Rear Axle Hub Stud and Dowel Pin Upgrade (1 Viewer)

[guzzla]

While I still think you can never have too much power, it would seem my rear axle studs and dowels do not agree. While loose wheel bearings are a common cause for such breakages, as it was for me the first time it happened, the other times the bearings have been perfect yet the locating pins end up getting pulverised.

The first time I became aware of the issue was after noticing 2 of the 6 studs had snapped just after a tricky section of off road track. Hopeful of making it just a few kilometers back to camp for a repair resulted in spitting the axle clean out whilst traversing a rocky area. Once home and with things apart, the loose wheel bearings were the most obvious cause. Still, I thought there must be a stronger option for the pins and studs. So after some research, I drilled 2 extra 7mm dia dowels and fitted 6, grade 12.9, 8mm x 40mm x 1.25 socket head cap screws (SHCS). And for the best part of a year, all went well.

But over the last 6 months I noticed a couple of axle dowel pins walking out after a bit of driving (on and off road) so I'd tap them back in with a hammer and check the SHCS's for tension. Often they'd be loose but the bearings were always tight when checked soon after. Just recently I pulled the rear axles to check the bearings and take a closer look. That's when I noticed on one axles 2 dowels had snapped and one SHCS was slightly deformed. One the other axle, 3 dowels were stuffed and 2 SHCS were bent. With not enough time for a proper repair I replaced the bent SHCS and only one of the 4 damaged studs, leaving me with 2 pins in one and one in the other. Where the pins had snapped had also deformed the top edge of the hub they seated in so I knew it was far from ideal but it'd have to do for the time being and I'd just take it gently... or so I told myself

As an aside, at Xmas I had a Detroit locker fitted in the rear to replace the ARB. I should point out that while I love the Detroit infinity times more than the ARB and I highly recommend them, it would be remiss of me to not admit the Detroit does place added strain on the axles. In normal situations / otherwise standard vehicles, I highly doubt it's an issue to even consider, but when you up the power and torque like I have, and use it, otherwise non issues can become real ones. However, I've come to accept that with great power comes great responsibility in beefing up everything it breaks in its wake

So last weekend after a great trip away (new MTZ's killed it everywhere I went) I was airing up and noticed some oil spatter on the DS rear wheel. Closer inspection revealed 3 loose SHCS. I managed to tighten 3 of them, snapped the head off one as soon as I touched it and the other two felt too dodgy to tighten, so I slowly backed away from the mess and drove home. Once home it was time for a strip down and a good look at WTF was going on and how to fix it.

Removing the SHCS from the already damaged drivers side resulted in another 2 snapping after a few back out turns. The other three came out ok but were noticeably bent. The two dowel pins were fragmented beyond recognition. Removing even standard snapped off studs from these hubs is a right PITA and the dowel pins are even worse being hardened steel. So this sucker is heading straight for the bin. You can also see the deformation on the hub face caused by the dowel pins being overloaded. Some serious force has occurred to do that sort of damage.


Remnants of a dowel pin. One of eight :roll:


The original (285,000km) axles splines and shaft are in perfect condition, especially considering the punishment they have copped over the years. It's testament to Mr Toyota making a damn good product. But the same can't be said for the axle mounting flange. years of beating on it to loosen the cone washers (I know it's not the right way but it's easier sometimes ) and general wear and tear have taken their toll. They'll be kept as spares now...


After speaking with my diff repair guy for a while, he was adamant that despite all the 6 studs holding the axle in, much of the driven load goes through those two 7mm dowel pins in each axle. He's repaired enough of them to know. But first things first was to check the housing for straightness. I did this by bolting on a bare rim to each hub and placed a mark on the lip. Setting both marks plumb I took a overall measurement. I then rotated each mark 90deg and took the relevant measurements. There was barely half a mm in them and with a tolerance of 2-3mm, it was as good as straight. So on with the next step.

The plan was to drill and tap the existing 6 threaded holes and fit the 10mm studs used in the 100s.


This is the 10mm and 8mm cone washers side by side. It might only be 2mm bigger internally, but there's a s*** load more meat on the bigger 10mm cone washer. And that creates a problem...


Here's the 10mm cone washer in position. If I were to have the axle recesses machined to suit the bigger cone washer, It'd virtually blow out the edge of the axle flange in the process. Toyota solved this on the 100s by using a slightly bigger hub and matching axle flange.


So, what I plan to do is this; The 100s also use 2x 10mm axle dowels instead of the 2 x 7mm pins used on the 80s. Just like I did in the original axles, I'm going to fit 4 new axle dowel pins but use the 100s 10mm pins. At 30% bigger and double the quantity, I'm hedging my bets these pins won't be breaking any time soon.

