# Annoying Axle Hop



## ezobens (Jan 4, 2005)

I have been searching the archives but can't seem to find an answer to my question. My 04' GTO has an annoying axle hop whenever I 'accelerate aggresively' from a stop or shifting under rapid acceleration (car is a 6 speed). Is this something I just have to live with or is there a TSB to correct this condition? For reference, the build date on the door jamb is 10/2003.
Any advice would be greatly appreciated.
Thanks!
Elm.


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## djdub (Oct 23, 2004)

ezobens said:


> I have been searching the archives but can't seem to find an answer to my question. My 04' GTO has an annoying axle hop whenever I 'accelerate aggresively' from a stop or shifting under rapid acceleration (car is a 6 speed). Is this something I just have to live with or is there a TSB to correct this condition? For reference, the build date on the door jamb is 10/2003.
> Any advice would be greatly appreciated.
> Thanks!
> Elm.


Sounds like the "think in the trunk" TSB. Call the dealer and ask about it. The fix is... replacing the bushings.


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## GTODEALER (Jan 7, 2005)

I have recently installed the SLP h.d. sway bar we stock as well as the poly end link bushings and it helped tremendously!!!!!!! I still notice it on blacktop but it has completely stoped on concrete surfaces. We are in the process of becoming a BMR dealer which offers a rear end upgraded mount that is supposed to stop it completly (with sway bar)!!!!! :cheers


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## bsmcall (Sep 11, 2004)

ezobens, 

To help eliminate wheelhop on YOUR Gto, do the following:

1. Check tire pressure (around 32 works for me)
(Many dealers overlooked lowering the tire pressure from 60psi.)

2. Verify that your dealer has performed the TSB regarding "thunk in trunk"
(Have someone inspect the floor pan and differential case for obvious
contact or movement.)
(This involves replacing the differential mounting bushings to prevent 
contact of the differential case with the floor.)

3. Verify that the shipping spacers were removed from the front springs.
(They're orange plastic and they don't belong.)

:cheers Hope that helps. :cheers


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## Guest (Jan 30, 2005)

*normal but fixable*



ezobens said:


> I have been searching the archives but can't seem to find an answer to my question. My 04' GTO has an annoying axle hop whenever I 'accelerate aggresively' from a stop or shifting under rapid acceleration (car is a 6 speed). Is this something I just have to live with or is there a TSB to correct this condition? For reference, the build date on the door jamb is 10/2003.
> Any advice would be greatly appreciated.
> Thanks!
> Elm.


my 70 gto 469 cubic inch 10:97 quarter mile had the same problem with street tires, try slicks or leave trac control on ,or for an automatic find the convertor limit side step the brake let it roll a few feet then nail it !!! :cheers


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## ezobens (Jan 4, 2005)

*Axle Hop continued...*

Well I checked under the car- No orange spacers up front and I don't see any evidence of the differential or driveshaft making contact on the floor pan anywhere.
The noise I am hearing isn't so much a 'Thunk in the Trunk' as the TSB may be addressing, but more of an actual hopping of the axle(s) upon acceleration. Nothing is hitting the bottom of the car, it's the tires bouncing on the pavement.
In the old days, we'd slap some traction bars on the beast, but with the IRS, what are my options?
Thanks!
Elm.


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## bsmcall (Sep 11, 2004)

What tire air pressure are U running?
I dropped from 38 to 32, big help.


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## fwyflyr (Nov 27, 2004)

*Wheel Hop*

I got it too. We all probably do. I'm planning on the SLP sway bar also. Other than tire pressure, don't know what else to do.


