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Anon
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CF Rear Diff change

I just need to pick your brains.
I'd like to change the diff in my CF250 Advantura to give it a bit longer legs on the long motorway journeys in Europe.
At present I hardly ever use 1st gear to start off as it's so short and comfortable travel (engine wise) is at 50 - 55mph. I thought by changimg the diff I can change all gear ratios evenly and effectively have 4 fully usable gears.
I don't want to go down the 5 speed or overdrive route as it's too much hassle and have been told and read that some old Cresta/Victor rear diffs will fit in the CF diff housing.
I've found a 1975 Victor FE axle. The rear diff cover is smaller (I think) as it's only got 10 bolts as opposed to the 12 bolts on the CF. But if it's only the crown wheel that's smaller, the whole diff should still fit in the larger CF housing providing the diff cages are the same.
I got somebody who will set the diff up for me with shims etc if it fits.
Any input?
Wed 21 Oct 2015 @ 21:58 Edit this messageQuote this messagePMQuote this message
Anon
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Gearbox.

Hi XSFrank,

If you are able to pull away in second with ease I think you must have the Bedford low geared box, It is not commonly known but I have worked with these gearboxes for years and there is a low and a high geared Bedford four speed gearbox.
And they both use the same cross-members and prop-shafts, I have the higher geared box in my Bedford and it rolls along nicely at sixty and I still manage to get twenty miles to the gallon.
The Vauxhall Cresta rear axle is the one to go for if you want to go for a higher geared diff.

doujoy

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Thu 22 Oct 2015 @ 09:27 Edit this messageQuote this messagePMQuote this message
Anon
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Finding a Cresta axle will surely not be an easy task these days but I would love to gear mine up a bit.

My Haynes manual tells me that there were 4 rear axle ratios fitted to the CF, mine appears to be the second highest gear ratio, from memory this was 4.56:1

You could check it by jacking the back up and counting the wheel turns per turn of the prop shaft, see what you have fitted. If I think on I will check those ratios and give you them in here.

Mike
Thu 22 Oct 2015 @ 09:33 Edit this messageQuote this messagePMQuote this message
Anon
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Mr D.S.Joyce. wrote:
Hi XSFrank,

If you are able to pull away in second with ease I think you must have the Bedford low geared box, It is not commonly known but I have worked with these gearboxes for years and there is a low and a high geared Bedford four speed gearbox.
And they both use the same cross-members and prop-shafts, I have the higher geared box in my Bedford and it rolls along nicely at sixty and I still manage to get twenty miles to the gallon.
The Vauxhall Cresta rear axle is the one to go for if you want to go for a higher geared diff.

doujoy


Thanks Doug,
So the next question is, have you got another spare 4 speed gearbox with the higher gears in your spares assortment or could you build one up from new & used spares? Is there any way of identifying higher or lower geared boxes from the outside or is it a matter of stripping it and checking.
I'll get under the van on Saturday and will see if there are any serial numbers on the box if Bedford ever used them.
Will also check which diff ratio I have fitted. I think I can do that by checking the type code.
I've not got a rev counter fitted and just drive it by the engine noise.
At more than 55mph it starts to scream to much for my liking and I don't like pushing it too hard. No need to up the fuel consumption and stress the engine.
Saying that, I have no problem acceleration up to 65mph when I overtake somebody. The van runs absolutely fine. But that is only for short stints.
BTW, as the van is off the road for the winter I've no problem getting the gearbox out and send off if it needs to be, so don't think I'm just contemplating this work. If I can get the parts I want it done ready for next year. We're off to Norway in August to see friend and have a 2-3 week trip around.

Cheers Frank
Thu 22 Oct 2015 @ 21:59 Edit this messageQuote this messagePMQuote this message
Anon
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ID marks.

Hi XSFrank,

Apart from the difference in the number of gear teeth there are no marks or numbers on the outside of the gearbox to indicate a higher or lower box, but some have a tin tab with a number on it held under one of the top tail-shaft bolts.
The gearing is the same in first gear on all the Bedford boxes but lower in second third and four gears on the lower geared box, that's what makes me think you have the lower geared box, hence the ease in pulling away in second-gear.
The difference is greatest in fourth because the lower geared box has five less teeth than the high geared box and that will be why you feel it is screaming over sixty MPH.
As for the diff is it a Salisbury axle you have or a Vauxhall/Bedford one, a Cresta one will be hard to find, not many of them around any more but you could check with the Vauxhall owners club.

doujoy

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Thu 22 Oct 2015 @ 22:35 Edit this messageQuote this messagePMQuote this message
Anon
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Gearing.