7mm dowel pin hole to left of 10mm pin shown



I'm also going to stick with the SHCS, for no other reason than they're so much stronger than the standard studs, and they make axle removal so much easier since no hammering is required to remove the cone washers. I also have a little experiment I want to try that might go some way to adding further strength to the whole show. Shown is a 40mm and 50mm SHCS. Regardless of the length, they all have 30mm of thread which is perfect as the hub has a thread depth of 30mm (once you clean them out all the way to the bottom using a bottoming tap)


This is a mock up of how the 40mm SHCS protrudes through the axle flange once the cone washer and spring washer are fitted. While there is a good 27mm of thread to get deep into the hub, the threaded section is also right at the transition point of where all the rotational / shear load is. In my non engineering mind, this also creates a weak point for the bolt since the thinnest part is prone to the most shear force.



So my solution to this is I'm considering the following...
This is a 50mm SHCS in place with a cone and spring washer fitted. Same thread length but longer shoulder. After a bit of measuring, I'm thinking drilling the top 7-8mm of the hub so the last bit of the shoulder seats below the hub surface to offer more strength against shear loads. I'll have to cut about 7-8mm of the end of the thread so it winds into the hub fully, still leaving me with more than enough thread depth for a secure purchase. I'll be testing in the old hub to make sure I can get a firm fit in all 6 studs without any binding, along with the very tight fit I need for the 4x 10mm dowel pins.


In the meantime, my new / 2nd hand hubs and axles turned up today. I'll keep you posted on how things work out. :? :mrgreen: :arrow:

 

[guzzla]

I would have finished both today had it not been for constant interruptions. Damn some people and their mind-numbingly boring idle chitchat when I'm on a mission!!! Anyway, at least got one finished. Bit of fluffing around at first testing on the old hub and stripping the new hub and cleaning it up, but the drilling went really smoothly once I got to that part. What I'd planned doing originally ended up working really well. Here's some pics of how it came together.

Since I didn't have a spare one yesterday for comparison, here's a 80s Dowel pin vs a 100s. It's only 3mm DIA bigger but it looks double the size.


Removing the existing dowels from the hub can be a real PITA. The easiest way is to flatten both sides with a grinder to give the vice grips something to grip onto and stop them from spinning. They will still take some wiggling but it'll stop you smashing things in frustration.


Using these SHCS, you need to tap the hub threads the last few millimeters to the bottom. Regardless if you're going to use the 40mm SHCS, or the modified 50mm version I detail later on , as you want maximum thread engagement regardless and to prevent bottoming out of the fastener before the correct torque is achieved. You're basically just cleaning out all the rust and crap that's been sitting in the bottom for eons.

Ideally, it's best to use a intermediate (or 2nd) tap to clean most of the thread out and the slight initial taper on this kind of tap makes it easier to get started, particularly if the threads are a bit burred to start. Next you'll need a bottom tap to allow you to cut a thread all the way to the bottom. A bottom (plug) tap has a blunt nose for just this job. In the pic, I made my own buy cutting a spare intermediate tap. As I have done, you might also have to grind the shaft a bit to allow you to get to the bottom of the hole. But only grind off the bare minimum because if it snaps, it's there for good and you will loose your s***, start smashing stuff and have to get another hub. So, when tapping these, take it easy and don't reef on the handles. I just use one hand and hold the tap holder in the middle. Lots of lube and and small back and forth motion is better than just twisting it in like Hercules.


As I mentioned earlier, I decided to go with the 50mm SHCS with the longer shoulder and recess it into the hub about 5mm. The reason for this is to transfer any potential shear force off the weaker threaded section and onto the meatier section of the bolt shoulder. I did this by setting the depth stop of the drill press to approx 7mm before proceeding to drill them out. Because you're essentially drilling a 7mm hole out to 8mm, the drill bit tends to jamb, so use lots of cutting fluid and go real slow. I used silicone spray for all the drilling and it worked perfectly. The long spray nozzle was great for keeping the lubricant where I needed it. In the next two pics you can see a test I did showing the approx shoulder recess into the hub. It would pay to run the tap through again to remove any burs.



The bolt shoulder is actually a bees dick under 8mm dia so using the 8mm drill bit gives it a nice fit without being too tight for potential to bind. Also, I now went through and cut 10mm off the thread with a grinder and thin cutting disc. I then placed a mark 30mm up from the end of the thread (green tape) and wound every SHCS into position to ensure they seated full depth. By cutting 10mm should make them about 3mm short of the bottom once installed to allow for bolt stretch and compression of the cone and spring washers.


With more arse than class, the centre hole on my drill press table is a perfect fit for the axle to fit through. So sitting the hub on top, I then fitted the axle though and bolted it up with the modified SHCS and cone and spring washers. Tighten them all down equally to make sure they all seat easily without any binding. It stays like this now until all the dowel pin holes are drilled. At this point I used the grinder to place a small, permanent witness mark to make reassembly perfect every time.


