HJ60 with H55F 5spd - Possible to get taller 5th gear? (1 Viewer)

[johnnyog]

Hi Y'all, I found a couple threads on this topic, but none had a final conclusion and happened 7+ years ago. Curious if anyone has managed to find a good way to get a taller 5th gear or better final drive for highway cruising in an HJ60?

Mine specifically is a 1988 HJ60 with an aftermarket Turbo mated to a 5spd H55F. Would love to do some longer Texas road trips, but I am a little apprehensive with the current reasonable highway cruising speed

 

[SteveH]

Some folks swap out the 4.11 third members for 3.73-ratio ones. And/or run 33 or 35" tires for a rubber-overdrive. Have you done any of those things?

 

[Earwigg]

How fast do you want to be going? 3.7s and bigger tires help.

 

[micruz60]

How fast do you want to be going? 3.7s and bigger tires help.

In Tejas? -To go faster than everyone else-

 

[HemiAlex]

How fast are you going? I’ve had my truck at 85 on an isolated highway here in Texas and if I had to correct at that speed, it would be bad.

 

[johnnyog]

So far I have 33" tires on and don't think the diff has been altered from stock yet. The specific situation I am thinking of is I-10 west, which has a posted Speed Limit of 80 for quite awhile, so I want to comfortably get a little closer to that. Not trying to be racecar, but want to get a closer match to those highway speeds without blowing up the ol diesel motor. She seems happy around 65ish on the highway now, but if she could do like 75 without too much of sweat that would make a big difference!

 

[johnnyog]

How fast are you going? I’ve had my truck at 85 on an isolated highway here in Texas and if I had to correct at that speed, it would be bad.

Haha, yeah I def don't need to do 85, just trying not to be TOO slow on the faster highways

 

[HemiAlex]

Are you running 3.70 or 4.11 axles?

Im going from 3.70 to 4.11 now. It will make a little more rpm in 5th and 4th will have some more guts. When I get into rolling hills it takes some speed and momentum to stay in 5th sometimes, and if rpm’s don’t stay high…I can really slow down.

The true 33” diameter of the 255/85-16 like what I run may be able to help you a little bit on the cheap.

 

[Earwigg]

Things are getting busy sounding at 2700rpm to get toward 80mph 3.7s might help

 

[mongoose2231]

My HJ60, 87, is 3.70 final equipped with 31" tires and I can comfortably cruise at 70 to 75 in 5th. If you have 4.11 final gearing, simply putting on 33'may get you what you need.
Based on what you posted above, even if you have 4.11 gearing, the 33's should get you 75 mph comfortably...

 

[johnnyog]

My HJ60, 87, is 3.70 final equipped with 31" tires and I can comfortably cruise at 70 to 75 in 5th. If you have 4.11 final gearing, simply putting on 33'may get you what you need.
Based on what you posted above, even if you have 4.11 gearing, the 33's should get you 75 mph comfortably...

This is my first diesel car ever, so part of this is that I am not sure what I should consider a "comfortable" RPM for a longer run time. Like could I theoretically run around 2500-2700 rpm for awhile on a hot day without worry?

 

[ceylonfj40nut]

2500 all day. Good target. Right foot is a major cause for unnecessary damage. Find a gearing/wheel combo that gets you around this target.

 

[johnnyog]

2500 all day. Good target. Right foot is a major cause for unnecessary damage. Find a gearing/wheel combo that gets you around this target.

Got it. I tested it out yesterday and I am at ~70mph at 2500 rpm, so not bad if that is a safe place to run at length!

 

[davegonz]

I think Georg (@orangefj45 ) sells overdrive gears for the splitcase. Might be an easier solution than regearing your diffs.

 

[OSS]

2500 rpm at 70mph is perfect. That engine can run at that rpm for more than 300,000 miles

 

[ceylonfj40nut]

^^^^^

 

[orangefj45]

Consistently running that engine at 2500 RPM is pushing it pretty hard.
I’d suggest either running slightly taller tires or adding the 10% OD gears to the Tcase.
Have you confirmed that your Speedo is accurate?

Happy to help.

Georg @ Valley Hybrids, Cruiser Brothers & Long Range America

 

[davegonz]

@johnnyog what part of ATX are you in? We have a pretty tight-knit group of diesel cruiserheads here in town. My old FJ60 that I converted to an HZJ60 had 3.70 gears and ran great. I would honestly look into Georg's OD gears for the t-case since it is a good DIY upgrade.

 

[OSS]

Here's the torque specs for the diesel 2H and the gasoline 2F (from SOR website)

Diesel 2H

Gasoline 2F

 

[johnnyog]

Consistently running that engine at 2500 RPM is pushing it pretty hard.
I’d suggest either running slightly taller tires or adding the 10% OD gears to the Tcase.
Have you confirmed that your Speedo is accurate?

Happy to help.

Georg @ Valley Hybrids, Cruiser Brothers & Long Range America

Good to know! I am def looking to be on the more conservative side especially since mine has an aftermarket turbo. Per the previous owner, the speedo is about 5mph pessimistic, but I haven't tested that yet. Thanks!