200-4R to TH350 Swap

B

Bludacious

Apprentice
Jan 2, 2018
62
8
After doing a solid 3 hours of research I have decided to swap a short tail turbo 350 in place of my exploded 2004r, since it's the cheapest way to get my daily back on the road and there is a rebuilder willing to skip the core credit on the new one if I give him my blown unit. But, I have a couple questions about the swap I want to clear up before I start.

Can I reuse / modify my 200-4R crossmember? I know people who do the reverse of this swap have to buy extensions, I've heard I can just shuffle the original X-member forward and drill new holes (85 Monte frame)? Welding and light to medium fabbing are no problem for me.

How will my revs and acceleration be with the stock HO 305 and 2.41 open gears? I do a fair bit of highway driving with the occasional long-distance high speed road trip (how d'ya think I blew out the 200?), but I don't want to lose a whole bunch of low end power since I need it to tool around the NH hills, especially in the winter. Eventually I plan on dropping a mild-ish 350 in it.

Will the bracket for the TV cable hold the kickdown cable with a little modding?

How long should the kickdown cable be?

Can/should I reuse my original torque converter?

Will my transmission cooler lines fit?

And finally, will my column shift linkage play nice if I adjust it and expose the non-overdrive gear markings printed on the speedo?

I tried to find a most of this info from searching other posts and other forums, but it seems the majority of people do this swap the other way round, so a lot of the stuff doesn't apply the same.
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
4,935
113
Melville,Saskatchewan
Yes, I reused my crossmember going from a 2004R to 350. I may have had to drill a couple of holes to make it work. The column will work but may need adjustment to line up. Stock size tires? Without a lock up converter and stock 25" tire height, expect 2200 rpm at 60 mph. You will lose a tiny bit of acceleration going from a 2.74 to 2.52 gear. Honestly the torque converter stall matters more. If you had a D5 high stall converter in your 2004R, you will want a 2000 stall minimum in the TH350. Is your 2004r a Monte SS trans? If so that would explain the no core necessary, it is very desirable.
 
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B

Bludacious

Apprentice
Jan 2, 2018
62
8
Yes, I reused my crossmember going from a 2004R to 350. I may have had to drill a couple of holes to make it work. The column will work but may need adjustment to line up. Stock size tires? Without a lock up converter and stock 25" tire height, expect 2200 rpm at 60 mph. You will lose a tiny bit of acceleration going from a 2.74 to 2.52 gear. Honestly the torque converter stall matters more. If you had a D5 high stall converter in your 2004R, you will want a 2000 stall minimum in the TH350. Is your 2004r a Monte SS trans? If so that would explain the no core necessary, it is very desirable.
It is the original LS/base gearbox AFAIK, although the motor was swapped with a Goodwrench crate unit which has the HO head castings, so not sure about what TC it may have at this point, I'll have to check the service receipt for the install. I'm running 15x7s with 26" tall tires now and I just don't want it to be screaming (much louder than it already does) on the 60-70% of my commute I spend on a fairly open and not closely monitored stretch of freeway if I can help it.
 
Tc77

Tc77

Not-quite-so-new-guy
Sep 19, 2018
34
18
If my memory is correct. The cooler lines will work but are opposite. You will need a new slip joint. And I think the torque converter is different also.Depending on how much he wants for a core . I would hold on to the 200 they are getting really hard to find.
 
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B

Bludacious

Apprentice
Jan 2, 2018
62
8
If my memory is correct. The cooler lines will work but are opposite. You will need a new slip joint. And I think the torque converter is different also.Depending on how much he wants for a core . I would hold on to the 200 they are getting really hard to find.
If I'm supposed to be able to reuse my original driveshaft, what would I need a different slip joint for? Don't all the GM TH transmissions except the 400 and 4l80e use a 27 spline shaft? From the GM transmission measurement sheet the turbo 350 should only be about 5/16" shorter than the 2004r. Is this really enough of a difference in driveshaft engagement to make it unreliable/unsafe?
 
