[grivera]

Originally Posted by 78w72

i have kind of the opposite of you, my PTFB connectors are welded at the rear frame rail & bolted to the front subframe, i did this in case i ever need to remove the front subframe. i will let others comment on the power level they are good to, but IMO subframe connectors arent really rated for power, they strengthen the car/frame no matter the power level... but at some point racers do weld them at the front & rear.

it comes down to how much of a race car you intend this to be, sounds like its mostly a street car & i dont think youd see any real benefit welding them at the rear too. plus it will be a hassle to ever remove the subframe for you or the next owner. with drag radials & limited track time its probably not worth it, they are doing their job as is but again all depends on how much you plan to race the car.

Thanks - I prefer to have them bolt in but want to make sure they provide adequate protection from twisting.

[HWYSTR455]

IMO, 50 year old driveshafts are worthless, and I would never put anything with even OE power levels of the day in front of them. They were borderline when new.

If you're getting a new shaft made, upgrade to 1350s, period. What's the saying about the weakest link again? Yeah.

If the slip yoke is OE or old/unknown origin, it should be replaced regardless of power level.

Same on diff, if pinion yoke is OE, or of unknown origin, replace.

The new yoke MIGHT be slightly different than the one coming out, so, you MIGHT have to crush the sleeve slightly more. You can replace the pinion yoke and not have to setup the gears again if you are careful, and know what you're doing. Crushing a sleeve that's already been crushed is not easy, and it may weaken it, but you really don't know if you will have to until you try and check preload.

If the rear has a lot of miles on it, take the dive. If it goes away faster than it would have if you left it alone, it won't be by much of a margin.

.

[78w72]

worthless? borderline when new?? i dont know about all that... for OE power, OE driveshafts in good shape are perfectly fine.

i think the track record of my OE shaft i posted above speaks for itself. & back in the day 99% of these cars used a stock shaft on mild built engines with a lot more power than stock & rarely ever broke. i had lots of friends back in the 80s & 90's with non stock cars of all makes that used stock shafts & nobody ever broke a yoke or shaft on the street or light duty racing with radials.

im sure there are some that had issues but its rare at best & calling a early to mid 70's TH400 OE yoke/shaft "borderline" for stock'ish cars making all of 200-350hp is a stretch.

i fully agree that the higher HP cars are making today should have a better shaft/yoke, but for a street car on hard street radial tires, the tires will break free before enough stress is created to break a shaft/yoke in good condition 99+% of the time.

[Schurkey]

Originally Posted by 78w72

i fully agree that the higher HP cars are making today should have a better shaft/yoke, but for a street car on hard street radial tires, the tires will break free before enough stress is created to break a shaft/yoke in good condition 99+% of the time.

Friend of mine had a '68 Chrysler Newport as his "high-school" car. 383 2bbl. The car would have been ten years old or newer. The thing had enormous torque--power-braking would scare people in the next lane over, it was like the car was going to lift up one side and tip over.

Wound the driveshaft up like a pretzel leaving a stop sign. Car coasted to a stop on the other side of the intersection. I won't promise the car had radials. Might have been mostly-worn-out stock-size bias ply tires on stock wheels..

Quick trip to one of the local Treasure Yards netted him a bigger-diameter shaft from a full-size Chrysler with a 440 as original equipment. Fit like it was meant to.

[JUDGE3]

Had my stock steel driveshaft changed to 1350's and a forged sonnax yoke.

$325 driveshaft/$120 yoke money well spent.

I have a moser 12 bolt with the 1350 yoke as well.

I used the global west weld to the rear subframe, bolt to the front.

don't look under your car and have to ask, where's the beef!

[grivera]

Always amazed at the varied opinions on this forum…One thing of note is I’ve owned the car 27 years and the original 400 was tired when I acquired it so not sure what level of abuse the factory driveshaft endured…

[78w72]

Originally Posted by Schurkey

Friend of mine had a '68 Chrysler Newport as his "high-school" car. 383 2bbl. The car would have been ten years old or newer. The thing had enormous torque--power-braking would scare people in the next lane over, it was like the car was going to lift up one side and tip over.

