Maybe you’ve been following all my posts on here while I got my 512 going and built a 54 pickup around it, including hitting the learning curve hard becoming a 727 builder. I put about 100 miles on the truck so far and I’ve been having a blast!

This morning I put it on my buddy’s dyno and found a bunch of torque down low- a nice flat torque curve almost all over 500 lbs in the operating range I use on the street.

Well my front driveshaft yoke didn’t like all that torque very much! About three blocks from home I experienced a sensation that is unfortunately familiar- I got to use my driveshaft loop. Boo! A helpful neighbor driving by in his pickup truck pulled me home and since I found a universal bearing cap on the ground I was crossing my fingers it was just a U-joint.

I had a pretty bad feeling that wasn’t the whole story because I left a small trail of ATF with a little puddle at the end. The truck is too low to see under without jacking it up so before doing that I walked back over with some kitty litter to see what other prts I could find.

First I picked up some chunks of front yoke. Feeling hopeful? Then some chunks of cast aluminum with threaded areas. Maybe the un-used mounting section near the rear of the tailshaft?

Nope. The universal must have wedged crooked while broken and under power. It ripped the tailshaft off the case, pulling threads here and chunks of trans case there. The busted yoke is stuck hard in there too I bet there’s bent stuff inside. She’s fragged!

So now it’s time to put some sta-bil in the tank and start looking for a new big block 727 core. Good thing I have a bunch of 727 building experience now! I only have 100 miles on fresh clutches and steels and my worked valvebody & deep pan will swap to a new core so this should be more labor than $$ but it still hurts.

Along with building another fresh 727 I plan to get a new driveshaft made and I want to upgrade my 9.25 axle yoke and 727 yoke to the strongest units I can afford without going overboard- it’s only a street hotrod on summer tires not a topfuel car.

What parts do I want to go with and who makes/sells them? Feel free to PM me if you are my guy and any info is appreciated.

Radar

I would go with a billet yoke and upgrade to 1350 u joints if possible. I have no idea who to reach out to about a pinion yoke. Probably start with Dr. Diff.

My bet is you broke the joint and that broke the yoke? and then the tail shaft. Been down that trail myself. Worse case scenario. New tail shaft housing and possibly a tail shaft. I have a shaft here from a buddy's 66 Coronet. Broke the joint driving down the freeway. The shaft is bent at a 30 degree angle. Replaced the shaft and tail housing (along with welding up the floor pan and gluing the console back together). No other trans parts were replaced. been probably 10 years since, still fine.
Doug

I also run a 512 and they are a beast. We have been getting all our stuff from A&A and my Engine builder is the one who puts them together. . ....They are very helpful in getting the right parts for your build.....CRT is a trans guy on here as well and can supply you with the right parts I am sure as well. How did you learn to do your own?

Honestly half the fun of this hobby is trying to figure out how to do stuff I didn’t think I could do. I had a mentor teach me how to wrench on harleys- shade tree engine building at its finest. He was a professional diesel mechanic and always had the fastest harley around but wouldn’t admit that it was more than stock with a little cam in it. He taught me not to be afraid of tearing into stuff and trying things. All my mopar and v8 experience is from my wrenching buddy who’s a chevy guy and from asking questions here and slantsix forum when I had my first project car.

I also bought a 727 rebuilding book and there is an excellent step by step on youtube too on the 727. The clutches in a 727 are very similar to those in a harley shovelhead and evo respectively except with springs to disengage and hydraulic apply circuits where the harleys have spring pressure to apply and mechanical disengagements. The rest of the parts are actually pretty simple and I learned from doing it the wrong way then having to go back in and fix my mistakes.


Thank goodness I fumbled through the rebuild on this broken trans myself- I have $100 in a core and a few hundred in parts etc. the seal and bushing kit is cheap and the rest of the parts should swap as long as I can salvage a good amount of guts out of this one. Obviously not the sprag and probably not any shafts but I will have my pick of some parts that made it depending on what core I find and its condition.

The biggest thing for trans rebuilding was getting my shop super clean and laying out fresh newspaper so I could stack everything in the order it came out. The mistakes I made were first a bonehead one- the extension for my deep sump was on backward so my pump couldn’t suck any ATF, then I had broken a sealing ring on the oil pump reaction shaft on installation. The oil pump goes in last and it’s a tight fit with an o-ring seal and in my inexperience I couldn’t feel that I was snapping a ring that was hanging out of its groove as I sucked the pump home with its bolts. The sealing rings hold in pressure to apply the front clutch so I had no 3rd gear and reverse was auickly burning clutches trying to apply with a bad leak.

You should try doing one- $200 beats the heck out of paying somebody $1000 and there’s no magic in there just a lot of parts that meed to work together like in a motor.

Anyway, I’ll look into the billet trans yoke and I already have the bigger size yoke for the axle but when I did a shim kit/ crush sleeve eliminator while setting up my rear I just put the smaller size yoke on. I need to upgrade that too and maybe a billet one if available since it looks like my front universal didn’t break it looks like I shattered the front yoke, threw caps, and cranked off the tailshaft with sideways prying force. Oh man the ride home at 3mph with the driveshaft slapping around the loop under there was a terrible sound.

