93 Hdj81 37" tires and diff gears? (1 Viewer)

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I'm looking to put 37" tires on my 93 HDJ81, Automatic, Full time 4wd. Anyone have experience running this set up on stock diff gears? with other diff gears? offroad and highway performance?
 
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Is yours 3.73 stock? Just swap or sell for 4.11’s.

Many that convert to diesel want higher gear sets, should be pretty easy to swap on a trade ad if that’s what you have and should work alright with your 37’s
 
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Is yours 3.73 stock? Just swap or sell for 4.11’s.

Many that convert to diesel want higher gear sets, should be pretty easy to swap on a trade ad if that’s what you have and should work alright with your 37’s
I have 4.11's . Basically with the low end torque of the 4.2liter diesel, is it neccessary to re-gear the diffs?
 
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Mmm. Necessary... No. put the tires on, if the change in gearing with the tires as a factor bothers you go lower later, maybe 4.56:1, but run it as is and see.

4.11’s are pretty low gear for my 38’s at present, with a low revving 6BT and NV4500 with OD of 0.73 it’s still a pinch low geared for daily driving. Going to 42’s with one ton axles (4.11’s as well) and expect the overall product to be geared acceptably.

Having said that, no first hand input about the HDJ, but I think you’ll be fine
 

mudgudgeon

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Is the turbo and fueling stock?

I'd consider re-gearing, depending on what sort of wheeling you do.
I had a hdj81 on 35"s, 4.11 gears, and 5 speed trans.
In steep country, it lacked torque for crawling up rocks etc
The HD-T engine is a bit low on torque until the turbo boosts up. 1250-1500rpm up it's fine, it's just the really low rpm stuff
Being auto, the stall converter gets past that.
 
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I have run 37s on a 94 HDJ80 with A442F for 50k miles plus with extensive off-road. Diffs are re-geared to 4.88. Is it necessary - yes, absolutely! Without a re-gear you will lack sufficient power to hold speed up any reasonable incline. You will also find low range 1st is way too high when off-road. Not re-gearing will also hugely exacerbate heat build-up in the auto box as it will be unable to stay in lock-up on the highway.The A442 is prone to overheating anyway, the last thing you want to do is make this worse.

To safely and effectively run 37s with the A442 and a stock 1HD-T you will IMO need to re-gear to 4.88 as a minimum. I’d also strongly advise fitting the biggest trans cooler you can.

If your 1HD-T is putting out more power, then maybe the re-gear is less necessary for highway driving. However, you’d then need the transfer reduction gears for off-road and would definitely require a trans cooler.

I do quite a bit of off-road touring that includes sand, mud and rocks. My set-up has evolved to the point that it is now adequate. This includes: 4.88 diffs; chromoly axles/CVs (I have original Longfields but would advise RCV); 3.11 low range reduction gears; extreme valve body for the A442 including manual lock-up in all gears; and a big trans cooler. Transmission fluid is also Castrol Transmax Z.
 
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I have run 37s on a 94 HDJ80 with A442F for 50k miles plus with extensive off-road. Diffs are re-geared to 4.88. Is it necessary - yes, absolutely! Without a re-gear you will lack sufficient power to hold speed up any reasonable incline. You will also find low range 1st is way too high when off-road. Not re-gearing will also hugely exacerbate heat build-up in the auto box as it will be unable to stay in lock-up on the highway.The A442 is prone to overheating anyway, the last thing you want to do is make this worse.

To safely and effectively run 37s with the A442 and a stock 1HD-T you will IMO need to re-gear to 4.88 as a minimum. I’d also strongly advise fitting the biggest trans cooler you can.

If your 1HD-T is putting out more power, then maybe the re-gear is less necessary for highway driving. However, you’d then need the transfer reduction gears for off-road and would definitely require a trans cooler.

I do quite a bit of off-road touring that includes sand, mud and rocks. My set-up has evolved to the point that it is now adequate. This includes: 4.88 diffs; chromoly axles/CVs (I have original Longfields but would advise RCV); 3.11 low range reduction gears; extreme valve body for the A442 including manual lock-up in all gears; and a big trans cooler. Transmission fluid is also Castrol Transmax Z.
Thank you for the info! I've already added the trans cooler. I'm not familiar with the extreme valve body for the A442 including manual lock up in all the gears. What exactly is that? Thank you again for the first hand experience.
 
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Thank you for the info! I've already added the trans cooler. I'm not familiar with the extreme valve body for the A442 including manual lock up in all the gears. What exactly is that? Thank you again for the first hand experience.
This is the valve body I have Nomad Heavy Duty Valve Body to suit Toyota LandCruiser 80 Series Electronic 4 Speed (4 Solenoid) | Wholesale Automatic Transmissions - https://automatictransmission.com.au/shop/nomad-heavy-duty-valve-body-to-suit-toyota-landcruiser-80-series-4-speed/ If you scroll down you’ll also see the lock-up switch though IIRC there are instructions on how to do this on Mud - be worth a search.
 
