|April 14th, 2006, 09:27 PM||#1|
Join Date: 11-05-05
Location: Lost in the mitten!
Ford's (In)Famous TTB suspension
I was going to write a decent FAQ post on the TTB suspension, how it works, why it "sucks" and how many misconceptions are out there about it, but I came across this post on another site......
Keep in mind that the info is geared toward the ranger/bronco II/explorer, but still applies to the F-150 (and leaf sprung TTB 250's)
Ford's TTB (Twin Traction Beam) is probably one of the most hated, yet misunderstood suspensions ever to be invented. Virtually any offroad trail you go on, seems like someone will always be around somewhere with multiple reasons as to why it's no good, and that you should get rid of it.
Perhaps even you yourself have struggled with some aspect of it, and thought that nothing could be done about it except to swap the entire axle & suspension out for a solid beam axle, who's offroad capabilities are rarely ever disputed.
But just how bad are these problems? Are they a normal trait of this suspension that nothing can be done about? Or could there be an underlying issue that's correctable, causing the problem? (that is if it's even a problem at all. Some of the myths I've heard passed around about these things are not even true).
The purpose of this post is to bust through some of these myths and help you to understand what causes some of the common issues that are often associated with this suspension, and an explaination on how to go about remedying them. You may be surprised at how simple some are to fix, and could potentially save you the hassle of having to do an entire axle & suspension swap. huh.gif
My TTB keeps wearing out my tires too fast (or wears them funny)
This is probably by far the most common complaint on these things.
The common assumption is that the excessive tire wear is caused by the constantly changing wheel CAMBER, yet camber actually has very little to do with it.
The real cause lies in the angle that the steering (tierod) linkage sits at after a tall suspension lift has been put on it. This high angularity of the linkage causes radical changes in the wheel TOE as the suspension cycles up & down (or when the vehicle is loaded), and literally causes the tires to be dragged across the road toward (or away) from one another at times while rolling. The stock "inverted-Y" style linkage and its very short driverside tierod further compounds the problem.
Bad toe behavior will easily wear out a tire 10x faster than the camber variations that are a normal characteristic of the suspension.
(click here for an explaination of 'camber', 'toe', and 'caster' (also related)).
The aftermarket suspension industry has done an extremely poor job on matching the steering up with the lift height on taller lifts. Drop pitman arms help, but they do not fully correct the problem when the lift height exceeds about 3-4". This unfortunately is why this issue is so common, and occurs mostly on lifted suspensions. Problems with tire wear are far less common on stock trucks.
This picture shows the type of angle you often end up with on a 6" or taller lifted suspension. As the suspension compresses, the resulting bumpsteer splays the tires outward in opposite directions from each other, causing the rapid increase in wear.
This truck would literally squeal the tires through drainage dips and left turns at times it was so bad.
The best way to alleviate this problem is to do a steering linkage swap for something that will better follow the axlebeam's arc of travel.
This pic shows the truck fitted with a fairly simple "K" style linkage (using a centerlink) that replaces the stock "Y" linkage.
Surely you've probably heard about the importance of keeping the draglink angle parallel with the trackbar (panhard bar) on a straight axle so you don't encounter bumpsteer. The concept is hardly different here, except that it goes for each wheel individually. The above linkage's tierods are much closer to parallel with both TTB arms than with the stock linkage, and helps reduce or eliminate the toe variations responsible for the increased tire wear.
(some details on making use of a Superlift Superrunner kit can be found here, or you could instead fab your own linkage using heim ends if desired)
The other option is to lower the lift height of the suspension a bit (trimming fenders or adding a bodylift to compensate).
Many lift brackets have two sets of holes that can be used for the axlebeams. Moving the axle to the upper bracket hole will help improve the steering's geometry with the axlebeams. If your truck is a Supercab, in some cases you might even be able to keep your current lift coils for no loss in lift height (but a big gain in diff clearance), and still be able to align it.
But my steering angle is fine. Why won't this @#*!% thing align properly? I've taken it into the shop 6 times and they say thats it's normal?
Well, this is absolutely NOT normal at all!! These things certainly didn't roll off the dealer lots out of alignment, so something is certainly causing it to be unalignable.
The aftermarket suspension companies are again largely to blame here, as this again occurs far more often after a lift.
A TTB has a fairly narrow range that the ride height must be within in order to facilitate an alignment. The liftkit industry did not do a good job in selecting the proper spring heights for the various bodystyles and engines available (Supercab/Reg cab/BroncoII/4cyl/V6/etc.). They kindof just lumped them all onto one (in rare cases two) coil sizes for everything. Obviously a big heavy Supercab is going to sit lower on the same springs than a smaller 4cylinder truck, so this could easily cause a non-alignable condition to occur. Fortunately the solution to this issue is probably the easiest one of any.
