2nd/3rd Gen Tacoma frame beaming/resonance?

[aliu6294]

As you all know, the Tacomas have a C-channel rear frame section that seems to be quite flexy. For my truck at least, being a DCSB, it appears that having a large amount of weight (200+ lbs, bumper + topper + RTT) behind the rear axle has created a sort of a resonance/beaming node around the axle. At roughly 35-40 mph, and 70-80 mph, particularly on segmented concrete highways, the back of the truck looks like it starts to bounce up and down, creating a bucking feeling in the cab, probably around 4 Hz. The severity of the beaming increases/decreases with more/less weight, respectively.

Logically it makes sense that adding weight to the front/rear of the frame via bumpers and such creates a standing wave/barbell type of situation where the weight at the ends is acting on the nodes (axles), inducing a bending force on the middle section of the frame where the cab mounts are. More so on the rear of the frame where it's less stiff. It seems as if the resonant frequency in my situation has coincided with highway speeds.

Does anyone else running a rear plate bumper/tire carrier experience a similar issue?

I'm sort of just curious how common this is (if everyone experiences this to an extent, or if I'm in a unique situation), as there wouldn't really be a solution other than stiffening the frame to alter the harmonics.

 

[bkg]

I'm sort of just curious how common this is (if everyone experiences this to an extent, or if I'm in a unique situation), as there wouldn't really be a solution other than stiffening the frame to alter the harmonics.

Do you have sliders? I noticed on my 2010 that after sliders (All Pro) were installed, a lot of the "road flex" went away. May be worth checking that out... or go after reinforcement plates.

 

[DaveInDenver]

Interesting observation. I get this sensation in my truck and I was assuming it was a spring rate or damping issue and that I needed to re-valve my shocks to deal with it. Never really thought it might be a frame flex or oscillation until now.

My truck is a Access Cab, so same wheel base as yours. I do have sliders, but they are bolt on Mobtown (fairly rigid). It's significantly worse with bikes in the my hitch-mounted bike rack, so about 100 lbs hung from the trailer hitch. I'm running Dakar CS047R and 2.0 FOX IFP non-reservoir rear shocks, stock tune. I have a topper, stock rear bumper, normal (read: excessive) daily load of recovery junk.

Should mention my old truck did this to a little lesser extent. That was 1991 XtraCab, 3" shorter wheelbase but fully boxed (e.g. rigid) frame. That was a damping mismatch, going to OME heavy settled it down quite a bit. So that was my assumption but there's no reason it has to be the same reason with my Tacoma.

 

[aliu6294]

I have the Mobtown sliders as well. They did improve things slightly compared to factory, but if it is a frame resonance issue I would think that adding stiffness to the C-channel portion of the frame is likely to do more to alleviate the issue than adding stiffness/weight to the reinforced/double walled portion where the sliders bolt in.

Interestingly enough, I also have the same rear shocks as Dave, so it's possible the shocks are exacerbating the issue via incorrect damping? It very clearly looks like just the rear of the truck is bouncing though, not the whole thing. You can see the movement in the mirrors.

The issue really became apparent for me when I added a swingout hitch receiver to mount a bike rack to. It does get slightly worse with the bikes on it, but the swingout + rack itself probably adds up to 150 lbs or so, so the weight of the bikes are less consequential. I would imagine that those with a swingout tire carrier would suffer the same issue, if not worse.

 

[tacollie]

I have noticed the same thing with my truck. I honestly think it's a little bit of everything. I had sliders on my 05 and they helped so I bought sliders for my 09. I thought it was the OME socks on the 05 so I put 5100s on my 07. That made it worse. So I put Icons on the 09. That helped but only when it's loaded down(approximately 600lbs). Loaded down I still get it sightly but it bearable. With the 5100 it was miserable to drive. I kind of want to get the adjustable Fox's in the rear but I don't really feel like spending money on the truck right now.

 

[DaveInDenver]

LOL, I've been kicking around FOX with DSC adjusters, too. Glad to know I'm not the only one.

I'm surprised no one makes side plates like they do for 1st gen trucks. There are a couple of guys making kits to box the frame but that's all I'm aware. Seems like with the weight some people bolt on this would be more common.

