Project: Designated Driver

[pdm]

Project: Designated Driver (I killed the clunk!)

UPDATES and MODS
->April 30, 2011. Fixed the clunk! New Trac-Loc
->March 26-27, 2011. IRS and diff rebuild: 4.10 gears, carbon clutches, ARP bolts and studs, Lube Locker gasket, LPW cover, cobra pinion brace, FTBR bushings and mounts.



Finally getting started on my daily driver!

A few goodies just showed up from Tousley Ford, American Muscle, Lethal, and of course Bruce at FTBR! Thanks to all of you for the A+ customer service and fast shipping! Hopefully, I can get all of this installed over the weekend. :lol: Looks like I'll be driving the '78 to work on Monday.

 

[01strokersnake]

IRS stuff! Nice!

 

[MickeyD]

Hope things go well! I plan on doing some similar mods in the next couple weeks and cannot wait

 

[pdm]

IRS stuff! Nice!

IRS + FTBR

Hope things go well! I plan on doing some similar mods in the next couple weeks and cannot wait

The weekend can't get here fast enough!

 

[pdm]

IRS and Diff rebuild

Well, I'm back for an overdue update.

First impressions:
I've been driving on new 4.10 gears and FTBR bushings for a few weeks, and the handling improvement from the FTBR bushings is beyond explanation. If I could only swap gears or bushings, it would be the bushings. This car has completely stock suspension and tire size, and the cornering ability easily surpasses that of a stock bushing cobra with lowering springs, shocks and struts. Even being a rubber band (convertible), I can't believe the way it turns! It has slight oversteer as it enters the corner and the rear end follows perfectly all the way through. There is really no way to understand how much difference they make if you've never driven with them. Under hard acceleration, the car now pulls in a perfectly straight line. Even with a vert on stiff tires, stock springs, and no aftermarket subframe connectors, my wheel hop is gone! I get just a little on 1-2 shifts if the tires and road is cold, but otherwise, I get a smooth burnout every time.

As far as NVH...
Noise: I have the clunk (more on that later) and the bushings do make it more pronounced. With stock exhaust, I have to try really, really hard to notice the noise from the 4.10 gears. With any exhaust mods or the radio on, there is no way to hear the gears if they are properly setup. FRP is the only way to go for gears.
Vibration: no change.
Harshness: Much smoother ride! Shocks and springs do an excellent job of absorbing road forces when the suspension is operating properly. The stock bushings do not allow the control arms to articulate freely, so they are forced to absorb some of the road force. 3/4” of vulcanized rubber does a very poor job of this (especially when it has 130k miles on it and is breaking down), and the road forces end up being transferred directly into the unibody (and the seat of your pants). If anyone is reluctant to install these bushings because they want to keep their “smooth” ride, do not be deceived, these bushings are how you achieve a truly smooth ride.
This install is not for the faint of heart. Not everything fits perfectly. You have to get a little creative. I would have never guessed that the bushing install would be more of a pain than a diff rebuild. This would have been much easier with a little help, but I ended up doing the whole thing solo.

Friday night…

Man, that’s nasty!

This thing doesn’t just fall out

On the operating table

Got oxidation? I broke one of the front diff mount bolts that was seized up.

Typical leaky diff

Front diff mount bushing

Saturday…

New carbon friction discs in for a soak

Cruddy old thing. The gray circles around the pinion bolt holes are deposits of a “grease” of diff fluid and metal from the worn spider gears. Note: There is a lot of wear on these gears, and they will need to be replaced at a later date.

Stripped down and cleaned

New FRPP races, bearings, seals, and ARP bolts. The carrier is setup with standard clutch placement that I’m not a fan of (shim, friction, steel, steel, friction, steel, steel, friction, side gear) and a stock s-spring. Main bearing preload is a light 0.015” and backlash is a tight 0.006”-0.009”

New LPW cover, Lube Locker gasket, and ARP cover bolts.

Later in the week after getting new front diff mount bolts…

New FTBR bushings and mounts all buttoned up

Pics are a little sparse. I got carried away with the gear and bushing install and didn’t get many installation pics.

