rear 4-link is starting to take shape

[Quick & Dirty]

This discussion is a little old, but the info may help others.

not oversteer - REAR steer. meaning, when the articulated, the wheel moves forward instead of down slightly rotating the whole axle perpendicular to its axis which causes it to steer or walk.

how can you avoid it? by design the axle is going to move back a little when the suspension is compressed.

That is determined by the Roll Axis, an imaginary line between the intersection points of the lower links and the intersection of the upper links.
This axis should be as level as possible for minimal steer, and pointing slightly downward toward the center of the vehicle for stable handling.
Triangulating the lowers is necessary for good roll axis, unless the lowers are nearly parallel to the ground.

 

[mavereq]

I change out in June but I am attempting to stay local. Ray mentioned that you were working to get out here. Should be some spots opening up in a year (most of the companies are deployed/deploying - so alot of personnel change over).

i hope the timing works out. all of my family is in washington. it would be nice to take leave and travel other places.

 

[mavereq]

This discussion is a little old, but the info may help others.





That is determined by the Roll Axis, an imaginary line between the intersection points of the lower links and the intersection of the upper links.
This axis should be as level as possible for minimal steer, and pointing slightly downward toward the center of the vehicle for stable handling.
Triangulating the lowers is necessary for good roll axis, unless the lowers are nearly parallel to the ground.

that makes sense. so far the suspension looks like it's going to work well. i won't know for sure until i get it together and i don't want to tempt murphy so i won't make any claims till i know for sure.

 

[mavereq]

quick n dirty, you might be able to answer this question for me. i've had a few people mention that they want their uppers longer for better pinion angle but everything i read says the uppers should be shorter. the only thing i've read that mentions a reason for shorter uppers mentioned having rear steer with longer uppers. what's the real deal?

 

[Quick & Dirty]

I don't think the length has much effect on rear steer, that's dependent on the intersection points which is more about the angle and separation. Of course, angle and length are related due to fitting it in the frame.

Desired pinion angle depends on the type of u-joints used in the drive shaft.

With single u-joints the pinion should stay parallel to the t-case output. So short uppers will swing the top of the diff forward more on down travel to keep the pinion level.

With a CV-joint like a stock Bronco driveshaft you want the pinion to keep pointing up toward the output. In this case more equal length uppers and lowers will swing the axle in an arc like a radius arm. (Assuming the typical wheeler setup with fairly horizontal uppers and upward angled lowers.) The trick becomes balancing pinion angle with anti-squat.

 

[KennyB]

I got my Leafs off, and ALL My Parts in...2 Ballistic Joints, and 6 Jonny Joints Brackets and Metal from RuffStuff, Ballistic, and Gen Right. Then, I had a Kitchen Accident, and spilled some Boiling Fudge all over my hands and Arms... SO,.... My Mock up is a little slow with the Bandages... .
I reworked the Cross Member, Plus, Lifting the Main Gas Tank 2". I ordered some Stock MOOG Springs (16" out of frame) for Mock up... I bought them at Summit for $76... Free Shipping...

Upper Links x y z
Frame End 38.00 8.50 25.00 in
Axle End 2.00 5.50 26.50 in
Lower Links x y z
Frame End 42.00 13.50 21.50 in
Axle End 3.50 20.00 16.00 in


Static Anti-Squat 81 % Travel Anti-Squat: 79%
Roll Center Height 31 in Travel Roll Center: 31.71
Roll Axis Angle 1 degrees (Roll Oversteer) Travel Roll Axis: -0.40°
Instant Center X-Axis 60 in Pinion Change: 1.02°
Instant Center Z-Axis 24 in Travel Amount: -7.00
Travel Increment: 1.00


Spent a LONG time with the Calc. and got an acceptable Compremise...

 

[DanWheeler]

quick n dirty, you might be able to answer this question for me. i've had a few people mention that they want their uppers longer for better pinion angle but everything i read says the uppers should be shorter. the only thing i've read that mentions a reason for shorter uppers mentioned having rear steer with longer uppers. what's the real deal?

This is from a post I made over at pirate. I can't answer the question about whether or not to have longer or shorter uppers but I can tell you that I will likely be going with equal length arms converged at the frame for my 3-link. I was under the impression that 90% of rear 4-links had shorter uppers.

