driveshaft difference? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dinnut · 03-06-2004, 11:47 PM

i want to put a th400 behind my 350, i have a th350... do i have to modify the driveshaft or is it the same length and all?

**CPNE** · 03-06-2004, 11:54 PM

The slip yolk is splined differently but I think the lengths are nearly identical

ZOOMY · 03-07-2004, 03:02 AM

It also matters if your th350 had a short or long tailshaft.

SS55 · 03-07-2004, 04:02 AM

TCI has a good chart that shows the dimensions for various tailshaft lengths on the TH-350 & TH-400. Also, the TH-400 uses an electrically operated kick down rather than a TV cable.

http://www.tciauto.com/tech_info/trans_dims.htm

A.P. · 03-07-2004, 06:30 AM

SS55
How you connect the electrically operated kick down?

A.P.

Suicide-D · 03-07-2004, 11:35 AM

trans crossmember is different also

dinnut · 03-07-2004, 04:34 PM

the crossmember is different? how come when they sell them they sell them as automatic crossmembers? are you sure theyre different?

and cpne.... the spline yolk, what is that? im not very familiar with driveshafts. is this swap goign to be alot more than i think it is?
can someone who was done this tell me what they had to do?

**CPNE** · 03-07-2004, 04:49 PM

As far as I've been able to determine the auto xmember (supports) the rear of the tranny is the same for a th350 or th400. It sits slightly further back because the overall length of the 400 is a littler longer.

The yolk is the end of the driveshaft that slides into the end of the tranny.

dinnut · 03-07-2004, 06:07 PM

so the driveshaft will have to be modified for the th400 to work?

Longhorn Man · 03-07-2004, 06:37 PM

I am 99% positive the TH400 is longer than the Th350.
If so, the drive shaft will have to b modified, and if I am wron, then all you'll need is a new slip yolk on your front U-joint.

Suicide-D · 03-07-2004, 08:36 PM

Well I couldn't get the 400 to bolt up to the th350 cross member I had to take the one out of the truck the 400 came out of. Maybe I have some weird set up... but they looked different also. I was having a hard time getting it to line up and once I changed them.... zip went right in.

Longhorn Man · 03-07-2004, 08:46 PM

Quick question, why you want to go through the hassle of the swap? Is your TH350 dead, or are you pushing over 400 horses?
I just don't see much of a point in putting in a TH400 otherwise....But that's just me.

SS55 · 03-07-2004, 09:16 PM

As for the kick down switch, the originals were either mounted on a bracket at the carb and was actuated by the carb throttle lever or was mounted to the accelerator pedal on bracket by the pedal. Aftermarket companies sell switch assemblies to do this function. It is just a normally open switch that is closes when you stick your foot in it.

In my experience, the crossmembers were the same, but did have to be moved because of the trans mount locations.

You will definately need to change yokes as the TH-400 is a lot bigger and splined differently. The driveshaft will need to be shorter if going to a TH-400 from a TH-350

dinnut · 03-07-2004, 11:11 PM

my th350 is on its last leg. and before i start driving the truck, ill need a transmission that shifts

and also one day i hope to hotrod the 350 under the hood and then ill want a 400. anyway so i figure i might as well do the swap now. but if i dont do the swap ill just pull the th350 out of my other truck and swap the 2.
thanks suicide-d for your experience. seems like you answered my question... but, if all i had to do was move the crossmember and change the yolk, that would great and not that hard. seems like everyone had a different experience...

Tx Firefighter · 03-07-2004, 11:39 PM

The crossmember is the same. Just use the mount off of your old TH350. The 400 will require the crossmember to be slid on the frame, but that's why your frame has all of those holes in it.

jimfulco · 03-08-2004, 02:57 AM

If both trannys are the short-tail versions, the length should be almost the same.

03-06-2004, 11:47 PM	#1
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	driveshaft difference? i want to put a th400 behind my 350, i have a th350... do i have to modify the driveshaft or is it the same length and all? __________________ 70 longbed 496/th400/Ford 9"

03-06-2004, 11:54 PM	#2
CPNE Resident Curmudgeon Join Date: Dec 1999 Location: NH Posts: 6,662	The slip yolk is splined differently but I think the lengths are nearly identical __________________ Currently on or near the homestead: 67 Chevy SWB 2WD stepside 350/3 on tree (Pat's) 67 GMC SWB 2WD Fleet 402/auto (Brian's under construction) 67 Chevy 3/4 ton 2WD 402/auto (Business Hauler) 67 Chevy 1 ton dually 2WD 396/4 speed (Former business hauler, Needs TLC) 68 Chevy 1/2 ton Suburban 2WD 250 six/3 on tree (Brian's Needs TLC) 70 Chevy 3/4 ton 4WD 350/4 speed (Pat's - Disguised as a 68 GMC) 71 Chevy SWB stepside (Crushed by tree - parts donor) 72 Chevy 3/4 ton 4WD (Parts donor) 72 Chevy 3/4 ton 4WD Suburban (Parts Donor) 72 GMC 3/4 ton 4WD 292 six/4 speed (Mine - Disguised as a 67 GMC) 81 GMC 4WD Dually Dump Body 350/4 speed (Business Hauler) 82 Camaro Z/28 355/Super T-10 (Pat's toy) 93 Caprice 9C1 (Brian's Cop Car) 02 Toyota Camry (Reliable but a souless steel and plastic hulk) 2011 2SS RS Camaro M6 Factory Hurst Shifter Maybe I need to sell some of this crap Yet another Bozo with a sawz-all

03-07-2004, 03:02 AM	#3
ZOOMY Senior Member Join Date: Feb 2003 Location: WIS Posts: 1,752	driveshaft length It also matters if your th350 had a short or long tailshaft.

