Rear bump stops -- optional or necessary?

[Ldub]

your hard cornering roll resistance will suffer as these crazy rubber eights are termed spring helpers by Isuzu. Cut them at your own peril.

I don't think the rear bumpstops serve any function other than to keep the tires from contacting the body.

Yeh...def 2 schools of thought on that subject...

I use mine to keep the tires from getting "over stuffed" all up in dat fender well thang...

[tom4bren]

I hafta agree with Dub & Swede (Did I REALLY just say that out loud???).

It doesn't matter what you call those rubber donuts. It doesn't matter what Isuzu calls them. They serve the sole purpose of STOPPING suspension travel (in a bone jarring, blood pissing manner). If they are engaging whilst driving on road, you have something wrong with your suspension (design defect or worn parts). They should NOT play a part in helping with on road body roll.

If you only have a fraction of an inch of distance between the bump stop & the axle housing ... & you don't want to cut the stop, then you should be seriously considering replacement coils (either OEM or aftermarket). Coil springs do have a tendancy to sag with time & use (lets see, I'll set 1000 lbs on this here coil spring & let it sit for 13 years ... I wonder if the spring will deform???)

Or better yet - do like Mav did & add an airbag inside the coil ... infinitely adjustable & air makes a nice cushy ride!!!

[vt_maverick]

Or better yet - do like Mav did & add an airbag inside the coil ... infinitely adjustable & air makes a nice cushy ride!!!

No need to argue about this subject anymore IMHO. Cut your stops in half to stop the jarring ride then install an Air Lift system to stiffen your springs and reduce body roll. You can cut the stops and install the Air Lift system in your garage and the kit costs $130. That's cheaper than new shocks, coil spacers, or new coils. Everybody wins!

http://www.vehicross.info/forums/showthread.php?t=22408

http://shop.airliftcompany.com/produ...g_Leveling_Kit

[tom4bren]

Mav,

Since you're the guinea pig on air suspension upgrade at the moment: What pressure do you run on yours?

Tom

[Leon R]

You need to keep in mind that rubber isolators and springs are used in numerous applications!

Its main advantages are:

- High stiffness with relatively small size (not important or desirable on VX suspension, but great for motor mounts)
- Inherent damping, that is missing in metal springs (again, great for motor mounts, but shocks provide plenty of damping in suspension)

Its downside is:

- Deterioration over time (rubber gets harder/stiffer with age, until it cracks and becomes much softer)
- Varying performance (stiffness/damping) depending on ambient temperature (that should make our suspension MUCH stiffer in the winter)

Looking at our spring helper design, this is NOT your typical "bump stop"! It is designed to be relatively soft and to have a relatively long displacement!

But overall, rubber is NOT an ideal material for vehicle springs, especially for a varying climate vehicle with a considerable suspension travel. I am sure that Isuzu engineers were well aware of the above information. So why would they add this inferior component to their flagship vehicle?

Lets look at vehicle dynamics, why would you stiffen rear end? This isn't a tow vehicle and stock springs seem to be stiff enough own their own for normal driving. The only reason I can see is to make it safer during emergency maneuvers. Stiffer rear suspension also keeps the front end straight, reducing "plowing" effect in hard cornering. The downside is that you pay for it diminished rear end traction (especially when you hit bumps, right 89vette? ). But apparently, they were willing to live with it.

I suspect that they determined that they need more rear end stiffness, which could have been achieved by stiffer shocks, springs or rear sway bars. But some bean counter probably insisted on adding an additional section to an existing suspension bump stop, thus turning it into a "spring helper". In most cases, this is a cheaper solution.

This would also explain if people feel these "helpers" and complain about them more often in the winter months .

So while this was not a good solution, it was a solution to a problem that I am not sure many of us would want to experience...

My VX still has the helpers and it has been practically bumpy in the rear end, as of late . I am still not sure if want to cut them. I might remove them all together to test out the handling. This way, it will be reversible. Another solution might be to get new OEM helpers, if the original became too stiff.

[vt_maverick]

Mav,

Since you're the guinea pig on air suspension upgrade at the moment: What pressure do you run on yours?

Tom

When the VX is fully loaded for a trip (roof basket with spare and tools/fluids, hitch mounted rear cargo box, myself, wife, two kids, and dog) I run it at 30 PSI which is 5 less than the max rating. When empty I run it at 15 PSI which seems to give the right handling balance (little to no bouncing but without jarring your teeth).

