diff ratios

[fc_ute]

we are driving our ute to johns rod and kustom picnic in melbourne in november, and i,m worried about keeping up with all the v8's that are coming as well.
is there a difference in ratios between sedan,wagon or ute centres and if there is how can you tell them apart?

[RET]

I wouldn't be too worried about keeping up, although I haven't been to this run.  With most cruises you're usually in more danger of boiling from the frequent stopping than not being able to keep up...

But to answer your question.  There only one original and stock diff centre for all FEs and FCs, which has a 3.889 ratio.  Having said that, other Holden centres bolt straight in, including 3.55, 3.36, 3.08 and 2.78.  Anything shorter than 3.36 is going to put a lot of strain on first gear when you take off.  3.55 is a nice cruising diff.  My personal opinion is that 3.36 is a bit short for a grey motor, but there are plenty of people running them.  Both these ratios were fitted to EJ-HR, and it's my understanding that autos had the taller version (3.55) and manual transmissions had the 3.36.

As someone driving an FE with 3.36 ratio and a powerglide auto, I can see the logic in that.  

The other common alternative is to fit 14" wheels to the rear, which has a similar sort of effect as shortening the diff.  At least with a ute you've got room to carry two spares  

Hope that helps,

RET

[fc_ute]

it's not the cruising i'm worried about, just the trip across the nullabor from w.a!
i already run 14" all around and was going to put a set of volvo 15" on the back with real tall tyres on just for the long stretch.
so any red motor diff centre will fit? or only up to hr?

[RET]

Perth to Melbourne?  Pants off to you!

I didn't think there were any other red-motor diffs apart from those ratios I mentioned.  Obviously salisbury diffs etc don't apply.

I only mentioned EJ-HR because I was confident about which centre went with which transmission.

Happy trails!

RET

[EJ Dave]

Any 'banjo' diff centre will fit. I am not sure how long these were used but the main gasket that fits banjo diffs is specified from 1948 to 1978- so I guess that probably at least some HZs had banjos.

I replaced the 3.89 diff centre in my EJ with a 3.36 last year. The gear ratio is stamped on the outside of the crownwheel for ratios other than 3.89. I don't think there is any way to tell the ratio without pulling out the centre.

The EJ pulls the 3.36 ratio happily is far more relaxed at highway speeds.  To give an idea, at 100kmh with standard wheels and 1:1 ratio top gear (as in 3 and 4 speed gearboxes) the 3.89 gives 3400rpm (29kmh/100rpm), the 3.55 3100rpm (32kmh/1000rpm) and the 3.36 2900rpm (34kmh/100rpm). Another way of looking at it is that you will being doing the same rpms with the 3.36 at 70mph as you would be doing at 60mph with the 3.89.

Changing the centres is fairly straightforward. The only additional change necessary (unless you want to correct the speedo!) is to an EH-on rear universal joint and u-bollts because the diff yoke is different. The plus to this is that the EH style uni is alot cheaper than pre-EH.

I hope this helps.

David

[ACE]

 ;)HI fc_ute
  ALL BANJO CENTRES FIT, BUT MID HX AND SOME TORANAS CHANGED TO FINE SPLINE AXLES. I'VE HAD GREY MOTOR FC'S WITH
3.36 RATIO AND THIS WOULD BE MY SUGGESTION FOR YOUR REQUIREMENTS. HOPE THIS HELPS.
REGARDS ACE

[fc_ute]

thanks for the advice guys, i've got till october to get a few things finished and then it's the big road trip