03-07-2004, 04:02 AM	#4
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	TCI has a good chart that shows the dimensions for various tailshaft lengths on the TH-350 & TH-400. Also, the TH-400 uses an electrically operated kick down rather than a TV cable. http://www.tciauto.com/tech_info/trans_dims.htm __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino

03-07-2004, 04:34 PM	#7
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	the crossmember is different? how come when they sell them they sell them as automatic crossmembers? are you sure theyre different? and cpne.... the spline yolk, what is that? im not very familiar with driveshafts. is this swap goign to be alot more than i think it is? can someone who was done this tell me what they had to do? __________________ 70 longbed 496/th400/Ford 9"

03-07-2004, 06:30 AM	#5
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	SS55 How you connect the electrically operated kick down? A.P.

03-07-2004, 11:35 AM	#6
Suicide-D Registered User Join Date: Jan 2001 Location: Katy, TX...but the love of my life resides in Dublin,OH. Posts: 1,408	trans crossmember is different also

03-07-2004, 04:49 PM	#8
CPNE Resident Curmudgeon Join Date: Dec 1999 Location: NH Posts: 6,662	As far as I've been able to determine the auto xmember (supports) the rear of the tranny is the same for a th350 or th400. It sits slightly further back because the overall length of the 400 is a littler longer. The yolk is the end of the driveshaft that slides into the end of the tranny. __________________ Currently on or near the homestead: 67 Chevy SWB 2WD stepside 350/3 on tree (Pat's) 67 GMC SWB 2WD Fleet 402/auto (Brian's under construction) 67 Chevy 3/4 ton 2WD 402/auto (Business Hauler) 67 Chevy 1 ton dually 2WD 396/4 speed (Former business hauler, Needs TLC) 68 Chevy 1/2 ton Suburban 2WD 250 six/3 on tree (Brian's Needs TLC) 70 Chevy 3/4 ton 4WD 350/4 speed (Pat's - Disguised as a 68 GMC) 71 Chevy SWB stepside (Crushed by tree - parts donor) 72 Chevy 3/4 ton 4WD (Parts donor) 72 Chevy 3/4 ton 4WD Suburban (Parts Donor) 72 GMC 3/4 ton 4WD 292 six/4 speed (Mine - Disguised as a 67 GMC) 81 GMC 4WD Dually Dump Body 350/4 speed (Business Hauler) 82 Camaro Z/28 355/Super T-10 (Pat's toy) 93 Caprice 9C1 (Brian's Cop Car) 02 Toyota Camry (Reliable but a souless steel and plastic hulk) 2011 2SS RS Camaro M6 Factory Hurst Shifter Maybe I need to sell some of this crap Yet another Bozo with a sawz-all

03-07-2004, 06:07 PM	#9
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	so the driveshaft will have to be modified for the th400 to work? __________________ 70 longbed 496/th400/Ford 9"

03-07-2004, 06:37 PM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I am 99% positive the TH400 is longer than the Th350. If so, the drive shaft will have to b modified, and if I am wron, then all you'll need is a new slip yolk on your front U-joint.

03-07-2004, 08:36 PM	#11
Suicide-D Registered User Join Date: Jan 2001 Location: Katy, TX...but the love of my life resides in Dublin,OH. Posts: 1,408	Well I couldn't get the 400 to bolt up to the th350 cross member I had to take the one out of the truck the 400 came out of. Maybe I have some weird set up... but they looked different also. I was having a hard time getting it to line up and once I changed them.... zip went right in.

03-07-2004, 08:46 PM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Quick question, why you want to go through the hassle of the swap? Is your TH350 dead, or are you pushing over 400 horses? I just don't see much of a point in putting in a TH400 otherwise....But that's just me.

03-07-2004, 09:16 PM	#13
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	As for the kick down switch, the originals were either mounted on a bracket at the carb and was actuated by the carb throttle lever or was mounted to the accelerator pedal on bracket by the pedal. Aftermarket companies sell switch assemblies to do this function. It is just a normally open switch that is closes when you stick your foot in it. In my experience, the crossmembers were the same, but did have to be moved because of the trans mount locations. You will definately need to change yokes as the TH-400 is a lot bigger and splined differently. The driveshaft will need to be shorter if going to a TH-400 from a TH-350 __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino

03-07-2004, 11:11 PM	#14
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	my th350 is on its last leg. and before i start driving the truck, ill need a transmission that shifts and also one day i hope to hotrod the 350 under the hood and then ill want a 400. anyway so i figure i might as well do the swap now. but if i dont do the swap ill just pull the th350 out of my other truck and swap the 2. thanks suicide-d for your experience. seems like you answered my question... but, if all i had to do was move the crossmember and change the yolk, that would great and not that hard. seems like everyone had a different experience... __________________ 70 longbed 496/th400/Ford 9"

03-07-2004, 11:39 PM	#15
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	The crossmember is the same. Just use the mount off of your old TH350. The 400 will require the crossmember to be slid on the frame, but that's why your frame has all of those holes in it. __________________ I'm on the Instagram- @Gearhead_Kevin



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03-08-2004, 02:57 AM	#16
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	If both trannys are the short-tail versions, the length should be almost the same.

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