The Air Lift system is nice to have too for leveling your vehicle while towing/hauling, which of course was why I bought it in the first place. So even if you buy them and don't like the empty ride while inflated you can always deflate them and just use them when you're fully loaded.

[tom4bren]

Yah, I have them on the RV (Firestone version anyway). Never had any info on what pressure to run them. Taking a shot in the dark, I started running them at 30 psi. It seemed to work. Glad to know that I'm within the max rating though.

[evillecutter]

the nipples to air up and deflate the bags on my chevy truck are next to the license plate where did you put yours?

[vt_maverick]

I had the lines run into a "T" connector so there's only one valve. The new tom4bren bumper doesn't have holes for two of the bottom cladding screws so my valve is mounted vertically facing downward (outward) through one of those holes. Can't even see it unless you kneel down.

[tom4bren]

If I were to put them on the VX, I think I'd have the valve in the jack storage compartment.

[Makocross]

Has anyone tried replacing the rear spring with an air bag?

Mike

[Ldub]

I had the lines run into a "T" connector so there's only one valve. The new tom4bren bumper doesn't have holes for two of the bottom cladding screws so my valve is mounted vertically facing downward (outward) through one of those holes. Can't even see it unless you kneel down.

If I were to put them on the VX, I think I'd have the valve in the jack storage compartment.

FWIW...

If you install a "T" fitting, as opposed to two individual nipples, you are increasing body roll.

When one side compresses, it sends pressure over to the other side, increasing pressure...

Which will magnify body roll.

[vt_maverick]

Hmmm... good point Dub. Might have to split that line at some point then.

[blacksambo]

You need to keep in mind that rubber isolators and springs are used in numerous applications!

Its main advantages are:

- High stiffness with relatively small size (not important or desirable on VX suspension, but great for motor mounts)
- Inherent damping, that is missing in metal springs (again, great for motor mounts, but shocks provide plenty of damping in suspension)

Its downside is:

- Deterioration over time (rubber gets harder/stiffer with age, until it cracks and becomes much softer)
- Varying performance (stiffness/damping) depending on ambient temperature (that should make our suspension MUCH stiffer in the winter)

Looking at our spring helper design, this is NOT your typical "bump stop"! It is designed to be relatively soft and to have a relatively long displacement!

But overall, rubber is NOT an ideal material for vehicle springs, especially for a varying climate vehicle with a considerable suspension travel. I am sure that Isuzu engineers were well aware of the above information. So why would they add this inferior component to their flagship vehicle?

Lets look at vehicle dynamics, why would you stiffen rear end? This isn't a tow vehicle and stock springs seem to be stiff enough own their own for normal driving. The only reason I can see is to make it safer during emergency maneuvers. Stiffer rear suspension also keeps the front end straight, reducing "plowing" effect in hard cornering. The downside is that you pay for it diminished rear end traction (especially when you hit bumps, right 89vette? ). But apparently, they were willing to live with it.

I suspect that they determined that they need more rear end stiffness, which could have been achieved by stiffer shocks, springs or rear sway bars. But some bean counter probably insisted on adding an additional section to an existing suspension bump stop, thus turning it into a "spring helper". In most cases, this is a cheaper solution.

This would also explain if people feel these "helpers" and complain about them more often in the winter months .

So while this was not a good solution, it was a solution to a problem that I am not sure many of us would want to experience...

My VX still has the helpers and it has been practically bumpy in the rear end, as of late . I am still not sure if want to cut them. I might remove them all together to test out the handling. This way, it will be reversible. Another solution might be to get new OEM helpers, if the original became too stiff.

Well put. Great analysis.

Between this inexpensive suspension solution and the genetic-weakling transmission we have, I keep coming to the conclusion that the VX was more styling and novel mechanics oriented than a serious performance vehicle. I think it looked so tough everybody thought it would perform the same way......it was more of a way ahead of it's time science-fiction project. It was a brave endeavor, and I still love mine for it being so.

[89Vette]

Well put. Great analysis.

Between this inexpensive suspension solution...

Lots of vehicles have these types of travel limiters. Unless I see a link to something showing Isuzu really considered this an "active" part if the suspension, I think you're stretching to make the assumptions you're making.

I totally agree with your assessment on analysis though!