Rear axle: unit bearing cups or inner c/knuckle?

[Lil'John]

I am working on doing Tundra drop out thirds for front/rear of a project. The front is going to use 05+ SD knuckles. I want to use SD unit bearings in the rear.

I have found a few companies that make unit bearing cups like these:
2005+ Unit Bearing Cups – Weaver Fabrication
Rear 2005+ Super Duty Unit Bearing Cups (Pair)

The problem is cost. I can get a pair of inner c/knuckles for roughly the same ~$500 either cup sets cost. Then add in that the cup sets still require some sort of brake bracket setup and the cost starts to favor doing inner c/knuckle setup.

Unit bearing and axle shaft costs would be a wash for the most part. In the case of a knuckle setup, I would do the 1550 u-joint shafts.

Either version would require an inner axle seal.

If I did a knuckle setup, I would lock the knuckle to the axle somehow; tie rod end or heim at the knuckle??

What are the down falls?

I already know that rear steer isn't overly popular here or previous so I won't mark the potential of adding it as a plus

 

[YotaAtieToo]

Are you really asking about using locked out knuckles to save a few bucks?

Bit the bullet and get the cups, or take ub to a machinist you know.

Another option is using the sterling spindles and hubs. At least then all your breaks and bearings will be from the same truck and have the same pattern.

 

[Lil'John]

You want to ship me a few hundred to cover the difference? Yeah... I didn't think so.

I have ZERO interest in a welded spindle so thanks for that opinion that was never brought up as an option.

 

[Weasel]

What's wrong with rear steer?

Somewhere I've seen tie rods that attached to a tab on the axle tube to lock out the steering action.

 

[Lil'John]

What's wrong with rear steer?

Somewhere I've seen tie rods that attached to a tab on the axle tube to lock out the steering action.

There are many opinions that pop up when rear steer is brought up that I'm hoping to avoid. Things like it is a gimmick, severely weakened, best thing since sliced bread, etc.

I've seen the same approach for locking out steering. That method is being considered.

I see I forgot to bring up some other details. Rig will be on 35s that might upgrade to 40s. Technical wheeling over "hold my beer". Rubicon type crawling with no mud.

 

['84 Bronco II]

There are many opinions that pop up when rear steer is brought up that I'm hoping to avoid. Things like it is a gimmick, severely weakened, best thing since sliced bread, etc.

I've seen the same approach for locking out steering. That method is being considered.

I see I forgot to bring up some other details. Rig will be on 35s that might upgrade to 40s. Technical wheeling over "hold my beer". Rubicon type crawling with no mud.

Who the fuck thinks rear steer is a gimmick

It wouldn't be very hard to get bearing cups machined locally if the prices really are that far out of wack.

That said, if you already have all the components for rear steer, why not take the couple of hundred bucks you are saving and buy a cylinder?

Nothing wrong with running toe links to the axle housing either. You could adjust your rear toe like an IRS vehickle, although I don't see much advantage to be had for technical wheeling.

 

[vetteboy79]

U-joints that never see any angle typically aren't happy for long. The grease on the one needle that sees all the action gets pushed away and nothing happens to move any to replace it. Eventually you end up with a flat needle and/or a dent in the cap & trunion.

I mean, I guess you could add greasing your rear axle u-joints as a frequent maintenance item, but that whole idea seems silly to me in the pursuit of saving a few hundred bucks in the scope of a ground-up vehicle project. One shit experience with a u-joint on one weekend trip and you're by far in the red with that one.

 

[Lil'John]

Who the fuck thinks rear steer is a gimmick

It wouldn't be very hard to get bearing cups machined locally if the prices really are that far out of wack.

That said, if you already have all the components for rear steer, why not take the couple of hundred bucks you are saving and buy a cylinder?

Nothing wrong with running toe links to the axle housing either. You could adjust your rear toe like an IRS vehickle, although I don't see much advantage to be had for technical wheeling.

I' ve seen the gimmick/toy comment more than a few times so I can't call out a specific user.

