[Tim Corcoran]

OK you trans guru's here's my issue. Drove all the way from North Carolina to Norwalk to race (over 600 miles). On first time run I lost 2nd gear. This is a TH-400 with a manual reverse pattern valve body and a trans brake. When I shift into 2nd it's like it's in neutral. 1st, 3rd, reverse all work fine but no 2nd gear. Didn't make any noises or anything just 2nd gear was gone. Linkage is adjusted correct. Any ideas why I have no 2nd gear?

[Half-Inch Stud]

2nd went out for a smote after the trans brake insisted. Dogbone sprag rolled over.


Spring-Roller "sprag" would have held, but might take the Case Lugs out, because the Trans break insists.

[25stevem]

Your sprag is history!

[chuckies76ta]

Ya, agreed. Usually the sprag. Just remember that once the sprag rolls over, it is my understanding to also replace the drum. It is also my understanding that leaving the burn out box and having the tires hit the dry ground and that chirp is not good on the sprag.

[25stevem]

You should never just let off the throttle when your done with the burn out, the tires hook and it’s by by sprag!

[chuckies76ta]

Originally Posted by 25stevem

You should never just let off the throttle when your done with the burn out, the tires hook and it’s by by sprag!

Ok, Just so i understand you correctly, My wife has been doing the burn out in second gear for years. no issues. she does the burn out then releases the brake button and spins a bit more and walks the car out of the burn out box. but does not stay into it. sound ok?
Thanks Steve

[Mr Anonymous]

Just do 3rd gear burnouts.

[Tim Corcoran]

I always start the burnout on 1st gear then shift to 2nd then 3rd hold it for a few seconds in third and let it roll out under power then ease off the throttle. Is there a better way?

[mchell]

If you’re running a manual valve body, stick to 3rd gear burnouts….the sprag issue is one of the reasons I run a manual valve body ….so I can do third gear burnouts

I also noticed I can heat the tires faster because I’m getting instant wheel speed…..60’s also became more consistent

[mchell]

Example of 3rd gear burnout

Got a touch carried away….


https://share.icloud.com/photos/04bL...QVBgNrdjQQ4pIA

[AG]

I start in 2nd and immediately shift to third, let off the line lock and let the throttle go to roll out of burnout.

[Cliff R]

It's the hard "hit" that kills the sprag more than anything else.

Whatever burnout technique yoiu use just avoid a scenario where you are having it "hit" really hard in 2nd gear when cleaning off the tires.

I take a few steps when building the transmission to take some of the shock load out on the 1-2 upshift, which also helps some........

[chuckies76ta]

Originally Posted by Tim Corcoran

I always start the burnout on 1st gear then shift to 2nd then 3rd hold it for a few seconds in third and let it roll out under power then ease off the throttle. Is there a better way?

Tim: My understanding is stay away from the 1st to 2nd shift in the burn out box.

A really good read.

https://www.yellowbullet.com/threads...urnout.120213/

[mchell]

Yep….the 1-2 water box shift is a sprag killer.

I’ve not rolled a sprag since installing my manual valve body.

On the street, I have ZERO use for 1st gear and almost never bother using it. As a matter of fact, second gear is useless unless I want to show off. 3rd gear burnouts with street tires are easy. The manual valve body allows me the choices.

At the track, I will use 1st gear on the launch….no issues with the sprag for years with the 1-2 shift and drag radials with perfect traction.

[Tim Corcoran]

Thanks for the tips on doing the burnout without tearing up the trans, I wish I would have known this before I killed my trans. I have another T-400 that is fairly fresh but the bell housing is broken. Does anyone make a bell housing that has a BOP pattern that can be installed on a TH-400?

[Mr Anonymous]

Originally Posted by Tim Corcoran

Thanks for the tips on doing the burnout without tearing up the trans, I wish I would have known this before I killed my trans. I have another T-400 that is fairly fresh but the bell housing is broken. Does anyone make a bell housing that has a BOP pattern that can be installed on a TH-400?

