Rear bump stops -- optional or necessary?

[89Vette]

Recently, I did a commonly suggested mod to my suspension. I cut the rear suspension bumper stops on my VX. I hated the way it performed/felt over pronounced bumps in the road. It was particularly bad in two or three places traveled in my commute to/from work.

The worst was a particular hwy lane where the speed limit is 70mph and it's on a curve. With a bump/hump combo, the VX literally wanted to hop sideways a bit. Tracking in it's lane was a bit unnerving. Considering that my stiff-suspension C4 (Corvette) is meant to be as stiff, I had a basis for comparison.

And, the Corvette handled this path with considerably more grace.

So, I cut the bumbers...which had minimal clearance above the rear axle. There was only about 1/4"-1/2" between the bumper and it's corresponding axle-plate. Obviously, suspension didn't have to travel far, before that bumper hit.

Now that half is removed (that bottom loop), the change is significant. The low-speed bumps are as good as any other vehicle. And, that hwy turn now tracks correctly.

I seriously believe the VX was bottoming, and being "launched" thru the bumper-stop. IOW, that dip/hump was throwing the frame up into the air...thru direct connection via the stop. With 1/2 of it removed, the rear shocks have more travel -- and can do their job. The result is a suspension that works as desired.

Now, I can't speak to my config -- as compared to the OEM position. IOW, I don't know how much higher it sat when new. OTOH, the rear shocks don't seem lifeless and bouncy. I've also considered the 1" spacer lift -- but don't necessarily need it anymore -- despite having purchased the urethane "donuts". I'll still probably try them when it get's warmer...but I may have some travel limitation with my PS dual exhaust pipe routed between the differential and trailing link. (As it sits, I have zero contact.)

I still need to post pics/vid of how my dual exhaust turned out, but I'm waiting for a nice day to wash it up and have it look nice.

In the mean time, I think anyone observing this type of body control issue -- especially in the hwy should consider this mod. I actually believe it could make your VX safer. Of course, a lift, new shocks, or both might accomplish the same thing. This option just costs less. And, is good for people w/o leaky rear shock absorbers.

[VX KAT]

Good description and info vette. :thumbup:

For some more background discussion on this topic:

Detailed pics of my bump stops cut in half.
http://vehicross.info/forums/showthread.php?t=21549&highlight=bump+stops

http://www.vehicross.info/forums/showthread.php?t=19217&highlight=bump+stop

http://vehicross.info/forums/showthread.php?t=19628&highlight=bumpstops

http://vehicross.info/forums/showthread.php?t=20312&highlight=spring+helpers

.

[TheGanzman]

Did the very same thing, with the very same results; plus it's nice not pissing blood every fifty miles...

[Y33TREKker]

Anyone ever look to see what bump stops from other Isuzu's might be identical to the b-stops on a VX, if a person wanted to have an extra set to experiment with?

[tom4bren]

... plus it's nice not pissing blood every fifty miles...

TMI

[blacksambo]

I seriously believe the VX was bottoming, and being "launched" thru the bumper-stop. IOW, that dip/hump was throwing the frame up into the air...thru direct connection via the stop. With 1/2 of it removed, the rear shocks have more travel -- and can do their job. The result is a suspension that works as desired.

While your straight line ride may seem to improve your hard cornering role resistance will suffer as these crazy rubber eights are termed spring helpers by Isuzu. Cut them at your own peril. Remember Isuszu was sued in 1996 by Consumer Reports for Trooper roll over saftey issues.

[evillecutter]

ive read all the other threads about this and i dont see what all the hub bub is about - its pretty obvious by looking at the bump stops (or spring helpers) that they are there to help with cornering to keep the rear end stable - if you take them out you will have more travel in the shocks and maybe a more comfortable ride but you lose your stability - im on the fence about cutting mine in half - seeing as i dont drive like a bat out of hades most of the time i think i might enjoy having a little more travel in the shocks

side note: i think its funny how many people think they need new shocks because they have a stiff ride - that means your shocks are working correctly - the whole point of shocks is to get your wheels back in contact with the ground asap - its when they just keep bouncing that they need replaced

[Triathlete]

Another thing to consider...
If you are running larger tires there is a chance you will eat up your inner wheel wells especially if you do any off roading and flex out your suspension.

