Howdy!

I broke a stock 7260 727 slip yoke and took out my trans so I am stepping up to forged steel 1350 yokes and solid joints.

My driveshaft is short- around 39” U to U and my rear is a 3.21 gear so I probably won’t have to deal with having to stiffen up a long driveshaft or approaching critical or resonant rpm with it. I just want to make sure that I don’t make the shaft a failure point otherwise there’s no point in the beefed up yokes & U’s. It’s a hot street car application- approx 600tq 450hp and 5500 redline- way over stock but nothing crazy compared to a lot of folks around here! I’m not really looking at aluminum and certainly not CF.

My local driveshaft shop (Pete’s welding in Trenton NJ) says 3” by .083” dom is their go-to for hotrods but they can do 3.5”. I’m thinking the 3.5x.083 would be bulletproof for my setup?

While I am in the race section begging driveline advice- what’s the weak point for me now? I have a solid flexplate, fresh 727, steel yokes, 9.25 with a healthy 3.21 sure grip blueprinted with new upgraded yukon axles. I know the C-clip rear can be dicey but I jave jeep ZJ disc brakes on my 9.25 so if I did lose a c-clip I’d have time to pull over before losing a tire/wheel tub.

Also I am confused about proper street driving with the 727. I understand that breakaway low in D is 1st with no low band apply so the sprag is vulnerable. So if I’m going to do a rolling smokeshow starting with flashing the converter against the brake I should be in manual second? Or is manual 1 ok as long as I shift into 2 quickly and don’t pedal it?

I like cruising in Drive and one of the great joys of a hotrod is not only laying stripes at will with a little extra throttle but knowing how to just chirp off the line without really losing traction. Should I be more careful with breakaway low and only use Drive for relaxed cruising? Then if I end up shifting manually (tf2 kit) whenever I’m alone and playing with mustangs & camaros do I need to be careful with manual 1st or just pay attention to not pedal it and get back in hard hammering the sprag?

I’m probably overthinking it but my rear summer tires are getting shorter pretty quickly and I want to step up to M&H DOT drag radials and maybe try to run a low 12 in this pig before summer is over.

Thanks!

With good U joints and good yokes I would use the 2.5 or maybe the 3.0 .083 DOM tubing for that short rascal

Thanks Cab! I guess the short length plays into it more than I thought?

There is so much info on here about proper water box burnouts- anybody got anything for me on how to keep my 727 together on the street? This is my first hotrod with an automatic transmission and while I’m learning a ton about them from building one then shattering it and building another I would like to keep this one together for a while!

How careful do I need to be while playing with the trans in Drive? Or is that a no-no?

NO neutral drops or J-hooks [fast as you can in reverse, then hook low] - EVER !! []
how those pushbutton 727 transmissions didn't kill us back in the day, i'll never know.
my little brother even tried that with /6, 904 column shift darts. [i replaced many 7 1/2" rears with him doing that. wonder where he learned those tricks ? ]

I've never tried doing a water burnout with a regular full automatic valve body
You might want to apply the front brakes and start the burn out in low gear at very light throttle pressure so the RPM do not get above 3000 rpm before shifting into second or high gear Once it shifts out of low gear shoot for between 5000 RPM and 6500 RPM to get the tire speed up to make heat
I start my burnouts in 2nd gear and shift it into high on all my race 727 trannys with manual valve bodies, I try to keep the rpm below 6500 RPM also but I have seen the tach at or near 7300 RPM before I let up on the throttle to get the RPM down
What do you mean about "playing wit it in high gear" ?

I knew there was a reason Rockford got a new car every season!

My 2500 converter seems to flash to 3000 so there is no reason to drop it in gear from revved up neutral to send violence to the tires. I know that’s not a high stall to this crowd but like I said it’s my first automatic trans hotrod and it ain’t like grandma’s car.

So I shouldn’t be afraid to give it the beans a little from a stop in Drive? As as long as I don’t hammer on and off it in breakaway low? How about using the brake to get the tires spinning then laying 8’ or so of stripes before letting off? OK in Drive too?

Thanks!

I’m wondering the same thing. If your car is capable of spinning the tires anywhere from a stop to a 70mph roll, will it hurt the trans to do a burnout from a 30mph roll with the shifter in the D position?

Thanks Cab

I have a tf2 kit installed which is supposed to allow manual or automatic shifting. So if I want to drag race I can warm up slicks in 2/3 then slap up through the gears from 1 at the green lite with my ratchet shifter. While it’s in manual 1 I think the sprag shares duties with a band so that’s good.

