bigger cog in 5th

[sjp]

excuse my lack of knowhow ,but how easy ,or more to the point,how expensive will it be to change the final drive in my 105 cruiser to a higher gear, at the moment its only 500 rpm lower the 4th,has'nt the gxl got a higher cog in fifth.

[mico]

What gearbox is in it,if it's a R150f you can use the 5th gear out of a Supra (not sure what model) they are a decent O/drive should knock about 1000rpm off what 4th does

[sjp]

its the r151f,does 2400 rpm @100k/hr ,hoping to lower that to about 2000rpm

[dumbdunce]

gxl/dx matters not, it's the engine that determines the gearbox. the R151F is a gearbox borrowed form the hilux family to keep cost (and, argues Toyota, weight) down on diesel 105 series.

it may be possible to use the supra 5th gear as the R151 and R150 are essentially the same gearbox, with slightly different ratios in the lower gears.

you don't want to make your 5th gear too tall or the mighty 1HZ just won't turn it, you'll be flicking it back to 4th for ever little hill or headwind - the 105 is a heavy truck and the notice the hills.

another option might be to fit slightly taller tyres, something around 33" diameter will give you about 5% rpm reduction so 2400rpm will become 2280rpm at the same road speed, not much but might make it a bit quieter and still keep the motor spinning happy within its powerband.

cheers

Brian

[RUFF]

If these run the same box as the late hilux why do they shift like a truck? Or maybe mine had an issue?

[dumbdunce]

If these run the same box as the late hilux why do they shift like a truck? Or maybe mine had an issue?

they are usually pretty good for the first 50,000km or so, they have triple synchros on 1,2,3 and double on 4 and 5 from memory, but the constant load of 2.5T of truck takes its toll and they start shifting pretty rough. They are also very sensitive to oil additives and some oils will make them feel a lot worse than they really are. If it's ever been used to tow more than a box trailer full of firewood, that's enough to do it in.

[slowhilux]

I think the R150/151 have a 0.86:1 5th gear. The R154 (Supra box) has 0.75:1 5th gear. Unless the 1HZ is t/charged, it will struggle to turn the much of an increase in ratio, as Brian said.

[sjp2]

thanks guys ,enough said ,i'll leave it as it is .i beginning to regret the selling the 80 series

[pridhac]

My 1HDT powered 80s could use a higher 5th.

I run 33" MTR and it spins at 2800 at 110kph.

Can I put a R154 5th gear in it?

Lower revs at cruising speeds would be great, and I don't think the motor would struggle to pull a (significantly) higher top cog.

How easy will it be to source the required parts?

[slowhilux]

I doubt very much anything from an R series box will fit a H series, everything in a H series is bigger/stronger. i have neard of a few R151 equipped 105 series cruisers spitting the box's before 100K km. never heard of a H150/151, dying, even in big cruisers

[dumbdunce]

the 5th gear in the H150/H151 gearboxes is right in the middle, the gear doesn't come off the laygear so it's not changeable, even if parts were available.

your 1HD-T shouldn't be spinning that fast, I think mine does around 2400 at an indicated 100km/h. not 100%, if I have a chance tonight I'll take it for a spin to check.

[pridhac]

Cheers DD, a comparison would be great.

It does seem like too many revs. Curiously, fuel consumption remains quite good at around 13L/100Km.

A shame that 5th can't be changed. I dared to dream for a minute...

I have considered going up to 35" tyres to reduce cruising revs, but am loathe to do so as most of the K's this vehicle does are in town and surely fuel consumption would suffer.

Anyways, be great to hear what your 80 is doing at 110kph.

Cheers,

Chris

[pridhac]

Can anyone recall what revs at what speed their TD 80s do?

[slowhilux]

My 1HZ turbo does ( from old calculations ) 2270rpm @ 100km/h, with 315/75/16 tyres

[dumbdunce]

2550rpm@ indicated 100km/h which is a true 111km/h with the 315's, which is about spot on 2300 @ 100km/h - Phill's 315's must be a little bit bigger than mine.

by my calculations you should be a shade under 2700 @ true 110km/h, 2800 isn't right.

[+dj_hansen+]

Cheers DD, a comparison would be great.

It does seem like too many revs. Curiously, fuel consumption remains quite good at around 13L/100Km.

A shame that 5th can't be changed. I dared to dream for a minute...

I have considered going up to 35" tyres to reduce cruising revs, but am loathe to do so as most of the K's this vehicle does are in town and surely fuel consumption would suffer.

Anyways, be great to hear what your 80 is doing at 110kph.

Cheers,

Chris

Marks 4WD do an air operator overdrive... your probably want to be lying down when you find out the pirce tho... possibly have a few scotches aswell.

[slowhilux]

Brian,
The tread depth on the BFG Muds (my tyres) is 16.7mm, 884mm overall diameter. What are the specs on your tyres?

[dumbdunce]

Brian,
The tread depth on the BFG Muds (my tyres) is 16.7mm, 884mm overall diameter. What are the specs on your tyres?

The coopers are slightly smaller then: 879mm overall with 15.9mm tread, 5mm difference in diameter isn't quite enough to account for that difference, but the gauges are hardly accurate enough to see a 30rpm difference anyhow.

surprising the coopers have less tread than the BF's. I have over 70,000km on the coopers now and they have about 6 - 7mm tread left except where the chunks have torn off...

[slowhilux]

I have nearly 60,000km on the BFG's, and they have about the same 6-7mm tread left. got a feeling the BFG rubber is a bit softer, plus i only ever rotated them once . Have run 40psi in them most of their life.