[blacksambo]

Good point.

[blacksambo]

side note: i think its funny how many people think they need new shocks because they have a stiff ride - that means your shocks are working correctly - the whole point of shocks is to get your wheels back in contact with the ground asap - its when they just keep bouncing that they need replaced[/QUOTE]

Along this line, my '99 with 156K on the clock still has the original shocks and they work fine. I know this sounds crazy, but those OEM KYB's were super shocks and were designed to last the life of the vehicle. So think twice when you throw them out and all you plan is highway use.

[Triathlete]

side note: i think its funny how many people think they need new shocks because they have a stiff ride - that means your shocks are working correctly - the whole point of shocks is to get your wheels back in contact with the ground asap - its when they just keep bouncing that they need replaced


Along this line, my '99 with 156K on the clock still has the original shocks and they work fine. I know this sounds crazy, but those OEM KYB's were super shocks and were designed to last the life of the vehicle. So think twice when you throw them out and all you plan is highway use.

I have a set of fronts in the classifieds ;)

[Ldub]

Another thing to consider...
If you are running larger tires there is a chance you will eat up your inner wheel wells especially if you do any off roading and flex out your suspension.

That's why some of us who get all flexy off road, either add spacers between the frame & the bumps, or install higher profile urethane bumps...or both...:yes:

[blacksambo]

Good point.

[89Vette]

While your straight line ride may seem to improve your hard cornering role resistance will suffer as these crazy rubber eights are termed spring helpers by Isuzu. Cut them at your own peril. Remember Isuszu was sued in 1996 by Consumer Reports for Trooper roll over saftey issues.

I totally disagree. I just described (in my OP) how much better the VX handles when floating on springs vs rubber frame mounts. My specific case was in a curve/turn. And, BTW....That's why shocks were invented. Relying on bumper stops isn't my idea of great handling.

If you're having problems with body roll in severe cornering, you need more serious suspension changes than relying on rubber bumper stops. Bigger sway bars, stiffer springs, or whatever.

I'd add that cutting bumper stops isn't the right move if your running oversize tires. I also qualified that by saying lift/spring/etc...would accomplish the same thing (in my OP). With significantly bigger wheels/tires or off-roading, what I posted here will not apply.

[BigSwede]

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

[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...:smilewink

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

[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/product/493126/60797/_/Air_Lift_1000%3B_Coil_Spring_Leveling_Kit

http://shop.airliftcompany.com/dimg/thm/t300_77ba860e067e705f6e17989843635309.jpg

[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...:_wrench:

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...:yesgray:

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!

[Triathlete]

My VX is lifted so the stops do not come into play on bumps or when cornering. I also have so rear sway bar. I do not notice much more body roll than I did when stock.

[blacksambo]

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!


All you have to do is look at the cut-away drawings on the VX JDM brochure to see that the spring helper basically rides on the rear axel to know it had to be an active part of the suspension that was intended curbed body roll.

[Leon R]

Has anyone ever checked into Trooper sway bar or springs to see if they are stiffer than XV parts (I am assuming that it is the same general rear end design)?

[89Vette]

All you have to do is look at the cut-away drawings on the VX JDM brochure to see that the spring helper basically rides on the rear axel to know it had to be an active part of the suspension that was intended curbed body roll.

Is there an online link? In the "Rear Suspension" diagram of this link (http://www.vehicross.info/forums/showthread.php?t=20434) we don't even see the stops pictured. That tells me they're not considered an active part of the suspension.

[blacksambo]

Is there an online link? In the "Rear Suspension" diagram of this link (http://www.vehicross.info/forums/showthread.php?t=20434) we don't even see the stops pictured. That tells me they're not considered an active part of the suspension.

Thank you for your request. VT Maverick recently posted the entire JDM brochure on the board, which depicted the cut away reveal of the rear helpers' close proximity to the rear axel.