Wound the driveshaft up like a pretzel leaving a stop sign. Car coasted to a stop on the other side of the intersection. I won't promise the car had radials. Might have been mostly-worn-out stock-size bias ply tires on stock wheels..

Quick trip to one of the local Treasure Yards netted him a bigger-diameter shaft from a full-size Chrysler with a 440 as original equipment. Fit like it was meant to.

great story, i had friends in HS with cars & stories like that or their parents cars they borrowed & beat the crap out of.

i dont doubt driveshafts, yokes or u-joints can & do break. strange that mopar 2 barrel would do that but im not familiar with how theirs were made or if the 2 barrel versions were weaker than the bigger engine stuff... or the history, coulda been exposed to major shock or misalignment or whatever to twist the actual shaft like that.

just saying its not at all normal for that to happen in a street car, aside from some very uncommon stories like that where it happened to someone you know or maybe even yourself 1 time back 20-50 years ago on an unknown condition part. depending on the car & its purpose, a good condition OE d/s should be fine with some good solid u-joints.

[AG]

If you put any sticky tire on the car I would just get a new driveshaft with 1350 joints, a forged input and replace the yoke on the rear to a forged and never be concerned about breakage. Go on youtube and watch what happens when a driveshaft breaks going over 100 mph. It's one place you don't want to scrimp on.

[HWYSTR455]

If you choose to have a shaft made, the majority of the cost is labor and ends, it makes sense to just have a whole new shaft made. With u-joints, ends, and a slip yoke, expect to pay in the $350-$500 range.

After spending $15k-$25k on an engine/trans/rear, a simple $500 is a drop in the bucket for the piece of mind.

If you can't find a place local, Inland Empire, Dutchman, Denny's, Driveshaft Shop, all have very fast turn-arounds.

.

[FrankieT/A]

If you're going to 1350 U joints why would you not step up to a 3 1/2 tube? Rhetorical question...

It seems to me going to 1350's, a 3" tube is now the new weak spot. JMO

[JUDGE3]

statement and a question both beings I stayed stock diameter.

could/is tunnel clearance an issue increasing diameter?

on a street car with stock rear suspension, big bumps rear/yoke movement could it cause the shaft to bump? especially with a 4" tube?

with a driveshaft safety loop, even less clearance going bigger. talking stock suspension here. race cars are set up stiff with no movement like i refer to.

[Bill Eveland]

I've went 1.36 60 ft and 9.97 on a 3 " 1350 u joint Strange chrome moly shaft , i really don't see the need for a 3 1/2" shaft? Unless its not chrome moly? Thats with a transbrake also, i think for a street car wouldnt have any issues at all.

[HWYSTR455]

Not sure about 4", but know 3.5 is no problem, and would imagine 4 would also have clearance.

There are many factors for driveshaft design, too much to go into here. You can brush up on it by hitting vendor's website, most have good tech articles on it.

Here's a very basic one from MotorTrend:

https://www.motortrend.com/how-to/cc...alancing-tips/

Stated there, factory driveshafts are only balanced to 3000-3500 RPM. "They are rated for no more than 350ftlbs or 350-400hp".

Same article on 1310/1330 joints: " The smaller size basically becomes a fuse, and it will eventually fail."

That's pretty much for optimum setups, if your driveline angles are off, it happens sooner.

Then there's critical speed, the point the shaft turns to spaghetti. Smaller diameter tube, longer the driveshaft, heavier the driveshaft is, and heavier the car, start subtracting.

What's the saying around here? "You can fall off a log and make 500ftlbs/500hp."

Can't believe how many overlook such an important part of the driveline. $350-$500 is just not worth the risk, period.

