Driveshaft Question

[McVic]

Hi! I didn't see a "drivetrain" section so I thought this would be the next best place to post this question.

I have seen over the years of owning my CV the many discussions regarding our driveshafts and final drive ratios. The overwhelming majority say our stock steel driveshafts are too long to handle certain gears above a given speed, and even go into why aluminum and metal matrix have their limitations as well.

While I don't officially disagree with this I have always questioned why this is such a big issue in our modern Panthers when it wasn't for the old hot rodders (like booze runners) who supped up long cars for very fast highway running, or on full sized trucks/SUVs that can tear through the interstates, etc.

I also have never actually heard of or seen a driveshaft fail on a Panther, at the same time remember one guy showing a huge mathematical formula about determining critical speed for your driveshaft on your particular car. The same formula determining the accepted safe/critical speed for our Panther driveshafts was also giving foxbody Mustangs almost the same limits.

I owned a 90 Mustang GT, had it to a continuous 145 mph and never had an issue, nor did I ever hear of driveshaft issues with Mustangs while talking about them and I'm pretty sure there were a lot more faster Mustangs out there than mine (mine was almost stock).

I also have to question if it's so dangerous how are they able to get to max engine RPMs on a dyno run in 3rd gear when the driveshaft should have come loose or damaged something way before that?

Bottom line is I'm wondering is this just some groundless perpetuated fear about our driveshafts, or is it a legit concern?

The reason I ask is I'd love to put 4.10s in my CV, but I can only afford so much investment. The rear end materials, install and tune would be enough. I'm not looking to run over say 80-85 mph as I believe it's dangerous even on American interstates. Most of my driving is general rural/highway and city/town driving anyway.

[fastblackmerc]

There has been a few Marauders that have destroyed their tailshaft housing due to the drive shaft harmonics created with 4.10 gears (making the driveshaft rotate faster than designed causing it to distort). This was only after prolonged speeds of over 100MPH. I have 4.10's and traveling at 80+ with runs up to 120 and have had no problems.

BTW........ the 120 MPH was on the front straight at Charlotte Motor Speedway.

Normal driving with some high spirited passes will not cause any harm.

[Chayton]

Go fast enough and you will blow out your tailshaft seal(first sign of problem) continue driving fast enough and the entire tail shaft itself will poof. I have had the seal pop out on mine before

[RubberCtyRauder]

A mustang driveshaft is considerably shorter than a panther driveshaft. length adds harmonics

[justbob]

A mustang driveshaft is considerably shorter than a panther driveshaft. length adds harmonics

10" IIRC adding to mine.


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[RubberCtyRauder]

10" makes a difference right? wait, what site am i posting on? lol

[Bad_S55]

After my tranny blew up, I had it rebuilt with the longer Marauder/P71 output shaft & housing so I could use the aluminum driveshaft. I read up pretty heavily on critical speed with these cars, and didn't want to chance destroying everything even though I only have 3.55s. I like to go wide open on the freeway, so having a safer shaft was a good idea to me.

If you don't want to change the tailshaft, you could use the steel shaft yoke, a hybrid U-joint, the aluminum shaft, & a Fabtech 5/8 spacer.

[03Merc]

Here's My Tail Housing, I think I saw 128mph with very heavy vibration.


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[RF Overlord]

Bottom line is I'm wondering is this just some groundless perpetuated fear about our driveshafts, or is it a legit concern?

It's a legit concern, under the right conditions.

Since you mentioned a formula, I take it you read the article on Driveline Critical Speed posted by Dennis Reinhart, and written by Jerry Wroblewski. Jerry was a transmission engineer for Ford who was principally responsible for the 4R70W, and knows more about them than anyone alive. If he says it's a potential issue, then it is.

Having said all that, if you aren't into triple-digit speeds for prolonged periods, then you should have no worries with the stock driveshaft, but just pay attention to the tailshaft where the yoke plugs in. If you start to see fluid leaking, you know the bushing is being damaged and you should watch your speed until you get it addressed. You won't necessarily feel any major vibration because the issue is one of harmonic flex, not balance.

[McVic]

These were the EXACT kind of responses I needed. Thanks for all your input guys! The pic of that tailhousing is scary! I needed real world examples which I wasn't getting anywhere else on the net it seems.

Since this mod is possibly way off it's probably best I just flip the extra what $200 for an aluminum driveshaft if I can't source it from a junkyard. Whether it really is needed or not for my personal situation IDK. I would go with that and a spacer not only for ease of install but because I read someone say Jerry wasn't fond of that longer P71 housing.

Yea I believe we are referring to that same formula. I respect it as long as I know it's backed up in the real world, which apparently it is. As I said it seemed he had the same speeds for the Mustang which I find baffling, since it's a much shorter driveshaft as mentioned. I'll just take it for what it says.

