Gear ratios & highway speed

Bob Carriere · #1 25-12-11, 03:59

Fabricate some wheel adaptors to use modern large diametre tires.....

.... or replace both front and rear axles with modern axles, tires, brakes, etc....

I hope you have medicare insurance or some coverage for chiropractor services ..... 15,000 km in that cab could cripple you for life......

Good luck on your venture...... don't forget to take photos and psot them o n MLU.... some of us can't read....

Bob

Ken Hughes · #2 25-12-11, 08:12

Fit a GMC 5 speed gear box,and im sure that there are diferent diff ratios to be had.
20" wheels would be worth looking at as well,just thoughts really,but there is a C8AX here with a 5 speed GMC box fitted,worth looking into.
Your trip will be interesting to follow,merry christmas.

Lang · #3 25-12-11, 09:16

If you took out the front axles (should not need 4WD on this trip) it will improve things tremendously in the fuel consumption/noise/vibration/steering departments. Just disconnecting the drive shaft still leaves you turning over all the axle/diff machinery. If you want to go one step further you could drop out the transfer case for another 50% reduction in gear noise and get a prop shop to make a straight drive shaft.

Not a big job to change diff ratios and probably easier and cheaper than fitting other gear boxes. Half a day at the diff shop and drive away.

If you are going to fit a 5 speed gear box you would be better off with a Toyota Dyna box instead of a big clunky agricultural GMC box. Changing a gear box sounds simple but once started you chase your tail because the new box needs new mounts, gear stick hole has to be changed (and sometimes floor humped), tail shaft length may need to be altered etc.

Lang

lynx42 · #4 25-12-11, 10:19

Peter,
Good luck with the the Legacy trip. I think that is wonderful. If your passing my way there will be a bed available if needed. We could also join your trip for a few Km in our area to help promote the cause.Maybe all Australian MLUers can join for a while along the way as well.

An axle set from a C15A fitted with 20" wheels will be the easiest way to up speed the C8AX. The C15A has 8 stud wheels against the 6 of the C8AX. If you had a spare set of 6 stud centres you could also weld 20 inchers onto them but I guess they are pretty scarce on the ground.

Good Luck and safe trip.

Regards Rick

cletrac (RIP) · #5 25-12-11, 16:30

Older truck type 5 speeds usually aren't overdrives so won't help. Some newer small ones like the T10 would take a lot of work to make them fit but could be done.
The C8A uses one ton rear ends so different ratios might be available. Modern 16" tires are available in quite a few sizes and it shouldn't be too hard to find some bigger diameter tires. They fit the rims and as a bonus you'll get a lot quieter and smoother ride. 4 inches more diameter cuts engine RPMs by 20 %.

Phil Waterman · #6 25-12-11, 18:31

Hi Peter

This issue of more highway speed has been touched on before here is a link to some of them https://www.google.com/search?q=%22H...i&cr=&safe=off

Now on to some of the points that I have experienced in 33 years of driving a 101wb HUP and some 20 years of driving 134wb C60S.

The 20" wheels with 1100x20 tire sould definitely get you up to highway speeds of 60 MPH on the flat with the 216 engine. But I'm not sure the 216 will be happy with sustained driving at that speed for 15,000 Kilometers or nearly 10,000 miles. Remember that your distance target is over the rebuild distance for the engine, though your miles should be cleaner and mostly highway.

Reason I say the C8AX will do 60 MPH is that my C60S with its original 216 engine would pull down the interstate at indicated 50 MPH and corrected road speed of about 60 MPH (rubber overdrive) suspect that if you run military tires you will be replacing them about halfway through your trip.

Once drove my C60S leading a convoy with my foot planted on the floor, never shifting, for an entire morning top speed 65 MPH running away from the JEEPs on the down grades and down to 35 MPH on the hills. On other long convoys the CMP didn't seem to mind it as much as the CCKWs. You could always touch the transmission and transfer case of the CMP with your hand and not get burned, you could not say the same for the CCKWs.

When I up engined the C60S to a 261 it will pull away from most convoys if I want has more speed than I can use. Which brings us to another speed issue with CMPs particularly the 101 and 134 wheelbase they get very lively at speed, think you will find that 60MPH is about tops.

Next noise and vibration, good noise canceling headset with an intercom to talk with anybody riding with you will be essential. Drive train vibration will be something that you will discover for your particular vehicle there will be speeds that everything vibrates and speeds that things seem happier.

I did drive my HUP for an entire year with both of the front inner axles removed. Which did improve fuel economy and reduced the noise. With the axles out the front end is not turning the differential or front drive shaft.

If you go this route I would have your rear axle shafts magnafluxed to look for a problem right at the end of the spines.

One more suggestion get a infrared thermometer and make yourself a temp chart for all the critical points. Then check the temps at the end of the days run. May really help spot a problem in the making before it becomes a trip stopping break down.

Richard Farrant · #7 25-12-11, 19:21

Something else to think about, and I don't think has been mentioned, is raising the gearing with bigger wheels is fine for top speed, but it will mean higher ratios in low gears, and any hills may be more difficult, as the 216 is not blessed with a lot of power, I run a 28hp Bedford (72bhp) and is the British version of a 216, so know what this is like.