 

[tacollie]

I think it's because the shocks are outboard on the 2nd gens. But the Fox CDCs and then is about it! I probably won't but then for at least another year.

 

[dcarlin]

‘06 DCSB with hi-clearance rear, shell, rtt, etc. The resonance you’re describing is exactly what I experienced after adding the weight of the tent and CBI rear bumper (Dakars w/ AAL & OMEs). All-Pro bolt on sliders helped with the mid-section but, in my opinion, shifted the stress concentration to the axle area. I hit a patch of black ice on 395 and the resulting excursion actually crumpled the lower c-channel flange at both bump stop perches. Frame shop said I was deflected over 1-1/4” from factory ... all behind the bump stops. Ended up pulling bed, having them straighten it, then plated the outer face and boxed from under the cab to the rear bumper mounts. Obviously overkill in a preventative maintenance sense but the fact the bed pulls so easily and plate steel is cheap, cutting some outer plates and either welding them up or paying someone to run the beads is a worthwhile investment. Huge difference in amount of frame flex with the plate/box combo, eliminated a lot of squeaks as well.

 

[DaveInDenver]

Reinforcing my frame is something I will do eventually, but I haven't made up my mind to box the frame with the ongoing rust issues. Still thinking.

@dcarlin, did the reinforcement eliminate the oscillation, if you had it?

 

[dcarlin]

What I had previously observed were noticeable deflection behind the cab on fire roads including axial twisting of the bed and the dreaded shudder under acceleration discussed at length elsewhere (3degree shims installed). After the reinforcement, which admittedly included upgrading the rear shocks, the flex/twist are essentially gone and the acceleration shudder is markedly less. For the effort and minimal expense, the exterior playing as preventative maintenance makes sense to me and possibly gussets inside the c-channel frame fore and aft of the bump stop landing bucket. I used 10ga plate after finding it at a good price point, 1/8” would have been next choice.

 

[E.Roy]

A huge issue is the flimsy stock hangers on 2005-2018 Tacomas.

Archive Garage has addressed the issue with the Hammer hangers and the optional cross tube to tie the Hammer hangers, and by extension, the frame rails together. The system gives a big improvement in ride quality, the HH being the biggest portion of the improvement. This helps calm down the signature Tacoma chatter and jitters.

https://www.tacomaworld.com/threads/tacoma-hammer-hangers-mid-travel-soa-sua-archive-garage.519625/

https://archivegarage.com/products/tacoma-hammer-hangers

 

[DaveInDenver]

The hangers alone do this, @E.Roy? The cross beams look cool but require moving your spare from under the bed, right? That's not practical for me so I intended just to do heavy duty hangers only, mainly for insurance. I hadn't assumed they would stiffen the rear of the frame that much. I prefer not to deal with a swing-out, since hanging all the weight out there seems counterintuitive to stiffen things up. I'll eventually get a bumper, but it was just gonna be something offroad worthy with recovery points and a higher clearance hitch.

 

[bkg]

Want to have fun with frame flex? Do a brake check and watch the gap between the bed and cab...

I’ve noticed mine has gotten bad on a couple of spots on the interstate near me. Combo of road, weight and speed. Nothing I can do to change it (sliders, FRORF plates already in place) so I just drive faster or slower ... ?

 

[E.Roy]

The hangers alone do this, @E.Roy? The cross beams look cool but require moving your spare from under the bed, right? That's not practical for me so I intended just to do heavy duty hangers only, mainly for insurance. I hadn't assumed they would stiffen the rear of the frame that much. I prefer not to deal with a swing-out, since hanging all the weight out there seems counterintuitive to stiffen things up. I'll eventually get a bumper, but it was just gonna be something offroad worthy with recovery points and a higher clearance hitch.

Yes, the Hammer hangers alone make a noticeable difference. On my Double cab with stock springs I was shocked at how much it improved the ride.

The stock hangers are like bolting a leaf spring to another spring.
The difference is most noticeable over harsh bumps that cause high speed acceleration of the axle. I still remember my first drive in a 2011 Access cab, I was irritated by how poorly it rode on paved roads.