I'm in Calif so I doubt I'll find someone local that will do under $100/hr

I wasn't planning to devolve this thread into a rear steer thread I've actually got a cylinder but nothing else. I haven't found/looked for a cheap log splitter type value for control nor an electric pump(Grand Cherokee)

 

[Lil'John]

U-joints that never see any angle typically aren't happy for long. The grease on the one needle that sees all the action gets pushed away and nothing happens to move any to replace it. Eventually you end up with a flat needle and/or a dent in the cap & trunion.

I mean, I guess you could add greasing your rear axle u-joints as a frequent maintenance item, but that whole idea seems silly to me in the pursuit of saving a few hundred bucks in the scope of a ground-up vehicle project. One shit experience with a u-joint on one weekend trip and you're by far in the red with that one.

Interesting point. How long is not long? How much angle do they really need to move? I'm just thinking of vehicles driving straight down the freeway.

 

['84 Bronco II]

Interesting point. How long is not long? How much angle do they really need to move? I'm just thinking of vehicles driving straight down the freeway.

Just run a bushing style joint, but that would negate any cost savings you are trying to achieve. A small amount of toe would probably take care of the issue. FWIW I run .15° toe in on each rear tire on my DD Focus.

 

[Weasel]

Rear steer is awesome, driver might be not awesome.

Anyways if you think you might add it the the knuckles are a good way to go, if not then I'd do the cups. not extra ball joints, u joints, brakes could be slightly more difficult to mount, possible loss aof xle clearance with a knuckle hanging down.

 

[vetteboy79]

Interesting point. How long is not long? How much angle do they really need to move? I'm just thinking of vehicles driving straight down the freeway.

Coming from an industrial power transmission background.

If a particular application had consistently less than a few degrees of misalignment, with constant torque, we'd use a different style coupling - gear, jaw, tire, etc. Something that spread the pressure over more than just a single point of contact. U-joints by nature need to be rotated for an effective lifespan.

Realistically - what vehicle application driving straight down the freeway actually has u-joints constantly locked at 0 degrees? Front axle shafts rotate the joint a little bit every time you change lanes, a lotta bit when you make the turn from your offramp, and they (usually) aren't even transmitting torque. A rear pinion u-joint in a double-cardan setup is usually at 'zero', but moves when the suspension cycles, and I've read that most driveshaft builders would recommend a few degrees of misalignment anyway for the same reason.

(edit: yes as noted above, a bushing style joint would take care of that issue, but what are you really trying to solve here?)

 

[Bebop]

If saving a few hundred bucks is what determines a choice like this, you're in the wrong hobby...

If you want rear steer, build a rear steer axle.
If you want a straight axle, buy the bearing cups.

 

[Grendel]

I am with the build it right crowd, don't complicate stuff that doesn't need to be.

So if you want rear steer, do it that way.

If you don't, but the bearing cups.

 

[mobil1syn]

If saving a few hundred bucks is what determines a choice like this, you're in the wrong hobby...

If you want rear steer, build a rear steer axle.
If you want a straight axle, buy the bearing cups.

you sir take that logical thinking somewhere else.

 

[Lil'John]

If saving a few hundred bucks is what determines a choice like this, you're in the wrong hobby...

If you want rear steer, build a rear steer axle.
If you want a straight axle, buy the bearing cups.

Looks like we need a sticky on every offroad board that Bebop says if you don't spend hundreds and thousands of dollars you shouldn't be offroading Thanks for usual non-answer.

 

[Lil'John]

I could go rear steer and I'd still have the u-joint not turning due to onroad use between trails.

 

[mobil1syn]

I could go rear steer and I'd still have the u-joint not turning due to onroad use between trails.

correct, but youll have enough axle movement on the trail to keep everything lubricated. GM proved this with their rear steer 1500.

personally id run the semi float stock stuff until i could afford to scab a UB cup on the end of the housing.

rear axle brakes and brake brackets can be done on the super cheap, so im not sure why that is even part of the conversation.

 

[ScottRS]

Rear steer is awesome, driver might be not awesome.

Anyways if you think you might add it the the knuckles are a good way to go, if not then I'd do the cups. not extra ball joints, u joints, brakes could be slightly more difficult to mount, possible loss aof xle clearance with a knuckle hanging down.

