1970 C1600 International

Two speed diffs are great ,...but dont overlook the mention of 6 stud wheels ,and ratio may not be 5.83.....thats just the quickest ratio....so check the plate..or better ,the end of the pinion.

Apparently when the Perkins 354 was fitted the rear axle ratio was 5.28

I have a 1730A acco and it has a 5.41/7.44 ratio diff, Rockwell i think. Parts book says that is the faster ratio for that model, the other is 6.16/8.48. It has 20" wheels, hydraulic brakes, air shift 2 speed.

I think the 5.285:1 ratio diff available for Perkins powered C1600 is a single speed diff. At least that's how i interpret the parts book.

That is looking more like John's diff suggestion is the go.

With the power and torque of the Perkins with a 5.28 it makes the 5.83 look about perfect for the power and torque of the 281 petrol. Much better than what you have now. If you think she has more to give, the jump from 8.25 to 9.00 tyres might give you the extra few knots you desire without over cooking it.

Lang

Ahh, i forgot the C1600 has disc wheels, my acco has spiders. Sorry.

As I said before...when buying a diff for a certain ratio,always check the end of the pinion.....And .for information,the fastest ratio in the #2 Eaton is 5.83.....this is from the old Eaton parts book..

Hi Lang my C1600 has disc wheels with 8.25...... just wondering if 9.00 would fit these wheels ?

I will have a look in the Australian Tyre and Rim Association manual (ADR's use this as their wheel and tyre standards.)

I suspect that the actual rim width will be legal. Gut feeling is they should be OK for spacing between the duals also.

It would help if you could tell me the space between the tyres at the bottom where the bulge is. Could work it out simply mathematically to see if 9.00 would touch. If you have larger than 3/4 inch it should be ok.

Let me check tomorrow.

Lang

OK. From the bible.

8.25 tyres require 6.5 or 7 inch rims
9,00 tyres require 7 inch rims.

It is up to you, but if I had 6.5 I would not have any problems putting 9.00 on them for a lightly loaded vehicle not doing commercial work.

The section widths are interesting. 8,25 are 236mm while 9.00 are 259 exactly matching what I thought above - if you have more than 3/4 inch gap between the tyres at the bottom with 8.25 on you will be OK with 9.00.

Make sure pressure is what you want to run at before measuring. For comfort I think if they are standing up pretty straight stop pumping even if they are only 50 for an unloaded truck. If you are going to load her full you may need 70 or more. The book says 65psi will give you max load of 1,580kg per tyre for 8.25 or 1,870kg per tyre for 9.00. By the time you get to 100psi you can add about another 500kg per tyre carrying capacity.

The diameters are not greatly different 8.25 is 974mm while the 9,00 is 1019. Might give you about 5kmh boost in speed for the same revs.

Have got 9.00 on mine no problem 45mph on speedo 78-80 on gps

Hi Lang
The tyre gap at the bulge is 1 1/4" ( 32 mm )