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FFCobra Craftsman
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Discussion Starter #1
As you may know I upgraded my MkII over the winter. I have now run 3 autocrosses so have a few thoughts.
- The car is more stable than it ever was. It gets through turns in a rough section much better w/ one exception. At turn exit, full throttle accel I get wheel hop if the macadam is rough. Not sure the solution yet but am trying different settings on the QA1 DA shocks. May need to go to rodends on the LCAs
- Ride on the street is better. It is really nice when I installed 300# springs vs the 400# FFR supplied.
- I am using the brakes that came w/ the salvage parts. Vented rotors means the donor was a V8 car. The brakes are very good. Surprisingly the pads that were in there were pretty good. HPS 5.0 were only a slight improvement. But the best part is this; NO pad knockback means I have the same brakes all the way though an autocross run. On Hoosier A7s, w/ the solid axle, the pedal was always lower at the end of a run. Also the front to rear balance would shift toward the front as the pedal dropped.
- Overall the IRS is definitely a worthwhile upgrade.
 
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If my budget wasn't so tight I'd totally be upgrading my 3-link to the new IRS... hadn't heard about the knockback advantage before either, that's good news too.
 

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Axle side play

How has anyone reduced or eliminated their 8.8" axle side play? C-Clip eliminators?
Shim the c-clips, Knurl or bend the c-clips?
Any examples of C-Clip eliminators with rear disc brakes?
 

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FFCobra Craftsman
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Discussion Starter #5
Good question that I have no idea how to answer. Unsprung weight is certainly a lot less but I couldn't guess about total car weight.
 

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Premium Member
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5,801 Posts
How has anyone reduced or eliminated their 8.8" axle side play? C-Clip eliminators?
Shim the c-clips, Knurl or bend the c-clips?
Any examples of C-Clip eliminators with rear disc brakes?
I don't know about C-clip eliminators but I did have my traction-loc diff clutches and steels stacked in an alternating pattern and then shimmed as tight as practicable. This both reduced axle end play(the axle movement that causes knock-back) and supposedly, gives better two-wheel lockup for the traction-loc. As the clutch packs in a traction-loc diff wear, the c-clips and attached axles have more room to wander under varying side loads (like during cornering). This is what produces pad knock-back. Floating caliper designs, like Mustang or T-Bird rear brakes tend to cancel most of this knock-back since the caliper pads more or less self-center as the caliper moves/slides with the axle. Even floating calipers will not be totally effective in reducing knock-back once the diff wear begins to exceed certain levels. The only method I know to reduce it is install new clutches/steels and the tightest side gear shims you can fit. Once things begin to wear beyond a certain level, you need to do it again.

Sometimes pad knock-back has a simpler origin though. Many donor Mustang axles (as well as rotors/discs) have had a rough life. It's important to check to see if your axles and rotors are straight and true as well. Ask me how I know... :wave: Fixed piston calipers (like many aftermarket brands) are especially sensitive to knock-back, that's why they also sell knock-back springs which are meant to preload the caliper pistons to keep them closer to the rotor. Generally not required with floating calipers but I suppose it might save you a driving season if the alternative was the expense and time involved in rebuilding your traction-loc? Not sure if that's a sound recommendation or not, just acknowledging that they do exist.

Sean
 

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FFCobra Craftsman
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23,039 Posts
Discussion Starter #7
All the research I did said that c-clip eliminators were good for straight line stuff and not for cornering. I have a few friends who had 9 inch axle ends installed on their 8.8 so you end up w/ huge bearings and floating axles. That seems to be the best solution but it is not cheap. Both of them also fought gear oil leaks for a while too. Not sure why or the solutions but they did get them fixed eventually. I was getting closer to doing the 9 in ends but then the IRS appeared and I quickly dropped that thought.
 

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Unconventional Builder
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Did your relative raw times improve?
 

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FFCobra Craftsman
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Discussion Starter #9
I have no idea. I don't analyze that deeply. Also I am still on last years tires.
 

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Unconventional Builder
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I am still one 3yr old tires and no take offs this year. I am hoping to make it through this season without cording one. Looks like I will be purchasing new A7's, I want to get them next spring.
 

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I’m still working on my Coupe build (for the last 10 years...) but got bit by the autocross bug last year. I ran my 1998 M3 in D-stock but am now looking at changing direction on my Coupe toward Auto-X monster. I was aiming for a street build with a 302 with Webers, pin-drive width IRS, 15” wheels, and stock Fox-body Mustang brakes but am now thinking I need to look at swapping out the 302 for an LS engine, 17” wheels, and bigger brakes.

One question I have though is about the IRS. Is there a noticeable difference in how a standard-width IRS handles over a pin-drive width? There seems to be a better selection of tires for 17” wheels BUT not a very large selection of deep-dish 17” wheels for the pin-drive width IRS. I would think that the standard-width IRS may feel a bit more solid with the wheel bearings closer to the center of the rim rather than the wheel being cantilevered out away from the bearing as on the pin-drive width IRS.

Thoughts??
 

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FFCobra Craftsman
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Discussion Starter #12
The 2015 IRS only comes in one standard width as far as I know. On the old T-bird IRS they made the arms shorter to do pin drive width. That nearly always means degraded performance. W/ shorter arms the same amount of wheel travel means the arms go through a greater angle of movement. This means more roll center movement, more camber change, etc. As you have noted wheel selection drops way off and often means custom wheels. I usually buy Bullits from American Muscle for about $550/set of 4. IMHO the rears have plenty of dish although the fronts not so much.
 

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FFCobra Craftsman
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Discussion Starter #13
Another IRS update

Last fall at end of season I decided to try two changes. 1- more rear camber. I changed the camber from -1 1/4 deg to -2.5 deg and it seemed to help but it was getting cold so one can never be sure of changes at that time of year. My car has always been too loose over the years and this seemed to help. 2- less bump setting in the QA1 DA shocks. I Have always been running them on 0-4 of 18 possible clicks of adjustment so in the real soft end. I called QA1 and asked if they could re-valve them to soften up the bump and they referred me to one of their distributors. Talked to him and sent the shocks out last winter. He said he had softened it so former adjustment of 0 would now be about 4-5. so this gave me a 4-5 click softer overall shock. I have now run 4 AXs and am real happy w/ the results. The increased rear camber has gotten rid of the overall loose handling and the shocks have really helped on rough sections of the parking lots. Now the car doesn't feel like it is leaping and bounding in the rough sections. It feels like it is absorbing the rough spots much better. I am also changing the rear springs. FFR ships 400 and last yr I ran them and 450 and 500 (for 1 event). I run 300 over the winter for a nicer ride and the first 2 AXs I left them in the car. That was too soft so now have 350s in the car. I will continue to trade off ride height for more or less available travel, and springs, and shocks, to try to come up w/ the best combination. I may try some of the Koni soft progressive bump rubbers instead of stiffer springs. This is fun experimenting.
 
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