differential gears

[Guido]

I'm thinking of installing 3.73 gears, will it screw up anything with the computer? All I have to do is change the spedo gear right? I know on GM transmissions it's easy, how about Ford?

[LSCXTSY]

Guido-
I have a brand new set of 3:73's if you would like to buy them.

[pro-five-oh]

Go for it! The only concern will be fuel economy on the highway, but that Mark will launch nicely with 3.73s.

Another thing I noticed is that AOD cars with 3.73s get better fuel economy in the city because the car goes into OD sooner.

[Guido]

I know some cars came with a wide-ratio OAD that effectively makes a 3.23 equipped car seem like a 3.82 in first gear, but 3rd (1:1) and OD are the same? Did any Mark VII come with these? Mine is a '92 LSC. Is it worth it to put in the wide-ratio gear set? It seems like the best of both worlds - low end plus stock OD for the highway.

LSCXTSY: email me details (price, still-in-box, etc.) gui1973@yahoo.com Thanks.

[Lscman]

The AOD-E wide ratio gearset used in the Mark VIII was not used in any AOD transmission. Only 1st and 2nd gears are different ratios. They were first used in 1993 and can be retrofitted, if you're building a $1600 AOD performance transmission. However, expert Don Walsh of Ford Motorsport says the conversion is a total waste of time in most cases. The small amount you gain off the line is lost due to greater RPM drop during upshifts with the wider gears. A $100 aftermarket 2200 stall converter will launch the car harder than the $800 wide ratio gears and these locking converters do not have any significant drawbacks.

[Guido]

Would it be hard to find an AOD-E transmission at the wreckers?
Can you really get a locking converter for $100? When exactly does the converter lock up?
So then 3.73's plus 2200 stall converter should make a huge difference http://www.lincolnsonline.com/ubb/smile.gif That won't cause any computer "confusions" would it?

And correct me if I'm wrong but the 302 HO should be happy cruising at 3000RPM all day right?

[Lscman]

The newer AOD-E transmission is not simple to bolt-in and all AOD-E's do NOT have wide ratio gears. Wide ratio gearsets were developed for the 32V V-8 because they needed to rev up to build power. The AOD-E is designed to work in conjunction with a vehicle that has electronic transmission control integrated with the engine computer. A Mark VII computer does not provide this function and their valve body has totally hydraulically operated valving. Stand alone AOD-E electronic control units are available but they are intended for race cars worth $10K and up. What I meant is the AOD gearset can be retrofitted into an AOD transmission. Yes, I purchased a Recon brand 2200 stall converter with brazed fins that is stronger than a stock OEM unit for $85. Most transmission shops and jobbers can get those. B&M sells similar one's for around $150. The OEM converter stall is close to 1600 RPM. Another route is to install certain Ford 3.8L V-6 AOD converters which will provide a stall speed of about 1800-2000 RPM in a 5.0L HO. All AOD's and AOD-E's are considered "locking" type converter setups. This provides better fuel efficiency & more RWHP in 3rd and 4th gear and it reduces heat buildup in the transmission. AOD's have dual input shafts. AOD's do not lock up according to road speed or throttle position like most other's. They simply lock when they upshift to 3rd or 4th. This makes them efficient, operating much like a "clutchless/stickless" manual transmission. The familiar slip/bump feel you get on 2>3 and 3>4 upshifts tells you the locking action is working. The AOD does not slip in 3rd or 4th for more than a second or so after an upshift and this can be witnessed by viewing a tach. The 70's vintage AOD is not a very smooth shifting overdrive transmission. It is a durable and efficient one. They were designed to withstand the big torque of the 351M/400 motor era.

[This message has been edited by Lscman (edited April 25, 2001).]

[pro-five-oh]

Guido,

The B&M 2200 stall converter in my Cougar is great. Even with my stock 3.08s, the cougar launches pretty well and is a good match to a stock camshaft in a 5.0 HO. Since the converter and gears have no data exchange with EEC-IV, the car WILL run fine. http://www.lincolnsonline.com/ubb/biggrin.gif

I agree that the wide ratio kit is a waste of money, swapping to 3.73s is both cheaper and makes the car a lot faster. You are gonna notice a HUGE difference in acceleration with a looser coverter and that rear end.

LSCMAN: I thought the first AOD was in 1980 and was only mated to the 5.0. The older 70s Fords used a 3-spd, like a C-4.

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pro-five-oh http://www.geocities.com/jeeves77/cougarview.jpg
88 Cougar XR-7 5.0 HO
15.0@93mph, 3740lbs
83 Continental 5.0 LO
My Mark VII Page (http://www.geocities.com/motorcity/street/3545/mark.html)

[This message has been edited by pro-five-oh (edited April 26, 2001).]

[DrDragon]

Sorry but I'm just a little confused after reading this thread. The 90 MarkVllLSC I'm looking to buy has had the rear end replaced with a non posi and with higher gears. He (dealer) is offering to swap it out with a 3.73 posi out of a turbo Coup. "Disk to disk complete" Anyone know if this swap will work and is 3.73 too much? I think that there is some disagreament here.

