Pontiac GTO Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
156 Posts
Discussion Starter #1
Has anyone swapped out the TH400 for something with more gears? I just had the rear rebuilt. I had them add an Eaton posi and 3.55 gears. I love the low end but on the freeway the engine is really racing and everyone is passing me. I feel like I need another gear.

Can I swap out my TH400 for something with more gears so I can keep the low end and have a freeway gear? If yes, is it an easy swap out or do I have to change a lot of other components?

Thanks.
 

·
Registered
Joined
·
156 Posts
Discussion Starter #3
Is that a 3 speed? and Is it a direct swap? When you say a ton of HP... what do you mean? I am rather stock with a hot cam headers etc. probably under 400 somewhere.
 

·
Premium Member
Joined
·
4,705 Posts
A 200r4 is a close swap. You will need to move the X-member a little. 4oo HP is fine as long as you have the tranny built for it. It is a 4 speed automatic, the gear ratios start lower (higher number) and end higher (lower number).....the 4th gear is an overdrive gear. This will give you better highway performance....the OD gear is .67 therefore with 3:55 rear gears when in OD, the final drive ratio would be 2.38. Eric
 

·
Registered
Joined
·
128 Posts
the 2004r will work out good for you about 1" shorter than a 400 the mount is like 2"to the rear of the 400 your gear will work out good too i put one in my old pick up last year no problems they are somtimes hard to find good luck
 

·
Registered
Joined
·
460 Posts
On this note I have 2 Questions...

1. I am building a stockish 455 for my project and I am wondering if a 200r4 would handle the torque (probably in the 500+ ft lbs range) as much as the 400ish hp I am building.

2. I have a Hurst his & hers shifter, will it become unusable with a 4 speed transmission? Will I need to get a 4 speed shifter out of something late model that will fit in my console?

As always thanks all.
Scott
 

·
Registered
Joined
·
128 Posts
i am not sure on how much tourque they will handle the grand national guys keep them in their cars you could check out bowtie overdrives they are helpfull and good for advice
 

·
Registered
Joined
·
460 Posts
i am not sure on how much tourque they will handle the grand national guys keep them in their cars you could check out bowtie overdrives they are helpfull and good for advice
I have been planning to leave the TH400 in it up till recently, but my wife LOVES this car (hey I am not complaining) and is wanting to take it to the smokey mountains and on other "trips" and this is after cruising all of Route 66 as her "break in run" when we complete the restoration.

With THAT kind of driving, I'd like to have an OD.

That said, I do not want to loose my His & Hers, I love it.

I currently have the opportunity to get good core transmissions here local, a 200r4 or a 700r4. (CHEAP)

Would either work better than the other? No matter what I was in for a TH400 rebuild so I am having whatever I get gone through. So that's no problem either way.
 

·
64-67 Expert
Joined
·
8,569 Posts
Uhm...why the stiff gears? I would get rid of the 3.55's and install a 3.08 or 2.93 and enjoy the car. 3.55's are terrible for a street driven car, IMO.
 

·
Super Moderator
Joined
·
5,790 Posts
Check into a Gear Vendors overdrive unit. They bolt on in place of the stock tail shaft and will handle as much torque as you can throw at them. You'll need a shorter drive shaft, and probably will have to "massage" the tunnel for a little clearance. As a bonus you can use them to turn the TH400 into a 6-speed by engaging the overdrive between each gear.

Bear
 

·
Registered
Joined
·
156 Posts
Discussion Starter #12 (Edited)
Thanks Eric for your response. I mentioned it to a friend who is pushing me to switch to manual and put a T-56 in. He said that they are everywhere and a used one can be picked up from a pick and pull for cheap. He put on in his 69 Camaro and loves it. He said that I would have to do a little research but most parts from the donor could be transfered over. He thinks I would need a bell housing that would bolt up to both, a peddle and master, a crossmember, and to shorten my driveshaft.

Has anyone done this. Is it a huge pain? Can you think of anything else I would need? Is there a T-56 from a certain year and model that would bolt up easier than others?

Thanks
 

·
Premium Member
Joined
·
4,705 Posts
I have been planning to leave the TH400 in it up till recently, but my wife LOVES this car (hey I am not complaining) and is wanting to take it to the smokey mountains and on other "trips" and this is after cruising all of Route 66 as her "break in run" when we complete the restoration.

With THAT kind of driving, I'd like to have an OD.

That said, I do not want to loose my His & Hers, I love it.

I currently have the opportunity to get good core transmissions here local, a 200r4 or a 700r4. (CHEAP)

Would either work better than the other? No matter what I was in for a TH400 rebuild so I am having whatever I get gone through. So that's no problem either way.
200 4r with a SHIFTWORKS sells conversion kits 1964-81 GM factory automatic console shifters, column shifters, gauges and indash tachs kit. You will also need to add a cable to control the transmission pressure. This is called a TV cable, (transmission valve). The 700r4 is a great tranny, but only comes in a Chevy bolt pattern (I THINK), so you will need an adaptor plate. Eric
 

·
Registered
Joined
·
156 Posts
Discussion Starter #14
I just visited the local Pick N Pull. They had a couple late 90's camaro's and firebirds that were manual transmissions. I was just on the hunt not ready to actually pull anything. But once I figure out exactly which car to look for I'm going for it. Any transmission is $99.00. I figure for that price it's worth the risk. Has anyone done this? Will I need a new bell housing or would I be lucky enough that I would just bolt up. :)
 

·
Registered
Joined
·
156 Posts
Discussion Starter #15
OK. I give in. I am going to stick with an automatic. I have been looking at the 200R4 or the 700R4. The 200R4 is about the same size as the TH400 where as the 700R4 would require the shortening of the driveshaft. A little more work but I believe the 700R4 is a much stronger unit.
1st 2nd 3rd 4th Reverse
GM
Powerglide 1.76 1.00 1.76
TH350 2.52 1.52 1.00 1.93
TH400 2.48 1.48 1.00 2.00
200r4 2.74 1.57 1.00 0.67 2.07
700r4 3.06 1.62 1.00 0.70 2.29
4L60E 3.06 1.62 1.00 0.70 2.29
4L80E 2.48 1.48 1.00 0.75 2.08

I think I like the 700 gear ratio better. Can I use the torque convert from my TH400 in a 200R4 or 700R4?
 

·
64-67 Expert
Joined
·
8,569 Posts
Torque converters are a consumable, and are not swapped between trannies without a teardown and rebuild. The 700 and the 200 use a different converter, anyhow. The 700 is a stronger transmission, harder to fit, but a better basic design. The 200 is much more "bolt-in-friendly", but often failed when new behind 135 hp v6 engines. They need extensive and expensive modifications to live behind a Pontiac v8. A weaker basic design than the 700R4.
 
1 - 16 of 16 Posts
Top