BUGA Community
General Category => CF Bedford Chat => Topic started by: Bedfordcrazy on March 25, 2010, 05:12:05 PM
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hey guys, can someone confirm a terminology I have heard. Ever since i have had my van, everyone that has looked at it, or the diff, they ask if it is a highway diff. Is there such a thing as a highway diff or is that just a slang term, if there is what is a hyway diff. My understanding of a hyway diff is, a diff that can cruise on the freeway, and not rev hard. Is this correct ?
George. ???
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yup
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it's basically the diff ratio
2.75 to 1 or the other end 4.11 to 1
good for the drag strip or the highway
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yes George your right, one that cruises the hwy without reving the crap out of it, another way of redusing the revs on the hwy is with an overdrive trans. Put the hwy 2.78 or similar with an overdrive can cause alot of strain
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George
To understand the "highway diff" you need to understand the "diff ratio"
as said the diff ratio ranges from High 2's to low 4's. This ratio is the relationship between the number of revolutions the engine turns compared to the turn of the rear wheels which is determined by the crown wheel and pinion in the diff.
For every turn of the rear wheel you have X turns of the engine, where X is that relationship of the crown wheel and pinion.
How to find out what ratio your diff has can be as simple as looking at the dust cover disk on the yoke of the diff (the ratio is usually stamped on the disc) or by counting the numbers of turns of the tailshaft for a full rotation of the wheel.
So if you have say 3 tailshaft rotations to 1 wheel rotation you get a 3 to 1 ratio or as it is more commonly writen is 3.0:1.
This ratio can also be looked at like leverage the higher the ratio, the less force is needed to do the same work.
OK so now if we have two diff ratios (lets use BusyKiwi's numbers) what will be the different behavior.
So we have the same van same engine but all we do is change the diff how will the van proform.
Lets start with the 4.11:1 one first, the engine will have to turn over over 4 times for for one rotation of the wheel, now this means that for a given distance the engine will have to turn over more times so it would travel the distance slower.
But this greater leverage means that it could also do more work, as in move greater weight over that same distance.
So to move large weight, a sacrafice of top speed is made for increased load carrying, which is what the Beddys were designed for, also in England the likely speed the van would do is only up to 80kph.
With the 2.75:1 for the same distance the engine will turn over less or alterantly go faster for the same engine revs. This is what we want for the "Highway".
This ratio has less leverage and therefore would not be able to do as much work as the 4.11:1.
The 4.11:1 diff will get up to maximum speed quicker than a 2.75, but it will have a lower top speed.
In drag cars they want to get up to speed ASAP, and they have heaps of HP and only a short distance to do it so the High ratio is best.
Where as in a touring van you wan a balance between power, speed and fuel economy and the lower ratios suit that more.
Warren
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hey george just to add to what everyone else says..
and im not sure if im correct so correct me if im wrong..
no one talks about hwy diffs except round bedfords because of the standard diff issue..
so when we talk about a hwy diff generally talk about a bedford diff being cut and moded for a different centre in it to create a "hwy" diff..
if you just wak a holden diff in a van or something similar you will achive the same result but i wouldnt call it a hwy diff, more call it a standard diff with a reasonable ratio and not enough width for the bedford..
thats what i think anyway..
cheers
ben
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Thanks Guys, I have learnt a lot in the last few days, between my mechanic and you guys here i'm learning a lot about mechanical and fabrication, i have always had a passion for working on cars, one reason why i have my mechanic do the work in my workshop, so i can get my hands dirty as well. My hope is that when I start to show my van later this year, I will be able to answer all the Qs. that people may ask, because i helped on every part. All going well now, we should have all the mechanicals done by the end of april, and then we start sheet metal work.
George.
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Another question....
Do you have to change the tailshaft when you change diffs or modify the centres? I have a diff here from a Kingswood, haven't measured it yet or looked at the ratios..so if i did fit it (not sure if it will be the right one tho) would i need a tailshaft from a kingswood?
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i think at one time when corresponding with u ben , u refered to my 9 inch. . .diff that is ;D as a highway one after i had worked out it had a 67 bango casing an a 65 front piece a sort of hybrid of two different years put together to give it that ratio it needs for hway cruisin, made sense to me anyway mate, another gem from yor wealth of knowledge for which i am eternally grateful. ;)
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hey mark have sussed out different diffs in th holden range some can fit though it is extremly tight.. joe has done it an explained enough to me to to realise it woz easier to leave the ford 9 in an just bung a few bannanaskins in it to shut it up ::) . . only jokin bout the latter . but for sure joe is in the know on thatun
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hey markb not sure that a hq tailshaft will be right length but i will have the right uni and tailshaft yoke.youd just need to get it lengthened or shortened if its wrong length..
yeh probably have trouble with widths on a holden diff.. see how you go.. make sure its not 2.78 ratio either youll never get your van out of your driveway. althou you have a strong 6 ay.. hey man you should work on haveing your spare motor on a front end and everything.. thats what ill do one day have a spare motor front end and gearbox all sitting there in case something ever happens:) ben
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Benny, that's a flocking brillient idea bro ;D now that makes heaps of sense ay? That has to be one of the smartest things i've heard of. Do any of the vans your gonna wreck have front ends still? i'd still put new tie rods n bushes etc. on it - so doesn't have to be great??
