4.6 ratio

[TuffTD42]

Hi guys, maybe someone can explain why i come up with the following.

I swapped ratio's from 4.11's to 4.6's yesterday. I checked the rear ratio on the vehicle i was pulling it out of to make sure they were 4.6. I didn't check the front, but now I have installed them I rechecked because I didn't get the jump up in rpm at 100kph I thought I would get. Approx 2400rpm @ 100kph on 35's. From what I've read should have got around 2600rpm on 35's.

I put a piece of tape on one wheel nut & on the guard & marked the yoke. I got my oldest son to turn the wheel one revolution while I counted the revs of the yoke & got approx 4.6-4.7 turns. So the rear should be 4.625:1. We done this to the front & the front gives half, approx 2.3 revs. I am racking my brains but can't figure it out. I thought the front yoke would have to turn the same amount of revs as the rear?

As I'm not the smartest cooky maybe someone can point out why the front turns half as much as the rear.

cheers Jono.

[MudRunnerTD]

I am not sure there TuffTD42, i like your measuring trick though

on a side note the measurement you get on the front is exactly half what you are expecting to get so is a division of 4.6 and there is some logic there. If it was 2.15 on that logic it would be 4.3s and so on.???

If the car they came out of was a runner and you did not mix up the fronts when you took your other one out then i dont think you should do your head in mate, it will likely be the output from the Transfer and by design.

If in doubt take it to the dirt and put it in 4x4 and you will not get more than 3m without knowing your answer mate. Gently!

[TuffTD42]

Cheers mate. The front gets half of the rear @ 2.3 approx.

[gq4200]

Front is an open diff you need to keep one wheel on the ground while doing this test. With LSD rear you need both off the ground. Other thing is try driving in 4wd. If the front ratio is different to the rear you will know quick smart as it will be doing all sorts of nasty things.

[the evil twin]

snip...now I have installed them I rechecked because I didn't get the jump up in rpm at 100kph I thought I would get. Approx 2400rpm @ 100kph on 35's. From what I've read should have got around 2600rpm on 35's.

Were you using your speedo or GPS to check the 100 KPH revs? If it was your speedo there is your problem as the "revs per 100" won't be affected by the diff ratio as the speedo pick up is in the Gearbox. You could put 10:1 in the diffs and the RPM versus Speedo will still be the same. All you have done is changed your speedo versus actual error as you will actually be doing about 40 KPH.
If you used a GPS then something else is suss if you still have the same revs

Front is an open diff you need to keep one wheel on the ground while doing this test. With LSD rear you need both off the ground. Other thing is try driving in 4wd. If the front ratio is different to the rear you will know quick smart as it will be doing all sorts of nasty things.

Agree 100%... try the same test again but with someone holding the other front wheel or with only one front wheel jacked up

[YNOT]

Front is an open diff you need to keep one wheel on the ground while doing this test. With LSD rear you need both off the ground. Other thing is try driving in 4wd. If the front ratio is different to the rear you will know quick smart as it will be doing all sorts of nasty things.

Were you using your speedo or GPS to check the 100 KPH revs? If it was your speedo there is your problem as the "revs per 100" won't be affected by the diff ratio as the speedo pick up is in the Gearbox. You could put 10:1 in the diffs and the RPM versus Speedo will still be the same. All you have done is changed your speedo versus actual error as you will actually be doing about 40 KPH.
If you used a GPS then something else is suss if you still have the same revs



Agree 100%... try the same test again but with someone holding the other front wheel or with only one front wheel jacked up

This is how he got the incorrect reading. By turning one front wheel while the other is being held stationary the diff side gear is able to rotate the sun gears meaning the diff pinion only rotates half as far as it otherwise would. He needs to have the vehicle on the ground and push it forward in a straight line so both front wheels rotate together.

Tony

[the evil twin]

Hiya Tony,

Yeah, pretty much gotta be eh... and I reckon the reason the revs didn't change at 100 KPH between the 4.1's and the 4.6's is that the 100 KPH was off the Speedo

[patch697]

Hiya Tony,

Yeah, pretty much gotta be eh... and I reckon the reason the revs didn't change at 100 KPH between the 4.1's and the 4.6's is that the 100 KPH was off the Speedo

Yep agree with ET here......

No change in the speedo/ tacho relationship would only be he's not changed the speedo drive to mach he's new diff/tyre combo.

[portal pat]

2400 at 100kph on 35s would be right with 4.6s old mate. I have 35s with 5.0 diff ratio (i.e. 4.11x 1.22 portal hub reduction = 5.01:1) and I get 2650 at 100kph. So you are on the money and should be loving it!

[iht2670]

Yep agree with ET here......

No change in the speedo/ tacho relationship would only be he's not changed the speedo drive to mach he's new diff/tyre combo.

Yes this would be correct.

Steve.