Lincoln Mark VIII Rear End?

[AndySwen]

Anyone have any experience with the Mark VIII rear end? I am considering one as I like the IRS and it does not need to be modified to easily fit the chassis.

Thanks

[Richard Hudgins]

Andy,

JBL uses the alloy Ford 8.8 unit as standard. They get this unit from ford SVO. It comes with traction-loc diff and 3:73 gears.

I think the case is the same as the Lincoln unit. The Lincoln probably has the traction-loc, but I am sure that the gears are much lower.

[427sharpe]

The Mk8 irs is the same unit in the Mustang Cobra--and it is very stout. the TBird unit is almost identical, the exception that the Lincoln center section is aluminum. the Super Coupe uses the same unit as the Mk VIII, as does the Mustang Cobra. Plenty of gear choices as well. the only knock on the unit has been a weakness in the driveshafts themselves in hi output applications under extreme duty conditions. If you plan to push your car HARD, regularly, I would get a set of hd axles made up. Best place to find a set is in one of the hot Rod mags for import cars, if those guys can make a set of FWD axles that can run in the 9's, i'm sure they can make some stout ones for you!!

[HighPlainsDrifter]

The lincoln has 3.08 gears and NO possi. To change to a possi and better gears costs too much, you're better off buying it from a svt mustang ala JBL. Unless you are a professional road racer a solid 9" ford rear is better in all resects than an independant rear and a cobra is way too low for anyone to even see what rear end is in it,so looks are out also.

[427sharpe]

I beg to differ--my street car is a Mark 8, and it has a positraction rear end with traction assist tied into it thru the ABS system. You can eliminate the 'anti spin' with a switch on the dash, but the posi remains. It also came oe with 3.55 gears, which I changed to 3.73.

[AndySwen]

HighPlainsDrifter:

Why do you feel the solid rear end is better except for hard core racing? I would expect the IRS to offer a smoother ride particularly if the road is at all bumpy like most here in FL.

[HighPlainsDrifter]

I sold my thunderbird supercoupe to get the cobra, so I know some of the options on them. The stock rear suspension has rubber bushings and does give a good ride.It is complex to set up the camber and castor on the rear,a good alignment shop needs to do it after the ride hieght is set.The stock rubber bushings also cause wheel hop on higher HP cars,need to change to poly bushings.The stock gears were 2.73 : 1 and possi. The mark vIII had 3.08's stock,not that you couldn't order other gears.The rear is rated at 330 ft/lbs of torque,with some safety factor built in. Most guys build their engine for 400 to 550 ft/lbs of torque.That needs a stronger rear such as a 9" ford.There are companies that make 9" ford IRS' ,such as Dutchman,I have their forged axles. If you use the stock IRS you will need softer rear springs as the t-bird and mark 8 weigh over 3,700 lbs and the cobra is over 1,000 lbs lighter and will need lighter springs and matching shocks as the stock shocks are computer controled for that exact car.I would contact a rod shop and pick their brain for the correct springs and shocks for a 1200 lb rear end weight.
Good Luck,
Perry.

[AndySwen]

I am looking at the E-M kit and the MK8 is one of the options they recommended. Their car is a little heavier but not significantly so - 2,750 lbs. I'll use a 427 but am not looking to race the car. It is a project for my kids and I to do together and we'll use the car for riding around with possible show/autocross in the future. I am more concerned with a comfortable ride and good performance as opposed to top end performance. I expect about 400hp out of the engine and was thinking of the Tremec tranny.

[Mike Braddock]

Andy,

The Mk8 rear will work very well in your car. EM has done their homework and sell a well engineered package. The IRS is better in all respects except price and ultimate strength. These units will take 500 hp and the same torque with no problems, so don't worry about that; it's not an issue. And will all due respect, HPD is incorrect about the gear swap as well--it costs little, if any, more than a standard 8.8" gear swap and all the parts are the same. The only item which is different is the aftermarket posi units, if you decide to go with one, as you need one that will hold the retaining rings which the solid 8.8" doesn't have. Auburn and others sell them.

3.73 gears and a tremec would make a wonderful combo. The IRS will give you a better ride and you'll recoupe the extra investment when it comes time to sell the car. Good luck and keep us posted.

Mike

[HighPlainsDrifter]

Mike;
Everyone has their own opinion, you may have access to 'cheep' labour and parts,good for you. Most of us have to pay the going rate. Paying $190 for gears, $330 for possi, new bearings ,seals,fluid,install kit $100, then $ 200 for installation. Eight hundred bucks plus the cost of the original 'used' rear end is alot of money and you haven't even replaced the U joints yet or shocks.The point was it isn't cheep to use an IRS. For a novice it's a complicated set-up. If you are a professional then it's a cake walk,but a man doing a project with his kids may want a more economical and easier set-up. Also 3.73 gears with a tremec will make 1st gear useless,lots of rubber.
I still wish you good luck on your car,remember it's your car,don't put something on it because of what someone says is better or wants to sell 'up' options.You can cruise for years on that extra money.
Perry.

