I have a 1971 Challenger that has a 505 inch striker build and a relatively stock 727. Has a forward manual valve body and a deep pan on it. My question is will the stock trans hold up to the torq and added hp of the motor. Been having slot of problems with the trans lately and it's driving me crazy.

My "spare" 727 for my old Mirada running a RB 498 was nothing special. Reverse manual valve body. Foot braked it into the 10's. I had enough parts to throw it together as a backup plan. Ended up selling it after getting rid of the car. So I'm saying "yes" it's capable.

now... would I run it with a stock front drum. NOPE!

Are 727's "bulletproof"? NOPE! I currently have a 727 in the duster behind our small block. it's been out of the car 4 times in the last two years with odd and not so odd breakage. Most recent I broke the lugs on the pump gear. Hoping it will last now with aftermarket large lug gear, but I'm piecing together a 904 because I like torture

Run far away from 1st gear burnouts. What are the problems you have been having?

Mine seems like it's slipping even though I have a manual valve body. Thought it wS low on fluid. Added more now it's to much, still "slipping" and a steady stream of fluid following the car. It slips on a take off.

When it does take off, it slams into gear

guess not being able to experience it first hand I'd wonder what the fluid looks/smells like. Next I'd probably drop the pan and see if it tells me a story. Drop valve body and air check would be the last thing before I pulled the unit out for an inspection.

The trans was rebuilt, probably less then 100 miles on it. Fluid is also new. What happens is say your at a stop light. Turns green. Hit the gas motor Rome go up and then it just slams into gear like it's low on fluid.

Any foreign material in the filter?

None. I just dropped it so I can find someone that can look at it and beef it up. Anyone know someone in metro Detroit area?

It sounds like it, the shifter or valve body selector, is not in each gear properly
Take the pan back off and put the shifter in neutral and then remove the shifter selector from the arm on the valve body and watch the manual valve to see if it moves when you lift the shifter cable clevis or shifter bracket off the selector arm, if it moves you need to adjust the shift linkage so it doesn't move when removed in neutral, first, second and high gear
Let us know what you find out How good is your converter? What brand and foot and flash stall rating RPM?
Good look on this

I would check the line pressure first.

Rear clutch problem....delayed engagement due to leakage. (rings/seals)

I use a relatively stock one behind my 505.

I rebuilt it using better clutches, removed the governor, used a FWD pattern mvb and put the amount of springs in the front drum that Turbo action recommended. Other than that, it is pretty much stock.

It gets regular beatings on the track and street but I never do a 1st gear burnout, either!

Make sure you use a bronze thrust washer as most kits come with the fiber one and mine likes to eat those!

I also have a Turbo Action converter and used the thrust washer that came with it. I don't think my rebuilder put better clutches or anything like that.

I am not running a big motor like you have but I have been running a pretty much stock 727 with a manual valve body behind my small block that makes well over 600 hp. I have been running it for 5 years with no issues.

^ This.

I ran a pretty much stock 727 for about 2 years in my cuda running mid 9s at 3800 lbs. It had a manual valve body, deep pan, and a bolt in sprag...that's it. Then the drum exploded and disintegrated the transmission.

My 727 is also very stock. I run a Turbo Action reverse manual valve body and a Dynamic 9.5 converter. I also installed a bolt in sprag (rear overrunning clutch) and eliminated the gov and blocked the accumulator. I use stock Mopar clutches and steels since I have a small supply of them I saved up over 24 years at the Dodge dealer doing auto trans repairs. I even use the stock Mopar seal kit which I also had. I dont race alot as I usually go to the track once or twice a year but I do alot of street driving. Mine has been in my 63 since 2006 and has never had a problem and is still working fine. Ron

Your builder messed up when he built the
trans.. as John said the issue will most
likely be a ring or a seal is bad.. a
pressure test should show it.. I run a
totally stock tran in my race car with a
trans brake.. been in there about 10 years
with 2 refreshens .. a light car is easy
on parts

What does removing the governor do? (I am tranny stupid )

No need for a governor if the trans has no method to shift automatically with a manual valve body.

It does nothing. Just another part to remove to eliminate the chance of having any issues and a tiny bit of weight loss.

I also run a 505ci in a 70 Challenger with a 3:55 gear. Here is my 727 modifications:

Stock front drum with 5 thin Alto Red clutches and Colene steels
Modified rear drum with roller bearing 4 Alto Red and Colene steels
Billet rear support with roller bearing
A&A super sprague
Billet front and rear servos
Billet band struts
Turbo Action manual valve body forward pattern LBA
Aluminum deep pan
PTC 9.5" converter 3000 stall

No problems in 11 years and I built the trans myself with the help of the late Carl Monroe's book

Call Bobby at Reliable Transmissions in Waterford, on Dixie Hwy.
248-623-2230 ...He is a race car builder, and knows his transmissions.

You have a rebuilder and you are asking on this forum what is wrong with your trans?

You need a new rebuilder. He's the one that should be diagnosing your problem.
And fixing it. It's not your shifter.

Now why would I go back for the third time? How many times do you get kicked by a mule before you realize it hurts? I'm not taking this trans out again so I took it somewhere else. Yea, the original guy has a warranty but what good is it if I have to keep taking it out?

I can relate VERY much to what you say,That stuff set me back 2 yrs in my goals.

ok- if you aren't going back to him again - then you are on the right track. If you want it fixed correctly the First time PM me and I can get you fixed if you want.
Sorry - just saw you took it somewhere else.