.

[Formulajones]

I'm running a 4" aluminum on mine and there is plenty of clearance everywhere.
Just a stock suspension street car and fun track days once in a while.

[ta man]

Originally Posted by Bill Eveland

I've went 1.36 60 ft and 9.97 on a 3 " 1350 u joint Strange chrome moly shaft , i really don't see the need for a 3 1/2" shaft? Unless its not chrome moly? Thats with a transbrake also, i think for a street car wouldnt have any issues at all.

Pretty sure the 3 inch Chrome Moly is good for 1200hp maybe 1500hp.
What one has to watch out for is not to go over the rpm rating for the driveshaft.

[JUDGE3]

glad I beefed up. this is unreal.

https://www.youtube.com/watch?v=Lw4VUgDxa5Q

[AG]

Originally Posted by Bill Eveland

I've went 1.36 60 ft and 9.97 on a 3 " 1350 u joint Strange chrome moly shaft , i really don't see the need for a 3 1/2" shaft? Unless its not chrome moly? Thats with a transbrake also, i think for a street car wouldnt have any issues at all.

I have a Strange Engineering CM DS with CM input and rear yokes. It is 3" and it is good to 7800 rpm and I shift at 6500 rpm. It is approximately 49" long. You have to spec a DS according to your max rpm and material of construction.

[grivera]

So today I learned my front u- joint is 1310 and the rear is 3R. I ordered a forged 1350 slip yoke and a local driveline shop will build a 3” DS with a rear 1350/3R conversion joint.

[78w72]

a cromo 3" 'shaft with 1350 forged yokes is not anywhere near $350 or even $400-500 from what i have seen, cheapest i found is strange at $600+ shipped, other places like dennys & even local were as much or more. this is for a 3" cromo shaft with th400 forged 1350 ends for a 2nd gen firebird, maybe much shorter ones are a little cheaper but not seeing anything close to $350... got a link to a company that makes a fully forged 1350 shaft & yoke for $350 or even $450 HWYSTR?

pretty sure factory shafts & yokes vary in strength based on the engine & vehicle, i doubt a late 70's or early 80s firebird with a 301 or 305 making all of 150 hp uses the same rated shaft as a early to mid 70's 400/455 or other makes with 454s & 460s etc etc. saying ALL stock driveshafts are rated for no more 350 ft lbs cant be true, when a stock early 70's 455 had 450+ or close to 500lb/ft. GM or any company would never put a 350lb/ft rated shaft behind a 455 or other big torque engines.

i fully agree a beefier shaft & yoke is best for cars making bigger power or that are raced, im not suggesting anyone at that power level or purpose use a stock shaft, although countless people have for decades with very low failure rates. heck it took ta man getting into the 10's & probably decades of serious abuse to break his stock one at the yoke & mine is doing ok after just as much abuse behind numerous torquey engines & now knockin on 10's door... but i realize thats pushing it even with the new 3" .083 shaft & solid u-joints but stock yoke i have, i will be buying a strange forged 1350 asap at my current power level & i should have done that right off the bat but that doesnt always happen when youre doing a full resto & engine build, you tend to cut corners on some things.

i still feel a cromo forged 1350 is not needed for the average guy on the street with a mild (at or below 400lb/ft or 350-400hp), they do make other options like nodular iron yokes that are much stronger than stock cast iron, pair that with a .083 3" non cromo shaft & solid u-joints & it will live behind a mild 400 or 455 on the street at half the price of fully forged. just mentioning some options when youre not a racer making 500+hp & 600lb/ft of torque.

https://www.strangeengineering.net/p...range-hd.html/

[Schurkey]

Originally Posted by grivera

So today I learned my front u- joint is 1310 and the rear is 3R. I ordered a forged 1350 slip yoke and a local driveline shop will build a 3” DS with a rear 1350/3R conversion joint.

Using that conversion joint as a "fuse"?