[justa6]

Re your>>>The IRS is better in all respects except price and ultimate strength. <<<

I'd like to add another thing that the Live axle is better than the IRS. Drag Racing. IMO, there is no doubt that equal for equal the IRS doesn't "do it" for drag racing. Also I've ridden in a LOT of IRS Cobra's and haven't found one that rides as nicely as my Johnex with its Ford 9" rear. Only problem is with any Ford with a Trac loc is that they are really weak posi units. Replace them with a Power Trax or a Detroit Locker and add the Daytona Pinion support and forget about rear end problems. Great 60' times and really good ride. What's not to like...There have been some good articles about IRS vs Live axle and the bottom line is that they can both be good or bad depending on the parts used. t

Also to High Plains Drifter, who says a 3:73 and Tremec makes 1st gear useless. My car does 1.40's 60' times with a 4:11 and a Tremec. I haven't found many Cobra's with any engine that do much better than that and mine is only 274" and a "6". Also it turns 10.8's with no nitrous or turbo so I'd say it depends on the combination whether a Tremec and deep gears do well together...IMO, of course.

Regards,

[Mike Braddock]

HighPainsDrifter,

I was just trying to point out that you can easily put a late model IRS in one of these cars for less than $800 including the original purchase price, gear swap and posi rebuild. This is comparable to the amount of $$ many people have in their solid rear axles after a gear swap and disc brake upgrade. There is nothing wrong with the stock posi for the above intended use (street, autocross and maybe open track events). I was mentioning what to watch out for if he does decide to upgrade to an aftermarket posi unit, not that he needs one.

I don't really understand your comment about how paying $190 for gears, $330 for possi, new bearings ,seals,fluid,install kit $100, then $ 200 for installation...plus the cost of the original 'used' rear end is alot of money. How is it any more than putting a solid axle in the car? You still have the same prices--regardless of the labor price

Finally, I know about a dozen guys running IRS with over 450 ft-lbs of torque with no problems. So the strength in cars that weigh this little just isn't an issue as you stated and I wanted to make that clear to Andy. And even if you go with a solid axle, there's no reason to run a 9" in these cars unless you need to be able to swap out gears quickly at the track (or your frame is just setup to take one). An 8.8" solid axle is a stout rear end when setup properly. And 3.73's with the tremec do make a a nice setup. Yes, first gear is a little short, but you get used to it. I certainly would not call it "useless".

Bob, you are correct about drag racing and solid axle cars . The reason I made the above statement was because I had read Andy's previous post:

Considering Everett-Morrison

and so I knew he wasn't into hard-core drag racing like some of us. And I agree with you that the solid axle cars can be made to handle and ride very well indeed. On the other hand, I've seen many claims that a properly setup IRS car can be made to handle and ride better .

Since Andy was asking about the MkVIII rear in particular I was giving him some info on that, not trying to recommend one vs the other. I think a general rule of thumb is that for serious track events/racing, the IRS is a better choice. For serious drag events, the solid axle is better. But there will always be exceptions based on how particular cars are setup. You put it well whe you said they can both be good or bad depending on the parts used.

Mike

BTW, there was a guy at my local drag strip who replaced the IRS in his late model cobra with an 8.8" solid axle and picked up 1.2 seconds...you would think someone at Ford could design a decent IRS for that car ...

[Mike Braddock]

And oh yeah...your 60' time just blows my mind! What kind of tires were you running??

Mike

[HighPlainsDrifter]

Just a 6....Bob you are a real sleeper,that is a real race engine turning 10's, it would be lucky to turn 16's if it wasn't.You definatly have your act together,must be fun blowing away bigger engines! I said the steeper gears were useless on milder big blocks ,as in his application, for 2 reasons. 1st you waste all that beautiful low end torque and 2nd you'll be shifting outta 1st at 10 mph, gets to be a pain when the cobra is a cruiser.Your race cobra is perfect with the low gears,you probably start off in 2nd around town,i used to do that with my mustang also.
Perry.

[justa6]

Your right about the gears and torque. MOST Cobra motors are Torque monsters and certainly don't need deep gears and a Tremec trans. I was just making the point that "some" of the Cobra's around can use deeper gears. My little motor makes good horsepower and Torque for its size. But my 390 ft/lbs of torque, although good for a 6 and 274" isn't squat compared to the big motors. Also for those who are confused by all this my motor pulls hard to the 8200 Rpm rev limiter setting so it likes the very deep gears which is why the 60' times are pretty good.

As far as what tires I use right now I'm on 8" M/Thompson ET STREETS. I'm changing over to 10" ET streets for this year. A buddy of mine says the better bite will get the "6" down to 1.30's 60'. If he is right I'm shooting for mid 10's which is the limit, IMO for the power available. I've been giving some thought to putting Nitrous in it for this years R & G and seeing if we can get it into the very low 10's (9's?)... Still not sure whether I want to go to the "gas" or leave it normally aspirated... Any ideas?

Regards,

[HighPlainsDrifter]

Nitros can be effective or disasterous. I don't understand why you would tamper witha great combo that you have now. Running that fast 'on motor only' is quite an accomplishment. Going on the bottle will take some of that away.
Good Luck at R&G,
Perry.

[justa6]

Your right about the Nitrous. The only reason I'm thinking about it is that the Stage II Buick V6 that I'm running is VERY strong. When it ran at Indy for Menard they were only 188 cubic inches and put out 900 HP. I talked to the chief engineer at Buick about these motors and he told me that the original motors (not all mains were cross bolted) would start to fail in the mid 1100 HP range. That was why they detuned them (lowered boost pressure) for Indy so they could go the 500 miles. I agree with you that a mid to high 10 second normally aspirated motor is more impressive than a 10.0 NOS motor. I would only "play" with the NOS to see if it would go into the 9's and then take it back off (maybe

Just a thought and I appreciate the input,

Regards,