Last edited:
Gonzo1970

Gonzo1970

G-Body Guru
Supporting Member
Sep 30, 2018
565
93
You wouldn't see me getting rid of my 200-R4.. No sireee...

Popping in a TH350 for temp use because they're cheap as hell, sure.. but I would be rebuilding that 200-R4 to withhold about 100 more HP than I have in the mean time.

They're expensive, but can be built to hold quite a bit of HP.

Good luck!

-Gonz
 
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H

hoffa65

Greasemonkey
Mar 11, 2019
232
43
Atlanta GA
slip yoke is the same
cooling lines are opposite
TC is different
crossmember should work with a little modding, 350 xmembers area dime a dozen, keep to 2004r xmember if you don't use it
TV cable is different then the 350 detent cable, should be able to use a mid 80's 350C detent cable for a Gbody
RPM's are going to go up a good bit if the 350 is non lockup
keep the 2004r and get it rebuilt it is a better all around trans when they are build correctly. add some hard parts and a good shift kit and a cooler and it will out live the motor. your long high speed runs did not kill it, it was the increased HP/TQ of the 350 and if the lockup function was not working for a long time that generates excessive heat

post up a pic of the trans tag for the 2004r
 
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TURNA

TURNA

Geezer
Jul 24, 2009
8,432
113
Socialist NY
I think your doing it backwards!
 
B

Bludacious

Apprentice
Jan 2, 2018
62
8
slip yoke is the same
cooling lines are opposite
TC is different
crossmember should work with a little modding, 350 xmembers area dime a dozen, keep to 2004r xmember if you don't use it
TV cable is different then the 350 detent cable, should be able to use a mid 80's 350C detent cable for a Gbody
RPM's are going to go up a good bit if the 350 is non lockup
keep the 2004r and get it rebuilt it is a better all around trans when they are build correctly. add some hard parts and a good shift kit and a cooler and it will out live the motor. your long high speed runs did not kill it, it was the increased HP/TQ of the 350 and if the lockup function was not working for a long time that generates excessive heat

post up a pic of the trans tag for the 2004r
Sorry if I confused anyone, the motor is a bone stock smog 5 liter pushing 200hp<. The lockup connector hasn't been connected for around 10-15K because I scrapped all the emissions stuff when the ECM randomly died on me, and I was aware they generated more heat that way. I figured it probably had some role in the fate of the box, that and the fact I don't think the fluid's been changed since it left the factory floor (whoops!). Will get the trans tag whenever I start yanking the thing out.

You wouldn't see me getting rid of my 200-R4.. No sireee...

Popping in a TH350 for temp use because they're cheap as hell, sure.. but I would be rebuilding that 200-R4 to withhold about 100 more HP than I have in the mean time.

They're expensive, but can be built to hold quite a bit of HP.

Good luck!

-Gonz
I was already having reservations about giving them the core for a $100 discount, but now I am almost certainly going to keep it. Like I said this is my daily vehicle so I just need a cheaper box I can drop in for a bit, perhaps the 200 will be my winter project in the shop where it's warm...er. I definitely know I want to have OD back ASAP but not in the market to spend 1100+ on a new unit or the 1500 the local trans expert quoted me to redo mine right now.
 
el camino ss 84

el camino ss 84

Master Mechanic
Oct 23, 2016
307
43
Nw okc
I did a swap from turbo 350 to 2004r in my elcamino with ease.so you shouldn't have issues swapping the other way. Driveshaft and slip yoke are the same. Column shift linkage is the same except the adjustment is up more on the shaft that runs from firewall to trans for the turbo 350. Detent get one for like a 82-84 monte Carlo or elcamino with a 305 sbc. Crossmember is the same roughly if your trans mount in centered. If the mount is offset then you would be better getting a different crossmember or making your own. Trans lines are the same just need to be bent a little inwards for the turbo 350 than the 2004r. Dent cable bracket might need to be replaced and use a different one to give you enough throw for the cable to work if your using a qjet. If your using a holley base carb bracket is the same item #20-95.the you ever decide to get to rid of your 2004r i will buy it no matter the condition as long as the case is in good shape .
 

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