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Poly Bushings on GMPP trailing arms.

Booba5185

Booba5185

New member
Hey everyone,

I wanted to share a little project I've been working on for a bit. I picked up some round (not square) GMPP trailing arms, and decided to go for some poly bushings. A lot of people swear by the UMI and BMR arms, but the arms themselves don't make that much of a difference the bushings do. The strength of trailing arms only comes into play when in Reverse, the lateral arms take all the weight when cornering. We all know the problem with the stock arms is they bend easily, but I have yet to see anyone bend or break one from cornering. Curbs, rust, those are the things that do them in. Either way I upgraded to Dormans, and now upgraded to GMPP rounds. At some point GM started using Dorman's square style in place of the rounds. Mothers day is coming up and my mother-in-law has a 99 GP, so she get's my Dormans, lol. Anyways, the difference people feel is the poly bushings in the BMR\UMI arms, the stock bushings are soft so they allow the entire rear suspension shift slightly. Poly doesn't allow this as we know.

So I pressed out the stock bushings:


Then I measured the stock tubes with my caliber and found that the Energy 3.2125G (or R if you wanna go fast since they're red) would be the closest fit. I called Energy with my measurements to make sure, and they agreed. I bought some on Amazon for $35 for the set, and this is how they fit:




Needed some cutting, lol. 7mm on the wider bushing and 14mm on the narrower side. I used my Dremel to take off the majority of the poly.
Measured:


After cutting:


Then I used my hand held grinder to clean it all up and flatten everything out. I knew I'd have to take more off before the final install, so I left myself some extra material:


And finally installed:




All I have left to do is cut the sleeves down and install them. I might have to drill out the front trailing arm bracket to 9\16" since that' what the Energy Sleeves take for fasteners, we'll see. The stock sleeve does fit for the front, but it's about 1mm to short. I might run it, I might not. We'll just have to see.

What do you guys think?
 


Cool mod, I'd like to try it on stockers just for kicks. Let us know how she does on the road, I bet its gonna be noticeable. Just be wary of potential binding during the first few try-outs.
 
I'll take it easy around the first few blocks and listen to it all, and gradually work my way into it. I think it'll be alright since they use poly on the BMR\UMI\HT. Eventually I'll be doing lateral arms too, but that'll be awhile. Thanks guys
 
Ran into a little speed bump, Energy's measurements are off. I guess 9\16" isn't the same for them. They say their sleeves are 9\16", but the sleeves are barely over a half inch. The rear bolt's threads won't fit through the sleeve, so I'll have to ream it out a bit, or something. I'm not 100% sure what to do yet, lol.
 
That's a little snag. Hopefully you can figure something out. This looks like a nice little upgrade. I should send you mine and have you do them lol. Now that you mention it, we had issues with the BMR's on my brothers 03 GP sleeves as well. If I recall correctly we enlarged them a bit.
 


Take sleeve out drill out the bushing go to the hardware store find a tube that fits over the bolt you need and re install
 
I think it'd just be easier and\or cheaper to drill out the sleeve. The OD of the sleeve is 3\4" so if i drill it out to 5\8" it'll still have 1\8" thickness, so I think I'll be good. I just need to track down a buddy with a 5\8" drill bit. Worst case scenario I'd bet I could just take the sleeves into work and have a maintenance guy drill them out for me in a few seconds, lol.
 
Realizing where I work, a facotry using lathes, mills, and all that jazz, I talked to a few friends and called in a favor. An engineer buddy of mine (he's actually an engineer, no self proclaimed, lol) took the sleeves from me today and will be drilling them out and cutting them on his mill for me. Not sure when he'll be done, but I'm sure I'll be putting them in this weekend. I'll get better pictures of everything and the install when there's more info...and something else to take pictures of. I will say I compared the stock rubber to the poly and it's a night and day difference, the stock rubber is closer to a sponge than it is a bushing.
 
Here they are, it should all bolt right in. Except I just jinxed myself, lol. Once it doesn't rain for a day or 2 I'll throw them in. I hate working in the mud:




Here's the machining:


Thoughts?
 
So I was down and out for a few weeks, but I finally got around to installing these today. I had to bend the trailing arm bracket a bit to fit the poly bushings in, but nothing too difficult. I've taken it around the block a few times, up to about 40 MPH and no sounds or binding that I can feel. I did try to whip the ass around a little bit and there was a very noticeable difference. Everything seem very firm back there, I can't wait to see what the lateral arms will do. Would I do this again? In a heartbeat. It's fun doing something different with good results!
Comparison next to Dorman's that are maybe a year and a half old, maybe 8,000 miles:

Installed:




Space from arm to wheel:


I was generous with the grease, so we'll see how long before I get any noise.
 


Lol. These are unique, and probably perform the same. It was a fun project, but I didn't end up saving all that much money.
 
but yea them bmrs though



OmiEtfa.jpg
 
I did use some on the front mount, but I forgot about the one against the knuckle. It's easy to pull them off, so next time I might just drill and tap them for a grease zerk. I guess I wanted to see the difference they make before put that much work into them. BMRs are nice, how much to they weigh? I know these GMPPs are lighter than the Dormans, even with the poly. Will the weight make a difference? I doubt it. I have bullitts so the whole weight thing is out of the window.
 


Don't hold your breath, it'll be a while, lol. I gotta move and such. I was thinking the Ingalls, they look beefier than stock and I could put poly in those.
 
I got a stock set of rear laterals if you need brand new I was gonna hack them up to use as the foward lateral arms but went full bmr
CB5iYQr.jpg
 
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