Yellow Bullet Forums banner

1 - 20 of 35 Posts

·
Registered
Joined
·
186 Posts
Discussion Starter #1
So as the title says.. I've rolled 2 sprags now on a relatively mild non exotic setup. Its a 1968 Core TH400 with a Jake's performance rebuild kit using borg warner clutches and a 4L80E stack in the intermediate. I have a Hughes forward pattern manual valve body and use Dex 6 fluid. The car is a 74 corvette 5.3 LS engine with a cam, headers, head work, and little nitrous. The first time it happen i raced it a bit beat on it on the street and one day it let go. Then i replaced it with a TCI sprag and changed the bands at the same time and inspected everything and it all checked out good. The second time street driving i got the car rolling in 1st punched it ran it to 6800-7000 rpm slammed 2nd gear and bam it revved to the moon just like the 1st time sure enough sprag rolled. I haven't been able to find any credible measurements of what the inner and out race should measure out at i am curious if when the sprag flipped the first time it shaved a small amount off and now its too loose allowing it to roll easier? just a theory... I have another core here i am going to pull the drum out of its from a 67 truck that had 41K original miles so i figure it has been piss pounded its whole life and maybe the drum and a new 34 element sprag will do the trick. Its no fun not being able to do WOT 1-2-3 shifts. Any help or direction is much appreciated. Thanks in advance
 

·
Registered
Joined
·
81 Posts
Inner sprag race should measure 3.1590 if it is less then that I would source out a new direct drum. Last one I purchased it was around 90 bucks new from GM. If you flipped the sprag I would also discard outer race and replace also. Just my 2 cents .
 

·
Super Moderator
Joined
·
19,584 Posts
Shift shock creates a torque spike that can't be tolerated by any sprag. Im guessing you may have a 400HP motor by description so having 4 flat plates and line pressure above 170 psi is just destroying parts faster than you can feed them to the trans. If a sprag flips , the drum is garbage as well the outer race is most likely distorted.

3.159 OD is minimum numbers in a performance build.


Hutch
 

·
Registered
Joined
·
186 Posts
Discussion Starter #7
I appreciate the Info and responses. Hutch, with that being said where does a guy go from here? I feel I've put all decent parts in it for the power it's making. I would just like to be able to enjoy the car and if I feel like holding it to the floor or a weekend muscle car race I dont want to yank the transmission out. It's just so suprising to me that my uncles 70 monte with a BBC and bone stock 400 holds up and this one isn't. And I'd say he is harder on it and puts more miles on a year then I do. I just would like to fix it right and enjoy the car again.. it's got me thinking about throwing a super t10 back in the car...
 

·
Registered
Joined
·
186 Posts
Discussion Starter #9
Will that Coan drum be a long term fix? I am assuming with using 4 flat plates and the valve body and Sonex pump mod that is why it keeps hurting the sprag along with assuming my drum and outer race were damaged after the first time it rolled I'm guessing it allowed it to roll even easier. But ultimately I want it fixed as in doesnt break every time I drive it hard.
 

·
Registered
Joined
·
186 Posts
Discussion Starter #12
Any preference and or part numbers on a "good drum" and sprag? I've used TCI, and Borg Warner 34 element sprays and they looked identical. Also do you think I should put a wave steel back in and try a mix of thin thick steels to get pack clearance right with the 3 wave friction stack? Thanks for all the information everyone.
 

·
Registered
Joined
·
186 Posts
Discussion Starter #13
Hipster the car has 3.55 rear gears 275/60/15 tires. And I am using a Jegs brand 10" "nitrous" convertor.
 

·
Premium Member
Joined
·
16,583 Posts
Those specs obviously result in a damaging shock load @ the shift. One of the down sides of dual purpose cars that many seem to have these days make it a little harder to keep drive line parts alive due to the cheap and easy horse power available. Heavy street legal cars, road friendly rear axle ratios, relatively tight converters, boosted/hosed engines = recipe for disaster.
Try to get what I'm on about with this old example. Had a pal w/68 Camaro, 12.0 car, 14x32, slide a 1.82 glide in the hole, foot braking mind you, broke the planets twice in three weeks. What in theee fuck. Then it hit me, dude was running a fkn 4.10 gear. My car was mid 10's, same weight, 15x33's 5.12 rear axle, same junk 6cyl 1.82 planets foot braking, never broke them. Only difference was the rear axle ratio, learned me something.
 

·
Registered
Joined
·
24,643 Posts
Those specs obviously result in a damaging shock load @ the shift. One of the down sides of dual purpose cars that many seem to have these days make it a little harder to keep drive line parts alive due to the cheap and easy horse power available. Heavy street legal cars, road friendly rear axle ratios, relatively tight converters, boosted/hosed engines = recipe for disaster.
.
Sounds like me .....lol


Went with this :

http://www.coanracing.com/coa-22817-super-drum-ii-kit-steel.html
 

·
Registered
Joined
·
186 Posts
Discussion Starter #18
Lol it just sucks the thing makes good street power but nothing crazy. It sucks something as "strong as the coveted th400" is getting its ass kicked by a little 5.3 and some nitrous. (Granted when I'm being mean to it I'm being mean haha) I'll throw a drum and 34 element in it again with a 3 clutch stack and maybe put some wave plates back in the transmission and try to not have it matted at the 1-2 shift and not spray till in 2nd gear. Over winter it's getting a T10 for the nostalgia and extreme fun the car was 4 speed.
 

·
Registered
Joined
·
186 Posts
Discussion Starter #20
Haha I know right. The car is a riot when it's working and with the ms3pro I have driveline speed sensors so I can manage wheelspin and it just hooks and books with the 275 DR on back
 
1 - 20 of 35 Posts
Top