 

[pdm]

There is a severe amount of slack in the spider gears! Way more than is acceptable. 130,000 miles of wheel hop and on the original diff fluid has taken its toll on the gears, but amazingly the half shaft joints and splines are in great shape. After taking a long look at things, I believe that they are the cause of my clunk. I will have another update in a couple of weeks as she goes back under the knife for a carrier replacement and a change to the limited slip setup.

 

[mmustangsrus]

IRS + FTBR

The weekend can't get here fast enough!

:rockon: :banana: you are gonna love it when its done but HATE IT while your working on it

you should go ahead & grind down the "LFP" on the diff cover before the instal alot people are having that issue

but FTBR FTMFW :rockon: congrats !!!! epper:epper:epper:

 

[pdm]

Thanks. I ground down the logo some, but I plan to take some more off when it comes back out, just to give myself a little more room during install.

 

[Gallows]

I have a 99 IRS to rebuild but it already has 31 spline carrier/axles, BF rear brace and MM front brace. What purpose does the LPW have? Thicker and stronger?

 

[Fast99Snake]

are those SFC's bolt-on?
probably a good idea to lay down a few welds next time your under there, bolt-on subframe connectors are a big no no.

otherwise looks gr8, I love the FTBR kit in mine, along with the tru-trac diff and MM/Bilstein Coilovers it's a whole 'nother animal.

 

[pdm]

I have a 99 IRS to rebuild but it already has 31 spline carrier/axles, BF rear brace and MM front brace. What purpose does the LPW have? Thicker and stronger?

The biggest difference between your setup and a LPW is the load bolts that load the main caps. It holds everything in place if something were to let go.

 

[pdm]

LOL!! Thanks for the warning, but those lightweight things are the factory subframe connectors. They're about as useful as tits on a boar hog. The only reason they're still there, is because I don't have anything to replace them with. Sometime in the near future, I'll be installing a set of home brew upper and lower subframe connectors, as well as a 4 point roll bar. Don't worry, it won't be bolted together.

 

[pdm]

Fixed the clunk!

THE CLUNK IS GONE!!! :burn:

Well, my assumption was correct. The excessive gear lash in the original Trac-Lok diff was causing my clunk, and here’s how I fixed it.

With a fresh, complete Trac-Lok diff from Tousley Ford and the carbon clutch pack and side gear shims from the initial install, I went to work on the new setup. First I noticed that the new diff had more lash in the gears than I would like (a likely culprit to the presence of the clunk in some brand new cobras). I tore it down and made a few comparisons. The old spider gear shims were quite a bit thinner than the new ones (I did not mic them, just a physical observation). I started off with stacking the clutches in alternating order with 4 frictions on each side. I tried different side gear shims until a 0.025” one on each side allowed me to rotate the spider gears into place by lightly tapping them with a dead blow hammer. The Trac-Lok carrier is a perfect gauge for finding the right shim. If it doesn’t fit, the shim is too heavy, and when they just barely fit, you’ve got it right. I installed the “S” spring and checked the lash in the gears. It was minimal, but they were not bound together. Just the way I wanted it.

Fast forward and everything is buttoned back up. Time to fill ‘er up with a bottle of Motorcraft friction modifier and 2 1/3 qt. of Mobil 1 75W-90. Next to a pump, the best tool for filling the diff or transmission is an enema bag. It’s a heavy 2qt rubber bag that comes with a fitting, hose, clamp, and a plug to seal it up and store for later use. I keep several of these on hand with various gear and transmission fluids in them. Bring on the jokes, but it’s fast, easy, and there’s no cleanup.

Test drive: Fire it up, slam it into first, and… nothing… no sound. I head down the street and downshift as I come to a stop. Jam first again, and… nothing… THE EVIL CLUNK IS DEAD! If I get in and out of the throttle hard, I can hear a slight clunk, but that is the only time… not while shifting N-1, N-R, or any other time shifting. It was so nice driving to work this morning. There’s a long hill with a stop light at the bottom. After coasting down this hill, it always clunked when I hit first to take off again, but not today. As far as the Trac-Lok setup, I love it. The friction is perfect. Good traction, but no binding in a sharp turn. I am a happy Cobra owner once again!:banana::burnout: