The other problem with the JK box from a rallying piont of view is that the LSD is a pawl type and a bit brutal in operation.

The Plate type manufactured by Tran-X is a better bet for loose surfaces.

If there is enough interest I would like to arrange to make this type of box but I don't have access to a gearkit for the reverse engineering.
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Post by TommyDeVito » Tue Apr 26, 2005 10:39 am

The idea of fitting a 5-speeder to my fast road car is one that keeps coming back time and time again. I think it probably will until I actually do something about it!

Thing is, for a road car (being used for every journey, so high-ish mileage), I can't imagine a JK 5-speeder with dog gears would be a good option taking the noise and wear into account.

I know Skoda 5-speeders have been talked about before but for me that's out of the question because I'm not going to cut the car about [more than I already have!].

Another option I heard about was to use the transaxle box from an Alfa 75 (correct me if I've got the wrong model there) and flip the diff upside-down. I was told someone is currently doing this to a Davrian - could make for a useful bit of tech discussion.

There was also talk recently in PPC magazine about the use of a VW bus transaxle (someone was putting a Subaru engine in something and had written a tech query about suitable boxes). Supposedly they're quite small, quite light, quite strong and are available as 5-speeders. My old neighbour is into VW's, maybe he can point me in the direction of somebody who's got one of these boxes lying aroung.

Ultimately (money no obstacle, which ain't gonna happen), I'd have a JK 5-speeder with the ratios made specifically for fast road and occasional motorway use. But if JK's are only available as straight-cut dog boxes it probably wouldn't be that great.

A chat with Dennis is needed for me I think......... :-)

I've got images in my head of me doing a hot-lap of San Marino in my Chammy and actually being able to make the most of it with a lovely 5-speed box. Mmmmmmmmmm.........................
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Post by mtnbikepoacher » Tue Apr 26, 2005 2:19 pm

My experience with Bus and van transaxles is that they are heaaaaavvvvyyyy. Like, trow your back out heavy, but then I typically deal with the 4wd versions. But I'll just say you can't load your arms up with them like you can with the Imp tannies.
Everytime I work on something that light, a smile comes to my face :lol:

I have an email off to J/K, but nothing back yet. I had not intended on chasing down the 5 sp. option, but maybe I'll inquire if they get back...

Al
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Post by TommyDeVito » Wed Apr 27, 2005 2:20 pm

Al,

This letter in the mag that the geezer had written said the code number for the bus transaxle was 091 (4-speed) and 094 (5-speed). I think it was just for RWD versions. Apparently the casing is made of magniesium. I have no idea if these could possibly be used in an Imp (probably not) but from an engineering point of view it's always worth a look.

Let us know what JK say if they get back to you. When I emailed them a few months back they did get back to me. If I can find the price list attachment they sent me, maybe I'll post it up.

As a little trvial sidenote about gearboxes, one of the Quafe (sp?) family lives right round the corner from me - I used to do a post round off of his road. I would go and have a chat, if only I could get past the electronic gates and 100 yard driveway!

Cheers.
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Post by GarethS » Thu Apr 28, 2005 10:04 am

With the bus transaxles I have heard that to get the driveshafts lined up the Imp engine is pushed back 1 or 2" hanging the weight further out over the rear (and requiring adjustments to the crossmember I guess).

Another suggestion I have heard is using an Audi transaxle (from 5 cyl 80s and 100s I believe), I will have to check if the diff needs to be flipped on this as I cannot remember which end of the engine it is at in it "normal" home.
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Post by rootes » Thu Apr 28, 2005 10:48 am

How about a renualt 16 tranaxle? it is even the correct way around...

Si
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Post by TommyDeVito » Thu Apr 28, 2005 12:19 pm

Yeah? I'd not heard that one before. Nice one - 'nother one to add to the list.
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Post by aldrin » Sun May 01, 2005 12:03 am

rootes wrote:How about a renualt 16 tranaxle? it is even the correct way around...

Si
When did you last see a renault 16 ?
Am I thinking of the right one sporty coupe thing from the early 70's echos of the later fuego ?

Which one did the lotus europa use ? (wrong way round for imp)

There is of course the renalut 4/5/6 range which had the gearbox in the right orientation but some of the engines ran backwards :?

I think on some of the 4/5/6 boxes the diff was reversible.

On the subject of europa's I was looking for imps in the geneva motor museum this afternoon (none on display but I think they had one the a couple of years ago) when i noticed that the europa 'series two' badge is very similar to the imp 'coupe' and 'super' rectangular badges may be another cross over part.

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Post by rootes » Sun May 01, 2005 9:35 am

aldrin wrote:
rootes wrote:How about a renualt 16 tranaxle? it is even the correct way around...

Si
When did you last see a renault 16 ?
Am I thinking of the right one sporty coupe thing from the early 70's echos of the later fuego ?
Image

but your right not very common...

Si
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Post by aldrin » Sun May 01, 2005 11:35 am

rootes wrote:
aldrin wrote:
rootes wrote:How about a renualt 16 tranaxle? it is even the correct way around...

Si
When did you last see a renault 16 ?
Am I thinking of the right one sporty coupe thing from the early 70's echos of the later fuego ?
Image

but your right not very common...

Si
The coupe thing I was thinking of must be the 15 then, about 5 years ago I used to work witha bloke who had one, and renault had borrowed it for a milenium exhibit touring dealers, one of 2 known left in the uk.

Some how I don't think renaults would have the same hibernation tendancies as imps.

Aldrin
SMSport

Post by SMSport » Mon May 02, 2005 10:48 am

Renault 16 boxes are not great in terms of gear ratios and are quite heavy.

