Topic: Changing the 5th gear ratio on a R151F box...

[gotoy]

Hi,

I am running a R151F gearbox on a 1KZ engine, Toyota landcruiser.
What I want to do is change the gear ratio on the 5th gear to obtain lower rpm for highway cruising.
So my question is whats the best way to do it?
If it involves making the 1st gear ratio lower too, then thats a bonus.
I have been informed that the parts are available in a R452 box, however I would just rather find the standalone parts and install.

Anyones help of course greatly appreciated.

[jimbo74]

there is a set that will change the ratios, but i am not sure what the current ratio is... i know that it does make the 1st gear lower

http://www.marlincrawler.com/htm/transmission/3a.htm

[gotoy [OP]]

there is a set that will change the ratios, but i am not sure what the current ratio is... i know that it does make the 1st gear lower

http://www.marlincrawler.com/htm/transmission/3a.htm

I have been lookin at that and hence the post here. Also dunno if it changes the 5th gear.

[jimbo74]

do you know what the current ratios is? i will try and find out

[jimbo74]

First Gear: 4.313:1
Second Gear: 2.330:1
Third Gear: 1.436:1
Fourth Gear: 1.00:1
Fifth Gear: 0.838:1

that info is from here: http://en.wikipedia.org/wiki/Toyota_R_transmission so it may not be 100% for sure... but.... if it is correct, it wont do anything for the 5th gear.....

have you thought about changing the axle gearing? thats the only thing i can think of other than adding a klune type undersrive system like they have for samurais.. but i dont know if anyone has that for a toyota

[gotoy [OP]]

First Gear: 4.313:1
Second Gear: 2.330:1
Third Gear: 1.436:1
Fourth Gear: 1.00:1
Fifth Gear: 0.838:1

The ratios as you posted are correct. I have 4.88's in the diffs and quite happy with that on 35" XT tyres. However for normal day to day I am on 31" AT tyres. I just want to lower the 5th gear ratio for the highway.

[jimbo74]

running bigger tires day to day will essentailly make a higher 5th gear ratio

[gotoy [OP]]

Perhaps I just just forget the ratio and go for 33" tyres. Problem is then I cant enter car parks...but on 31" its perfect.

Still looking at the ratio change.

[DTB]

Perhaps I just just forget the ratio and go for 33" tyres. Problem is then I cant enter car parks...but on 31" its perfect.

Still looking at the ratio change.

Whats a "car park" ??

[jimbo74]

Whats a "car park" ??

sounds liek a parking garage

[gotoy [OP]]

I mean multi storey car parks. Underground can be included. Height usually restricted to  2.2m. If I use any tyres bigger than 31" then I won't have a roof.

Sometimes use my 4x4 as daily driver, hence 31" tyres.

[Rockcrawlintoy]

I mean multi storey car parks. Underground can be included. Height usually restricted to  2.2m. If I use any tyres bigger than 31" then I won't have a roof.

Sometimes use my 4x4 as daily driver, hence 31" tyres.

wow how tall is your truck. at 2.2 meters thats a hair over 7 feet even my truck will fit in there with 37s

[gotoy [OP]]

Must be 2m.