Next, it was time to drill the dowel pin holes. The pins measure 9.98mm, or damn near close enough to 10mm. With the axle flange bolted to the hub, I used a 9.9mm drill bit to drill the 4 holes as I want a friction fit in the hub to eliminate any chance of movement, as that leads to failure. The first two I placed in the original dowel holes and the other two I placed further round without affecting the 6mm axle removal threads. You will need to carefully align and clamp the hub down before drilling to minimise any movement as these holes have to be pretty spotty dog. As for all the holes, I had the drill press set to 280rpm and lathered it with silicone spray. The standard (no Cobalt coated) drill bits drilled the axle and hub without issue or any sing of getting blunt. The studs are 24mm long so I set the depth stop to 25mm just to be sure.


Next, was what everything leading up to this was all about... installing the pins. Test fitting the pins through the face of the axle was going to be way too tight to allow easy R&R of the axle at a later date. So, separating the axle from the hub, I enlarged the dowel pin holes in the axle flange using a 10mm drill bit. It allowed the pin to slide though with just a bit of force, perfect. But seating the pins into the 9.9mm hole in the hub was a different story. Placing the four pins into the freezer for 35min shrunk them just enough so I could tap them into position with a hammer. I did this with the axle flange once again bolted to the hub to prevent any misalignment. I started to use Loctite 609 but with such a snug fit, it wasn't remotely necessary.


And for the final trick, I removed the SHCS for the millionth time and R&R'd the axle to make sure it all worked perfectly. And to think I even doubted myself


Now to do the other one tomorrow, fit new bearings and bolt it all back together once and for all. And I'll be pissed off like no bodies business if I have to go through this again any time before never again

 

[Mr Cimarron]

Nice write up. I've been thinking of doing this as well. With the Cummins installed I now need to start up beefing up the axles to handle it.

 

[cody c]

Do you have spare shafts? Whats the plan if you break an axle and need to replace it? Is it gonna be hard to drill another axle shaft without a template and a 10mm bit handy, might want to grab a piece of 16 gauge aluminum, cut a hole through the center for the shaft and then drill through all the other holes to make a template, and then throw it and a 10mm bit in your tool kit.

I havent sheared any shafts myself yet, but Im running a SF, I have busted a couple R&P's and a birf though.

 

[Mr Cimarron]

Do you have spare shafts? Whats the plan if you break an axle and need to replace it? Is it gonna be hard to drill another axle shaft without a template and a 10mm bit handy, might want to grab a piece of 16 gauge aluminum, cut a hole through the center for the shaft and then drill through all the other holes to make a template, and then throw it and a 10mm bit in your tool kit.

I havent sheared any shafts myself yet, but Im running a SF, I have busted a couple R&P's and a birf though.

Good point. I have 1 extra set at the moment. If I did it I would probably do it on the LX as well so I could steal those shafts if needed as well. I like your template idea.

 

[guzzla]

That's a good idea I considered but it's really not worth the effort for me to bother since I've never broken an axle and wheel much easier than I use to. Most 4WD trips I'm away for 2-7 days and rarely not far from civilisation for spare parts. I do a big trip once a year for several weeks and for that I've decided to carry a spare standard hub instead. In the event I do break an axle far from home, I'll have to source a new axle from a wrecker since I've never carried spare ones and don't plan on starting. The replacement axle from the wrecker will bolt straight up to the spare hub I can fit at the same time. It would do the job well enough to get me home where I can machine up another in due course.

In reality, much of my hardcore 4WDing days are behind me and these axles only really break when the vehicle has 37+ inch tyres, is driving like an idiot, or both. They are otherwise inherently robust so the need to consider spares is actually very low priority. The reason I did all this was to strengthen the dowels that were breaking. The breaking of axles was never part of the problem solving and I certainly don't see it being one now.

 

[ChiTown]

Nitro uses an upgraded dowel set up in their rear axle kit and Trail Gear offers it for the front with their creeper drive flanges. They also offer upgraded ARP studs for the hubs.

 

[Backwoods Rambler]

GREAT TECH!

 

[Squash]

Nice,
Did a rebuild of the HDJ81/FZJ80 front axle with a HZJ79 drive flange, dowels and birf some machining required.

 

[Tapage]

which drill bit size you use to open those holes up to 10mm ...?

I might not upgrade my studs but for sure the dowels .. ( and increase the number too )

 

[guzzla]

which drill bit size you use to open those holes up to 10mm ...?

