HZJ80 Rear diff rebuild

[KiwiDingo]

So I posted pictures earlier in the what did you do to your 80 this weekend thread but had a question or two so thought I might make a post.

I'm waiting for my new crown and pinion to be ordered so got a bit of time to kill. Is there any tips/tricks I can do to the LSD clutch packs to make them actually function as they should? Or am I fighting a losing battle on that one.

Also has anyone gone from the standard 4.1 to 3.7 ratio and either loved or hated it? Love to hear your thoughts. I don't do any rock crawling/low range driving so the loss in that area doesn't concern me to much. I spend most my time driving on the highway at 100-110km/h which has me at 2400-2600rpm in fifth gear which is quite high. I can drive my car without ever using first gear too so it'll be good to actually start using the full 5 gears again with a better spread.

 

[KiwiDingo]

May have changed my mind on the 3.7 and going even further with the 3.5 from PDI.

3.55 Diff Ratio Crown Wheel & Pinion Sets - Pre Order

First question is “ Are the strong enough to consider fitting into my Landcruiser? ” Yes - from all installs they have proven themselves and are when fitted to Chris Hawkins HDJ79 Landcruiser which has done a 10.98sec ¼ mile. With these diff gears fitted he has managed to break two 4340 chrome moly

www.performancedieselintercoolers.com.au

 

[shocktower]

I have been looking for those 3.54 gears I hate going 2400 RPM to go 70 mph

 

[KiwiDingo]

I have been looking for those 3.54 gears I hate going 2400 RPM to go 70 mph

I feel the exact same! Been thinking about wanting to change ratios for quite some time now but always decided against it when I realised how much work it involves just to swap out the gears. I currently sit around 2600rpm cruising at 110km/h in fifth gear which is a bit annoying but the 3.5 should drop that down to 2200rpm

It was chit having my diff chew out on me but I guess it's a bit of a blessing in disguise because now I can put those gears in since I needed to strip the diff apart anyways. I was originally just going the 3.7 option because they would bolt straight onto my 80 series diff centers but I've just sourced some 79 series centers which will now allow me to run the 3.5 gears with the larger/stronger pinion with higher spline count and the crown wheel which has a different bolt pattern. Just need to use the side gears from my 80 center and it should hopefully go together all sweet.

 

[shocktower]

I feel the exact same! Been thinking about wanting to change ratios for quite some time now but always decided against it when I realised how much work it involves just to swap out the gears. I currently sit around 2600rpm cruising at 110km/h in fifth gear which is a bit annoying but the 3.5 should drop that down to 2200rpm

It was chit having my diff chew out on me but I guess it's a bit of a blessing in disguise because now I can put those gears in since I needed to strip the diff apart anyways. I was originally just going the 3.7 option because they would bolt straight onto my 80 series diff centers but I've just sourced some 79 series centers which will now allow me to run the 3.5 gears with the larger/stronger pinion with higher spline count and the crown wheel which has a different bolt pattern. Just need to use the side gears from my 80 center and it should hopefully go together all sweet.

So I need to find the 79/105 Centers just for the rear ? to use the 3.54 set up, I am glad I found them, I put a 6bt Cummins in my cruiser using the A343F and I want a little better top end

 

[KiwiDingo]

So I need to find the 79/105 Centers just for the rear ? to use the 3.54 set up, I am glad I found them, I put a 6bt Cummins in my cruiser using the A343F and I want a little better top end

Yes that's correct, your existing 80 series front diff center will fit the new gears but the rear needs the center from 79/100/105 series.

Or if you want you could just install locker of the same models instead of finding a factory 79/100/105 center.

 

[shocktower]

Ok I can get a 100 center for sure now I just need the shipping cost from Oz

 

[KiwiDingo]

At least the cost of the gears alone should be pretty cheap, especially when you take your exchange rate into account. Not sure how badly you'll get stung with shipping though as they are a weighty item?

 

[mudgudgeon]

So I need to find the 79/105 Centers just for the rear ?