Rear steer is awesome, I'm less-than. But I have rear steer to make me look closer to awesome.

Weight, cost, and complexity aren't great things voting for rear steer. By the time you get axleshafts, joints, outer knuckles, etc., it's going to cost more than non-steer, or be weaker. Maybe both. It will weigh more, that's not even a "maybe". That said, if you're that close, have rear steer. If you truly plan on hard-linking it to not have rear steer, I would recommend against bothering with building it that way, there's just too many moving parts in there to buy it and then not use it, and too much cost, unless you own a junkyard and get all your parts for free.

So the questions not asked but I think relevant: What's the application? Tire size? Horsepower level? Wheeling style? Road driveability concerns?

 

[vetteboy79]

GM proved this with their rear steer 1500.

Which used CV's, not u-joints. Which is another way to go, but like the bushed joints, skews the numbers even further away from reasonable.

 

[Lil'John]

correct, but youll have enough axle movement on the trail to keep everything lubricated. GM proved this with their rear steer 1500.

personally id run the semi float stock stuff until i could afford to scab a UB cup on the end of the housing.

rear axle brakes and brake brackets can be done on the super cheap, so im not sure why that is even part of the conversation.

Good observation on the GM rear steer.

I bring up the brakes because the bracket is another cost on top of the bearing cup. I am ignoring the added cost of the caliper and rotor since no mater the direction I go, those are new.

Rear steer is awesome, I'm less-than. But I have rear steer to make me look closer to awesome.

Weight, cost, and complexity aren't great things voting for rear steer. By the time you get axleshafts, joints, outer knuckles, etc., it's going to cost more than non-steer, or be weaker. Maybe both. It will weigh more, that's not even a "maybe". That said, if you're that close, have rear steer. If you truly plan on hard-linking it to not have rear steer, I would recommend against bothering with building it that way, there's just too many moving parts in there to buy it and then not use it, and too much cost, unless you own a junkyard and get all your parts for free.

So the questions not asked but I think relevant: What's the application? Tire size? Horsepower level? Wheeling style? Road driveability concerns?

I'm not hugely worried about another ~100 to 200lbs of added weight at the ground.

As I noted, I've priced out an axle vs a cup and it comes out a bit cheaper. But to put some numbers on it:
I can get knuckles and inner c's for a bit less than the cups... $400 if I don't shop vs $500 for cups
Unit bearing cost is the same.
Rotor and caliper are the same.
New 1550 axle shafts ~$170 each side... double splined shaft $400 a pair plus another ~$200 for a drive flange
Tie rod ends and bar - free with axle plus ~$30 per tie rod end
Cost to have reputable axle builder to graft cup or inner c - same

Great question on application. I've got two projects that I'm considering:
Proj 1 that is high on list: mild 472 cady, SM465, 35 to 40" tires (starting at 35) I forget my number crunching but I think I came up with maybe 220hp and 450 ft-lbs
Proj 2 that is low on list: turbo 5.3L LS, 4l80, doubler, 43" tires... unknown HP... I'll play with tune for low and high octane.

Both will be wheeled technically... I made stock birfields survive behind a V8 and SM465. Neither is trailered so road use is on the list. I've got 35 backroad miles to Rubicon, 80 mixed miles to Fordyce, and ~130 miles mixed to my favorite camping site.

 

[Bebop]

Looks like we need a sticky on every offroad board that Bebop says if you don't spend hundreds and thousands of dollars you shouldn't be offroading Thanks for usual non-answer.

If you're here asking questions it's because you are searching for advice from people that have more knowledge or experience than yourself. If you're here hoping to only get answers that validate your ideas, sorry, you're not gonna get that from me. Nor the other guys here that are experienced in the matter. See above.

And if you're intimately convinced that what you have in mind is the "right" answer, go ahead, built it and I'll be the first one to admit I was wrong.

Cost to have reputable axle builder to graft cup or inner c - same

Unless you buy builder Cs from Dana (which doesn't fit in your budget), you'll have to have the stock Ford C's machined. Assuming you have a 3.5" OD axle tube, it's fairly simple since you can simply machine that diameter in the stock Ford axle tube. But you're going to pay for the hour or so of labor to run the lathe.

