Zr2 front suspension

Chuck FB · June 28, 2025

10 minutes ago, revrnd said:

Anyone have a U bolt nut kicking around that they can thread a known metric bolt into?

I can crawl under my truck tomorrow and check.

I am so limited in the metric bolts and nuts I keep on hand but a while back when I was looking at the ubolts and measured the unthreaded rod and came up with an approximate 5/8 or 16mm diameter and also noted that the outer diameter of the theads is larger due to how they formed the threads, I took a 3/4 course nut and it spun on easily although it was loose side to side. That told me the approximate thread pitch as I never did pull out my metric thread pitch gauge to get an exact figure. Unless I am off and I believe I mentioned this in another comment that its highly likely the thread is a 18mm with a 2.5mm pitch. However its not an 18mm diameter rod so bolt charts won't take that into account, nor would it be easy to find out what actual material GM is using for the ubolts. The only thing I can say with certainty is that a deep 1 1/16 socket fits perfect and that should equate to a 27 mm socket .. so if one does not own much for metric tools the standard socket works perfect !.

kylant · June 28, 2025

the u-bolts are M18x2.5

Chuck FB · June 28, 2025

5 minutes ago, kylant said:

the u-bolts are M18x2.5

The thread I would agree with but not the actual rod diameter from what I at least measured the other day. I'd have to remeasure using a micrometer to say with 100% certainty. Its quite noticeable when looking at where the threads end and the solid rod continues, how the threads are larger in diameter than the rod itself.

Epsilon Plus · June 30, 2025

On 3/17/2025 at 11:02 AM, GMCnewbie said:

Here's the other images of the Cognito sticker. Nothing really helpful to identify the spring rate.

I'm still hunting around with this. I plugged the 1.02mm difference into AI against my stock 4800lb rate and told it length was approx. 59"

It calculated a rate of 4345lb with the 1.02mm drop which is awfully close the the 4400lb lowest available GM stock bar.

Also, if you plug "33293 torsion bar" into Google you'll find 19332932 which is a discontinued torsion bar from a 2000 2500.

I'd still like to know what the bar rate thing is on the parts.gmparts site. If you look up the 4400 bars (driver is 84745473) in the fitment notes it says BAR RATE= 190

My 4800 bar (driver 84745477) says 212.

That is a -10.37% difference. AI had that 4345 bar at a 9.5% difference from 4800. 4800 to 4400 is a -8.33% difference.

There are some 2wd work trucks that end up around me sometimes. I need to get under one and do some digging next opportunity and see if they are the ones that get the 4400 bars (likely).

Chuck FB · June 30, 2025

1 hour ago, Epsilon Plus said:

I'm still hunting around with this. I plugged the 1.02mm difference into AI against my stock 4800lb rate and told it length was approx. 59"

It calculated a rate of 4345lb with the 1.02mm drop which is awfully close the the 4400lb lowest available GM stock bar.

Also, if you plug "33293 torsion bar" into Google you'll find 19332932 which is a discontinued torsion bar from a 2000 2500.

I'd still like to know what the bar rate thing is on the parts.gmparts site. If you look up the 4400 bars (driver is 84745473) in the fitment notes it says BAR RATE= 190

My 4800 bar (driver 84745477) says 212.

That is a -10.37% difference. AI had that 4345 bar at a 9.5% difference from 4800. 4800 to 4400 is a -8.33% difference.

There are some 2wd work trucks that end up around me sometimes. I need to get under one and do some digging next opportunity and see if they are the ones that get the 4400 bars (likely).

You got me with this bar rate number, I imagine it relates to something such as how much the bar ramps up in pounds per some measurement distance, certainly a number I've not noticed before.

Those two wheel drive trucks, yes if they are within the years that have the same bar fitment as these 2020 plus chassis have ( or are there a few years prior that these current bars also fit into dimension wise ) , then having the ability to look at the bars to measure accurately as well as take a part number off of and if your able to see the door post sticker to confirm what front axle rating they have. Piece all the info together and compare the diameter to the mystery Cognito bars. What are the odds that they have been laughing all the way to the bank and pretending stupidity at the company, we may figure this out yet.

I have not seen a two wheel drive truck for a number of years now, on dealers lots or used for sale. What was so common up here for so many years has now become the unicorn in the newer model years that is. Still some older trucks on the road that are two wheel drive but less all the time as they rust up if used in our winters.

