Dec 5th not April 1st

E-by'eck · Post by **E-by'eck** » Wed Dec 05, 2012 7:48 pm

Restoring my 1962 3.8 roadster and have just had my gearbox rebuilt by a local friend/specialist now retired who has been in the Jaguar business for many years. It is a 4.2 gearbox which was mated to the 3.8 engine when I bought it and its serial number puts the gearbox age around 1966. When he picked it up, he said that it was a Close Ratio Box ?? I told him it was not the case as the serial number did not have the required CR identity. Box now returned and he has confirmed it is indeed Close Ratio... he was not surprised as he tells me that Jaguar built many 4.2 Gearbox Units this way with CR gears around that time due to a significant parts ordering error in the factory. New News?? Old News?? April 1st?? :? :?
Graham

Post by **Heuer** » Wed Dec 05, 2012 8:44 pm

All EJ gearboxes are "close-ratio": http://etypeuk.com/forum/viewtopic.php? ... lose+ratio

PeterCrespin · Post by **PeterCrespin** » Wed Dec 05, 2012 11:48 pm

Makes me laugh the way some people equate 'close ratios' with 'go faster' and therefore somehow inherently desirable. Not saying Graham is doing that at all, but a stint as a serious cyclist or competition motorcyclist would soon relieve anyone of that notion.

They have their place, of course, but with the wrong engine tune or diff they could be anything from a waste of time to a downright performance killer.

I'm wondering if this specialist lives in Dereham?

Pete

Post by **1954Etype** » Thu Dec 06, 2012 10:29 am

When I did my 2.88 diff swap I replaced the internals of my CR box with the later ratios as it suited the new ratio better.

E-by'eck · Post by **E-by'eck** » Thu Dec 06, 2012 10:05 pm

Thanks for the replies from all... the link you provided was very useful David. Didn't realise the subject had opened such a can of worms (box of gears?) so recently ... most get a better grip of researching topics before posting Sorry!
I am just looking to restore a great drivers car.. the prospect of a CR gearbox was initially unattractive but if CR really means standard box, I am reassured... Graham

PeterCrespin · Post by **PeterCrespin** » Fri Dec 07, 2012 2:50 am

No can of worms from my side but think about Angus's scenario. All Jag 4-speeds have a 1:1 top gear so that's a given. If you select a low-geared diff like 3.54 (or 3.77 / 4.1 in other models) the speeds attainable in each gear with a close ratio box will be much closer together. With a big torquey motor like the XK, changing gear becomes a nuisance and a chore unless you are racing on a very tight circuit. You'd have a taller bottom gear with a close ratio box, which is handy with a short diff ratio, but basically the ratios and diff would be mis-matched .

If on the other hand you choose a tall top gear like Angus, first gear in a close ratio box is very tall. The close ratios work better with tall gearing but again with a big torquey motor they aren't really essential. Angus went for 'wider ratios' to get a decent low-speed pick-up despite 2.88 and having driven his car it is very relaxed but still with a decent turn of speed and well able to bridge the slightly larger gaps between ratios without dropping off the torque curve, even though he has a tweaked motor.

So a close ratio box suits tall gearing on engines with a peaky power delivery. Unless you tune the nuts off an XK it has enough torque to cope with wide ratios and you get a more versatile car. None of the Jag boxes are all that radical although the Moss 3.8 box has a low first that makes up for the slightly lower torque if you gear up. The KPN 4-synchro cluster has the lowest synchro first which makes that gear pair good with a 2.88 if you want to keep your traffic light credibility. The cluster only exists in a few overdrive boxes (2.8 XJ IIRC) but can be transferred to a normal 4-synch box.

Next time you come up behind a cyclist look at the derallieur gear block. A steep slope on the sprockets from a monster bottom 'granny gear' next to the spokes to a tiny top gear sprocket just inside the frame is a wide ratio block for use on a low-geared slower bike for use off-road or in hilly country. A much flatter slope and 6-7 rear sprockets that look fairly similar in size (close ratio) indicates a big front chain ring (tall gearing) which makes life very tough at slow speeds and hills but lets the cyclist pick a range of options to keep 'on the boil' with a good cadence at high speed. In car terms the first is Brands Hatch Indy circuit or Mallory gearing, the second is Silverstone or Snetterton. 'Close ratios' are not a synonym for 'higher performance gearbox' in the average road car that gets used in everything from town to motorway.

Pete

E-by'eck · Post by **E-by'eck** » Fri Dec 07, 2012 8:18 pm

Pete.. thanks for the interesting explanation. The 4 speed box I have is indeed EJ ( CR ). My 3.8 diff is 3.31.... reading Philip Porter Original Etype for the 4.2 this diff ratio was an option for UK cars.

Question?? why was the 4.2 EJ CLOSE RATIO gearbox mated to a 3.31 diff by the factory for UK cars if this made the car less appealing to drive?? Is there some significant difference between 3.8 & 4.2 engines (torque??) to account for this?

Graham

PeterCrespin · Post by **PeterCrespin** » Fri Dec 07, 2012 9:44 pm

I can't remember the reason. I did read it somewhere about the change but bear in mind I said none of the Jag clusters are extreme and the differences are pretty subtle.

3.31 is not an extreme diff either and then there's the issue of the 3.8 red-lining at 6000 instead of 5500 for the more torquey 4.2 engine. About the only noticeably 'sub optimal' combo IMHO would be a Moss box (stump-puller first) with a 3.77 OR 4.10 diff, because that would mean you'd be changing into second before you'd crossed the lights. But guess what? Even that combo makes sense for some people and it is of course what Jag used in heavier cars like the Mk2 et al to launch them off the line.

My only point was to offer some rationale why 'close ratio' is not a Holy Grail of performance. I followed up from Angus, who paid good money to get out of a close cluster and give his highly-geared car a bit more oomph off the line to go with the tall cruising 2.88 ratio. With racing bikes it was standard practice to cart a box of sprockets and chains around if you had no notes from a previous visit to a circuit. The aim was usually to hit the red line in top at the end of the longest straight just before the braking point. With cars it's not that easy, so pretty much any gear cluster is a compromise. As usual, the factory got it pretty much right in each market, even if tastes (and fuel prices) create differing preferences today for some owners...

christopher storey · Post by **christopher storey** » Sat Dec 08, 2012 2:51 pm

E-by'eck wrote: Question?? why was the 4.2 EJ CLOSE RATIO gearbox mated to a 3.31 diff by the factory for UK cars if this made the car less appealing to drive?? Is there some significant difference between 3.8 & 4.2 engines (torque??) to account for this?

Graham

Generally speaking, it wasn't . By the time the all synchro EJ box was introduced , (very late 3.8 and the first three years of short wheel base 4.2s , UK & European cars had the 3.07 ratio as standard , and whilst 1st is a bit on the high side this only produces any kind of embarrassment on very steep hill starts, and it does give the wonderful 2nd gear which , allowing an easy 70 mph is much more useful for overtaking than that of the later boxes which for practical purposes run out of puff at 55 - 60 . The EJ which you have is in my view far and away the best box to have

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