The Mustang Forum for Track Enthusiasts

Track Mustangs Online was built specifically for those who track their Mustangs!

Rear axle hop during track braking

blacksheep-1

TMO Addict
2,357
1,863
Hey Racer47, ever hear of a guy named Wayne Anderson? He's one of my cronies, lives about 5 minutes away from me.
 

blacksheep-1

TMO Addict
2,357
1,863
Did he run some ARCA and Truck races? I think thats him but I don't know him personally.

Anderson runs primarily super late models, the Dokkens and the Reutimans are also from around here, central Florida is loaded with good racers.
 

racer47

Still winning after 30+ years
252
264
SE WI
W2W Racing
20+ Years
I think its the same guy I'm thinking of

There are a lot of late model racers around the country. Its financially the best top level racing available. There are still a lot of fans in stands which local sponsors like. Rules are setup to maintain some reasonable (although still high) level of spending. Plus its really good racing, door to door, bumper to bumper, seldom alone on the track. I've been running a 4 cyl mini stock with my son. Every week we take home ~$75 ($125 prize money minus two $25 pit passes). Sure $75 is nothing but the car only cost $2k, tires $40, stock motor, stock brakes, stock struts. I used to spend $1k for one SCCA GT1 National race. I like road racing but the cost is way out of control. There is no prize money. Not nearly enough fans. Plus all the travel costs, $500 entry fees, hotels, etc. Its just a ton of money to run by yourself for a significant part of any race.

This was kind of detour but this thread has kinda run its course anyway.
 

blacksheep-1

TMO Addict
2,357
1,863
Yep, same guy. I agree with the insane costs of road racing, maybe we'll start a thread on it. but we need to get back on topic.
 

blacksheep-1

TMO Addict
2,357
1,863
speaking of back to the topic, I think I would try a massive different setting on the rear shocks, or maybe even throw another set of over the counter shocks on the car and see what happens.
 

blacksheep-1

TMO Addict
2,357
1,863
this is also the reason I recommend folks stay with 1 brand of suspension parts, for instance Ford Performance, The parts are well thought out, they are designed to work together and the results are predetermined so if something goes sideways, you immediately know why.
 

302 Hi Pro

Boss 302 - Racing Legend to Modern Muscle Car
1,830
297
Northeast
Interesting thread, I don’t know the latest remedies you’ve tried, but I too agree on rear shocks & their settings. When I raced a bit & had a bumpy track to deal with, I went to softer rear settings on my Koni Yellows, but never had rear axle hop on breaking.

My only other thought is the rear trailing arm position. I’ve always had best performance with the trailing arms having a downward angle to the axle while maintaining a proper driveshaft/pinion angle.

Good luck.
 

67GTA

TMO Advanced
174
178
SoCal
speaking of back to the topic, I think I would try a massive different setting on the rear shocks, or maybe even throw another set of over the counter shocks on the car and see what happens.
Interesting thread, I don’t know the latest remedies you’ve tried, but I too agree on rear shocks & their settings. When I raced a bit & had a bumpy track to deal with, I went to softer rear settings on my Koni Yellows, but never had rear axle hop on breaking.
Thank you @blacksheep-1 and @302 Hi Pro for the suggestions on rear shocks. The KW V3’s have approx 18 clicks of rebound and compression adjustment available. This setup was on the car when I bought it, and I didn’t feel the need to adjust settings at all the first year while just getting seat time and focusing on basics. When I finally did check where the settings were at for reference, the rebound settings were near full-hard on all 4 corners and compression was set to almost full-soft. I opted to back rebound off on all 4 to a mid range setting, and also bring compression up by a few clicks. From a predictable rotation and forward bite perspective, the collective adjustments (bigger tire, non-binding UCA, and shock settings) made a huge improvement. I’m convinced now that those same adjustments also pushed anti-squat just past the threshold, introducing the axle hop issue.

Here’s a quick recap of what the planned remedy is:
  • Removing non-adjustable Whiteline LCA relocation brackets - replacing with J&M units with 3 different holes. Plan to run 2” (top) hole to start after verifying trailing arm angle is near level at static ride height.
  • If problem persists at next track session, I’ll adjust rebound settings back up to original settings of nearly full-hard, and back off the bump setting towards original softer setting.​
Next track day is nearly a month out. While it will be hot, I’m planning to go back to Buttonwillow to compare back to back results on the same track. I’ll make sure to update here afterwards.
 

blacksheep-1

TMO Addict
2,357
1,863
Thank you @blacksheep-1 and @302 Hi Pro for the suggestions on rear shocks. The KW V3’s have approx 18 clicks of rebound and compression adjustment available. This setup was on the car when I bought it, and I didn’t feel the need to adjust settings at all the first year while just getting seat time and focusing on basics. When I finally did check where the settings were at for reference, the rebound settings were near full-hard on all 4 corners and compression was set to almost full-soft. I opted to back rebound off on all 4 to a mid range setting, and also bring compression up by a few clicks. From a predictable rotation and forward bite perspective, the collective adjustments (bigger tire, non-binding UCA, and shock settings) made a huge improvement. I’m convinced now that those same adjustments also pushed anti-squat just past the threshold, introducing the axle hop issue.