Surely you can't be seriously asking me if I used a 10mm drill bit to make a 10mm hole

 

[guzzla]

Got it all finished today, including fully rebuilding the hubs with new bearings and seals. Also fitted new wheel studs since the donor hubs were 2nd hand and I hate old wheel studs. With new wheels and tyres as well, I'm hoping for many happy trouble free travelling miles.

Sure was nice installing the axle and having to give it a gentle tap with the mallet to seat it snuggly on the dowel pins. Couldn't have asked for a better fit.

Passenger Side:


Drivers Side:
Note one of the dowels 2mm below the face of the hub. It must have had some pressure on it when I pressed in the wheel studs. Pissed me off when I saw it since I went to so much effort to make them all flush. But my dumbest mistake of this project was installing all 6 wheel studs on this hub the wrong way round - which is how the dowel pin moved . Such is life


The front hubs are due for a rebuild shortly so might see what I needs modifying there. In the meantime, I'll keep this post updated on how this little project performs in the comming months of punishment.

Thanks for watching.

 

[scottryana]

Looks good! Should provide a lot more resistance to breaking. I also sheared the studs on the rear axle. Mine happened running the "stronger" Poly Performance axles I switched back to stock and haven't had issues since.

 

[kiwidog]

Think Tapage was asking the drill size you used for the dowel hole in the hud not the flange, 9.9mm so you get an interference fit when you shrink the pins is that correct?

Good write-up, exactly the kind of thinking a good machinist would go through. Thanks for documenting it so well , I'm sure some fellow mudders will take inspiration from your work.

Thanks jb

 

[guzzla]

Think Tapage was asking the drill size you used for the dowel hole in the hud not the flange, 9.9mm so you get an interference fit when you shrink the pins is that correct?

Good write-up, exactly the kind of thinking a good machinist would go through. Thanks for documenting it so well , I'm sure some fellow mudders will take inspiration from your work.

Thanks jb

Yeah, I wasn't sure what he meant to ask. But you're correct, I drilled a 9.9mm hole through the axle and hub as one. I then ran the 10mm bit through the axle only. Make sure you separate the axle from the hub first as you want to keep the edge of the hole in the hub perfectly square. I just used a cordless drill to go from 9.9mm to 10mm. I found the pins went in a bit easier on the 2nd axle after being in the freezer for 1hr instead of 35min. I think If I did it again, I'd just drill a full 10mm hole and just the Loctite 609. It would make dowel removal a little easier if you ever needed to. I'd probably have to stick my whole hub in the freezer over night to get them out. But at least I know they're not going anywhere.

Scotty,
I just have standard axles. I was about to pull the trigger and get a set but I read a few too many people were having unexplained issues with them and you've just added to the list. I also realised it's not the axles themselves that are the issue for me - it's the weakness of the dowel pins and the original axle flanges that were pretty beat up.

It seems the OEM axles really are the best option, and for $150 for a 2nd hand hub and axle, I'm happy to keep using them considering new OEM is about $1200 a side. The only benefit, if you were breaking axles regularly, is the newer OEM 80s axles are an extra 2mm dia for added strength (with a different axle seal as well) according to the parts guy.

 

[scottryana]

Yeah I agree, my axles were ok, but with the extra tough chromoly axles it seems like they would transfer all the power to the studs and sheer them where maybe the stock axles have a little more give or twist.

 

[Tapage]

Think Tapage was asking the drill size you used for the dowel hole in the hud not the flange, 9.9mm so you get an interference fit when you shrink the pins is that correct?

damn .. thanks .. in my first question .. well it looks kinda dumb ..

I found the pins went in a bit easier on the 2nd axle after being in the freezer for 1hr instead of 35min. I think If I did it again, I'd just drill a full 10mm hole and just the Loctite 609.

never use it before .. would read about it .. and in a related question assume a bench drill ?

Yeah I agree, my axles were ok, but with the extra tough chromoly axles it seems like they would transfer all the power to the studs and sheer them where maybe the stock axles have a little more give or twist.

I thought was the other way around .. being stock axles the less tolerant to twist

 

[guzzla]

Yeah Tapage, a bench drill is a must for this project. You really want the holes as straight as possible and the bench drill gives you so much more feed control. Clamping the hub to the drill bench is also a good idea to stop any movement if the drill bit grabs. But a liberal dose of cutting fluid works wonders.

 

[BOOSTED80]

Great write up Guzzla.. I sheared off all my studs today so it looks like I will be doing the 10mm dowel mod as you have done.
How has everything been holding up since you did it all ?

 

[nathd0ggy]

im about to do the same to the rear FF in my 80series, i sheered all the dowels and i have used the 12.9 bolts already and they sheered, so im going back to ARP stud upgrade kit and using the 10mm dowels from 100 series landcruiser x4 per axle

has this 10mm x 4 per axle solved the problem or are you still having problems?