Hi XSFrank,

I have spent a bit of time today checking through the spares cog box to see what I have and I would be able to put together a main-shaft cluster but do not have a lay-shaft to match.
Have you been able to identify which gearbox you have in your Bedford at the moment?

doujoy

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Sat 24 Oct 2015 @ 20:57 Edit this messageQuote this messagePMQuote this message
Anon
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Hi Doug,

Sorry about the late reply. I ended up working yesterday morning and then it rained all afternoon so didn't get the chance to look at it.
But it was nice and sunny today so spend a few hours under the van checking it over before the winter rest.

There were no tags on the gearbox, but I took the diff cover off and I have the 4.625 Ratio with 8-37 gears. The axle is a Salisbury type with 12 bolt rear diff cover and 1 1/16" hex filler plug.

The diff actually looks really good, but then it's only done just over 70k miles now. One thing I've never seen before though on any car I've worked on, there is a little fibre matt which is held in the bottom of the diff with a spring type clip which also has a magnet attached to it.
I guess it's to stop dirt from the bottom being picked up by the turning crown wheel. The magnet obviously to keep tiny filings out of the oil.

Next thing I'll measure the crown wheel and see if there is another GM diff apart from the Cresta which may fit.

My gearbox is a little wet on the outside, but then, so is the engine which I'll fit a few new gaskets to this winter.
So is it worth me pulling the gearbox out, putting it on a pallet and send it to you?
I want to make a few calculations as to what RPM's I'm travelling this week.

Cheers Frank
Sun 25 Oct 2015 @ 16:46 Edit this messageQuote this messagePMQuote this message
Anon
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My different has the felt pad and magnet too Doug
Sun 25 Oct 2015 @ 18:05 Edit this messageQuote this messagePMQuote this message
Anon
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Salisbury axle.

Hi,

The old Vauxhall Cresta does not have a Salisbury axle but is higher geared, and for my money you cannot get a better axle even Land-rover used them instead of their own make, the green pad and magnet are normal to all Salisbury axles just another sign of quality.
I certainly would not change it but maybe go up a wheel size, the crown wheel and pinion are matched so a change of crown wheel on its own would not mesh the curve and depth of tooth would not match.
If and when you remove the gearbox you will find markings on the input shaft let me know what they are and I should be able to tell if it is a low or geared box you have.

doujoy

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Sun 25 Oct 2015 @ 19:41 Edit this messageQuote this messagePMQuote this message
Anon
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Okay I've already got my old maths books out from when I was at college and have done some working out based on the tyre size and diff ratio I have.
I've said before I feel the van is most comfortable travelling at about 50-55mph. That's because at 50mph with the standard 195/14 tyre, the engine would do just under 3000rpm which would make it not too noisy. Any more rpm's and it'll start to scream. Doing 60mph the engine actually does about 3600-3700rpm. That's all based on the 1 to 1 ratio of 4th gear and 4,625 diff.
So if I want the engine to be nice and quiet, not strained and get a very good fuel consumption on our long motorway journeys, I'd need a 3.77 diff or lower. This would allow me to travel at about 3000rpm, doing 60mph. Perfect for German motorways and not to get overtaken by every lorry on the way.
Just a few numbers from the calculations.
The circumference of a 195/14 tyre is 2097mm or about 6ft 10".
At 50mph it does 636rpm.
At 62mph it does 795rpm.

So if anybody out there knows about any scrap Crestas rotting away in somebody's garden or yard, please let me know.

Cheers Frank
Sun 25 Oct 2015 @ 19:45 Edit this messageQuote this messagePMQuote this message
Anon
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Thank you Doug. I was typing when you replied and I didn't realise.
So is the Cresta axle an English type axle with the diff fitted in from the front like on many Fords?
Sun 25 Oct 2015 @ 19:50 Edit this messageQuote this messagePMQuote this message
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Looking at your numbers.

Hi XSFrank,

I have the same diff as you have and at 3,500 rpm I am travelling at 60MPH, checking your gearbox will be interesting, and I am running on 185/14c tyres.
So you do seem to be under geared, but if you are able to get a Cresta axle the lower gearing might be a good thing.

doujoy

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Sun 25 Oct 2015 @ 22:27 Edit this messageQuote this messagePMQuote this message
Anon
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Hi all,
Just a little update on my CF modifications.
I've been successful and have managed to get a good Vauxhall Viscount differential to put into my motorhome to improve on the top speed and keeping the motorway RPM's down.

Well it wasn't all that easy and I actually bought a complete car. It's sat in somebody's garden for nearly 10 years and the body is completely shot.
The plan is to strip the car and sell off all good parts to Cresta & Viscount owners so they have some useful spares to keep their cars on the road and looking good.
I've already taken the diff out and been in contact with Adrian Bailey to get the pinion seal and diff cover gasket so I can swap it over before the weather turns cold and too wet.
Had to fabricate a special socket to get the pinion retaining nut off as it sits so far in the diff housing. I've cut the right size socket in half depthways, then welded a piece of scaffold bar in to make it deeper and go over the pinion.

