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Rear axle weights - WHY?

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0
Anybody know what the purpose of the weights on the rear axle, http://forums.themustangsource.com/f813/weights-rear-axle-tubes-509644/ is ?

Normally, you try to have as little unsprung weight as possible on a car. Racers with live rear axles go for aluminum axles and differential housings to improve handling - and here's an example of the opposite. Baffled! :eek:

Wondering if I would gain something by ditching them or if I would make something worse...

/the Swede
 
96
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Well, I can stand some added NVH - the Boss isnt exactly quiet compared to my BMW 5 series :) - but would I gain some handling if I removed them?
 

ArizonaBOSS

Because racecar.
Moderator
8,552
2,392
Arizona, USA
No noticeable performance gain if you remove them. They add mass to the rear axle assembly which changes the natural frequency to lessen gear whine harmonics that are transmitted to the cabin.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
they used to have (pre-2005) a single weight hanging off the pumpkin, just below and behind the pinion flange. once you add stiffer control arms, your nvh goes up anyhow, so chuck 'em.
 
steveespo said:
Removed mine and installed 12 mm stud with ring loop to use as tie down points when trailered. Ran 110 track miles Saturday with no NVH increase. Saved 6lbs.
Steve
Thanks for the tip, I can shave off 6 lbs of the 15 I put on with the Watts link in basically the same location. NVH.....in my car....um yea. ::)
 

drano38

Wayne
1,130
318
My '10 GT did not have them from the factory. At highway speeds, it would hum. TSB installed them, and quiet now.
Take them off--if you don't mind any added noise, you're good to go.
If you can't stand the highway hum, put them back on.
 
steveespo said:
Removed mine and installed 12 mm stud with ring loop to use as tie down points when trailered. Ran 110 track miles Saturday with no NVH increase. Saved 6lbs.
Steve
I pulled mine off this morning and weighed them. I only saved 4.8 lbs. Boss stuff must all be lighter :p
 

Domestic Product

Big fat tires and everything !
Hey, I was thinking the opposite. Adding rear ballast? Back in the day a 1970 Boss (race car) trans am car "weighed 3,068 lbs. not including the 266 lbs. of rear ballast centrally located over the rear wheels for a 52.8/57.2 weight distribution"(from Donald Farr's Boss 302 book) for a curb weight of 3,334 lbs. My goal with our 3,632 lb. cars with a 55/45 weight distribution would be to get something closer to 50/50. Take weight off the front and add some to the back. Add some good coil overs and corner balance the car. I think we could move closer to the ideal 50/50.
Front, replace hood with carbon fiber, delete ac and anything else not needed in the engine bay. Move the battery to the right rear trunk and add 100 lbs. over the rear wheels or what ever was the net weight of removed front weight to keep the weight the same or less overall. A 2012 m-3 is 51/49. I feel weight distribution is more important then just taking weight off. Imagine your car on track and at speed with 52/48 weight distribution!
Just ideas at this point, going to run stock for the year as any mod funds are going to fixing the transmission. I will post this under transmission thread.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
true, except weight is preferred to be in a sprung location. it does little to help when attached to the axle. so, remove them from the axle and throw them into the rear bumper support beam! getting the weight as far back as possible has a greater effect on the weight balance than just the amount of weight. when you replace the 48lb turd of a driveshaft with a nice 19lb aluminum one, don't toss it. strap it to the rear bumper beam ;)
 