Equal Length / Parallel Uppers and Lowers:

no surprise there. Caster stays exactly the same.

Equal Length / Converged Uppers and Lowers: (less separation at the frame)

pinion rotates up slightly with less separation at the frame

Short Upper / Long Lower

this one is interesting because the caster stays the same until you get all the way down to as low as it will go then the pinion suddenly rolls down. You have to go past the point of it even being realistic to get the pinion to roll down.

Long Upper / Short Lower

with the longer upper, the pinion roll up is immediately noticeable and gets more drastic as the axle goes lower. If you want to keep you pinion pointed at your transfer case, this is the way to go.

 

[mavereq]

i gotta ask dan.... what's up with those gloves?

 

[KennyB]

"Guru-Gloves"

 

[OX1]

quick n dirty, you might be able to answer this question for me. i've had a few people mention that they want their uppers longer for better pinion angle but everything i read says the uppers should be shorter. the only thing i've read that mentions a reason for shorter uppers mentioned having rear steer with longer uppers. what's the real deal?

After dans post on pirate, and a couple other recent pirate threads, I tried my rear setup (on the calc) with 20 inch uppers and 40 inch lowers, then 40 inch uppers and 20 inch lowers. Either way, I get negative pinion angle up to an 11" droop. It may have to with the fact my upper is dead level and my lower is angled up only slightly.

The 2 biggest things that affected rear steer for me was vert angle between uppers and lowers and horiz seperation between lowers (oddly enough). I can shorten or lengthen my uppers 5 inches and rear steer changes maybe 1 degree. I move my lowers outboard @ the axle 2 inches and rear steer changes 3 degrees??

 

[DanWheeler]

i gotta ask dan.... what's up with those gloves?

what gloves? I'm just pale. Don't get out much - always in the garage

seriously though - gloves are awesome. I dont even think, I just put them on when I walk in the garage door. I go through boxes of them but they are cheap at Harbor Freight. I wouldn't normally care but it looks bad at work when my hands and fingernails are dirty.

Mav, if you ever move up to Washington, lock up your Bronco because if you leave it out, I may cut the frame right down the middle and steal the back half

got any updates?

 

[mavereq]

i don't have any updates on the project really. i have a rolling frame but am working out some issues on the pulley setup. i have another lower pulley enroute so hopefully that fixes everything. here's a pic of the rolling chassis.

on a bright note... i'm hearing rumors that i may indeed be moving to washington very soon. they're only rumors at this point as i haven't received orders, but i'm keeping my fingers crossed.

 

[mavereq]

oh, and at least one of my axle seals is leaking. i haven't tilted the axle the other direction since i filled it up so i'm not sure on the other side yet. are these axles just a pain to seal up or what?

 

[DanWheeler]

here's a pic of the rolling chassis.

on a bright note... i'm hearing rumors that i may indeed be moving to washington very soon. they're only rumors at this point as i haven't received orders, but i'm keeping my fingers crossed.

daaaang, that looks great! I'll have to go check your 3-link thread again. I dont understand how you got that UCA inside the frame without hitting the starter on uptravel.

On behalf of NorthwestClassicBroncos.com, we would love to welcome you and your truck into the club.

 

[mavereq]

I really look forward to moving back home. I still don't have orders in hand so I don't want to jinx myself but I'm stoked about the thought of being back there.

I'll post up some more pics for you. I had to grind the bellhousing a little bit and I used the extreme motormounts. At full stuff i still have a little room. I have the link a little below the centerline of the frame so there isn't as much vertical separation as I'd like.

 

[hardcharger]

damn that looks awesome. nice work man, that is on my list of things to do in the next couple years to mine as well.

 

[mavereq]

daaaang, that looks great! I'll have to go check your 3-link thread again. I dont understand how you got that UCA inside the frame without hitting the starter on uptravel.

On behalf of NorthwestClassicBroncos.com, we would love to welcome you and your truck into the club.

i registered over there. good stuff.

 

[mavereq]

damn that looks awesome. nice work man, that is on my list of things to do in the next couple years to mine as well.

thanks man. it's nice to have it rolling now. that took forever.

 

[Gravel Maker]

Great Job, looking really good!

 

[mavereq]

I finally got to play a little. Monster Mike brought his ramp over. So far the suspension is working great.