They aren't directly interchangeable. 79/105 uses thicker axles with different spline count

 

[mudgudgeon]

They aren't directly interchangeable. 79/105 uses thicker axles with different spline count

Also, you can't go 105 centre and 105 axles, Toyota changed the hub stud PCD, axle flange diameter, and hub stud diameter

 

[KiwiDingo]

They aren't directly interchangeable. 79/105 uses thicker axles with different spline count

Yep, exactly the reason why I'm swapping out the side gears with my 80 series ones.

 

[mudgudgeon]

Yep, exactly the reason why I'm swapping out the side gears with my 80 series ones.

Ah, cool. Missed that bit.

 

[KiwiDingo]

Ah, cool. Missed that bit.

Yeah I'm pretty sure I mentioned it in one of my first posts, could be wrong though.

Those side gears were the ones I was most concerned about with damage before I pulled the diff apart. I'd not long ago changed my axles to chromolly and had a fear that I'd turned them all to mush but they looked perfect.

I'm not up to the stage of putting it all back together yet, still waiting on parts, but I'm trying to figure out a good method of holding the diff center still while torqing the crown gear bolts and also the housing while tightening the pinion nut. If anyone has any handy suggestions I'm all ears

 

[Kernal]

Check out ZUK's web page, he has tons of photos showing his workshop, bench, tools, jigs he built to hold the diffs while working on them, and how he rebuilds differentials. You could also drop him a line if needed:

Toyota Gear Install Eaton

ZUK shares many close-up good pics of Toyota gear installs

www.gearinstalls.com

 

[KiwiDingo]

Thanks @Kernal , Just had a look at his website. Some great info/tips/photos on there.

 

[shocktower]

They aren't directly interchangeable. 79/105 uses thicker axles with different spline count

So why do they say I need to change the centers, if the axles are different, I should be able to just have then installed in my Diff.

 

[KiwiDingo]

You need to change the centers because the PDI 3.5 crown gear wont bolt up to the 80 series center. That's why you need to install the side gears from your 80 series center into whichever center you choose to use then your existing axles will still fit.

 

[mudgudgeon]

So why do they say I need to change the centers, if the axles are different, I should be able to just have then installed in my Diff.

Toyota made changes to the rear diff for the 79/105 series.
They increase crown wheel thickness, changed crown wheel bolt spacings and size.
I think bearings were also increased in size in the centre, but not certain.

Toyota increased axle thickness, and went to 32splines for the axles.
They also increased the hub and axle flange diameter. Hub stud thickness was increased. Hub stud PCD was also changed.

80series rear crown and opinion aren't interchangeable with a 79/105

You can fit a 79/105 third into an 80 housing, but axles become a problem. UNLESS you do what @KiwiDingo is doing, and swap the side gears in the third to 80series side gears.

I think the housing studs for the third member also increased in thickness, but can't remember for sure.

I hope I didn't muddy the water with my earlier post. I missed that @KiwiDingo is using 80 side gears

 

[Boing]

Toyota made changes to the rear diff for the 79/105 series.
They increase crown wheel thickness, changed crown wheel bolt spacings and size.
I think bearings were also increased in size in the centre, but not certain.

Toyota increased axle thickness, and went to 32splines for the axles.
They also increased the hub and axle flange diameter. Hub stud thickness was increased. Hub stud PCD was also changed.

80series rear crown and opinion aren't interchangeable with a 79/105

You can fit a 79/105 third into an 80 housing, but axles become a problem. UNLESS you do what @KiwiDingo is doing, and swap the side gears in the third to 80series side gears.

I think the housing studs for the third member also increased in thickness, but can't remember for sure.

I hope I didn't muddy the water with my earlier post. I missed that @KiwiDingo is using 80 side gears

I think the "late" style Toyota 9" third is the same third member since the dawn of time and is completely interchangeable... ARB 142 vs 152 would account for the different bolting ring gear....
1.31" 30 spline vs 1.37" 32 spline, 60 thou bigger diameter shaft, side gears within the ARB are interchangable...

I wonder what the ID of a Toyota spindle is, I would bet it would allow a bigger shaft to pass through... Since 80 hubs use the same wheel bearings as all other (older) toyota axles...