Here’s a quick recap of what the planned remedy is:
  • Removing non-adjustable Whiteline LCA relocation brackets - replacing with J&M units with 3 different holes. Plan to run 2” (top) hole to start after verifying trailing arm angle is near level at static ride height.
  • If problem persists at next track session, I’ll adjust rebound settings back up to original settings of nearly full-hard, and back off the bump setting towards original softer setting.​
Next track day is nearly a month out. While it will be hot, I’m planning to go back to Buttonwillow to compare back to back results on the same track. I’ll make sure to update here afterwards.

FWIW we never had axle hop and we had to use the stock suspension locations by the rules. As I recall we had to run a Steeda (or maybe FP) adjustable upper, Ford Performance lowers. FP panhard bar and hi zoot Penske shocks, it was really that simple.
 

Grant 302

basic and well known psychic
I originally had Ford racing lca brackets. But then another local guy bought BMR lca brackets. I measured them and the top hole on the BMR was 1/4" or 3/8" higher than the fords. So I bought BMRs.
Not sure how that’s possible. The top hole on the Ford Racing bracket is as close as you can get to the ear/tab on the axle side:

C9FC08A2-2712-46C8-A3CA-ACAE1A26284B.jpeg


The holes are exactly 2.0” on center. No way for the BMR bracket top hole to be 1/2” or 3/8” as claimed and be a bolt-on part.

I measured.
 

racer47

Still winning after 30+ years
252
264
SE WI
W2W Racing
20+ Years
dont give a shiznit what you think, i had them both, i measured them both and spent money to go with the bmr for the stated reasons
 

67GTA

TMO Advanced
174
178
SoCal
Here’s a quick recap of what the planned remedy is:
  • Removing non-adjustable Whiteline LCA relocation brackets - replacing with J&M units with 3 different holes. Plan to run 2” (top) hole to start after verifying trailing arm angle is near level at static ride height.
  • If problem persists at next track session, I’ll adjust rebound settings back up to original settings of nearly full-hard, and back off the bump setting towards original softer setting.​
Next track day is nearly a month out. While it will be hot, I’m planning to go back to Buttonwillow to compare back to back results on the same track. I’ll make sure to update here afterwards.
Wanted to close the loop on this after having a chance to install and run the new setup. With the J&M relocation brackets installed and the LCA in the top hole (2" from stock), the angle of the LCA at static ride height is now just shy of 1* (downhill from chassis to axle). This change completely remedied the axle hop, yet no drastic decrease of forward bite on throttle pick up. Braking is very predictable now, and could be pushed right to the point of ABS starting to step in without upsetting the suspension. Appreciate everyone's suggestions and input.
 

302 Hi Pro

Boss 302 - Racing Legend to Modern Muscle Car
1,830
297
Northeast
the angle of the LCA at static ride height is now just shy of 1* (downhill from chassis to axle).
My thoughts too (post #48). I’m happy to learn you’ve now fixed your rear axle hop on braking for corner entry. She should have an improved WOT launch as well.

Good luck & good racing.
 

blacksheep-1

TMO Addict
2,357
1,863
good, glad you found the issue, and thanks for telling everyone the remedy.
so do you think it was the angle that caused the hop, or flexibility in the old trailing arms, or the bushing material?
 

67GTA

TMO Advanced
174
178
SoCal
good, glad you found the issue, and thanks for telling everyone the remedy.
so do you think it was the angle that caused the hop, or flexibility in the old trailing arms, or the bushing material?
I’m pretty certain it was the angle of the trailing arms. The Whiteline relocation bracket’s only hole is a 3” drop from stock. The 2” drop on the J&M bracket reduced the trailing arm angle by 2*. The Whiteline LCA’s that I removed were relatively new and have the Max-C bushings on both ends which are pretty stiff.

Unrelated, but I will say I was pleasantly surprised with lower NVH levels with the new J&M poly/rod combo trailing arms. Now with spherical bearings at all 3 axle connection points, poly at the chassis LCA connection and Whiteline Max-C at the chassis UCA, the noise levels are no worse, and possibly a bit quieter than it was previously. But most importantly - no more noticeable bind!
 

Grant 302

basic and well known psychic
The Whiteline relocation bracket’s only hole is a 3” drop from stock.
4” drop. Measured that too.

The 2-3/4” position should be useful too, being 1-1/4” above where you were with the Whiteline bracket. From there you can also fine tune with ride height since you have adjustable perches with the KW. Depends what you can tolerate ride height wise and if you have any preferences for roll steer or want to increase ability to corner exit, etc.
 

blacksheep-1

TMO Addict
2,357
1,863
oddly, the IMSA and PWC cars had to use the stock pickup points, aftermarket lowers and adjustable uppers, never had wheel hop..strange, maybe the shock package influences this more than I realized.
 

Grant 302

basic and well known psychic
oddly, the IMSA and PWC cars had to use the stock pickup points, aftermarket lowers and adjustable uppers, never had wheel hop..strange, maybe the shock package influences this more than I realized.
There’s some of that in play. A decent damper, properly adjusted won’t hop as violently or for as many cycles.

But like I suggested earlier, ride height plays a large part. And from what I remember, you and Phoenix didn’t use brackets...so I wouldn’t ever expect it to be an issue for you.
 

TMO Supporting Vendors

Buy TMO Apparel

Buy TMO Apparel
Top