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Discussion Starter #1
Hi all
I am building a 74 dodge dart into a bit of a drag car.
Has a 500ci stroker motor on methanol, powerglide and a 9 inch. Car is mini tubbed with the leafspring inboreded and 35 splines axles and 325 tyres.

I am looking at getting a tailshaft made, will the car require a one or two piece tail shaft?

Drive shaft measurements are
Drive shaft:
L 151.5cm (60")(from pinon bolt face to seal)
Carrier 91.8mm
U bolts 42.6mm
27 splines
Engine Is probaly going to make 650-700hp and turn at 7500rpm.

So what do you guys reckon?

Edit: I will add that there are two driveshaft manufacturers in my area, one will only build a two piece saying it a to risky to run a single piece.
The other said single piece will be fine.
 

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60" is quite long for a driveshaft.

The critical speed chart (that I think I saved from mark williams) doesnt even go to 60" but you can see even a 4" aluminum is borderline at 56"

I cant see how a single piece could be fine unless its carbon fibre. You dont want to hit that critical speed (ive done it once). If you dont know what happens, the tailshaft/driveshaft begins to wobble, it starts to resonate along its entire length like a guitar string being plucked... too much of that and it will fail spectacularly.

Thats the downside to glides in long wheelbase cars, im not sure if you have the short tail or the long one, if short then changing to a long end will shorten the distance by 3 1/4"

And you might be able to gain another inch with a longer yoke on the 9" if you have the shorter one.

I see youve written 60" to transmission seal so you need to put a slip yoke in there and measure from uni to uni, so the measurement will be shorter than 60" but youre still pushing it even if it was a 56" shaft.

 

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Discussion Starter #3
Thanks for the replie,

Are the critical RPM the shaft RPM or the engine RPM?

Also they are good ideas on how to reduce the distance. Not sure if my glide is long or short will have to compaire some pictures.

Strange the 2nd company said a single piece will be fine, will habe a further chat with them.

 

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Banksters Paradise
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I know the aussie dollar is shit right now but inquire about a PST carbon fiber shaft. Because a 2 piece driveshaft isn't something you really want in a 500ci methanol big block. Are they planning to run a center bearing? If so, F that. The torque will destroy it in no time.
 

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Thanks for the replie,

Are the critical RPM the shaft RPM or the engine RPM?

Also they are good ideas on how to reduce the distance. Not sure if my glide is long or short will have to compaire some pictures.

Strange the 2nd company said a single piece will be fine, will habe a further chat with them.


When youre in top gear the glide is 1:1 so engine rpm and driveshaft rpm is the same, thats your critical speed.

Ask them what diameter they had in mind and material, Im guessing steel. Youd want it to be 4" and get the length down to 56" at least, at that point the stated critical speed its right at your max rpms and some would argue youd probably be ok.

But a 3.5" diameter would be no good.
 

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Discussion Starter #6
The first company that wanted me to get a 2 piece said I would need to get brackets made to hold the bearing, would also need to reinforce the floor where the brackets would mount.

No joke about the Aussie dollar, hurts ordering anything from the states.
 

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Discussion Starter #7
@lumnan8

This was there quote, so would be no good.

1 pce driveshaft. Powerglide to 9". 1515mm seal to center of uni.
Both options will be 1350 series heavy duty solid cross Dana Spicer universal joints, hand picked, forged weld yokes and 3.5" seamless tube.

Option 1 with forged slip yoke $less
Option 2 with forged fully machined slip yoke $more
 

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@lumnan8

This was there quote, so would be no good.

1 pce driveshaft. Powerglide to 9". 1515mm seal to center of uni.
Both options will be 1350 series heavy duty solid cross Dana Spicer universal joints, hand picked, forged weld yokes and 3.5" seamless tube.

Option 1 with forged slip yoke $less
Option 2 with forged fully machined slip yoke $more
Yeah you are too far over the critical speed with a 3.5" . Some others here might add their 2c about a 4" shaft which is borderline ok if you know the length you need from the center of uni to center of uni joint, and its 56 or less.

Ive got no experience with center bearings for hi performance stuff, I know people do it, some others here might chime in. Personally id prefer a 1 piece wherever possible but I know its not always do-able, especially in longer cars with overdrive transmissions.

You could buy your own slip yoke that you would run, like a sonnax 1350, put it in the trans till it bottoms out, pull it out an inch then measure from where the center of the front uni would be to the rear one, thats the actual shaft length and the length you need to consider regarding critical speed.
 

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Banksters Paradise
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No joke about the Aussie dollar, hurts ordering anything from the states.

You always have the option of selling the glide and put a th400 in it instead. For 700hp, a basic rebuild with full manual valve body th400 with Borg warner clutches and just an aftermarket front clutch hub and 34 element sprag, will work nice. Nothing big dollar required.

But you will need some proper rear suspension setup as the 2.48 1st gear in the th400 will hit a lot harder off the line than the glide will. But you can be just as quick by putting a bit less converter in the th400, than the glide.. and let the lower gear do the work instead of the converter.

There is even a longer extension housing/output shaft available for the th400.. a 9.5" long versus the typical short 4", the long wheelbase cars ran them factory over in the states. I've seen them hold 1k HP so there's no strength issue with the longer output shaft. I have one in my Camaro... the 9.5" extension housing, and it made my driveshaft only 37.5" long LOL. So i got away with using a basic 3" one piece chromoly shaft. Many people don't know about the longer extension housing for the th400, and the benefit of it being able to run a much shorter driveshaft. Or they think it's weird or not strong enough.. which is BS. Maybe over 1200hp i'd start to worry about it and want an aftermarket billet output shaft.
 

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Discussion Starter #10
Sounds like I have a lot think about.
Here I was thinking the drive shaft was going to be the easiest bit.

Bought that box when I was going to pro charge the car years ago. It's not too late to change to another box but it's close too being.

Might just save up for now till I can afford the correct shaft and focus on everything else to get the car running .

Thanks heaps for all the advice and please keep posting info and ideas.
 

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This diagram shows the lengths. You add the tail housing measurement to the case measurement to work out the total length of the trans. For the th400, it's 25" plus either 4" or 9" or 13" for the 3 different tail lengths that are available. The above length that is shows, is for figuring out the trans mount, and is not exactly accurate, because the different length th400 tails also have the trans mount in a bit different place to each other.

 

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I know i didn't mention the cadillac one because i haven't seen it proven to hold 700+ hp. But it probably will.
The length reminds me of the end of a 727, probably not easy to break unless you get close to 4 digit power. Ive got the housing in a box somewhere now but interestingly enough i recall it had 2 bushes in there for the yoke to run in vs the usual one on the other extension housings... they look like normal t400 bushes but two of them spread apart a little.
 
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