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Discussion Starter #1
In my '95 Cougar, of course everybody knows, I have the stock drive shaft that will possibly damage my driveline if I exceed about 120-125MPH with my 3.08 gear. Does anybody know what the limitations on a Mark-VIII shaft is and what my possible top speed would be if I change my 3.08 to 3.55?? I hate stopping at 115 because I'm scared to damage the trans tail-shaft.

Meow

Clay
 

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Get a '93 MARK VIII drive sahft-----it's the ONLY year they made them in a one piece aluminum---you should be good to about 130+.........and I believe that's including gears up to 3.73:1 ratio.........however I'm not absolutely sure on that.
 

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cman2007 said:
So what is the difference if I get a shaft from any other year Mark VIII?? Are they not aluminum or just not as durable?

They call me shaft,

Clay
Read my post above........"Get a '93 MARK VIII drive sahft-----it's the ONLY year they made them in a one piece aluminum". That's the differrence between the differrent years of MARK VIII driveshafts. The '93 was the ONLY year they made one piece aluminum driveshaft for the MARK VIII's. I believe all the years of the MARK VIII's had aluminum driveshafts......but here's the key word---ONE PIECE.....meaning no seams......which obviously means the one piece in the '93s is way more durable than the 2 piece aluminum driveshafts found on the other models. Granted, any of the aluminum driveshafts are better than what we got on our MN12's.......but the '93s are the better way to go.

Hope this helps.
Slowride
 

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Discussion Starter #5
Ok now I really understand. I obviously have never replaced drive shafts before and don't know much about them. Soo, I would imagine that the length is the same and splines?? (i'm going DS hunting on Monday) Hmm, maybe if I find a '93 Mark in the junkyard, I'll yank the engine, too. :D

And yes... that helped alot. thanks

Shafty Bussiness,

Clay
 

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Slowride said:
Get a '93 MARK VIII drive sahft-----it's the ONLY year they made them in a one piece aluminum---
wrong. early 94s got them too.
 

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GreenBird said:


wrong. early 94s got them too.
Well that may be......but not awhole lot of the '94s did.........and the ones that did, they only got them because Ford wanted to use up their inventory of the '93 driveshafts and / or the earlier '94s were built in late '93, using '93 parts. Which goes back to my last post---which wasn't entirely wrong---'93 was the only year they produced the one piece driveshafts.......which may have ended up on some early '94s...but they were made in '93 .


I told him the '93 because he'd have an easier time finding one (a '93 MARK VIII)than finding a '94 MARK VIII with a one piece drive shaft....especially since he didn't know the differrence between the driveshafts and years.
 

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This has probably been answered before but I couldn't find it, but is a 93 Mark VIII driveshaft the same length as a 95 T-bird's? Would I have to modify anything else, or does it fit right in?
 

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Discussion Starter #9 (Edited)
I beleive so about the length, because the Mark is the same platform of the T-bird and the Cougar.

Now, I have a question about the half-shafts. Would they hold up to probably 130+ speeds? Especially with 3.55 gears?

Clay
 

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The problem with mn-12 driveshafts is that they are crimped two piece units , and start vibrating at higher RPM's after being damaged by excessive totque/ force, like towing a boat , or waaay hard drag raceing ....The vibration damages the tailshaft and tranny, and could possibly fail..... There is a rear loop to protect from that.... as long as the vibration isnt present, there is little danger of failure... some will notice it when switching from stock 3.08 gears to 3.55 or above, and then its necessary to fix asap, a metal matrix shaft from dynotech is a pricy , but good solution, and there are also custom carbonfiber ones made in Clearwater, which are top drawer pieces, if you can afford them.... the MK VIII is probably the cheapest route , if you need it...
 

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Discussion Starter #11
Thanks, that helps. I want to replace the DS before something does happen. When I put 3.55 gears in I know the drive shaft max RPM will be exceeded cause now I probably border line it when I get on back roads and cruise about 115MPH. But, what about the half shafts? Won't they do the same thing or the joints get damaged? I know I'll have to replace them if I ever get enough torque w/ slicks stuck to the ground. But what about now at high speeds?

