[455rebel]

Haven't benn on here in a while! Benn collecting parts, and finalizing my retirement. Have all parts to rebuild my 455. I'm guessing bout 400hp, 500+tq. Have the stock turbo 400 with a shift kit, and a governor kit set to shift @ 5K. Have 3:15 posi gears. Tranny still all else stock, as it came out of the 60K mile Bonnie. Time to freshen it up when I do the engine. It's benn great with No problems or slippage. Any recommended mods for a mild 455? Already shifts firm, barks second on demand. Is a raybestos std kit ok to use. Living on retirement so budget is important, but I don't want to cut any important corners! I'll probably use a mild converter in the 2.5K range. Thanks and all opinions welcome.

[steve25]

With your intended power level and if the car will never be run at the strip with slicks on it, then just have it rebuilt with a B&M rebuilt kit and then reuse the current shift kit parts, as there's no need for the HD sprage to be installed.

I would then run a seperate trans cooler that is atleast 6 X 12 inches in area in front of the radiator and your golden for a long time!

Love those AMC 3.15 gears!

[455rebel]

So b m kit has better clutches, ? If I were to use slicks, what's the spray cost you mentioned, and would that be enough?

[Cliff R]

Here is what you want to use, a complete kit with bushings, thrust washers, bands, filter, modulator, etc.

https://www.ebay.com/itm/THM400-400-...ty!43050!US!-1

If you type in TH400 rebuild kit on Ebay you'll find quite a few similar offerings.

I use and prefer the "high energy" frictions in the units we build here.....Cliff

[Mike Davis]

Originally Posted by Cliff R

Here is what you want to use, a complete kit with bushings, thrust washers, bands, filter, modulator, etc.

https://www.ebay.com/itm/THM400-400-...ty!43050!US!-1

If you type in TH400 rebuild kit on Ebay you'll find quite a few similar offerings.

I use and prefer the "high energy" frictions in the units we build here.....Cliff

X2 on what Cliff says. I have that in my TH400 in a 775HP 9 second street/strip car. Usually get about 5 years out of a trans before I do a PM/freshen and they look good when taken apart.

The TH400 does not need much help to survive up to 700HP

[ponyakr]

Just curious. If it only has 60k on it, and will bark the tires when shifting, why do you think it needs a rebuild ?

The 1st Bird Stocker I built had a junkyard long tail TH400. Ran high 12's & won lots of races that year.

When I switched over to a 455, with similar power to what you mentioned, it broke the intermediate sprag, in 2 different TH400's. One was a "Full Competition" TCI, with reverse pattern valve body. They had kept the stock sprag in it. Those won't survive a hard 1-2 shift, behind a 500 torque 455, if you get traction.

So, if you ever plan to have enuff traction to break the sprag, I'd definitely include a 34 element sprag upgrade in any rebuild.

If your trans is the older model, with a 16 element sprag, the 34 element sprag is a simple replacement part. If yours is a later model, you'll have to replace the entire drum/sprag assembly. One of these from a 4L80E will work. There are usually lots of these on Ebay. Many are already rebuilt, ready to install.

https://www.ebay.com/sch/i.html?_fro...ag&_sacat=6028

This article has some good pics, showing the difference between the sprag & roller clutch style set-ups. According to the article, the roller clutch style started in around 1971. Previous years came mostly with a 16 element sprag. As you can see, the drums are different. Back in the '70's, my trans guy told me that I needed a 500 Cadillac sprag in my drag TH400. I didn't know how many elements they had. He just said they were HD & was what I needed. He bought 'em from a local GM dealer. So, I assume they actually came in TH400's that came behind 500 inch Caddy engines. Maybe the 472, also. Don't know. Maybe some of the experts here can tell us exactly what year GM switched over to the roller clutch/drum set-up, and if the 500 Caddy TH400's actually did come with a 34 element(or at least a heavy duty of some type) sprag. Also, what other GM vehicles came with the HD sprag ? BBC truck maybe ? Any GM 455 powered vehicles ?

https://www.crankshaftcoalition.com/...0_rebuild_tech

[455rebel]

So the kit cliff mentioned, a 16 sprag, and drum. Mine is a 1973 unit. Then I can safely run sticker tires without breaking the tranny?

[ponyakr]

What I'm saying is that if your tires(whatever type they may be) hook, during a hard WOT 1-2 shift, anything less than a 34 element sprag, is very likely to break.

