Will air bumps help my application?

[rattle_snake]

Wondering if a dynamic/air/hydraulic style bump stop will be beneficial in my application over a fixed squishy one.

Short version: Front axle up travel is limited due to tire-to-fender contact when flexed. Bump stops are adjusted to protect fender in this case. When travelling at higher speeds the limited up travel causes axle to hit both bumps. Will an air bump stay rigid enough keep tire out of fender at crawl speeds but also compress at high speed impact to gain effective up travel?

Application: 1972 F250, <6k lbs. Front radius arms, 14" Fox 2.0 CO, 250/350# springs, tuned by accutune. Limit straps. D60, 40s. Slider has 1" gap at ride. Front fenders have already been sectioned, stretched, trimmed. Axle centered. Don't want to hack a bigger hole.

Approximately 3" of axle-to-bump gap (aka up travel). Suspension will allow 6" of up travel with bumps/fenders removed. Down travel is limited to about 5.5" The opposite side drooping out to limit strap raised tire up making situation worse. Tire to fender gap is about 6". Currently bumps are located just outside the frame. Moving them out farther will help somewhat, would mount bump cans a few inched outside of frame, behind CO so pad would contact link bracket. Move limit straps in front of CO.

Seems like a bump with 2" of travel would be enough. Pinch style to allow adjustment.
Goal is to be able to push the truck faster on rough dirt roads without bottoming out hard on front bump stops.

Pic of setup

Recently painted so don't want to hack shit up. Could raise ride height to improve up travel but want to keep it as low as possible.

 

[YotaAtieToo]

Sometimes you can get creative with bumps to alow more vertical uptravel, but limit flex uptravel if that makes sense.

Having them mounted higher but further out should help with this.

 

[SLOWPOKE693]

I wouldn't touch a thing on that truck and just enjoy driving that sexy bitch to the mall.

In my opinion your only option for more go fast uptravel would be 37" tires and air bumps mounted higher but low enough to keep the 37s out of the fender at full stuff/lock while rock crawling.

 

[mobil1syn]

youll be essentially sitting on the bumpstop at ride height with that setup. if you want go fast, you need uptravel.

also if the math is works the way i read it, you have a 14" shock but are only using 12"?

 

[rattle_snake]

I wouldn't touch a thing on that truck and just enjoy driving that sexy bitch to the mall.

In my opinion your only option for more go fast uptravel would be 37" tires and air bumps mounted higher but low enough to keep the 37s out of the fender at full stuff/lock while rock crawling.

I can only do about 45 over the speed bumps at the mall, not fast enough.

I had though about smaller tires briefly, but it felt wrong, so I considered complicating things and wasting money instead.

youll be essentially sitting on the bumpstop at ride height with that setup. if you want go fast, you need uptravel.

also if the math is works the way i read it, you have a 14" shock but are only using 12"?

OK so if I understand you, the bump should be set to be fully compressed at actual limit (tire/fender in my case). If i used a 3" travel bump with my 3" of up travel it would contact at ride.

I was hoping to be able to use the bump such that the uncompressed pad would be were the fixed one is now and still allow further up travel (but dampened by the bump). Sounds like it won't do what I want.

And yes I'm not using all the travel the shock has. Price of tower+shock was essentially the same for 12 or 14" so went big, well because. Down is limited by driveshaft. Up limit is diff to engine x-member, unless a bump stop. So I have an effective vertical travel of 8.5" out of the 14s. Flexed out it is 18" at outside of tire which is enough for any mall or gym parking lot I have been to lately.

 

[SLOWPOKE693]

Smaller tires only feel wrong right up until the 40s contact the fender and tear it up...

I'm going back to 37s on the wife's JKUR for similar reasons. The 40s looked pimp but the rig iss way more wheelable on 37s than it is on 40s because I don't have to limit steering and uptravel to keep the tires out of the fenders.

 

[HYDRODYNAMIC]

Increase ride height 1.5" and add 2" travel air bumps.
If you can, mount the air bumps in front or behind the coil over. Not to the inside. Wider the better for keeping the articulated tire out of the fender while keeping max vertical up travel.
Move your limit straps to the front or elsewhere and make a air bump strike pad on top of the upper radius arm bushing location. Mount air bump off side of frame.

 

[Sterlingfire]

Nope... no real way to fix it. Probably best to just scrap it out. I'll be over with a trailer this weekend to pick that worthless junk up for you. Hell, I'll even do it free of charge because that's the kind of guy i am


Truck is
Gonna have to get creative with the mounting. Good luck!

 

[Eric]

First of all, sweet truck!!!