[pro-five-oh]

DrDragon,

There is no diasgreement on the 3.73:1 issue. You'll go faster around town, but will lose fuel economy on the highway. It's up to you, do you want a Mark VII as a cruiser or with some more acceleration?

In your case, swapping an ENTIRE turbo coupe rear is impossible...the Tbirds had 4-lug axles, not 5-lug like a Mark. (I have the tbird rear axle on my 4-lug Cougar)

You can swap the 3.73:1 ring and pinion very easily, so I am assuming the dealer meant to say that.

[This message has been edited by pro-five-oh (edited April 26, 2001).]

[DrDragon]

Thanks pro-five-oh, would it still be one legged though? I would want posi.

[Guido]

Thanks for all the info, I'll keep it simple: gears, then if that's not enough the converter is next.

I'm unclear on one thing though...
it's the actual AOD that locks up (through the dual input shafts) as opposed to the converter?

The way I see it gears will definitely hurt fuel economy on the highway, but won't they improve economy in regular rush hour traffic? I think the Mark needs as much torque as it can get to get it moving so the closer the motor is to its torque peak, the better the economy.
A converter should do the same as long as the extra torque is not lost through slippage.

[Lscman]

Many stock Mark VII's have the 3.27 ratio. The 3.55 that comes in most T-Bird Coupes will hardly be noticeable. It's less than 10% increase in RPM. If you're going to the trouble make sure they're 3.73's. Yes, locking converter description is a misnomer....the transmission locks and bypasses the torque converter thru the dual input shaft setup. The solid one piece input shafts that some 400+HP racers run defeat the locking feature and result in lots of fluid heatup that must be released with trans coolers.

[pro-five-oh]

DrDragon, the ring and pinion the dealer will install in that Mark can go either posi or open end. It depends on the differential already in the car.

Look at the axle code on the driver's side tag (near the door striker) of the Mark. Look under the "AX" column. It will either be a "5" or "E." The "E" is a Trac-lok. If it is a "5" it can be converted to Trac-lok.

[This message has been edited by pro-five-oh (edited April 27, 2001).]

[perry 91lsc]

LSCXTSY: email me details also (price, still-in-box, etc.) andrew@bigwulfman.net. Thanks. Also I live in suffolk county so u wouldnt hafta ship if i decide to buy em

[Guido]

Do you need to use limited slip additive if using synthetic gear oil?
Why does the manual state DO NOT change fluid before 90K miles (or maybe it said 100k)?

[perry 91lsc]

Does my 91 lsc have an 8.8"rear?

[pro-five-oh]

Perry: Yes, you have the 8.8" rear.

Guido: the Mustang shop that put the 4-whl discs in my Cougar used royal purple diff. oil, but didn't mention a limited slip additive. Better ask around.

[Lscman]

Some limited slip additive is already in most gear lubes. That is why the bottles say they're compatible with posi's. Extra additive is highly recommended by dealers and repair shops because it avoids customer complaints. The slip/grip phenomenon you get without enough additive can cause noise much like chatter in low speed hard turns. This is because the posi clutches are working real good and trying to grip. The additive reduces the clutches ability to grip which prevents differential windup, tire hop and differential slack noise. The sound/noise is harmless and is an indication your posi is working real good. Additive greatly reduces the "breakaway torque" value and allows one wheel to break traction and it reduces clutch life due to added slippage. I NEVER use additive.

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Rick, Road Track Terror in my '88 Mark VII LSC. See ya at Northeast Events! Pgh, PA

[Guido]

For the last month or so the rear-end makes a "groaning" sound when turning at slow speeds. It has 90K miles on it.
This weekend I'll put in Castrol Syntec 75W-90 (with no additive) and I'll keep everyone posted with the results.

Guido

[pro-five-oh]

Does it groan after you release the brakes? Marks are notorious for caliper moan as you let off the brakes and hit the gas. Even my Cougar with rear discs does it occasionally.

[This message has been edited by pro-five-oh (edited May 05, 2001).]

[Guido]

Well well well, what a surprise!!! Popped the cover, took a look inside and guess what...no posi!!!! That sucks! And after spending 1 hour trying to get the fill plug out I just gave up and put the fluid in from the breather. The job's done, no leaks...and the moan is still there. I'm almost sure it's not the discs because it only does it when I'm turning. I notice it on the highway on-ramp. Maybe the synthetic fluid will take care of it if I wait a few days.
Could it be a bearing? Wouldn't a bearing make noise while I'm going straight also?

Guido

PS My data plate in the door jamb has an "E" for the axle code. Does that confirm an open diff?

[mdcluth]

My '86 LSC does the "moan thing" when I'm backing up while turning with brakes applied lightly. I believe it's just pad drag. There is very little movement in the pads to begin with, and pads are very square to the disc. I don't feel any heat back there either, so I just chalk it up to something I can live with. Hardly noticeable anyway. In fact, I might be the only one that can hear it. My wife thinks I hear things anyway.
That's not what the voices tell me!

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"Lincoln Moves Me"

[Guido]

The more I think about it the more I think you're right mdcluth. Maybe the pad is lose or something. I might try putting silicone or tightening the clip. It just bugs me.