The engine that broke two 16 element sprags in my cars, was a 1970 455, with #64 heads, out of a running '70 GTO. Only change I made was to an 041 clone cam & Rhoads lifters.

With hard, narrow street tires, would probably have never had a sprag problem. But, the 13" slicks didn't slip much during the 1-2 shifts.

https://www.google.com/search?q=weak...hrome&ie=UTF-8

By the way, if you break the sprag, sometimes you can just shift to 3rd & keep on driving. When the sprag broke in my TCI "Full Competition" TH400, the driver said it would shift to 3rd. We had time for another time trial. So, I told him to just hit the ratchet shifter twice, real quick, & see if it would shift from 1st to 3rd. It did. It ran a couple of tenths slower. But, we dialed it in accordingly, & he won that race ! It is quite memorable to me. Happened at the track in Hallsville Texas. I think the year was 1979.

https://www.chevelles.com/forums/217...-2nd-gear.html

[Dragncar]

One thing, the center support bushing need to be US made. Stay away from any offshore bushings. If it says Clevite on it you are good.

[AG]

I rebuilt the TH400 in my race car with a B&M Transkit and TCI 32 element sprag, holds up fine going 10.0 at 3500 lb.

[ponyakr]

"...TCI 32 element sprag..."


I assume that is a typo, and you meant 34 element. I've never heard of a 32 element. '

I don't remember how many elements the Caddy sprags had. All I remember is that they were referred to as "heavy duty". But I was told that many of the big name trans builders reboxed the Caddy sprags & sold 'em under their brand name. Don't know when they all switched to some other supplier.

I assume that GM may still sell the 34 element sprag, for the 4L80E trans. Don't know. Don't have a GM part number.

Hey, after much searching, I did find a 32 element sprag. I suppose it might be the same part that we called a 500 Caddy sprag. Have no idea. Looks like the part number is 1371A.

https://www.gmtransmissionparts.com/...element-th400/

https://globaltransmissionparts.com/...AaAj0FEALw_wcB

[Cliff R]

A new 4L80E direct drum runs around $80-120 bare. You can search around some and find a nice used one or "refurbished" with the sprag, spiral lock ring, molded apply piston and steels/clutches for about $125-250.

Nothing wrong with an early TH400 smooth drum, but make sure you get the good sprag for it and spiral lock ring for the retainer. There were some cheap offshore 34 element sprags in circulation for a while, insist of USA made Borg Warner or similar quality.

I like and use the later molded apply piston, if nothing else it sure makes it easy to assemble the drum. 5 frictions with .090" steels is adequate for any power level but you can build a high capacity direct drum by either using .078" steels, shorter apply piston, or even aftermarket .060" steels in various combinations.

For the most part the TH400 doesn't need a lot of help anyplace but we have options to make it better than what it was.

There actually isn't anything wrong with a factory "notched" direct drum and roller clutch set-up. It is IMPOSSIBLE to roll one over like a sprag type clutch, however when it does fail it's a disaster as it typically explodes and puts a lot of metal into the assembly. What leads to early failure with the direct drum sprags are not using the factory smooth/waved frictions in the intermediate clutch pack or the waved steel, disabling the accumulator, then drilling huge holes in the separator plate for "window shattering" shifts. It's the shock-load that kills the sprag not overcoming it's holding capacity with big power.....IMHO.

https://cliffshighperformance.com/Qu...-transmissions

Resist the urge to "tack" weld the factory type retaining ring in place for the 34 element sprag and get the 4L80E spiral lock instead. Welding is just a bad idea and I've had a good many TH400's come in the shop where the weld failed and the snap ring kicked off the end of the drum......Cliff

[455rebel]

I'm 61 now, not planning on slicks and kinda on a budget, so I think I'll get the kit cliff recomended and a mild converter and be happy just shredding tires on the street.
They ant any street racing hear anymore, nobody even cruises. Don't know what the young kids do now. 1 town east of me 12 miles has a Friday night cruise in all summer, and another 10 miles west on Saturday. That's where most of my time will be spent.
With the occasional smoke show at a red light if I get that look from the guy in the next lane!
Ps-budget converter options?