I'm also assuming you're having your axle retubed too. I don't know many "reputable axle builders" who will graft C's on a stock tube rear housing.

Edit for pics to show that I'm not talking out of my ass.

 

[ScottRS]

I'll nitpick a bit:
$170/side for new 1550 isn't custom length shafts (that I know of); can you use stock length shafts from a '05-up Superduty (another assumption on my part) in this? I'll assume yes or you wouldn't be suggesting it. Also isn't 4340 or better, but it sounds like at least on 35's, should be fine. 40's I'd be more concerned (and you'll be spending more money). I will prod you a little (gently) about that $400 a pair for double splined shafts (the $200 drive slugs are a wash) being likely a far superior axle shaft to the $170 a side stock Ford stuff, so not really a fair comparison there IMO except simply on cost.

Can the rig in question reasonably clear rear steer tire swing? Particularly with 40's? That's a big packaging headache, I don't have a lot of rub, but I do have a little rub in several places. And I have a rather long wheelbase in order to keep that rub from being on my kids.

IIRC, isn't one or both of your project options for this an FJ60 variant? That will have some weight to it, and assuming ball joint Superduty knuckles, you'll see some accelerated ball joint wear there in all likelyhood. Not crippling, but probably every few years, change joints. More often with bigger tires. If you're not getting the benefit (fun) of steering it, that's just an ongoing cost like brake pads, just more work to change. Unit bearing knuckles are pretty quick/easy to do ball joints on, so maybe not a major issue for you.

The log splitter valve and associated plumbing can be in your hands for probably as cheap as $200. Or you can spend more to your heart's desire, but I don't see a lot of benefit. You can daisychain the rear to run off your front steering pump, I guess I'm shockingly lucky on what I personally build for steering to make it work (and I hear others can't seem to), but complexity goes down fast when you knock it down to one pump.

If you're truly not going to bother steering it, and can use the stock length axleshafts and all that, I see no major downside other than weight to putting steering on like you've laid-out. If you set up to let the steering actually work, and can use stock axleshafts, I'd say grab an extra pair, take them with, if you break stuff, address from there. If you're at "have to spend $$$ to get custom length 1550 shafts just to not steer"... I'd call that silly. But I might be called silly myself for dropping my kids off at school in a rearsteer tube car.

 

[Grendel]

Also, you're on crack if your Cad 472 is under 350hp/420tq.

I can do that with a cam and low flow heads, plus intake and a tune.

 

[mobil1syn]

New 1550 axle shafts ~$170 each side... double splined shaft $400 a pair plus another ~$200 for a drive flange

uh you need custom shafts since youre running a tundra center with the 36sp unless youre dropping the coin for 35sp side gears ... so stock shafts are out

 

[Lil'John]

Bebop Thank you for bringing meat to the table. When I start posts, I am seeking data and not unsupported "opinions". If I'm looking at an idea, I'm looking for why it is bad and not a generic "everyone does it this way". I rarely bring up a thread seeking information with a path 100% set.

The axle guy I am using has done axles for at least two decades that I've known him and probably closer to three. He is a certified welder(don't recall what certifications) and has done plenty of axles retubed, grafted tube to tube, and grafted c's to end of existing tube. I trust his work.

I'll nitpick a bit:
$170/side for new 1550 isn't custom length shafts (that I know of); can you use stock length shafts from a '05-up Superduty (another assumption on my part) in this? I'll assume yes or you wouldn't be suggesting it. Also isn't 4340 or better, but it sounds like at least on 35's, should be fine. 40's I'd be more concerned (and you'll be spending more money). I will prod you a little (gently) about that $400 a pair for double splined shafts (the $200 drive slugs are a wash) being likely a far superior axle shaft to the $170 a side stock Ford stuff, so not really a fair comparison there IMO except simply on cost.

Fair enough. I can get a 35 spline shaft shortened for ~$100. As noted, I'm a technical wheeler. My cost nitpick is more toward getting setup and going. Most things have an upgrade path and this is one of them.

