Driveline/Differential Decisions
 

Time to procure that ERA rear suspension for my 289 FIA!:3DSMILE:

Bob, I have some questions:

I'm leaning toward a Tremec 5-speed. Summit lists three different gear ratios. With my objective being streetable drivability plus some "spirited back country windy road driving" can you recommend which ratio I should choose?

Also, with the transmission choice picked out, what differential gear ratio should I run?

I'll be calling Peter for a quote for the rear suspension plus some other goodies.

Anyone else have recommendations for the Tremec 5-speed? Which gear ratios did you select and why. What differential gear ratio are you running?

By the way, the power plant will likely be a 347 @ 425 bhp.

Dangerous Doug

I went with the ERA outboard brake rear. There were some issues with some folks, not all, concerning wheel hop with the Jag rear (and changing the pads on inboard brakes is another point). The ERA rear gives me no hop whatsoever. I have the Spax dampers set at 12 (which is two clicks softer than right in the middle) and Yokos on the rear. When I stick her she doesn’t hop, and she doesn’t squat; she just spins and goes. The rear end ratio is 3.54 and the transmission is a TKO600 with the .64 OD. Two issues surround the TKO600; the choice of the OD (.64 or .82) and the “stuck in gear” issue. Your choice on the overdrive will be governed by your rear end ratio choice and your torque curve. My FE puts out gobs of torque, and is smooth, at 2000rpm and less. Thus I can cruise at 70mph at 2000rpm where the wind noise is actually louder than the pipes. That’s very nice, but that’s all that fifth gear is ever used for. More folks on this board have chosen the .82 ratio than the .64. If given the chance to switch to the .82, I would stay with my .64; it’s perfect for me. If you’re not going with the TKO600 take a look at the gear ratios to make sure you’re happy in both low gears and high gears - all Tremec ratios are not the same and you want to make sure you know what you’re doing. You need to have a gearing calculator (many of them are on the web) handy to work out your transmission/rear-end/engine torque curve relationship. You will hear complaints that some folks’ first gear is unusable; some say their fifth gear is unusable. I will say though that there is a benefit to having a first gear that allows you to go slow when you want to; you might want to keep that in mind. That allows for easier take-offs, less strain on components, etc. On the other hand, the one time I let my brother drive my Cobra he started off in 3rd gear – but the FE didn’t seem to mind it and it would have taken him to 100mph before he would have had to shift! But that’s an FE for you. Good luck.

Doug,

My preference with your engine would be a 3.54 dif ratio and a Tremec with a .82 fifth. Your engine might not be all that happy on the highway with the .68 top gear. The TKO 600 has slightly better intermediate ratios for "racing" but probably not something you'd notice otherwise.

Great inputs. Thanks.

Bob, would the 3.54 Diff. + Tremec 5spd w/0.82 fifth be the typical factory built car spec?

DD

Here's some data I found on TKO 500/600:

Ford TKO-500 (TCET4615)
3.27
1.97
1.34
1.00
0.68
3.00
1895.00

Ford TKO-600 (TCET 5008)
2.87
1.89
1.28
1.00
0.64
2.56
1975.00

Ford TKO-600 Road Race (TCET4617) <=== This one sounds the most interesting to me, based on inputs here.
2.87
1.89
1.28
1.00
0.82
2.56
1975.00

I've got over 2000 miles on my TKO-600 and have not had any problems with the transmission. I went with the 2.87 first gear, the 0.64 5th, and a 3.54 rear. It has been a good combination. I'm running a 289 stroked to 331 putting out approx 390 HP (flywheel) at 6100 rpm.65 mph at approx 1700 rpm and I've still got good low end power for passing.

I'm glad that I went with the 0.64 for highway cruising (20.8 mpg), but if I had it to do over again, I'd probably opt for 3.77 gears for more power in 5th.

Definately go with a TKO 600, .82 5th and 3.20 rear. It gives you a useable 1st AND 5th gears. I love it.

Good input. 20.8 mpg? I could live with that!

Called Peter for a quote. A little sticker shock on the price increases on the rear suspension, but I guess I need to pay the piper (or the Peter, in this case...).

I'm considering the inboard brake solution now. Think I'd regret it later? Price difference is the driver, as the total solution works out to be about $1k less expensive than the ERA outboard brakes solution.

How much is the ERA outboard brakes rear suspension "kit"? They still offer that? Will I save enough money to offset the cost of Rogaine and Excedrin (in other words, if I try to build the rear suspension kit myself, and I going to be pulling my hair out and banging my head on my work bench?)

DD

The wheel hop you mentioned earlier on the Jag rear.I fixed mine by mounting the lower control arms on opposite sides and adding a rearward control arm from the original mount (now facing back) to the frameas far back as I could get.It has worked great for many years and does give you a little toe tweeking if you use left and right heim(rose) joints

I think most people are pretty happy with the Jag rear. And, once upon a time, I believe ERA offerred a "Wheel Hop Damper" -- I don't know if they still do or not. I couldn't find anything on it on their web site so perhaps I'm imagining it.:JEKYLHYDE

EDIT -- Well I wasn't imagining it. See this posting by Excalibur from February, 2005. http://www.clubcobra.com/forums/era-speak-bob-putnam/61260-era-708-a.html

Well, good to hear. At $5200 for the ERA setup = $200 for ebrake cables and $350 for the sway bar, I had to rethink the direction I was taking.

I'll inquire the wheel hop damper.

On the inboard brake pads, you have to remove the suspension to service, or simply get the car up on jackstands?

Incidentally, I have the standard front brakes.

There's a little trap door behind the seats, but it's still a bit of a nuisance to change them I'm told. On the other hand, you don't do it all that often anyway. And BTW, if you upgrade to the ERA rear you probably will have to upgrade the front brakes as well to the bigger Sierras.

I opted for the ERA suspension for : better cooling with outside brakes, bigger brakes, ease of maintenance, weighs 50 lb. less, and then they recommend you get larger front brakes. You'll like the bigger brakes if you do any track time. My Unique FIA had 12" Will woods (like the optional ERA brakes), and they really work - once you get them warmed up. The optional ERA suspension, in my mind, is a great investment both for owning the car, and for me (or my estate!!) selling it at some distant time. Can't wait to see it installed. Rick D

I have a 3.31 rear and the TKO 500 with the .82 5th gear. When I bought the trans, the TKO 600 was not available yet. If I were buying today, I would get the TKO 600 for the better 1st gear ratio, but would still use the .82 5th. With the .82 5th, the engine turns about 2600 rpm at 70, which is very comfortable for cruising. At any rpm less, the engine would be lugging. When selecting your gear ratios, keep in mind at what rpm your cam shaft is designed to work the best at and try to end up with the gearing that will get you in the cam's intended operating range.

As for the ERA rear, I have the std jag rear and have absolutely no problems whatsoever with wheel hop. However, that being said, if I were to do it again, I would get the ERA rear if for no other reason than servicing the brakes. You can access the inboard brakes through the trap door, but it would be much easier to service outboard brakes. Plus, the ERA rear is awfully purdy!

Changing the rear pads on the inboards is really very easy.You have to get under the car ,but once its in the air its a cinch! If you have an access hatch its even easier.

Talked to Peter today regarding the ERA rear in "kit" form, and it sounds like they've worked out a good compromise. They offer the rear suspension in kit form with the difficult stuff done (stuff that requires special tools and such). This works perfect for me. I really had my heart set on the ERA suspension, and was bumming with the price change, but the "kit" thing should work well for me.

I may still need that Rogaine, but it has nothing to do with ERA.