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Hey MarkB....I have a HQ diff in my truck and if memory serves me right,it has a ratio of 2.75? :-\ It was put in by the previous owner which said they bought an old HQ wagon and swapped over the whole drive train except the tailshaft. That was another whole story in itself because it is a lwb. My truck cruizes along quite easily on the freeway. But it will pull a heavy load as long as you take it easy. Has a 173 auto in it. Apart from the diff being a bit narrow i find it a good diff. ;D
(http://i198.photobucket.com/albums/aa315/johnabbott_2007/Diff01jpg.jpg)
(http://i198.photobucket.com/albums/aa315/johnabbott_2007/Diff03jpg.jpg)
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Awesome, thanks John ! So the original Bedford tailshaft was used for the HQ diff? And if so, is this the case with any diff? Can you just use the original Beddy tailshaft? or is it about the uni joint..or ... um....er.... yeh - i'm confuzzled....might just call one of you blokes for a chat soon me thinks ;D
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Mark...I ended up having a custom tailshaft made up by a company here in Perth (Hardy spicer) bloody brilliant mob. The original lwb one was just an abortion of a thing. >:( Maybe one of the other members would be able to tell you.? Anyhow its not to hard to get one made up for your application. ;D ;D
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yeh i got a few front ends coming up..
yeh go the holden tailshaft bro.. would be easier cause it will all bolt up as long as its the right length..
ben
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Ok I have a lot of catching up as I plan the drive train, but back in the day I am sure that the salisbury 3.08 diff was all the go is this still valid or are there better options, and as cars are generally narrower than the cf what is required to address this problem
cheers Paulo
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The Salisbury diff is still a good option to keep the Holden stud pattern, or some people fit a later commodore diff (VL-VN?) to get disc brakes on the rear. If you're fitting a V8, a nine inch diff from a mid 60's galaxy is the go, large finned drums and the right width (about 1450mm from memory) for a Bedford. Will fit 15x10 wheels at the rear with flares.
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Thank you Zeeman
I am more likely to go with an updated 202 from the commodore VK, as I am finding out that red tape here in SA is very expensive, I will be converting to all round disc brakes power steering and fuel injection setting it to run on unleaded, and move the old girl a little toward the 21 century while trying to keep the engineers payments to a bare minimum,
Paulo
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Sounds like a good plan. Consider a V6 conversion too, the VN-VP series motor is cheap, reliable, and has overdrive transmission already. Plenty of conversions been done before, so should keep the engineer hassle to a minimum. Lots of threads on here about brakes & power steering, Transit power rack & HQ discs used to be the most common, but there are a few other options nowadays.
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bedford diff housing is1568 mm flange to flange and 1728 drum to drum, vs commodore is 1455 f to f and run a 722 mm short axle and 820mm long axle, so you cut short side of housing, sleeve and extend to run 2 long axles, now 1555 flange to flange. disc to disc is1677 so to get tracking same as front you change offset of commodore rims to hq back space. or restud pcd of axles to hq and run hq rims.
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If you are going for a VK EFI. you will need to modify the engine bay a bit to fit it in. Also, don't forget, there are options of fitting a 4 speed holden auto or 5 speed celica to a red motor.... and keep Regency happy... (regency is the inspection station for all those non- adeladians).. As far as I know, as long as the engine is the same type, there should be no issues, just an identity check prior to rego. And that does not require a pit visit... as long as it LOOKS LEGITIMATE!! Anything that look dodgy, they can "require" you to have a full inspection. What I do is have everything nicely "marked" to make their job easier...like highlighting the engine/body number - chalk works well.... and, well, you know what I mean. Make it look standard...quiet.... an...um...unobtrusive... and they will sail it thru! And if it has SA rego already, well, it's just walk in! - I don't think having EFI is an issue... and they came with 202's.
As for diffs... well, that depends on what your running...tyres/gearbox ratio and engine power band. My traytop runs a 3.5 diff with a 186/trimatic... and I am fiddling to get better drivability- apparently it has 100 ish rear wheel HP, but my economy sucks!.
I run the standard drums and find them acceptable- never had fade. All it means is that I don't get 10 feet from the car in front before I brake!
Cheers & good luck... Russell