Clay
 

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Half shafts are expensive little buggars, but at 188,000 miles and my torque and hp theyre still hanging in there (at least till I get better hooking rear tires), so based on my own experience, I would say dont worry about them, Except If you find a good set of MK VIII's (built heavier)at a junk yard, for cheap, grab them in case you need them down the road.... In any case theyre short, solid, and torque , not RPM causes failure for the most part
 

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the 93 mark 8 half shaft better than the 96 tbird stock shaft?
the one in the yard i only pick up the driveshaft and lower control arm. 93 mark half shaft better or the sc shaft better?
 

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Not sure about sc half shafts , but the MK half shafts have more meat than stock birds
 

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The HALF SHAFTS from the MARK VIII's, the T-BIRD SUPERCOUPLES, and the V-8 BIRDS AND COUGARS are all the same!!!!!! THe only guys that will benefit from the half shafts from these cars are the 3.8L V-6 guys!!!! The half shafts from the MARK VIII's, V-8 BIRDS AND COUGARS, and SC BIRDS can handle up to (I believe) 500 WRHP.......and they are all THE SAME!!!!!!!!!! THERE IS NO DIFFERRENCE unless you have a V-6..........those have weaker halfshafts. I love it when people post an answer about something.....and don't have all the info on.

THe problem with the MN 12 DRIVESHAFT is the fact that it's a steel shaft as compared to Aluminum. The steel driveshafts are heavier.......thus, it has more rotational mass......that's why the factory speed limiter is set at 105mph to 110 mph (the stock MN 12 driveshaft is only "safe" to 115mph). The MARK VIII driveshafts are all amuminum.......so they are better at higher rotations (higher speeds or high rpms with higher gears {3.55:1, 3.73:1, etc.}). The thing is though........that most of the MAKR VIII driveshafts are 2 piece---meaning there are 2 seperate pieces that are welded/ crimped together. This OBVISOUSLY makes them slightly weaker because there is a "seam"....which could "break". They are still better than the stock MN12 Birds and Cats beacause they are made from aluminum...which has LESS rotating mass...which does make them more stable at higher speeds / rpms---even with higher gear ratios. Howere, the '93 MARK VIII driveshafts are recomended----THEY ARE A ONE PIECE shaft---which means no seam that could possibly break. They are also good for speeds at about 130mph +........and work pretty good with higher gear ratio's...and are definately better than the 2 piece aluminum driveshafts found on all other years of the MARK VIII's (with exception of a few '94's).

The ONLY thing the rear loop does is keep the driveshaft from hitting the ground in the event of a failure / break........and even it is considered weak. ALSO, it doesn't matter how much racing or towing you do.......as long as you don't exceed the maxium rotational speed of the driveshaft.....it will hold. The vibration happens when you exceed it's maxium rotional speed.........due to it's mass......not due to damage from racing or heavy towing. If you damaged it while racing or towing, you'll notice it long before you reach higher rpms / speeds. Normally what will break in that case is the half shafts and U-joints..........but not USUALLY the driveshaft itself. In any event, the vibration will be felt at higher speeds........with NO damage from racing or towing. Once you reach it's maxium rotational speed........the driveshaft will vibrate REGUARDLESS.......NOT because it's damaged. And the higher gears you use......the sooner the vibration will ocurr until you upgrade to an aluminum driveshaft.

ABout the only thing I read that was accurrate is the fact that the vibration.....over time, can damage the tail shaft and tail shaft seal and cause the driveshaft itself to fail---meaning break---- which will more than likely take out the rear end as well.

I hope this helps!!!!!!! I'm not trying to flame or dog anyone.........but accurrate info is best.........just seemed to me like there was alot of guessing going on.

Later

Slowride
 

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Leland Jacobson said:
Not sure about sc half shafts , but the MK half shafts have more meat than stock birds
Which stock Birds / Cats-----V-8's or V-6's???? V-8 Birds / Cats / SC Birds / and MARK VIII's are all the SAME!!! The only ones that are weaker are the Birds and Cats with the 3.8L V-6 motors.
 

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Discussion Starter #17
Okie-dokie... I knew mostly about the vibration from the stock V-8 birds and cats but didn't know about the Mark VIII (93 mainly). Its good that you wrote that for others to read. But, I mainly want to know is what would posibly be my max speed with 3.55 gears?? I know that with my stock shaft and a 3.55 i would probably top out at 97 MPH (DS RPM at about 4800). The haft shaft thing was just a thought of maybe the joints not holding higher RPMs. Although the tires don't spin nearly as fast as the drive shaft.


Thanks for the info

Clay
 
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