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I have run 37s on a 94 HDJ80 with A442F for 50k miles plus with extensive off-road. Diffs are re-geared to 4.88. Is it necessary - yes, absolutely! Without a re-gear you will lack sufficient power to hold speed up any reasonable incline. You will also find low range 1st is way too high when off-road. Not re-gearing will also hugely exacerbate heat build-up in the auto box as it will be unable to stay in lock-up on the highway.The A442 is prone to overheating anyway, the last thing you want to do is make this worse.

To safely and effectively run 37s with the A442 and a stock 1HD-T you will IMO need to re-gear to 4.88 as a minimum. I’d also strongly advise fitting the biggest trans cooler you can.

If your 1HD-T is putting out more power, then maybe the re-gear is less necessary for highway driving. However, you’d then need the transfer reduction gears for off-road and would definitely require a trans cooler.

I do quite a bit of off-road touring that includes sand, mud and rocks. My set-up has evolved to the point that it is now adequate. This includes: 4.88 diffs; chromoly axles/CVs (I have original Longfields but would advise RCV); 3.11 low range reduction gears; extreme valve body for the A442 including manual lock-up in all gears; and a big trans cooler. Transmission fluid is also Castrol Transmax Z.
A very informative post, thank you. I run a stock 1HD-T with 265/75 R16 and 1:4.10, and still find overheating in the A442F when running on deep sand in flat surfaces in hot environments. I never allow the radiator cooler go beyond 95ºC (203 ºF), which often requires stopping and letting the engine to idle for some minutes. Of course, this is because the radiator shares the engine and the trans cooling. This is why I would appreciate further details of the 'big trans cooler' you mention.
 
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A very informative post, thank you. I run a stock 1HD-T with 265/75 R16 and 1:4.10, and still find overheating in the A442F when running on deep sand in flat surfaces in hot environments. I never allow the radiator cooler go beyond 95ºC (203 ºF), which often requires stopping and letting the engine to idle for some minutes. Of course, this is because the radiator shares the engine and the trans cooling. This is why I would appreciate further details of the 'big trans cooler' you mention.

Screenshot_20210105-051407_Chrome.jpg
 
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A very informative post, thank you. I run a stock 1HD-T with 265/75 R16 and 1:4.10, and still find overheating in the A442F when running on deep sand in flat surfaces in hot environments. I never allow the radiator cooler go beyond 95ºC (203 ºF), which often requires stopping and letting the engine to idle for some minutes. Of course, this is because the radiator shares the engine and the trans cooling. This is why I would appreciate further details of the 'big trans cooler' you mention.

Screenshot_20210105-051407_Chrome.jpg


Screenshot_20210105-051407_Chrome.jpg


Screenshot_20210105-051401_Chrome.jpg
 
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I run 35s on a 1HDT. Instead of gears, I ended up with a better turbo and an intercooler. I have an auto. But I have plenty of torque for slow crawling in my rig. Personally, I think the 1HDT is almost a waste without an upgraded turbo, as it runs hot and you can't tune any power into it. When I got my rig, it felt dangerously slow. Now, it feels like a "normal" vehicle... but on 35s. I can pass on a highway going up a hill at 75 or 80 mph without high EGTs, in most cases now.
 
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I run 35s on a 1HDT. Instead of gears, I ended up with a better turbo and an intercooler. I have an auto. But I have plenty of torque for slow crawling in my rig. Personally, I think the 1HDT is almost a waste without an upgraded turbo, as it runs hot and you can't tune any power into it. When I got my rig, it felt dangerously slow. Now, it feels like a "normal" vehicle... but on 35s. I can pass on a highway going up a hill at 75 or 80 mph without high EGTs, in most cases now.
What turbo and intercooler did you install? Boost psi? Thank you!
 
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That's exactly the setup I'm leaning towards. I'm trying to decide between moonlight airbox and PDI airbox. I also wish PDI had a 4" snorkel, if they did, I would order everything from them and be done. Did you tune your air/fuel ratio after install or did you have a diesel shop do it? Looks great!
I'm running a Gturbo GTX at 23psi, PDI intercooler and PDI airbox. This setup has worked well for me for the last couple of years, including
 
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Also, that bumper is awesome, build yourself?
That's exactly the setup I'm leaning towards. I'm trying to decide between moonlight airbox and PDI airbox. I also wish PDI had a 4" snorkel, if they did, I would order everything from them and be done. Did you tune your air/fuel ratio after install or did you have a diesel shop do it? Looks great!
 
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That's exactly the setup I'm leaning towards. I'm trying to decide between moonlight airbox and PDI airbox. I also wish PDI had a 4" snorkel, if they did, I would order everything from them and be done. Did you tune your air/fuel ratio after install or did you have a diesel shop do it? Looks great!

I did a simple EGT based tune and haven't played with pump timing... there's probably more power left on tht table. I ended up with the PDI because it uses the 200 series filter over the duramax filter of the moonlight box because it is 25% bigger. Does that make a real difference in my case? Probably not. But, I blew up a turbo due to restriction un the intake path so I wanted overkill.
 

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