(read here for a rundown on how to check & adjust the ride height on yours)
A 2nd common reason for this to occur is probably simple incompetence (or lazyness?) on the part of the alignment technician doing the job. It would seem that the training given to a lot of these guys on TTB suspensions is inadequate, as more than once I've been able to take a TTB vehicle that was deemed unalignable by a shop, set the tires perfectly straight, and have it tracking straight ahead down the road without pulling to one side (all while just using plain, simple homemade tools).
Perhaps the caster AND camber adjustment being integrated into one adjuster (bushing) is what's throwing them (that, and the factory style fixed-degree bushings were a dumb idea IMO. Aftermarket fully adjustable-degree bushings (Ingalls #594 for the D35) make alignments much much easier to accomplish on these things, as they come with a little chart that tells you exactly what to do to add (or subtract) whatever degrees of caster or camber that is needed to dial it in)
I've been doing at-home alignments for awhile now, and have never had one that could not be properly aligned.
If DIY alignments are over your head, I'd probably seek out another shop to do it (provided your ride height was OK). 4WD shops that regularly modify suspensions may be your best bet, as they probably deal with these things on a regular basis.
Something to watch out for is that they do NOT pick the tires up in any way while aligning it. This will lead to an improper alignment every time guaranteed. The tires need to be firmly on the movable plates of an alignment rack with full weight on them for it to come out properly.
But a TTB axle will never flex or perform offroad like a straight axle can.
Well, this is only partially true.
TTB lift coils downright suck. They are much too stiff to allow any decent flex. You put those same coils on a straight axle and it ain't going to flex at all either.
A simple swap to some better coilsprings will make all the difference in the world here.
TTB suspensions are easily capable of 18+" of articulation on a Ranger, Explorer or Bronco II with only a minimal amount of modification. While a straight axle is capable of exceeding this number, how much flex is actually needed in order to have good performance?
When you exceed about 18-20" flex (without also widening the track width), you begin to trade off some of the vehicle's roll stability for that extra flex unless you can also greatly lower the vehicle's center-of-gravity. This isn't always easy to do on a vehicle with full (or even trimmed) fenders and large tires.
Lots and lots of flex certainly can make an excellent ramp (poser) truck, but it doesn't always translate the same in terms of trail performance.
Here is an example of what a pair of Jeep XJ lift coils (along with extended radius arms) can do on a TTB axle on a Bronco II. These springs usually have a compression rate of around 240lbs-in, whereas standard TTB lift coils are an exceedingly stiff 400-550lbs-in. It's little wonder why they don't flex with such coils in it.
Some additional info on the BII XJ coil swap can be found here.
Rangers/Explorers, and Ranger Supercabs will require a bit stiffer coil in the 300-325lb-in range due to being a bit heavier. Some early ('66-'77) Bronco coils fall within this range. There are a few companies out there that can custom-make a pair of coils for you as well, if needed.
You'll find that softer springs will have a longer free length for a given lift height than stiff coils. This helps the suspension to flex down further to better keep the tires in contact with the ground for traction.
The other thing to check is your shock length. Often times they're too short, which can cut off a good portion of your flex. An explaination for how to check for shock length can be found in the link in section #2 above.
Extended shock mounts can be added to increase the available travel as well.
It should also go without saying, ditch the swaybar if it's still on there.
But isn't a TTB axle weaker than a straight axle?
Well, it depends which specific axles you are comparing.
The TTB Dana35 axle used in most '90-'97 trucks has a lot in common with Dana44 axles used in fullsize trucks (such as the axleshaft joints) and uses a hi-pinion gearset for added strength in a front axle. It is by no means weak at all (the stock locking hubs excepted, read here about better hubs for it).
All Rangers/BIIs built prior to 1990 will have a Dana28 front axle. This one probably would make a better door stop than a driveaxle. Its tiny axleshafts just don't lend themselves well to hard offroading, even with stock-size tires. This of course isn't directly related to the TTB suspension itself though.
A D35 axle from a later Ranger/Explorer is basically a bolt-in swap for a D28, and can support 35x12.50 tires. (some info here)
But how can an axle thats "broken in the middle" be just as strong?
Well, simply put, the center joint & slip-shaft on a TTB is not subjected to the same operating angles you normally have at the steering knuckle joints. The slip-shaft also has a very large spline diameter (much larger than where the shafts engage the side gears inside the diff). It is unlikely to see a failure here.
The few failures I have seen often involved something binding up somewhere. Places to check are the u-joint yoke with large amounts of flex/droop, and possible binding of the axleshaft within the "window" on the passengerside axlehousing. A bit of clearancing with a grinder will allow some more movement if needed.
Shown is a center yoke that has been clearanced for additional wheeltravel.
The large axle spline can also be trimmed about ½" with no loss in strength if it bottoms in the yoke at full droop.