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## GTODEALER (Jan 7, 2005)

SLP sway bar helps, dont forget urethane end links!!!!! I stock them, the sway bar is $149.00 and the end links are 34.95. E-mail me at [email protected] I'm a SLP dealer and a Procharger dealer and in the works of a BMR dealer so I should have you covered at all angles!!! :cheers


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## ezobens (Jan 4, 2005)

I'll need to play with the tire pressure to see if that helps-

GTODEALER, 
How would a sway bar prevent axle hop?
I'm not an engineer but it seems that sway bays only affect cornering or perhaps if one wheel is bouncing and the other isn't.
If both wheels are bouncing simultaneously, how would a sway bar prevent it?
Thanks!
Elm.


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## GTODEALER (Jan 7, 2005)

A sway bar connects to both rear wheels "stabilizing" the individual "a" arms. If the sway bar is stiffer it produces more of a resistance for the "a" arms to start hopping. It's not a solid axle so it is treated as seperate intities, one side can't hop more than the other if equal pressure is applied, especially if the two sides share the same stabilizer. The only reason I know this is when I used to race 12 second bracket fwd cars. They do all kinds of crap to keep them from "wheel hopping"! Same concept minus steering capabilities. :cheers


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## Guest (Feb 1, 2005)

*wheel hop*

installing aftermarket parts to solve an age old problem,its very easy the more money you spend the better it has to be! also spending money for a larger sway bar and links will lighten your wallet, wheel hop affects you,me
john force,don garlets, even fred flintstone when he finally got some super soft nikes, its a age old problem heavy car pinion climbs ring gear housing
twists tires grabs and slips pinion angles change hoppity hop, check out some
chassis set up books at the local library or speed shop, hop to it!


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## GTODEALER (Jan 7, 2005)

Anything I can find that will help I will share, I understand that "wheel hop" is an age old problem but that doesn't mean that it can't be fixed! I agree that a sway bar in itself isn't going to completely eliminate wheel hop but it sure as hell helped my car and thats good enough for me. :cheers


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## ezobens (Jan 4, 2005)

I guess that leads me back to my original comment-

If it's the pinion angle changing during acceleration that is inducing wheel hop, a sway bar won't help much. That is why they have sway bars and traction bars- They are designed for different handling issues. FWD is a different animal completely. Since the wheels have to turn, you don't have many options outside of a sway bar.

GTODEALER made a comment that his hop is virtually eliminated on concrete but not on asphalt- Asphalt tends to provide more traction than concrete (in most cases on average roads) so I'm still not convinced the sway bar helped much. I can accelerate on finished concrete all day with minimal hopping, but asphalt is another story.
Unfortunately, here in Northern Illionis, a majority of the roads are asphalt and concrete is saved for the expressways (in certain areas) where I won't be worried about axle hop while driving at 80 mph.

My contention is that regardless of the size of the sway bar, if both wheels are hopping, the sway bar does vitually nothing since it will move up and down with both wheels in unison by design. Sway bars use twisting motion from side to side to help keep the opposite wheel planted on the pavement during cornering etc but I still believe in straight line acceleration, a sway bar does little if anything.
Just my 2 cents-

It sounds like we are kinda SOL for the moment until something either factory or aftermarket is designed to assist us in our plight. :willy: 
Elm.


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## fwyflyr (Nov 27, 2004)

GTO DEALER, can you post some pics of the BMR mount that will supposedly eliminate Wheel Hop when used with an HD sway bar?

If talking about a "live axle" I would agree with ramairws6with respect to axle "wrap", But I do not see how our IRS would allow that much change in pinion angle. 

IMO. This problem cannot be completely eliminated without losing some ride quality. By the time you have taken all the "slop" out of the suspension, it still comes down to where "The rubber meets the road"!


