What diff is it ????

Gday all.
Have just picked up a pretty clean Inter C1300.
It's an older restoration but pretty close to original as I see it. Might be corrected by any of the viewers at the Albury/Wodonga group meeting today, but I'm happy with the purchase.

I have only had it for a few days but the 400K drive home from Geelong told me that the diff ratio is too low for what I want to do with it.
I travelled home at 90Ks (speed measured by a GPS) and wouldn't have felt comfortable pushing the motor any harder (although I had no tacho to give a true reading) even though the throttle was only a quarter way to the floor for most of the time, which leaves me with 2 options as to fixing it. Bigger tyres (20") or a highway diff.

As the truck is set up with a 14' beaver tail tray (and, yes it meets the 60% rule to the millimetre) I am a little hesitant to go the road of bigger wheels. Doesn't seem logical to increase the tray height on something that has a cut back rear end for loading.
It also has the disadvantage of being extra hard to pull up (Braking wise), and it's not over exciting as it is.

I jacked it up in the carport this morning and got the kids to help me with a ratio count. It came in about 10% short of 5 rotations, so I am calling it as a 4.88:1 diff centre.

So here's my question. If I want to go chasing a different ratio diff, what do I call this type of diff. I have know idea as to the correct description.
I seriously doubt it would be called a Rockwell or Eaton, so what do I tell the fella on the other end of the phone what it is I am chasing???

As for the ratio. I believe that something very close to 4 would be what I am after. 4:11 or high 3s would be perfect as it would give me a highway speed of about 110 at the same revs I am doing now.

All and any help with this would be much appreciated.

Cheers. Cobba.

Cobba, I am no expert at all, but I discussed this topic with Bob at Midlands recently, and if I recall it right you will have a DANA (spelt???) diff and Inter had only one ratio in the smaller truck, but Dodge and Ford used DANA too with various ratio's so you can pop the centre from a better ratio one of the others in to yours..

but I do stand etc.... (and probably will be)

/me

i dont know to much about diffs ..but from memoery there wasnt much difference in the ratios of the small dodge and inter diffs ...but i think ford mite use the same? diff in their F series F350 maybe..most likely they would have a better ratio as well if they do

The one I've got in my F250 cruises all right at 100 km/h. They are a salisbury type diff though, so you'd be changing the whole axle, unless you can get someone to do the crown wheel and pinion in the truck.

I would have thought a diff ratio of 4.88 would cruise comfortably at 100km's.Wouldn't that be considered a fairly high ratio for that model inter?

Might be worth hooking up a tacho temporarily to see what revs it is doing at 90

i dont think the inter motors rev much past 3000rpm ..at 3500rpm they would be getting a bit loud

The Inter motors, in order, produce maximum HP at the following RPM ..

6 cyl .. AGD-240 (tilt valve) .... 135 BHP at 3800 RPM ..
6 cyl .. AGD-264 (tilt valve) .... 142 BHP at 3800 RPM ..
6 cyl .. AGD-282 (tilt valve) .... 148 BHP at 3800 RPM ..
8 cyl .. V-345 ....................... 165 BHP at 4000 RPM ..
4 cyl .. 4-152 ....................... 82 BHP at 4400 RPM ..

All the 6 cyls, and the V8, will pull up to 4500 RPM on the governor .. and the 4-152 will pull nearly 5000 RPM, pedal to the metal.

The 6's and V8 will sit on 3500 RPM very happily, and pull 4000 RPM continuously on the road .. all you need to do, is keep the fuel up to them ..

Try some of the American diff places for gears and centers. I know a guy who bought a early 70's F350 for the diff and put it in to a Similar sized inter and got some taller gears and a locker for it from the U.S for it. While the dollar was in the 90's it worked out almost cheap.
Try
www.ringpinion.com
www.strangeengeering.net

Gday all and thanks for your input.

I have looked around on the Internet to check out Dana rear ends and I am not sure mine is one of them.
All the Dana 60s and 70s that I came across were what I would call unit construction, as in the diff is assembled as an entire unit into the housing.
My diff is a removable centre, similar to a Ford 9" except a fair bit bigger. It's a bit dark and cold to go and have a real look but I am guessing it would be about 14" in diameter where the flange bolts to the housing.

aktipete, I reckon your right. I should hook up a tacho and see what it really is running at, but my gut feeling is that it's up in the high 3000s at 90Ks. I ran it up to 100 a few times coming home passing slower vehicles (Yes there were some people slower than me ) and I really wouldn't have felt comfortable holding it there for more than a minute.

onetrack, You are a wealth of knowledge. I have no reason to doubt you but I am surprised to here that a long stroke motor like the big Inter six would comfortably rev so hard.
And you spot on with your comment about keeping the fuel up to them. I am using a litre for every 3.5Ks I do. That's less than 10 miles to the gallon in the old scale. Another good reason to change the ratio I reckon.

Cheers. Cobba.