The Ultra-Bell is BOP and Chevy both. I went to it after mine cracked. I solved the problem, then did the ultra-bell. It is THICKER about everywhere, so you can't run a large diam converter. My engine is also set back 1", and the clearance from the bell to the firewall makes it a precise bitch to get in and out. Next time the drivetrain is out, its Hammer Time. I can touch this.

[Cliff R]

Loosing 2nd gear is not always "rolling over" the sprag. Even so it's gets the blame when these discussions come up. I've been into more TH400's that most who will read this, many had lost 2nd gear.

There are several failure points with the direct drum and intermediate sprag. Inner race, outer race, the sprag itself and the retaining ring. Most failures I've seen have been a result of kicking the OEM type retaining ring off the the drum. It was a poor design and many "builders" would "tac" weld the snap ring to the drum, which was about as effective as cutting off your arm and putting a bandaide on it!

To use the upgraded 34 element sprag you must use a smooth direct drum. Most drums are not the smooth variety, they have to be sourced from an early TH400 or 4L80E transmission. In the early 1970's they switched to a "notched" drum and roller type clutch. It is IMPOSSIBLE to roll the roller clutch over, it simply breaks the rollers or outer race when you exceed it's load capacity, which is actually quite rare I'd add.

So why aren't folks using the roller variety instead of the 34 element upgrade with the smooth drum. It's more about load distribution than anything else. There simply aren't enough rollers with a notched direct drum to evenly displace the load so more likely to explode the outer race or just bust the entire deal into a bunch of small pieces when you "hit" it hard in a racing scenario.

I think what happens in a lot of cases is that folks source out used smooth direct drums and don't closely inspect the components. Many will have "witness" marks on the inner and outer races showing slippage using the stock sprag. Adding a bunch more elements isn't going to fix that issue, a new 4L80E or used drum in much better shape should have been used.

Using a stock type snap ring is a death sentence even if you upgraded to the 34 element sprag. The factory knew this and used a really nice spiral lock ring on the 4L80E units. I wouldn't assemble an early smooth drum/34 element sprag without it.

So basically don't assume that when you loose 2nd gear you "rolled the sprag". The most common failure I've seen are kicking the snap ring off the drum, then the sprag fails. I've also pulled apart quite a few where the races were all torn up and the sprag simply couldn't hold effectively and/or rolled over trying to do it's job.

Even though to potential exists to just flat "roll" the better sprag over I don't see this as a big problem with TH400's. I've put a LOT of them out there in high performance applications and had one failure where the 34 element sprag rolled over. This was on a really fast car that lost traction on the 1-2 upshift, blew the tires off the car then grabbed really hard while still in second gear. With that sort of "shock" load the sprag just couldn't hold it.

I'll also add here that decades ago I knew a very successful transmission "builder" who claimed that the stock roller type clutch was fine for high performance use. In theory he is right, IMPOSSIBLE to roll it over, but they don't like high shocks loads any better than the "dog-bone" variety. What he did was to build the transmission to "soften" the 1-2 upshift in conjunction with using the stock roller type sprag. He would use a waved plate in the intermediate clutch pack and the stock type smooth/waved frictions. He also stayed a tad more conservative with separator plate hole sizing and left the accumulator functional. He claimed a 100 percent success rate doing this. Even though it's difficult to argue with success I still sourced out smooth direct drums, 34 element sprags (USA made), races in perfect shape and used the spiral lock ring. In later years I found it a LOT easier to just purchase brand new 4L80E drums vs tearing older TH400 units down just to find damaged races on the smooth drums and had to keep digging into cores to find good ones.

With the 4L80E drum I also used the molded steel apply piston and outfitted the drum with the stock type high-energy frictions. I put a LOT of those out there and have never had a single problem once no matter what type of burn-out technique the owner was doing........Cliff

[mchell]

One of the 34’s I’ve rolled ….no issues with the ring. Smooth drum.

Note the dogs on the sprag. EVERY one is rolled and frozen in place. The sprag spins freely on the drum in both directions.

[chuckies76ta]

Pic of Spiral locking ring for the direct drum.

[Cliff R]

"Note the dogs on the sprag. EVERY one is rolled and frozen in place. The sprag spins freely on the drum in both directions."

Ouch! The inner race is destroyed, I'll be the outer race isn't much better.......