[Half-Inch Stud]

Stock Converter
Hughes GM25
Go to ATI and get thie 10" 2800-3200 converter for ~$600 (assuming you have 3.36:1 or racier)

[455rebel]

Have the oem stock now, no problems. Afraid it won't work well with a larger cam(voo doo 704). What's the actually foot brake stall on the Hughes GM25?
And does it act like a stock one in traffic, pull away at light throttle, with 3:15 gears, I cruise at 2-2.5k a lot.
Thanks all.

[Cliff R]

The Hughs GM25 is a decent converter. I've removed several and replaced them with custom units. They did OK for the applications, a little additional stall speed and torque multiplication over a stock converter and fairly well coupled everywhere else.......Cliff

[Half-Inch Stud]

Sporty Converters dont play well (mushy pull-away) with Highway gears up to 3.08:1

So Stock or GM25 is your fun-range. For my knowledge & Experience, the ATI 2800-3200 10" is the tightest "Stop-sign drive away" available ( sure there might be others) with 3.31:1 gears and a stout 455.

[Cliff R]

HIS, you need to stop by next time you are in the area. I'll let you take the Ventura out for a spin. When you back out of the garage you're going to be thinking I've got a stock converter in place. The engine loads down some when the trans is placed in gear, no flash or flair up when you back out, the car moves with very little throttle opening or RPM.

Driving around at light throttle you'll never even know it has a "sporty" converter in it. Even if you stop and hold the brakes at tight as you can it will lug down and overcome the tires around 1800-1900rpms (which is probably lower than 95 percent of the aftermarket "sporty" converters as I've been able to get most to well past 2200-2400rpm's and a few even higher than that and they were larger diameter converters!).

Wonder over to a nice stretch of flat road, do a decent burnout with the line lock, stop, hit the throttle as hard as you can and it will flash instantly to 3600rpm's and locked solid from there to the shift point. Make sure to remove your hat and for sure don't have a half a can of pop in your lap, your hat will be in the back window and you'll be wearing most of your soda! You'll also have to reach over and flip the passengers floor mat back over.

Yes, you really do get what you pay for with customer converters, but they are expensive and certainly there are much less expensive units out there that make the grade for most of these applications.......Cliff

https://www.youtube.com/watch?v=6zVdoLR-VzM

[ta man]

Originally Posted by Cliff R

HIS, you need to stop by next time you are in the area. I'll let you take the Ventura out for a spin. When you back out of the garage you're going to be thinking I've got a stock converter in place. The engine loads down some when the trans is placed in gear, no flash or flair up when you back out, the car moves with very little throttle opening or RPM.

Driving around at light throttle you'll never even know it has a "sporty" converter in it. Even if you stop and hold the brakes at tight as you can it will lug down and overcome the tires around 1800-1900rpms (which is probably lower than 95 percent of the aftermarket "sporty" converters as I've been able to get most to well past 2200-2400rpm's and a few even higher than that and they were larger diameter converters!).

Wonder over to a nice stretch of flat road, do a decent burnout with the line lock, stop, hit the throttle as hard as you can and it will flash instantly to 3600rpm's and locked solid from there to the shift point. Make sure to remove your hat and for sure don't have a half a can of pop in your lap, your hat will be in the back window and you'll be wearing most of your soda! You'll also have to reach over and flip the passengers floor mat back over.

Yes, you really do get what you pay for with customer converters, but they are expensive and certainly there are much less expensive units out there that make the grade for most of these applications.......Cliff

https://www.youtube.com/watch?v=6zVdoLR-VzM

Cliff it would be interesting to see you test one of the "Buick" converters in your car to see how it is as far as street driving and track results?
I tried something similar last year replaced the Continental with a custom converter and even though it felt about the same on the street and highway..it was bad news at the track..didn't 60ft as well,lost 5 tenths and over 7mph and gained 1000rpm at the stripe. This is from a well known converter guy..I don't have any bad feelings towards him but most of the time converters can be hit or miss. It would be nice to have a converter company to have a converter "blueprint" that will replicate the old Continentals 99 percent of the time.
I have a local guy going through the same issue at the moment trying to find a good convertor for his car. He has a similiar engine to my car and only running about 118mph at the stripe with heavy slippage. We both figure he is losing at least 4mph..

[pastry_chef]

Originally Posted by ta man

in your car to see how it is as far as street driving and track results.

In your car Ernie.. THAT will be a test.