BTW the Viscount was the top of the Cresta range with vinyl roofs, de luxe trims and badges and although made from '69 to '72 they came with power steering, electric windows front and rear, automatic transmissions and were generally the most luxurious car Vauxhall had on offer at the time.

I've also now got to know of another Viscount locally through a friend and I've been in contact with the owner. Unfortunately the guy is a banger racer and the car is being prepared for a big classic race next year.
However I've been able to talk him into taking all sorts of good parts off the car and will hopefully get my hands on them.
He's a nice enough guy and to be fair the car is in a bad state too and would have required more work than is economically viable. It sat around for nearly 20 years!!!
I'll get the rear axle after the race which isn't until next June, so have a spare 3.5 ring & pinion.

Cheers Frank
Wed 11 Nov 2015 @ 20:30 Edit this messageQuote this messagePMQuote this message
Anon
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hey old son you could sell those wing mirror and the screen wipers dont just scrap it frank get some of your ££ back lol..

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Wed 11 Nov 2015 @ 23:36 Edit this messageQuote this messagePMQuote this message
Anon
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You lucky chap - would love to find a high ratio diff for mine, if you have a spare to sell I would be in the market for it :)
Thu 12 Nov 2015 @ 11:26 Edit this messageQuote this messagePMQuote this message
Anon
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guypjfreak wrote:
hey old son you could sell those wing mirror and the screen wipers dont just scrap it frank get some of your ££ back lol..


Don't worry Guy. That car will be stripped off everything valuable. The wiper arms are stainless steel and if they fit, will go on the motorhome :-)
Thu 12 Nov 2015 @ 19:22 Edit this messageQuote this messagePMQuote this message
Anon
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Mikecsailing wrote:
You lucky chap - would love to find a high ratio diff for mine, if you have a spare to sell I would be in the market for it :)


Hi Mike,
I won't get the other axle/diff until after the chap has raced the car in June next year, but will keep you in mind.

Cheers Frank
Thu 12 Nov 2015 @ 19:24 Edit this messageQuote this messagePMQuote this message
Anon
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That works for me Frank, thank you. I shall look forward to hearing how your van feels with the high diff in, much better I would think.

Mike
Fri 13 Nov 2015 @ 09:26 Edit this messageQuote this messagePMQuote this message
Anon
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Time for an update.
Been really busy with work and not had as much time to get on with the Bedford as quick as I thought.
The diff swap was not as straight forward as it appears from all the comments I read on various forums and people I spoke to.
To put it precisely, the only parts usable from a Cresta/Viscount/Ventora diff are the crown wheel and pinion. Nothing else fits, so it's not a "diff swap" in my books.
The whole diff carrier is bigger on the CF, so are the bearings, drive shafts etc.
First I had to make a drive shaft puller aka sliding hammer to get the drive shafts out as the bearings were nice and tight in the axle housing.
I thought I'm clever and get all seals and gaskets from Adrian Bailey beforehand so I had everything to get the job done. I ordered a new pinion oil seal, which, as parts are getting harder and harder to find, was his last one and cost me a whooping £39
Anyway once I had the pinion shafts out, I realised they are different lengths too. The Cresta/Viscount pinion is 1" longer, so I ended up having to shorten my propshaft. Something I thought was not necessary from the inital things I read.
The pinion bearings are the same size on both diffs, but the shafts are also different diameters where the oil seal sits. So the £39 CF oil seal didn't fit Money I could have saved.
Now try and find a pinion oil seal for a '69 PC Cresta. Again not something you can buy from a local motor factor anymore. I managed to get one from an oil seal specialist on ebay who was really helpful, but again it was the last one he had in stock. A proper 70's Payen part. Cost me £14 including postage
However, I got it all back together eventually and it's working a treat. 1st, 2nd and 3rd gear a nice drive around gears and 4th is a great dual carriage and motorway gear. My speedo is about 8mph slower now due to the different ratio, but since I often have a sat nav on, I can get a more accurate speed reading that way. Traveling at 60mph now is still nice and quite. Not so much strain on the engine.
I'm looking forward to our Le Mans trip in July to the 24h Classic race.
Frank
Sun 07 Feb 2016 @ 12:58 Edit this messageQuote this messagePMQuote this message
Anon
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A lot of hard work.

Hi XSfrank,

A lot of hard work but worth for the end result, apart from the rev's being and quieter there will be a fuel saving as well so you see the benefits this summer.

doujoy

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Sun 07 Feb 2016 @ 18:54 Edit this messageQuote this messagePMQuote this message
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