Upper link length on 3-link w/panhard?

[vetteboy]

Currently in the progress of a stupid big XJ build, parts of which include a 4-link rear and 3-link front w/panhard.

The front is getting set up on a Dodge D60, low-pinion. The single upper link (much like the URF-style) will run on the drivers side, which since there's no longer a transfer case on that side, leaves a lot of room for flexibility. Also since the trans is a NV4500 I've got nearly 10" above the crossmember to play with on that side, and I can angle the link to meet the axle pretty much anywhere on the right half of it.

So...the problem is the Dodge D60, which came with 5* of caster and 0* of pinion angle. I'd like to keep at least 3* of caster in there, which leaves me with a somewhat lame u-joint angle at the pinion. I'm running a small enough amount of lift that the angle is fine at static height, and it's fine if the diff drops down 6", as long as the pinion doesn't rotate down at all. What this works out to is that as long as the lowers and uppers are equal length, or the uppers slightly longer, I won't run into any u-joint issues.

(yeah, I know I can cut/rotate the inner C's...trying to avoid that if possible right now)

I know for the rear that keeping the upper links shorter, while not helping pinion angle any, lets you take advantage of the change in anti-squat over suspension travel. The big question: how much will this matter in the front, if I keep the upper link equal or slightly longer? Will it tend to unload more, give more torque rise, etc? I totally understand how the rear works but can't quite picture how the weight transfer will affect the front.

I guess specs would help. Lowers around 38-40", upper can be 33-43" with the available clearance. Currently sitting at around 90% anti-squat by the 3-link calc. Around 6" vertical seperation at the frame and 7 - 7.5ish at the axle.

I'll be posting a full write-up of this thing eventually, when I can get all the pics and stuff organized.

 

[vetteboy]

Ah well. Uppers a little longer.

In theory:

In practice...this probably looks familiar.

Yeah, it's all just tacked and rough cut right now. I want to make sure everything fits before I really burn it in.

With a non-flipped D300 and a NV4500 in place, you really have a lot of room for an upper down the driver's side.

Just gotta truss the hell outta the front diff for the upper mount and it'll be all set.

 

[CRASH]

What are you doing about exhaust? Still have room on the passenger side?

Oh, you ought to take the time to cut and turn the knuckles, you'll be a lot happier in the end with 5 degrees of caster and 13 -16 degrees of pinion up, and it'll keep the pinion out of the rocks.

 

[tealcherokee]

that does not look safe

 

[Mike L]

that does not look safe

Why?

 

[CRASH]

Why?

I don't particularly like how muc material got removed here:

Those donut NV4500 mounts take up a ton of room, the plate bends, and they eventually strip out the extension housing bolts. You ought to change that to a better style of mount, one that will not require so much material to be removed.

 

[vetteboy]

What are you doing about exhaust? Still have room on the passenger side?

Oh, you ought to take the time to cut and turn the knuckles, you'll be a lot happier in the end with 5 degrees of caster and 13 -16 degrees of pinion up, and it'll keep the pinion out of the rocks.

The space between the upper and lower mount and the floor is just big enough for a 2.5" circle to fit through. It'll be tight and might involve a sharp bend, or maybe smaller pipe, but it should be doable. The little bit of backpressure increase doesn't worry me too much.

Passenger side has zero room. :roll:

And that's not even tucked all the way up yet...

I still might turn the axle. Part of me wants to get it done w/o and see how it goes, and part of me just wants to do it right the first time.

that does not look safe

I agree. Tack welds should never be used in high-stress areas.

Got anything more constructive to say?

 

[vetteboy]

I don't particularly like how muc material got removed here:

Those donut NV4500 mounts take up a ton of room, the plate bends, and they eventually strip out the extension housing bolts. You ought to change that to a better style of mount, one that will not require so much material to be removed.

I plan on filling the area around that back in, and it will be braced back to the rear crossmember too. Think it needs more than that? It started life as 2x6x1/4" tube.

I'm also having another mount behind the D300, both to help absorb more torque and also take some of the overhanging load off the extension housing and 231 box.

I sorta liked the plate mount because the wider mounts put less torque on a single point.

edit: Also the upper mount in front is gonna be braced back as well, probably to one of the 2x2 tubes running between the f/r crossmembers.

edit x2: Just realized the angle of that pic makes it look worse than it is. After filling the opening in there will still be nearly 4" of material along the top.

 

[CRASH]

Actually, the wider mount forces more torque into the bellhousing.

The general idea on torque control is that you want to control the torque as close to it's point of origination as possible. This is the engine. So, you want three points of control, one on either side ofthe engine, and then a simple pivot to support the weight of the driveline.

Don't try and control engine torque way back in the drivetrain. If you stay with the plate mount, at least narrow it significantly. trust me, I ran one for years, and cursed it all the time. I had to straighten and/or reinforce that plate 3 times before i threw it out the window.

 

[vetteboy]

Actually, the wider mount forces more torque into the bellhousing.

Yeah, I see what you mean. Same reason why running the bushing-at-the-ends-of-a-crossmember setup isn't a great idea. What I meant to say was that the 'reaction' from the bushing itself is less with a wider mount (longer lever arm to control the same amount of torque). Sort of like the frame-rail bushing they used on the Ford 205's. Problem is if those mounts start becoming the limiting thing rather than the motor mounts themselves (if you're limiting the motor torque through the bellhousing rather than before it). I always thought this to be more of a problem with the really wide bushing setups, because the deflection is greater for the same amount of twist, but I can see the advantage of a single pivot too.

I'll probably be doing poly motor mounts anyway so those should absorb the majority of it. However I know you guys have been running this trans in there for a very long time so when I crawl under it today I'll see what else I can do.