whats the best diff ratio ?????????//

[guzzla]

looking at changing the diffs in the 80s. currently runs factory 4.111 with 35in tyres. research so far suggests that 4.56 will get me back to near factory specs which is what id like to achieve.
can anyone suggest otherwise ?

thankyou.

[matt.mcinnes]

looking at changing the diffs in the 80s. currently runs factory 4.111 with 35in tyres. research so far suggests that 4.56 will get me back to near factory specs which is what id like to achieve.
can anyone suggest otherwise ?

thankyou.

Just got my FJ 40 back from having 4.56's put in much better on its 34's. But depends what you want them to do. Remember this, the hight the ratio the smaller the pinion gear gets and the smaller the pinion gets the weaker it gets.

[dumbdunce]

looking at changing the diffs in the 80s. currently runs factory 4.111 with 35in tyres. research so far suggests that 4.56 will get me back to near factory specs which is what id like to achieve.
can anyone suggest otherwise ?

thankyou.

what engine are you running? if it is a 1HZ, consider turboing it up - similar cost to diff ratio changes, but with many more advantages - more power, potentially better economy, lower highway rpm, the 4.1 gears are stronger than 4.56 or 4.88's, and if you do happen to break a diff, you can just get one from a wrecker or whatever instead of having to shell out again for aftermarket gears.

if it is a 1FZ-FE then it should handle 35's and 4.1's without trouble. If it is a 3F or 3F-E then the truck isn't worth spending the money on for diffs or turbo. If it is a 1HD-(F)T, then turn the boost up a bit - zero dollar solution.

if it's the crawl ratio you are trying to fix up, I guarantee you will be disappointed with a diff ratio swap - a 10% reduction (4.1 to 4.56) is next to nothing, you probably won't even notice it. With an 80 your only real option is the cruiser crawler from Marks, but it's big dollars to buy and bigger dollars to fit. The upside of an 80 is the good factory crawl ratio and torque to spare - they crawl well even on 35's with factory gears.


cheers

Brian

[guzzla]

Matt, thanks for the heads up on the pinion weakness issue, i didnt know that. hopefully being twin locked it will give it somewhat more strength to compensate. good to know your happy with your results in your beast

Dumbdunce, its 96 model petrol 4.5l. i would like to get the gearing back to near standard as at the moment when crawling larger obsticals its necessary to give the clutch a fair workout. as for price i only have to pay for the centres about $1200 for the pair as im having the centres removed under warranty to repair the leaking lockers anyway. ive been told that at aprox 110kph with 4.56s il be doing 3000rpm and 3200 with 4.8s. im currently sitting at 2600 rpm with factory 4.111s. its not about power as i have enough considering, its about the gearing of the vehicle overall.besides, im taking advantage of the centres already being out.

i was following an identical vehicle to mine but with 33s and on one particulay hill i was constantly on the brakes and he never touched them (and yes we were in the same gear same range). would to 10% increase not multiply its self when in low range ?

[beanz2]

I am running 4.88s with 35" tyres in my troopy. Checked against a police radar the speedometer is accurate within 1 kmh, indicating that the gearing is very close to the factory set up. Yet, with the new 1HDT the 4.88's feels too low as there is so much torque in low RPMs. I'll eventually go back to 4.11s.

My point is if the engine has plenty of torque, too low a gearing can affect its roadability. For lower crawl ratios it's best to have a lower low range in the transfer.

Dave

[guzzla]

beanz2, thanks for the info. i have heard off a few people that 4.88s would be too low and most people have recomended 4.56s as the best compromise. while im not out to make it crawl like a slug i would like just a mild decrease in low range crawl speed.

i had considered the transfer case adapter as the ultimate fix but have a mate whos hade nothing but dramas with his resulting in his being removed, now hes $5000 down the shute. i also know a few others in a similar situation. when marks can offer a money back gaurentee they'll work, ill get em.

thanks for the advise guys much appreciated.

[dumbdunce]

i was following an identical vehicle to mine but with 33s and on one particulay hill i was constantly on the brakes and he never touched them (and yes we were in the same gear same range). would to 10% increase not multiply its self when in low range ?

10% is 10% whether high or low range - it's not much. It will be better but not heaps better - don't expect miracles! I still hold that the 4.1's are the pick - strong, cheap and readily available, and great highway rpm to boot. A big truck like the 80 needs a little momentum on the hills, it's only big rocks you need to work the clutch on!

This is completely out of left field; it may be possible to tune the 4.5 for better low end torque by changing the cam timing - specifically retarding the timing of both cams a little, and reducing/eliminating overlap (retarding the exhaust cam a degree or three more than the inlet cam). This will have a negative impact on peak power and higher rpm efficiency though - and i have no idead if they cam sprockets are adjustable or if vernier sprockets are available. Of course if you want real stump pulling crawl torque, you can't go past the diesels

cheers

Brian

[matt.mcinnes]

i was following an identical vehicle to mine but with 33s and on one particulay hill i was constantly on the brakes and he never touched them (and yes we were in the same gear same range). would to 10% increase not multiply its self when in low range ?

10% is 10% whether high or low range - it's not much. It will be better but not heaps better - don't expect miracles! I still hold that the 4.1's are the pick - strong, cheap and readily available, and great highway rpm to boot. A big truck like the 80 needs a little momentum on the hills, it's only big rocks you need to work the clutch on!

This is completely out of left field; it may be possible to tune the 4.5 for better low end torque by changing the cam timing - specifically retarding the timing of both cams a little, and reducing/eliminating overlap (retarding the exhaust cam a degree or three more than the inlet cam). This will have a negative impact on peak power and higher rpm efficiency though - and i have no idead if they cam sprockets are adjustable or if vernier sprockets are available. Of course if you want real stump pulling crawl torque, you can't go past the diesels

cheers

Brian

Some body spends far too much time reading