1hz high rpm in 5th gear (2 Viewers)

[Kamran Khan]

I don't have much experience with diesel engines. So whenever I am driving my car in 5th gear and I look at the rpm or hear the engine noise I feel like the transmission is in 4th gear but when I check the gear shifter it's in 5th.
Engine revs always fools me to think that maybe it's still in 4th gear, but every time I check it, it's the 5th gear. I am only used to smooth petrol engines. 1HZ is loud and rough like a tractor.
Is it normal behavior, or should I get the transmission and get it checked?
Thanks!

 

[s13koop]

Is this a manual cruiser?
The early H series is kinda known to have a high 5th gear
(edit)
It seems you have an HZJ105...?

 

[Kamran Khan]

Yes, it's 2005 manual 105. It has R 151F Transmission. I think H series transmission is in 1hdt.
I found two engines in used car parts marketplace. 2UZ and 1HDFTE with wiring and ECU for 5 grand each, but If somehow I can fix this high rev problem, then I don't like burning money on replacing engine and transmission.

 

[s13koop]

Is it swapped? I'd find it hard to believe there's an R series transmission mated to that thing.
Its been documented before here but a few have changed the 5th gear to use the H152 5th to lower the RPM

 

[Kamran Khan]

No, it's not swapped. It came from factory. Here is the picture of chassis plate.

 

[s13koop]

Well I stand corrected. Then altering my original comment, you may have to go with 5th gear from an R154

 

[Kamran Khan]

I just read @mudgudgeon comment about 5th gear failure on R151F transmission here R151f Swap? - https://forum.ih8mud.com/threads/r151f-swap.1278633/
I wonder if that is the case with mine too?

 

[Kamran Khan]

Well I stand corrected. Then altering my original comment, you may have to go with 5th gear from an R154

Does that mean I have to change the transmission to R154?

 

[s13koop]

No, just the 5th gear and related parts.
All R series parts should interchange.

 

[Kamran Khan]

Found this Changing the 5th gear ratio on a R151F box... - https://board.marlincrawler.com/index.php?topic=45357.0
I believe I need to switch to bigger tires to solve the problem. Currently, I am using factory stock tires.

 

[Kamran Khan]

So, basically I have two options, either replace the 5th gear with the one from R154 or switch to larger tires. Finding larger tire size is easy, but then it will struggle to go uphill.
Anyone knows what is the part number for 5th gear in R154 trans?

 

[Kamran Khan]

Just found that R154 is not a 4wd transmission, and it's made for sedan cars. Toyota R transmission - Wikipedia - https://en.wikipedia.org/wiki/Toyota_R_transmission

 

[Hulsty]

RPM's are normal, if you drop the rpm will it have enough power to pull the speeds you want? 3000rpm is fine, I've spun a 1HZ+T to 6000rpm.

 

[Kroll]

Your RPM's seem a bit on the higher side. I have a R151F in my HZJ79 with factory 4.3 gears in the axles and 255/85R16 tires.
When I am doing 120km/hr as per my speedometer my RPM's sit around 2500-2600.
A set of larger tires will give you a margin of "rubber overdrive."
My solution to get the RPM's down is to install a H152 transmission - it is a bigger job than just changing out internal gears.

 

[Kamran Khan]

Your RPM's seem a bit on the higher side. I have a R151F in my HZJ79 with factory 4.3 gears in the axles and 255/85R16 tires.
When I am doing 120km/hr as per my speedometer my RPM's sit around 2500-2600.
A set of larger tires will give you a margin of "rubber overdrive."
My solution to get the RPM's down is to install a H152 transmission - it is a bigger job than just changing out internal gears.

Would I need some sort of adapter to mate it with 1hz?
I can get the job done for less than 50 USD by a professional transmission shop, as long it doesn't need any adapter.

 

[Kamran Khan]

Gear ratio for 5th gear for R151 F transmission, is 0.838:1
Gear ration for H152F on this website Gearbox Upgrade - H152f H150f LTG4x4 - https://ltg4x4.com.au/product-category/gearbox-upgrade/ is 0.750
isn't the gear ratio on H152F smaller than R151F? If so, then it would mean the RPM in 5th gear would be higher on H152F transmission.

 

[Kamran Khan]

 

[Kroll]

Would I need some sort of adapter to mate it with 1hz?
I can get the job done for less than 50 USD by a professional transmission shop, as long it doesn't need any adapter.

To swap in a H152, you would need a H15# series bellhousing, and then you would have to swap out the input shaft and input shaft retainer on the H152 to fit a 1HZ/ 1HDT variant motor. Like I said, it's a bigger job. But you gain a stronger transmission capable of handling more torque.

Gear ratio for 5th gear for R151 F transmission, is 0.838:1
Gear ration for H152F on this website Gearbox Upgrade - H152f H150f LTG4x4 - https://ltg4x4.com.au/product-category/gearbox-upgrade/ is 0.750
isn't the gear ratio on H152F smaller than R151F? If so, then it would mean the RPM in 5th gear would be higher on H152F transmission.

You have it reversed. A lower number like 0.750 means that the motor spins less revolutions to turn the wheels one full rotation.
Your RPM's would drop.

Gearbox Upgrade - H152f H150f LTG4x4

ltg4x4.com.au

 

[mudgudgeon]

Is it swapped? I'd find it hard to believe there's an R series transmission mated to that thing.
Its been documented before here but a few have changed the 5th gear to use the R152 5th to lower the RPM

You have transmission series ass about

 

[AirheadNut]

Swapping the 5th gear from an R154 will not help; the countershaft ratio in an R154 is different from an R151 and swapping the 5th gear will result in a 1:1 5th gear ratio. Your options for swapping 5th gears in an R151 would be to use a Jeep AX15 5th gear (small amount of machining required) which would give a 0.75:1 ratio, or a Toyota R452 5th gear which gives a 0.69:1 ratio. I used the R452 5th gear and have been pretty happy with it, though the jump from 4th to 5th is pretty significant.