No I'm not interested in triple digit speeds. When on the interstate I'm a very careful driver and I follow our local 70 mph speed limit 90% of the time. One of my favorite designs of Fords has been their cruise control buttons on the steering wheel. :-)

I do get up to as high as 85 when having to get past the odd 18 wheeler who can't maintain at least 70 but then seems to gun it when I try to pass, but I don't like going much higher and it's a short burst.

[sailsmen]

12-12-2002, 11:47 AM
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Zack Zack is offline
Turbo Marauder



Join Date: Nov 2002
Location: St. John, IN
Age: 37
Posts: 13,452
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Angry 125+mph in the Marauder
This is my first post, great site by the way. To start off, I want List my Mods so far...
4:10 Gears
Reinhart Chip & Plugs
Flowmaster 2 Chamber Mufflers
Factory Spoiler
35% Tint
Let me say that this is how the car should have left the factory!
Thanks Dennis.
Now onto business...
Im getting on to I-80east last night .............................. .......Thats pretty good for the heavy Marauder. So with the good news off to the side, here is the bad.
At about 125 mph I felt a horrible vibration an attributed it to the driveshaft problem everyone is talking about. So I backed off the gas and had to watch the mustangs flashers pierce my eyes. I hate that ****.
Anyway, the huge smoke cloud soon followed behind the car. By this time im furious but close to home. With no driveability problems, I nursed the car back home a short distance away. When the morning finally arrived after a sleepless night, I ***esed the problem. Are you ready for this? The Output seal on the Tailshaft of the trans came completely out of the trans and was sitting around the driveshaft! Hows that for bad luck. Anyway, talked to my guy at the dealer and he was not at all surprised. He said that 2 years ago, the police cars were recalled for the same problem because ford increased the gear ratio of the rear end from 3:27 to 3:55, but did not upgrade the driveshaft to compensate for the higher rpms it would be turning. Dennis also told me a similar story and said the driveshaft starts to 'boomerang' at such high speeds and can pull the seal right out of the tailshaft, or break the tailshaft. Well, the Marauder is down for a week until My Metal Matrix Driveshaft comes in thanks to Dennis Reinhart. That man has been nothing but good help to me and the Marauder. I hope this doesnt happen to any of you guys out there. Ill keep you guys posted as to how it turns out
Zack
Homewood, Il
http://www.mercurymarauder.net/forum...ght=driveshaft

.................Edited to comply.

[88grandmarq]

It's a legit concern, under the right conditions.

Since you mentioned a formula, I take it you read the article on Driveline Critical Speed posted by Dennis Reinhart, and written by Jerry Wroblewski. Jerry was a transmission engineer for Ford who was principally responsible for the 4R70W, and knows more about them than anyone alive. If he says it's a potential issue, then it is.

Having said all that, if you aren't into triple-digit speeds for prolonged periods, then you should have no worries with the stock driveshaft, but just pay attention to the tailshaft where the yoke plugs in. If you start to see fluid leaking, you know the bushing is being damaged and you should watch your speed until you get it addressed. You won't necessarily feel any major vibration because the issue is one of harmonic flex, not balance.

Yep... Jerry talked about drive shaft critical here;

http://www.tccoa.com/articles/transmission/page17.shtml

basically harmonics cause the drive shaft to bow and eventually rips the drive shaft out of the extension housing.

[daddyusmaximus]

Besides custom, or aluminium driveshafts, is there a tailshaft seal that is stronger than factory?

My car has the stock 3.55 gears in it (as far as I know). It does have smaller tires on the rear, as it came with all four tires 235/50/18 from the PO.

Today I was feeling frisky, and on the way home from the VFW (deserted country road) decided to do a little speed run. For about 2 minutes, I had her at 120 (probably only around 110 with the smaller tires) and backed off because the road just wasn't smooth enough for high speeds. However there did seem to be a bit of a vibration after I let off.

I was thinking about the 4.10s everybody seems to love in the future. I would like to make sure it's safe if I'm never gonna do high speeds for more than a couple minutes every once in a while.

BTW, when the corn is 6 feet high on both sides of a narrow country road, it's like driving in a tunnel...

[justbob]

Steel shafts suck. I blew my custom one clean in half at the 1000' mark at the track. The brand new M3 a few cars back can vouch for me as he made some evasive maneuvers..

Sure my car is not stock, but the driveline angle is less than 1/2 a degree from stock and the shaft is damn near the same length.

The same design the local idiot driveline shop sold me on is used in competition rock crawling. Steel telescoping design. Strong right? But as mentioned, add harmonics at only 92 MPH or so and WOT at then only 456hp and BOOM.

The Driveshaft Shop hooked me up with an extended constant velocity style GT500 upgrade and never again even a hint of vibration or harmonics! I've only been up to around 120 so far and buried at 140 on the dyno, but I rarely ever hit triples anymore.

By ditching the steel and going back to Aluminum I gave the shaft its flex back. If it's too rigid your going to break things. Fast.


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[Chi Stallion]

Just be careful dealing with dynotech they will send you a half ass driveshaft that won't even fit and you'll be charged 650 dollars with no refund or return.