My build might be a bit different than yours.....I did two of what we call a "super trans" and the parts alone were +$1300....I have yet to break one...

I wish that was the deal. When the tailshaft went it didn’t just crack it pulled threads out of the main case in spots and chunks of case with 1/2 of the threaded holes in others. Honestly I can’t believe it didn’t break more stuff or leave all my ATF on the ground. I had just picked my 7 year old daughter up from school so I drove home real easy but she always asks to hear me bark the tires when we get back into our neighborhood so I stopped and gave the throttle a little stab- bang! Clang clang rattle rattle. My driveshaft loop is tied into the floor frame of the truck cab and all made from 1” .120”wall square tube- dumb strong so we were totally safe. She was really freaked out so I was really over doing the no big deal act- “we’re safe, close to home, I can push it into a parking spot and we can just walk home, I built it all myself once I’ll just do it again, it’s just a thing not a person, breaking stuff is just a normal part of the fun of hotrodding”

She bought the act but then kept asking why I was kept sighing after I got under to inspect it. I’m actually looking forward to building another 727- it’ll give me a chance to try a different ratio lever and get more comfortable doing it. I don’t mind short road trips to find parts and drag them home. I don’t much enjoy dropping or installing transmissions though that sucks and buying whizbang billet driveline parts is fun but I’d rather keep the $$ in my pocket...

Well I technically didn’t break the trans I broke the universal and slip yoke and they broke the trans! I tried to do a street build that would use the big inches to have more fun at lower rpms so I wouldn’t need a lot of fancy valvetrain parts or billet clutch drums & bolt in sprags. Plus the weak link was supposed to be the street tires not my driveline parts.

I’m guessing we started cracking parts on the dyno this morning- the rolling road always makes me nervous it can be real hard on equipment. It was worthwhile but even if my problems didn’t start there my torque curve saw MASSIVE improvement down low so my 2400 stall probably never saw that much torque before this last time I flashed it. My buddy with the dyno was rolling into the stall before WOT this might have been the first time I shocked the driveline with all the power we found at flash stall.

I busted one side of my old OEM stock 7290 U joint tranny yoke off in my Duster years ago, luckily it didn't break any thing else in the tranny or drivetrain
Same thing on a used 8 3/4 rear pinion 7260 yoke, I spread it apart far enough to allow a new U joint cup to slide out
Build it stout to start with just like it is a race truck now, especially if you don't want to do it again

Better change the sprag, or you are asking for trouble.

At least check it to se if it is hurt or not
I have all my race 727 built with bolt in spraques and solid steel or aluminum drums
I have one of the older Pro Trans 426 hemi S.S. tranny from back in the early to mid 1990s when they where still using the 727 parts in the stock type cases, I rolled the rear spraque in it when it broke a ring and pinion in my Duster with that tranny in the car

Some times that happens on chassis dyno’s. Not sure why, change of driveline angles because its strapped down or some thing else. I know of a max wedge car that had it happen. Check the sprag.

Just had a shaft made and upgraded to 1350 joints at the same time. Got the axle yoke from Dr. Diff with the rest of the parts to build the axle and the drive shaft shop provided the slip yoke. Drive shaft with joints and the yoke ran me $350.

I upgraded my driveshaft and yokes to 1350 size all from Mark Williams
https://www.markwilliams.com/driveshafts.html

I called board sponsor A&A trans and ordered a billet steel 1350 pinion yoke and trans slip yoke along with solid 1350 universal joints.

Check the sprag- hilarious! Not only did I not over rev but the back edge of the transmission case is shattered. I might re-use the rollers and elements but its all spare parts now.

After re-reading the posts above I started thinking about should I beef up the next trans more than it is.

If I add 20% to my rear wheel numbers from the mustang chassis dyno I get 435hp 632tq estimated flywheel power hitting my converter. I have my limiter at 5500 but on the street I shift at 4500 and don’t miss the extra 20hp I would get revving another thousand rpm.

I am thinking a healthy stock 727 can handle that no problem? I have the shifts firmed up some but not harsh with a tf2 kit and good clutches and bands- no trans brake, nitrous, slicks. 3200ish lbs on 255 series summer tires. I would have not been too surprised if I broke a small universal but a stock slip yoke shattering with street traction was a surprise. As far as I know (no internal autopsy on the bench yet) the yoke broke and the shaft took out the trans wedging and rattling around my super strong front driveshaft loop. My 727 seemed fine sending my little street 512 power to the axle.

I’m going to inspect the sprag in whatever core I use and replace with a nice bolt in if I have to but I really wasn’t trying to upgrade the clutch drums with lightweight or billet steel for a street build. I’m thinking my power level is similar to a nice diesel truck motor but not in a 6000 lb pickup- only just over 1/2 that weight and didn’t early cummins get 727s with just some extra clutches, maybe 4 gear late stronger spline & angle planets?

Am I being foolish? 727 internals get expensive real fast. I can get two cores to inspect and pick parts from for the cost of one steel drum...

The bolt in sprag is worth nothing. The A&A/CRT/TCI is better but cost $200. Spend the money on the drum and run the stock sprag.
Doug

One toe is worth at least $200.00, correct
You know you'll never try to make less power and go slower now, correct?