A 5 speed Renault R8 Gordini box may be quite interesting and there are some gearkits being re-manufactured in the South of France as this box was fitted into the Alpine A110 but prices are extreme.

The other interesting option for a competition car must be a 5 speed Hewland Mk 9.

This is based on a VW transporter box and is used upside down in most mid-engined single seater applications.

There are huge amounts of gear available from a large number of suppliers, the gearchange is wonderful and they cost between £1500-£2000 in good used condition.
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Post by timbeardsley » Tue May 24, 2005 6:59 pm

Just had an email back from Jack Knight today saying that they still sell 4 and 5 speed dog gear kits but no syncro stuff, now im waiting for a price and ratio chart
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Post by Jack Knight » Thu Sep 20, 2007 8:16 pm

If anyone needs gear data and raios etc please let me know. We produce both 4 and 5 speed dog boxes but would produce heilcal if there was enough interest.

We don't currently supply any Imp parts to any UK dealer or engine builder but you are very welcome to order direct. Please note this is not a sales pitch but posted in the spirit of providing accurate information
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Post by Lomond26 » Fri Sep 21, 2007 8:12 am

Hi all i'm new to the forum only joined the club recently so if i say something stupid just point it out politely please ........!!

Anyway this thread jogged my memory banks and thought i could let you all know my experiences with the box in question.

The JK 5 speed is a great box and perfectly reliable for road and competition use. It does have to be put in neutral before you reverse and you do need a cable arrangement to pull the reverse engagement in this neds to held there while you reverse. which means your reversing one handed, having said that its not really a problem. Guess you could make up some form of loccking mechanism to hold it in while you use 2 hands to reverse but never saw the point of that.

I used my 5 speed in a hillclimb/sprint davrian imp and to be honest i wouldnt recommend them for a hillclimb/sprint car. The reason being 1st gear is a dog leg left and back and this causes problems in srints hillclimbs when your looking for a quick getaway, my brain didnt always quite remember 2nd gear was in fact up right and up and not straight down!! And in all honesty you dont really need 5 speeds for sprints and climbs. The half knight as we called it with uprated 3 and 4th was perfect for a sprint car.

The 5 speed i had was used before i purchased it in a road going imp that was raced at both Ingilston and Knockhill and was a big improvement for racing. It was a mates and if my memory serves me right when starting he quite often did this from 2nd gear which didnt seem to waste to much time on a race grid not being on a hill and more time to make up for any mistakes!! The guy also used this box on the road and neither he or i ever had a single problem with it which I guess says something about the quality of JK components.

And just as im thinking back the 5 speed box plus a full race r23, twin 40 combined manifold 998 cost me the pricely sum of £1,000 back in 89. I even sold the davrian imp with the 5 speed its full race carter and slicks wets spares etc etc for 2K and the last time i saw a 2nd hand 5 speed box for sale 2,500 was being asked.

I've just returned to Imps and how times change!! Anyone asked JK how much they want for a 5 speed now?
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Post by stuart » Fri Sep 21, 2007 8:39 am

Excuse my naiveté, as a general question, would it be theoretically possible to build/obtain a box that would:

Have 5 gears
Helical cut (for noise)
Allow the imp engine to do around 4000 revs at 70 obviously without killing the performance in the lower gears.
Not have to modify the body shell.

Even if this couldn't be achieved with the gear ratios - would it be possible to modify the diff ratio much?

Then it comes down to cost - it wouldn't be cheap but....

If there is then I'm interested finding out...

Cheers,
Stuart
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Post by onomatopoeia » Fri Sep 21, 2007 10:14 am

Lomond26 wrote: I've just returned to Imps and how times change!! Anyone asked JK how much they want for a 5 speed now?
The gear set is £1750 on their website - doesn't say if that includes the VAT or not.

I have a 5 speed in my sprint & hillclimb Davrian, the only problem with the dog leg 1st is that finding second instead of 4th going up the box is more luck than judgement. The ratios in mine are very close, 12mph @ 1000rpm in 5th on 20" diameter slicks, but that suits the power curve of the engine and the 110mph or so top speed is exactly right for the fastest place I go.
stuart wrote:Even if this couldn't be achieved with the gear ratios - would it be possible to modify the diff ratio much?
Has anyone ever heard of an alternative final drive ratio for an Imp? I haven't, but I'd like a 6:1 or so.
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Post by Debs » Fri Sep 21, 2007 10:27 am

Jack Knight quoted me for a 5 speed 'box:

Rebuild your gearbox, fit new competition gearset and LSD £2,250.00 plus postage.

This is inclusive of VAT.
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Post by colin rooney » Fri Sep 21, 2007 4:03 pm

hi its an alfa 33 gearbox that was been worked on to go in the back of the imp you would not want a 75 box they are mega heavy and around 3foot long great box i use to dog mine and never had a problem with it

col
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Post by Turboimp » Fri Sep 21, 2007 5:56 pm

The Alfa 75 transaxle has the flywheel and clutch in it hence the size and weight , even more so with the twin plate clutch with the V6 .
I found the 33 transaxle fairlyt frail in the Alfa 33 , the gear wheels are thinner and have finer teeth than the Imp ones and they always had syncromesh problems , i did quite a few overhauls at one time , the layout is a copy of the Imp transaxle ... 4 wheel drive versions are quite simple , the mainshaft is extended out the rear of the transaxle with a flange for the propshaft ...
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Post by johnh875 » Sat Sep 22, 2007 11:31 am

Interesting... add a front diff etc and you could have a 4wd Imp!
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