1969’s build thread

[1969]

I had originally installed a U-bolt eliminator kit but decided I wasn’t a big fan of it, so swapped back to a traditional U-bolt kit from ruff stuff. Much better!

 

[gnpenning]

I had originally installed a U-bolt eliminator kit but decided I wasn’t a big fan of it, so swapped back to a traditional U-bolt kit from ruff stuff. Much better!
View attachment 915559

What didn't you like about the eliminator kit?

 

[1969]

What didn't you like about the eliminator kit?

Mostly just the size, they’re a bit larger than a standard setup.

 

[gnpenning]

More packaging than concern for strength?

 

[1969]

More packaging than concern for strength?

Just to be clear are you asking if I thought that the U-bolt eliminator kit was not strong enough? Or?

 

[1969]

Set the rear shocks to have 5” of up travel and 7” of down.

 

[gnpenning]

Just to be clear are you asking if I thought that the U-bolt eliminator kit was not strong enough? Or?

If you were concerned with the eliminators strength or any other issues that might effect durability.

 

[1969]

If you were concerned with the eliminators strength or any other issues that might effect durability.

No I didn’t have any concerns. They were big and beefy! But I’ve also never had an issue with a standard u bolt setup. Just ordered the eliminators to see and just turned out not to be for me.

 

[1969]

Ended up modifying the BC Broncos ZF5 crossmember so it would clear the transmission and work. Also had to modify the mounting holes for the transmission mount as they were not in the right place either.

 

[1969]

Got the front coilover reservoir mounts done

 

[1969]

NP205 crossmember is all done

 

[Yeller]

Nice looking, clean work.

May I ask the thought process behind the double crossmembers? The reason I ask is in my experience double crossmembers are hard on parts. Frames flex, I don’t care how rigid it is built. multiple mounts make bending moments in the transmission breaking cases, bell housing and even engine blocks. I’ve witnessed multiple failures that all had 1 thing in common, more than 3 points of contact. OE’s use 3 mounting points for a reason.

 

[1969]

Nice looking, clean work.

May I ask the thought process behind the double crossmembers? The reason I ask is in my experience double crossmembers are hard on parts. Frames flex, I don’t care how rigid it is built. multiple mounts make bending moments in the transmission breaking cases, bell housing and even engine blocks. I’ve witnessed multiple failures that all had 1 thing in common, more than 3 points of contact. OE’s use 3 mounting points for a reason.

Really no reason other than the 205 is heavy and people say that the tail housing on the ZF5’s are weak.. so just figured why not.

 

[Yeller]

The only broken ZF case I’ve seen was from the front drivieshaft being too long.

Just my opinion, one of them needs to go away. If you really feel the tcase needs support, make a cradle that supports both the transmission and the tcase that is then supported by a single mount.

Your build is super clean, just sharing my experiences that drive my thoughts and opinions. The groups I run with tend to be able to break a steel ball in a sandbox with a rubber hammer i’ve just spent way too much time repeatedly replacing broken transmissions because of how they were mounted. Simplified the mounting and never replaced another.

 

[1969]

The only broken ZF case I’ve seen was from the front drivieshaft being too long.

Just my opinion, one of them needs to go away. If you really feel the tcase needs support, make a cradle that supports both the transmission and the tcase that is then supported by a single mount.

Your build is super clean, just sharing my experiences that drive my thoughts and opinions. The groups I run with tend to be able to break a steel ball in a sandbox with a rubber hammer i’ve just spent way too much time repeatedly replacing broken transmissions because of how they were mounted. Simplified the mounting and never replaced another.

Hmm interesting! Why do you think that is ?

 

[Yeller]

Aluminum and magnesium don’t like being bent, they break, even though they are strong and rigid. The chassis will flex quite a lot which puts tremendous loads on the tcase adapter and bell housing. As the chassis flexes it tries to bend the transmission over the transmission crossmember. The tcase support is quite rigid as well with the 2 frame mounted spring eye bushings that are mounted near the center of the frame. Articulate the suspension hard and add traction from bound up tires the bending and twisting stresses are way higher than the case design was built around. Something sooner or later is going to give up. To alleviate the added bending and raising loads a 3 point mounting system is the way to go.

I’ve witnessed far to many transmissions with the tail housing and/or bell housing broken to not speak up.

I’m hoping your not offended, really trying to help you have a fun, safe, dependable rig that you’ve spent a lot of time and resources building.

 

[1969]

Aluminum and magnesium don’t like being bent, they break, even though they are strong and rigid. The chassis will flex quite a lot which puts tremendous loads on the tcase adapter and bell housing. As the chassis flexes it tries to bend the transmission over the transmission crossmember. The tcase support is quite rigid as well with the 2 frame mounted spring eye bushings that are mounted near the center of the frame. Articulate the suspension hard and add traction from bound up tires the bending and twisting stresses are way higher than the case design was built around. Something sooner or later is going to give up. To alleviate the added bending and raising loads a 3 point mounting system is the way to go.

I’ve witnessed far to many transmissions with the tail housing and/or bell housing broken to not speak up.

I’m hoping your not offended, really trying to help you have a fun, safe, dependable rig that you’ve spent a lot of time and resources building.

Good to know! No im definitely not offended and appreciate your input on the matter. Everything you are saying makes sense!

 

[1969]

@Yeller the frame side mounts and the support bracket in the center all have poly bushings and are not solid steel. Do you still think it’s an issue?

 

[Yeller]

I do. Worked on similar set ups that were in tube chassis’s that I can promise were far more rigid than a bronco chassis, even though yours has been reinforced where it matters it still has a fair amount of flex. Even though nothing is solid mounted without any rubber you still have some very high bending moments built into that. The spring eye bushings are the most rigid part of the whole design. If space allows I’ve been known to use them for crossmember mounting, but I still use a soft mount in the center to get back to a 3 point system.

Disclaimer for all Mechanical engineers, not poking at any of you directly every time I’ve had the debate about “why do I keep breaking transmission cases” it has been with an M.E. Until we get into moment of inertia with a sketch of a teetertoter, then they got it. Until then they looked at it as a continuous cradle from motor mounts on back, frame rails flex and twist, to a lesser degree so do tube chassis but there is flex.

 

[gnpenning]

Gm used a bracket that mounted the tcase to the frame with a couple of isolator donuts. In later years they changed to a rod from a trans/block bolt that ran to 2 bolt holes they used to mount to the frame. Both the 203 and the 205 iirc.

Don't recall the year switch.