You are right... drive slugs are a wash cost

Can the rig in question reasonably clear rear steer tire swing? Particularly with 40's? That's a big packaging headache, I don't have a lot of rub, but I do have a little rub in several places. And I have a rather long wheelbase in order to keep that rub from being on my kids.

IIRC, isn't one or both of your project options for this an FJ60 variant? That will have some weight to it, and assuming ball joint Superduty knuckles, you'll see some accelerated ball joint wear there in all likelyhood. Not crippling, but probably every few years, change joints. More often with bigger tires. If you're not getting the benefit (fun) of steering it, that's just an ongoing cost like brake pads, just more work to change. Unit bearing knuckles are pretty quick/easy to do ball joints on, so maybe not a major issue for you.

Good memory. Both are FJ55s with significant body loss. Both are losing about 1/2 roof(think extra cab conversion) and ~24" off the ass. Stock they come in at ~3500 to 4000lbs... I've seen a lot of different weights.

With 43x14.5s and a narrow full width(67"), I am 7" from tire to frame. I'm not expecting to have full turning capability.

The log splitter valve and associated plumbing can be in your hands for probably as cheap as $200. Or you can spend more to your heart's desire, but I don't see a lot of benefit. You can daisychain the rear to run off your front steering pump, I guess I'm shockingly lucky on what I personally build for steering to make it work (and I hear others can't seem to), but complexity goes down fast when you knock it down to one pump.

If you're truly not going to bother steering it, and can use the stock length axleshafts and all that, I see no major downside other than weight to putting steering on like you've laid-out. If you set up to let the steering actually work, and can use stock axleshafts, I'd say grab an extra pair, take them with, if you break stuff, address from there. If you're at "have to spend $$$ to get custom length 1550 shafts just to not steer"... I'd call that silly. But I might be called silly myself for dropping my kids off at school in a rearsteer tube car.

It sounds like it is mixed bag on putting rear steer on front pump. My cady is going to be doing hydro assist which makes it "even worse".

I'm not hugely worried about the speed of the rear steer if I go that route.

Also, you're on crack if your Cad 472 is under 350hp/420tq.

I can do that with a cam and low flow heads, plus intake and a tune.

My 220hp was off... that number is what the 472 starts at based upon data from Big Inch Cady and old MTS catalogs... 365ft-lbs torque. The intake adds ~30hp/ft-lbs, the mild 268 cam adds 25hp/15ft-lbs, and the sanderson headers are 10hp/15ft-lbs. One has to ignore the early 70s bullshit reported numbers. So my math says under 300hp and right at 420tq. It'll probably get choked when I drop a 2" TBI on top over the Quad.

 

[Lil'John]

uh you need custom shafts since youre running a tundra center with the 36sp unless youre dropping the coin for 35sp side gears ... so stock shafts are out

Correct. Yes, I'm considering 35sp side gears... my "local" axle guy does 35sp recuts for ~$100 a shaft.

 

[ScottRS]

IMO, resplined stock front inners are usually a strength downgrade from stock, so if you go that route I would recommend to plan on aftermarket shafts sooner than later.

The 7" you noted, is that from sidewall to frame? That's not much room.

 

[Lil'John]

IMO, resplined stock front inners are usually a strength downgrade from stock, so if you go that route I would recommend to plan on aftermarket shafts sooner than later.

What do you feel causes the down grade?

The 7" you noted, is that from sidewall to frame? That's not much room.

Correct. Sidewall to frame.

For a comparison, 60" wide axle with 35s is down to 4" for same frame. The front is closer to 11" with 35s which gives full turn on kingpin 60.

As noted, I'm not expecting full turning angle. My quick math for the 43s says I can pull off between 15-20 degree(~18). With 35s, that goes up a bit more(~22) I don't recall max turn angle but I thought it was 45 degree with extreme clearancing of the yokes.

 

[YotaAtieToo]

You want to ship me a few hundred to cover the difference? Yeah... I didn't think so.

I have ZERO interest in a welded spindle so thanks for that opinion that was never brought up as an option.

No, I rather laugh at you for building a steering not steering axle

That few hundred will easily be eaten up by u joints and more expensive axle shafts.

If you really want to build these type of axles, $200 is nothing.