Different style of bump will not change anything. The travel at full flex is not going to change. If you want to maximize bump travel while still keeping the tires out of the fenders at full flex then outboard the bump stops; ideally inline front-to-rear with the shocks. Even then you might still need to reduce your bump travel or add some lift.

 

[mobil1syn]

And yes I'm not using all the travel the shock has. Price of tower+shock was essentially the same for 12 or 14" so went big, well because. Down is limited by driveshaft. Up limit is diff to engine x-member, unless a bump stop. So I have an effective vertical travel of 8.5" out of the 14s. Flexed out it is 18" at outside of tire which is enough for any mall or gym parking lot I have been to lately.

get a spacer in the shock. relaying on the limit straps is asking for trouble.

end of the day the only way to get the suspension more time to do its work is uptravel, no way around that. if you dont want to hack your fenders, then a smaller tire it is.

 

[Weasel]

I'd stick with the rubber bumps and go with the smaller tires. I dropped the 40's from my truck and run 38's now for clearance. Cheaper as well, sorta.

So on the air bumps I've never seen a set that worked well on the street, they have alot of noise every time you hit them and while they work are not exactly soft like a rubber bump is. Now many that's tuning but on the race trucks they work fine ripping around the track. I'm assuming it's a deal where to get them to work well where they need to they become annoying everywhere else. Not sure what you can expect from a 2" canister of fluid.

 

[Weasel]

get a spacer in the shock. relaying on the limit straps is asking for trouble.

first time I've heard that. Everything else has been do not rely on the shock to limit travel and always use straps.

 

[gt1guy]

It sounds like you want the best of all worlds. With that in mind, I think you had the wrong front fenders painted all pretty.

1967 to 1972 F100 / F250 / F350 Fiberglass Front Fenders Raised Wheel Well Bolt On Mounting - Autofab

These front fenders are made with the door brace upper bolt mount. This is a separate part laminated to the back side door edge and allows for the upper inside door bolt on mount.

autofab.com

 

[mobil1syn]

OP im not sure what the deal is, you just need to rearrange a few things and you should have no problem tucking 40s

 

[mobil1syn]

first time I've heard that. Everything else has been do not rely on the shock to limit travel and always use straps.

straps save shocks, shocks should be able to go full drop without cataphoric failure. in this case based on the limited information presented, things have the potential to go bad for the OP if the straps stretched more than planned and were unchecked.

 

[rockota]

straps save shocks, shocks should be able to go full drop without cataphoric failure. in this case based on the limited information presented, things have the potential to go bad for the OP if the straps stretched more than planned and were unchecked.

belt and suspenders...

 

[Eric]

in this case based on the limited information presented, things have the potential to go bad for the OP if the straps stretched more than planned and were unchecked.

Still not understanding the point. Based on OP's description and photos, the shocks are operating in the middle of their range. Bump stops prevent the shocks from reaching full compression and limit straps prevent the shocks from reaching full extension. Sounds like life is good for the shocks?

 

[mobil1syn]

Down is limited by driveshaft. Up limit is diff to engine x-member, unless a bump stop. So I have an effective vertical travel of 8.5" out of the 14s.

Eric what i read is if the straps dont exist, the driveshaft gets pissed and depending the shituation could get ugly.

 

[Eric]

Eric what i read is if the straps dont exist, the driveshaft gets pissed and depending the shituation could get ugly.

Got it. My interpretation was that the limit straps were set to prevent the driveshaft from binding which happens significantly before the shocks reach full stroke. But yea, definitely a bit imprecise language.

 

[rattle_snake]

Yes the limit straps protect driveshaft at full droop. After hogging out the yolks to get more angle I was able to only lose 1.5" (with 1" safety margin) of shock down travel. Then the right coil hits the existing bump stop outriggers I made due to axle shift by track bar.

I'm kind of committed to the 40s at this point. For some reason every vehicle I have had always seems to get larger and larger tires....

I have farted around with different ride heights. I can get some additional height from more preload. currently it is at 1/4". I know this isn't the ideal way.

So based on what is mention here regarding bumps, I thinking pinch style cans with a fixed style bump in them, out-boarded as far as possible and adjustable. Then can upgrade to an air bump in future if I want. But this has caused shopping for a CNC plasma setup.
Cosine says moving bump outward 4" should allow bump to be up 1" higher (axle tilt at 15*). Add +1/2 ride height and that gets from 3" up to 4.5. Total vertical would be 9.5, 4.5 up, 5 down. Should be noticeable improvement.

That leaves more mods to front fenders, which is free just time. Compared to how far I have come, it's an incremental change. I think I can get another 2" from front fender and still make the trim work. If ride is left as is, I'm at 6 up and 5.5 down for a total of 11.5 vertical which is the safe limit of chassis and drivetrain

It sounds like you want the best of all worlds. With that in mind, I think you had the wrong front fenders painted all pretty.