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## GTODEALER (Jan 7, 2005)

Finally, someone understands! What ezobens and ramairws6 are not taking into consideration is WE HAVE IRS not live axles!!!!!!! The pinion angle doesn't change much in our car (if any), the carrier is connected by axles. If asphalt is stickier than concrete then why is the starting line of a dragstrip concrete??? Yes fwd cars have turning capabilities under power, however, how many people turn under hard acceleration????????????? You have to "stabilize" the a arms in IRS or it will wheelhop, this is not a live axle car so you can throw that part of your "chassis setup" out the window! BTW the picture of the mount is @ bmrfabrication.com, I don't have the ability to post pics :confused JUST MY 2 CENTS :cheers


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## ezobens (Jan 4, 2005)

I understand that we have IRS and that some of the variables change vs a live axle, but the purpose of a sway bar doesn't change- Otherwise they would market them more as a 'Traction' device than a 'Handling' device.
Case in point:
My 69' Vette has IRS, but axle hop is limited by a custom bar that connects the differential to the frame directly in front of the differential, not by adding a sway bar. Adding a sway bar on the Vette made NO difference in axle hop but it sure is flat in the corners!
On the GTO, I have virtually no axle hop when accelerating around a corner (on any pavement), so in that situation I have to think my sway bar is assisting in some way. It's the straight line stuff that causes the problem.
BTW, the starting line at the drag strip is made of concrete so it doesn't need to be repaved every month from cars burning ruts into the asphalt when doing burnouts- It has nothing to to with traction of concrete vs asphalt.


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## GTODEALER (Jan 7, 2005)

Believe what you want, the corvette your talking about also shares a single spring were as ours uses individual a arms and coils, either way we can argue all day long.....bottom line, my sway bar made a difference and I will continue to back the products I sell. Sounds to me like someone doesn't like to proven wrong.........topic over! :cheers


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## ezobens (Jan 4, 2005)

*Wrong? Who? Me?! LOL*

I've wrong lots of times- And will admit it readily.

I'm an old school guy and I like to get some valid technical reasons to do something before I drop $200 on harware.
I don't doubt the products that you offer are quality items and have benefits-You just haven't convinced me to this point that a sway bar doubles as a traction device to reduce/eliminate wheel hop in a straight line in this application. 

While you have indicated that you've tried it on your own car and it has virtually eliminated the problem on concrete and marginally on asphalt- This testimony alone doesn't give me enough of a warm fuzzy to take the plunge myself.
Perhaps a technical article in Hot Rod or similar publication would clear up any concerns I may have but to this point, I'm still waiting for a technical explaination as to why a larger sway bar would help reduce wheel hop in a straight line.

I hope you aren't taking this open discussion and my honest questions as any kind of personal attack- That is not my intent and apologize if I have offended you or anyone else.

I enjoy the discussions on this site and am only looking to find true solutions to common issues.
Elm. :seeya:


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## GTODEALER (Jan 7, 2005)

I understand it's not personal, and I appreciate your response. Maybe someone will do an article and explain it better than I can. I enjoyed talking back and fourth w/ you, if you need anything at all GM related or have any more ?'s you'd like to kick around PM me. :cheers


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## ezobens (Jan 4, 2005)

*Thanks!*

I appreciate the offer GTODEALER- 
I'm sure I'll be taking you up on that offer sooner than later  
If I get down to NRH in the near future (I used to live in Euless years ago), I'll look you up and see what kinda toys you have on that goat!

Elm.


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## fwyflyr (Nov 27, 2004)

Ezobens, You don't live too far from me. Machnesy Park is only a couple miles north of Rockford, in fact since I live in the "country" I have a Rockford mailing address. :cheers


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## ezobens (Jan 4, 2005)

fwyflyr,
I am familiar with Machnesy Park- I also live out in the 'sticks' so I am actually a stone's throw from Volo (where the auto museum is located).
Perhaps we will run into each other when the weather warms up around here!
:cheers


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## fwyflyr (Nov 27, 2004)

Right on. My GTO is in the garage under a cover until spring! :cheers


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## Guest (Feb 4, 2005)

*Pinion Angle?*

Your Spinning On Crete Unless Its Got Vht On It ,asphalt And Rubber
Bite Causing Wheel Hop, Lets Ask Someone With F1 Experience Why They Dont Get Wheel Hop?????


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