[thefirebirdm@n]

Have decided to put a TH400 in my wife's 68 Convertible mated up to the new 400 I will be building. Although I have had several automatic Firebirds over the years (mostly 2nd gens with TH350s) and one 69 GTO with a TH400 it occurred to me its been so long I have forgotten some things:

1) For the downshift or passing gear, all I need is a kickdown cable correct? One that connects to the carb linkage. Someone I talked to mentioned a kickdown switch that can be installed at the accelerator pedal? Not sure I'd heard of that before.

2) Can anyone provide specs for the stock torque converter I should be using. When we installed the now crapped out 2004R I re-used the existing flex plate so I just need a torque converter that will fit the TH400 and bolt to my Pontiac flex plate. I believe the stock diameter was 12.5" but can't recall stock stall speed, number of bolts that connect to the flex plate (3?), I believe their called pads? Any help selecting the right torque converter is appreciated.

Specs:
1968 Firebird
YC Code 400 building it to 325-350hp
3.55:1 rear end ratio
235/45/17 tires on 17" Year One Rally IIs

[b-man]

TH400 does not use a kickdown cable like a TH350 does, it uses a kickdown solenoid actuated by a switch mounted either on the accelerator pedal of the carburetor.

A 13" converter was used with 3 bolts holding it to the flex plate. Stall speed was somewhere in the 1500 to 1800 RPM range.

The TH400 uses a different yoke (32 spline) than the TH350 and you'll need to shorten the driveshaft by about 1" or a little less if you're using the TH350 driveshaft.

[thefirebirdm@n]

Thanks B-Man, I will have to research the kickdown solenoid. Think I'd prefer to mount it to the accelerator pedal. If anyone has a reference where to get one of those, let me know.

Current driveshaft was setup for a 2004R. Don't remember what the yoke is for that transmission, I'll have to look it up. Since the 2004R is also a longer trans the driveshaft may already be the right length but I may have to change out the yoke.

If I picked up a Torque Converter with a stall at 2000-2200 rpm how would that compare to the stock stall you gave me? I have some articles queued up to read. I never have been able to get my head around the concept of a stall speed.

[67 455 Bird ragtop]

It also uses a different cross member.

[thefirebirdm@n]

True! Fortunately, I have a friend that adapted his 2004R to a TH400 cross member so we are just going to swap. The one I have is custom and allows you to remove the pan without removing the crossmember.

[wovenweb]

The correct kickdown switch for a '68 Firebird mounts to the carburetor.







They've gotten much harder to find over the years. There was a gentleman who advertised in Smoke Signals, Tim Doonan, who used to rebuild them. Maybe check with him?

[b-man]

Originally Posted by thefirebirdm@n

Thanks B-Man, I will have to research the kickdown solenoid. Think I'd prefer to mount it to the accelerator pedal. If anyone has a reference where to get one of those, let me know.

Current driveshaft was setup for a 2004R. Don't remember what the yoke is for that transmission, I'll have to look it up. Since the 2004R is also a longer trans the driveshaft may already be the right length but I may have to change out the yoke.

If I picked up a Torque Converter with a stall at 2000-2200 rpm how would that compare to the stock stall you gave me? I have some articles queued up to read. I never have been able to get my head around the concept of a stall speed.

Jimmy,

Check with Cliff Ruggles if you're looking for a good converter. He can supply a 13" converter that drives pretty much like a stock converter (no excessive slippage) until you nail the throttle.

Myself I'm about to install a 13" Continental converter that I had built about 18 years ago and used for about 30K miles in a daily-driver '64 Tempest equipped with a 455/TH400/2.56 rear. I had it refreshed by Continental back in 2015 not long before the owner retired and closed the doors, I'm about to install it behind a fresh 421 backed by a TH350. Cliff used to offer Continental converters and has recently found a very good converter builder to fill the void.

Good luck, Bart

[wovenweb]

The Parts Place is selling this:

http://www.ebay.com/itm/1967-69-Pont...3D271949920322

In the past, they were using a different switch. I think the key is whether the switch is normal open or closed. I've asked a couple people I know back in O-HI-O if they have an extra switch lying around. These would be rebuilt originals and won't come cheap if they have one.

[thefirebirdm@n]

Originally Posted by wovenweb

The Parts Place is selling this:

http://www.ebay.com/itm/1967-69-Pont...3D271949920322

In the past, they were using a different switch. I think the key is whether the switch is normal open or closed. I've asked a couple people I know back in O-HI-O if they have an extra switch lying around. These would be rebuilt originals and won't come cheap if they have one.

Thanks, I would like to have a correct original. I will chat with you about it at the meeting tonight.

[thefirebirdm@n]

Originally Posted by b-man

Jimmy,

Check with Cliff Ruggles if you're looking for a good converter. He can supply a 13" converter that drives pretty much like a stock converter (no excessive slippage) until you nail the throttle.

Myself I'm about to install a 13" Continental converter that I had built about 18 years ago and used for about 30K miles in a daily-driver '64 Tempest equipped with a 455/TH400/2.56 rear. I had it refreshed by Continental back in 2015 not long before the owner retired and closed the doors, I'm about to install it behind a fresh 421 backed by a TH350. Cliff used to offer Continental converters and has recently found a very good converter builder to fill the void.

Good luck, Bart

Thanks Bart!!