Epsilon Plus · August 23, 2025

On 5/8/2025 at 8:27 AM, GMCnewbie said:

I went with the new Fox 2.5 HTO shocks along with the Cognito torsion bars on my gasser. The ride is so much better now when hitting speed bumps or anything else in the roads. I've never used the Bilstein 5100's. I've heard their fairly stiff which is why I didn't go with them this time around. I had the 4600's on a pair of Rams from the factory and hated them on both trucks. I wasn't a fan of the Fox 2.0 shocks, but they greatly improved ride quality over the 4600's on my old Power Wagon.

Which way did you mount your rears? Everything I'm reading says Fox prefers body on top, shaft down. I just got my HTOs in and I'm ready to put them on. I bought the 1.5-2.5" lift variety due to the ZR2 mods.

GMCnewbie · August 23, 2025

2 hours ago, Epsilon Plus said:

Which way did you mount your rears?

Great question. I didn't even think to check the position as I installed the new shocks the same way GM installed the stock ones. So I have mine body-down. I thought it was odd, but i figured GM engineers were smarter than myself. lol

GMCnewbie · August 23, 2025

Sorry for going dark for the last few months. Ive been traveling a lot for work and haven't had a lot of free time. I finished my suspension work and wheel install roughly two months ago and have maybe 100 miles on the truck since.

kylant · August 23, 2025

Fox shocks mount shaft down.

I "upgraded" my HTOs to Accutune tuned Fox 2.0 reservoirs. The HTOs are for sale for anyone looking.
I'll make a good deal on them

Edited August 23, 2025 by kylant

Epsilon Plus · August 23, 2025

11 hours ago, GMCnewbie said:

Great question. I didn't even think to check the position as I installed the new shocks the same way GM installed the stock ones. So I have mine body-down. I thought it was odd, but i figured GM engineers were smarter than myself. lol

I'm going to try the Fox way. I'll report in if something weird happens.

Apparently, their reasoning is the steel shaft being more exposed at the bottom has less chance of a damaging impact that could cause a seal leak compared to the aluminum body. This is probably more for off-road trucks than hiway trucks, but that's their game.

GMCnewbie · August 24, 2025

11 hours ago, Epsilon Plus said:

their reasoning is the steel shaft being more exposed at the bottom has less chance of a damaging impact that could cause a seal leak compared to the aluminum body.

That makes sense. I didn't think about it as I was dealing with heat exhaustion while working on my truck and just put them in same the way the crappy stock Ranchos were. I'll change mine around one of these days.

Epsilon Plus · August 24, 2025

You'll notice that the fronts are body up too compared to Rancho or Bilstein.

Chuck FB · August 24, 2025

I've always wondered what the long term effects would be on shocks with no protection on the rod, on a front axle there isn't the same amount of direct crap flying straight at the shocks as there is on a rear axle. Its one thing on paved roads that never have winter sand/salt spread on them but can't somehow see a bare rod doing very well on gravel roads and winter roads spread with crap. Has anyone reading this ran a bootless shock for some years to have experience in such conditions ?

Epsilon Plus · August 24, 2025

On 6/30/2025 at 9:14 AM, Epsilon Plus said:

There are some 2wd work trucks that end up around me sometimes. I need to get under one and do some digging next opportunity and see if they are the ones that get the 4400 bars (likely).

So far I've tracked down (3) gas 2wd work trucks and (2) of them were crew cabs with the same bars as me. The first one I found that actually had the 4400# bars I didn't have my damn caliper!

Somebody is going to find me in a parking lot under their truck measuring and thinking I'm chopping off their catalytic converter!

Chuck FB · August 24, 2025

15 minutes ago, Epsilon Plus said:

So far I've tracked down (3) gas 2wd work trucks and (2) of them were crew cabs with the same bars as me. The first one I found that actually had the 4400# bars I didn't have my damn caliper!

Somebody is going to find me in a parking lot under their truck measuring and thinking I'm chopping off their catalytic converter!

You need an official looking uniform and printed on your shirt "Inspection Osifer"

If GM would have specs on the diameter of each rated torsion bar size, that would make it too easy of course. I am guessing that you found out from GM what the sticker part number is for that #4400 torsion bar and you saw it on that one unicorn truck and no measuring instrument was available.

Edited August 24, 2025 by Chuck FB