[vt_maverick]

Here's what sambo is talking about. If you zoom in on the rear tire you can see the stops (it's much clearer in the actual brochure, this is a pretty poor scan). What's difficult to discern is how far they're sitting above the axle; the cutaway superimposes the rotor so you don't get a clear idea of where the top of the axle shaft really is positioned relative to the stop.

http://www.vehicross.info/gallery/data/3284/JDM_Brochure_1_Page_20.jpg

On the other hand, this page is in the section of the brochure where Isuzu highlights all the cutting edge technology used in the VX. Note that the stops do not appear in this diagram of the suspension set-up, although it could be argued that they were purposefully removed to more clearly show the sway bar attachment points.

http://www.vehicross.info/gallery/data/3284/JDM_Brochure_1_Page_11.jpg

Let the debate continue...

[Leon R]

Well, of course they aren't highlighting it!

1. It is a piss poor way to execute stiffer suspension. Not something you would brag about!
2. It was probably an afterthought, that was likely added AFTER marketing material was created.

But, to me, this was clearly an active (be it passive? ;)) part of the rear suspension.

[Maddawg]

Got in here a bit late on this discussion but I cut mine in half shortly after purchasing my VX, the jarring ride was tooooo much. Even so I was still experiencing a noticable stiffness in down travel. I put some grease on the contact point of the axle, took it out for a street test ride thru some mild dips and pot holes. Came home to see if there was grease now on the bottom of the rubber bump stops. There was. I removed them completely. BIG difference in the suspension travel, but let me mention I still had the stock wheels and tires so no problem with making contact with the clad. Further, there was absolutely no noticeable difference in cornering even at high speed. Now with my oversize tires and wheels with the 0 offset it was necessary to reinstall the bump stops. I had to use the cut off portions as well by mounting them on top of the bump stops with longer screws, it does the job quite well. So, if you have a stock suspension setup on the rear and not happy with the ride, take them completely off. But,save them, you can reuse them later on if you decide to go to over size tires and wheels.

The front had a harsh ride too. I took off the front sway bar, it was tooo stiff also. Big improvement in ride, no noticeable difference in cornering at all, I still have the rear sway bars. So before you poo-poo this tip, try it.

[blacksambo]

Well, of course they aren't highlighting it!

1. It is a piss poor way to execute stiffer suspension. Not something you would brag about!
2. It was probably an afterthought, that was likely added AFTER marketing material was created.

But, to me, this was clearly an active (be it passive? ;)) part of the rear suspension.



Let me second your comments.

If you study the cut-away view you can indeed see the axel and helper in very close proximity. Anecdotally, on our two '99's the axel to helper gap is less than a half-an-inch. Also, once the VX moves foraward, at any major speed, this gap would naturally close shut, so you are always riding on the helper.

[Maddawg]

Note that the stops do not appear in this diagram of the suspension set-up, although it could be argued that they were purposefully removed to more clearly show the sway bar attachment points.

http://www.vehicross.info/gallery/data/3284/JDM_Brochure_1_Page_11.jpg

Let the debate continue...

Most likely not shown because their not part of the axle assembly. They belong to the frame assembly.

[vt_maverick]

And springs are?

[Ldub]

Are springs are?

http://1.bp.blogspot.com/-WPRfG2GpMtY/TjTURggLd9I/AAAAAAAAFB4/ZGN7PeXJly8/s400/Blackbeard.jpg



Sorry Mav...:flower:, when I see it, I have no control...:laughing:

[Vendetta]

Religion, politics, and bump stops. I'm sorry, "spring helpers." Wait, scratch that, "suspension dampers."

-V

[blacksambo]

Religion, politics, and bump stops. I'm sorry, "spring helpers." Wait, scratch that, "suspension dampers."

-V


Very creative!

[89Vette]

Another benefit....

Passengers that ride in the back now say it's more comfortable back there. Bumps are less severe -- like they should be. Yes, the springs/shocks are getting to do their job instead of rubber mounts.

I'm more convinced it was the right move for a stock height VX.


BTW....How about "Frame grommets!" LOL Also, why wouldn't springs be part of the axle assembly? When you pull a car backwards, SOMETHING's gotta wind up to make it shoot forward! All my toy trucks do that anyway! <sheep-eating-grin>