Domestic Product said:
Hey, I was thinking the opposite. Adding rear ballast? Back in the day a 1970 Boss (race car) trans am car "weighed 3,068 lbs. not including the 266 lbs. of rear ballast centrally located over the rear wheels for a 52.8/57.2 weight distribution"(from Donald Farr's Boss 302 book) for a curb weight of 3,334 lbs. My goal with our 3,632 lb. cars with a 55/45 weight distribution would be to get something closer to 50/50. Take weight off the front and add some to the back. Add some good coil overs and corner balance the car. I think we could move closer to the ideal 50/50.
Front, replace hood with carbon fiber, delete ac and anything else not needed in the engine bay. Move the battery to the right rear trunk and add 100 lbs. over the rear wheels or what ever was the net weight of removed front weight to keep the weight the same or less overall. A 2012 m-3 is 51/49. I feel weight distribution is more important then just taking weight off. Imagine your car on track and at speed with 52/48 weight distribution!
Just ideas at this point, going to run stock for the year as any mod funds are going to fixing the transmission. I will post this under transmission thread.
I just added 15 lbs in the same location with a Whiteline Watts Link so I'm just mitigating that a bit. When you find all the extra weight to take off the front end please fill us in on it. ;) There's about 30 lbs total in the A/C system so you really have to decide if it's worth it. The biggest benefit to that could be cooling by removing the condenser and increasing airflow to the radiator. The hood's worth 17 lbs if you go FG and 25 lbs if you go CF. The battery relocation is a good idea for F/R weight distribution as well as getting it lower in the car, but a 50/50 F/R split is not realistic without adding overall weight to the car. Our cars start at 55/45.

https://trackmustangsonline.com/index.php?topic=496.0
 
I just changed my rear diff fluid and added fill and drain plugs to the cover. Had to pull the Panhard rod the get the cover off and was tempted to pull these off. I'm good with a little extra NVH, not so good with dead weight. Since I haven't driven the car since Nov, decided to wait until I have a chance to drive it a bit and get used to it again just to have some sort of baseline on how much they change the way the car feels. Probably take them off next weekend.
 
pufferfish said:
true, except weight is preferred to be in a sprung location. it does little to help when attached to the axle. so, remove them from the axle and throw them into the rear bumper support beam! getting the weight as far back as possible has a greater effect on the weight balance than just the amount of weight. when you replace the 48lb turd of a driveshaft with a nice 19lb aluminum one, don't toss it. strap it to the rear bumper beam ;)

Exactly, I am going to look into welding steel plates to my rear bumper. Best place to put weight as it is as far back as possible. I ran Daytona with a spare tire in the trunk for a little extra grab.

Going back to what Domestic Product is saying most of that is correct. You hit a few key areas and I have done some of this. Check out the new 302S front bumper that Mark from FR made available for us to get, he says it is 6 pounds off the front not including the weight of the splitter bracket. We weighed out that new bumper and one sitting in the shop and it was 3 or 4 pound less but they had modified that front bumper already. I need to get a weight of my front when I take it off.

Check out this thread, I'm going to update that with some coil over info.
https://trackmustangsonline.com/index.php?topic=4434.msg70690#msg70690
 
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167
Is it possible that removing them could be the cause of a sort of roaring noise from the back of the car at high speeds? I removed the weights a couple of weeks ago when I installed my Whiteline LCA relo brackets and today I heard a sort of roaring noise that got louder and louder as the car hit some pretty high speeds (only 71mph, officer!). It almost sounded like tire noise except that I had never noticed it before at similar speeds.

Thank you in advance.

John
 

pufferfish

Supporting Vendor
1,094
66
Maryland
KBBoss302 said:
Is it possible that removing them could be the cause of a sort of roaring noise from the back of the car at high speeds? I removed the weights a couple of weeks ago when I installed my Whiteline LCA relo brackets and today I heard a sort of roaring noise that got louder and louder as the car hit some pretty high speeds (only 71mph, officer!). It almost sounded like tire noise except that I had never noticed it before at similar speeds.

Thank you in advance.

John

no way to be sure except for to quickly throw them back on and drive the same route.
 
592
167
I guess I was just curious as to what sort of NVH increases people were noticing upon removal of the weights. I can't reinstall them without removing the relo brackets or grinding the weights to fit around them unfortunately.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
bummer. well, the whole NVH issue is entirely subjective. every car is different. some cars don't show any degridation of quality and others do. then you can throw different people into various cars and they will interperet NVH very differently. there's also an automatic heightened awareness after vehicle changes. i talked about this in my aluminum driveshaft install thread. the mind doesn't focus on the minutia of the car NVH until there is a reason to pay attention to it. so, you feel like there is additional NVH after your changeout, but it may very well have been there all along. i don't know how long its been since you swapped the parts, but give it a couple of weeks to forget about it. if its still bad, its probably an issue and you will have to figure out how to geth them back on there.
 

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