But TTB is still IFS. IFS sucks offroad
This is probably one of the more blatent misconceptions around.
IFS as a whole has gotten much of it's bad rap from the lack of flex and durability inherent in many of the conventional A-arm & torsionbar setups found in late-model vehicles. The TTB's components simply do not compare to such setups.
Another common arguement is that the leverage inherent in a straightaxle helps force one tire downward for better traction when the opposite tire is forced up (while climbing a rock, for example). While this is true, it's not near as significant as commonly thought to be. The downforce created at that wheel tends to be offset by the lifting action going on at the wheel that's climbing up the rock.
An independent (TTB) suspension is capable of maintaining a similar downward pressure through use of the longer, more flexible springs described above (#3). This allows the wheel climbing the rock to flex upward easier (reducing the amount the body lifts up), which by not lifting as much, further helps the opposite spring in keeping downward pressure at the other tire for a similar gain in traction. Short, stiff springs simply cannot do this well on an IFS.
Because a TTB is relying more heavily on the springs for this function, coil selection does become a bit more important than on a straightaxle.
OK, but all that wildly changing camber still causes it to handle like crap offroad.
How sure are you that the camber is what's responsible for the poor handling, and not bumpsteer (toe)?
Referring back up to #1 above, a poor steering setup that's unable to properly control the wheels is going to cause a lot more handling issues than the camber.
The effect from camber alone is quite subtle by comparison (and if desired, can be further controlled through use of a limiting cable or strap connecting both sides to reduce the suspension's dropout while climbing up steep hills for example, but without reducing articulation at all (same function as a 'center limit strap' as sometimes used on straight axles). The need for something like this goes down as wheelbase gets longer though.
So what kind of abuse can a TTB take then?
It's capable of standing up to most of what you'd normally throw at a straight axle.
Some have cited the aluminum centersection as a possible weak spot, but a simple skidplate can eliminate most worries there.
About the only other area on the axle itself that you could potentially encounter any bending would be the open-channel backside of the TTB arms. Welding a plate in to box them up would easily match the strength you'd find in the round tube structure of a straight axle.
Bending of the beams is quite rare though, you have to be beating on it pretty dang hard to bend it. Normally a bent beam happens from some sort of collision, not from hard offroad use.
A seperate area of concern that sometimes comes up is with cheap liftkit brackets. With some kits, you may encounter some bending/cracking of frail brackets with hard use, and may need some reinforcement. This obviously wouldn't be any fault of the TTB axle itself.
You could easily compare this type of failure to that of trackbar brackets common to straight axles. Such a failure doesn't deem a straightaxle as inferior either, the liftkit product is what failed.
The Skyjacker and James Duff TTB suspension kits have repeatedly proven themselves to be very durable and are highly regarded for their brackets.
Well, the SAS is still much simpler, as all this TTB stuff is just too complicated for me.
This could potentially depend on who you are more than anything else...
Some minds work better at tinkering with things, whereas others demand a more basic approach.
A TTB undeniably does require a little more thought while setting one up, mostly due to the fact that the wheel camber is tied in with its ride height, and needs a bit more fine-tuning than would normally be required on a straight axle. The fact that the number of quality aftermarket bolt-on parts for a TTB suspension is relatively small leaves a fair amount of homework to be done as well. As such, it's not going to work for everyone in every case.
But there are plenty of factors that need to be considered with a complete swap also (things like caster settings, designing and fabricating all of the needed mounting brackets for it, etc.). You will still need to set up your steering linkage and its angles also. The fact its a one-of swap means nothing will be "factory" anymore, and you'll need to be good at finding all the various different parts needed for it.
Is it easier to fix whichever issues are present on your existing setup? or would it be easier to swap the whole axle?
Only you yourself can answer that, but the above information should hopefully be of some help in making the decision.
(Write-up credited to 4x4junkie from therangerstation.com)
One thing I'll add is this - if you dont have a whole lot of fab skills, or dont want to swap in a solid axle, TTB works fine when you get the quirks worked out of it....it is a pain, but this post should outline the major issues when setting it up - it's much easier to know this stuff before hand as opposed to trial and error....
Last edited by chris1044; April 14th, 2006 at 09:37 PM.
|April 3rd, 2009, 10:21 PM||#3|
Join Date: 04-03-09
Thanks for explaining in detail i have seen alot of trucks with TTB and i thought it was just a standard solid front axle but up until this point i didnt even know tht this type of suspension stup existed but i have seen it before.
|April 24th, 2010, 12:29 AM||#8|
Join Date: 05-31-09
Location: Alpena/ Trenton
If you drive straight and tires aren't mark on cement once you turn to left or right there are tires mark on cement. It eat tires very bad. It look like toe were off too much.
3 shops reject when they saw 95 F250. They didn't want to do alignment on it.