By playing around in D I mean when I am using Drive and letting the transmission shift for me. The kit makes my shifts pretty firm and a decent amount of throttle will make the trans hold my gears to 4500 or a little higher. What makes me nervous is that if I understand it right when you’re in Drive and take off from a stop that’s breakaway low- like 1st but with no low band apply so no engine braking and only the sprag holding the rear drum. So not the same as hammering it in a full manual valve body that has engine braking and will heat up the atf trying to take off from a stop in 3rd with 1:1 gearing.

Matter of fact I think the TF2 kit allows downshifts at any speed but selecting 2 might still cycle through breakaway low as well?

Drag strip procedure has been beat to death here- burn em in 2, etc, but if I want to surprise a mustang at a stoplight and I’m in Drive/auto, give it too much gas & fry tires instead of jumping am I all done or can I pedal it a little to get traction again? Or will that kind of shenanigans hammer my sprag in short order?

I’m not doing neutral drops or any stupid stuff.

Most of the 727 failure occur when the stock front drum goes hog wild on RPM, above 21,000 RPM is the number that is stuck in my head due to a drivel line failure at WOT, probably not that high though
I don't think you will have a problem back pedaling on the throttle in gear as long as you don't let off and then hit it hard to WOT and have the rear tires pinning like crazy while doing that
My old pump gas Duster use to break the 315x60x15 ET Street radials loose at or above 60 MPH by flooring it and make the six pack open quickly I quickly learn to react by letting off the throttle some to restore traction

Traction on the street, while normally not as good as at a track, it will be more inconsistent. In other words, I believe it can spin up and suddenly start hooking when you roll out of the water or hit a different surface. Or it can be a controlled burnout, then hit a slick spot (oil, crosswalk stripe, etc.). Not good either way.

I prefer Spicer solid u-joints. If you have grease fittings in between the caps, make sure they are "in compression" when under load. OEM yokes have been known to spread and eventually spit out a driveshaft.

Just a few things to think about.

FWIW...the driveshaft in my cuda was made by a local truck/driveline shop. It is a 3" diameter shaft and I was told .090" wall tubing. It may very well be the same .083" tubing your shop uses. It's been in my car for several years and has taken a lot of abuse. Close to 3900 lbs running high 8s and using a transbrake.

I dropped off my slip yoke and solid 1350 joints at the driveshaft shop this morning. He said same price for 3” or 3.5” and I have plenty of room for 1/4” per side clearance so I went for the 3.5”. I’m thinking this should be plenty strong- time to find the next weakest link!

I really hope the weakest part of my driveline will always be the tires vs the asphalt. That was my original plan- I’m only running 255/50-17 rears and plan to upgrade to the M&H 28” drag radials. I thought for sure in a pickup even with a heavy wood bed I would always break traction before parts.

So it looks like it just is what it is playing in the street with a tf2/727. Don’t be a jerk or 15 year old in a stolen car and cross your fingers the fun lasts awhile. I will definitely use manual 2 for any planned rolling burnouts that start from a standstill with my foot on the brake- treat the street like a water box. But if I’m in Drive and want to play a little bit I’ll just try to be smart. I can’t really use full throttle until third gear anyway so mashing it is only a recipe for instant smoky fishtails.

I had been leaving it in D, holding the brake, mashing the gas, waiting a second for the street tires to get a little greasy hot then letting off and leaving 8-15 foot stripes all over the place. Not for fun or to show off- I’m a grownup 😉 I do it for the kids!

Where’s the beef?

Small mopar joints to 1350s with billet slip & pinion yokes.

curious me. when your shaft was balanced, how high an RPM was it balanced to ? TIA.

I got it done at Pete’s welding and driveshafts in Trenton NJ. I just called and asked- he said they balance at about 3000 rpm. If my math is right with a 28” tire and 3.21 gear that’s 80 mph in 3rd.

Dunno if that’s good bad or average but I’ve had a few shafts done by them and never a problem. What rpm would you be hoping to hear? Does Mark Williams balance their CF shafts to a higher speed like ludicrous or plaid? I’m just psyched to know it won’t be breaking the shaft, yokes, or universals again soon!

What rear suspension do you have in.. does it control the pinion wind
up?

9.25 rear, 3.21 sure grip. New yokon axles, crush sleeve eliminator, 1350 steel yoke.

Axle is located with saggy 6 leaf a-body (short front segment) xhd springs, ride height set with airbags. Slapper bars control windup. Body separates a little on launch which is what I want- put that weight on it!

was hoping to hear above the typical 500-800 RPM that most truck shaft shops balance to.
you done good, son ! now to find the NEXT weak link.

She’s all back together! I got a little help today and it went way easier with more hands.

what transmission mount are you using ?