1967 to 1972 F100 / F250 / F350 Fiberglass Front Fenders Raised Wheel Well Bolt On Mounting - Autofab

These front fenders are made with the door brace upper bolt mount. This is a separate part laminated to the back side door edge and allows for the upper inside door bolt on mount.

autofab.com

Yes I had looked at those but don't really want the bulge. The fender lip needs to go up into the bump line.

OP im not sure what the deal is, you just need to rearrange a few things and you should have no problem tucking 40s

haha yup just a few slight mods and any tire will fit.

this was phase 1

Already did similar raising and widening the rear so just more cut-n-weld up front. A few ways to slice it.

 

[vetteboy79]

Got it. My interpretation was that the limit straps were set to prevent the driveshaft from binding which happens significantly before the shocks reach full stroke. But yea, definitely a bit imprecise language.

You're not wrong. All he's saying is use the limit strap to save the shock, but have the shock limited internally to save the driveline if the limit strap fails.

 

[Ghetto Fab.]

Yeah, smaller tire, redo the fenders again, or attempt to mount the bumps as far out as possible from the frame are pretty much your only options.

Can you potentially pull the fender wider so the tire tucks into it instead of having to cut it again?

I just linked the front of my runner. Its only got like 3.5" of uptravel with 2" bumps. I don't ever feel the bumps hit though, and I don't ever really fell the front end bottom out either, but I know I'm using the 2" of stroke on the bumps as its wiped clean. I'm probably not going as fast as you, but my point is that bumps can be tuned a bit to remove the harshness. I only charged these to 100psi out of the box and they seem to work great. YMMV of course.

Kevin

 

[rockyota83]

Smaller tires only feel wrong right up until the 40s contact the fender and tear it up...

I'm going back to 37s on the wife's JKUR for similar reasons. The 40s looked pimp but the rig iss way more wheelable on 37s than it is on 40s because I don't have to limit steering and uptravel to keep the tires out of the fenders.

i think the truck would look better with 37s at current ride height, i dont think it looks that good with the 40s and sitting so low, but looks shouldnt matter as much as performance so that doesnt really matter

my vote is increase ride height or put 37s on it

other then that yes air bumps are better then rubber/poly

 

[rattle_snake]

I farted around and reworked the straps and bumps. Moved straps forward of coils and put bump cans on out riggers behind. Added land pads to radius arm brackets. Spray paint, beer and so on.

Increased preload to raise ride 1/2". 5+ down, 3.5 or so up. still need to test & tune to see what improvements were made exactly.
For now I just made a tube to hold a fixed bump, and went with a foam bump. it's same size and thread as existing poly bumps, so can interchange if one works better than the other. Can go to a hydro bumps in the future but money can be spent in other places first.

Could a shock shaft bump help in my case?

 

[HYDRODYNAMIC]

Need to flex out and see how much it helped. Looks alot better.

 

[Beat95yj]

If you had not done all that beautiful bodywork, I would’ve tried a autofab glass fender. It moves the wheel opening into the fender. I have them on my 67. They’re pretty good quality.

To answer your question I have played with bumps a little bit and to get it to compress at low speeds and be stiff at high, I would throw more disc in it and drop the nitrogen pressure. But I would probably look at other options before I went crazy with that.

 

[rattle_snake]

Good looking old Ford.

Finally got to test and tune the new bump setup. About 1/2" more bump gap from outboard mount, 1/2" from ride height increase. Foam bumps are really soft so lowered bump 1/2 to compensate for compression. So gained about 1" of effective up travel, at about 3-3/4". Hit some decent dips and gutters on pavement and front end is smooth, but now rear end is the problem. Need to add ride height there, thinking time for a new set of decent spring packs.

Squishy...

Slight tire interference on front edge of fender but can turn lock to lock while at full bump.

 

[Yotota]

Killer truck!

What's the problem with the rear suspension?

 

[mobil1syn]

Killer truck!

What's the problem with the rear suspension?

im guessing flat springs and compression shackles

 

[rattle_snake]

Thanks. rear bottoms out now first instead of front. So goal is to improve in similar fashion.

And yes, and yes.
flat 20 yr old junkyard 63s with overload removed. 3" block. Homebrew hangers, shackles and so on. 12" Fox 2.0 tuned by Accutune. Floating traction bar.

Was thinking something like Deaver G7. I tow occasionally with this truck and not sure 1/2 ton versions are enough.

https://deaverspring.com/product/chevy-gmc-2500hd-2wd-4wd-1999-2010-4-inch-lift-rear-spring/

This is minus weight of bed and shit in it (40" spare, tools, ect)