Made som good progress, and reccomend this swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jermasaurus · 05-21-2005, 04:55 PM

Well, I had been having problems with my TH350 like it would shift different every day, 3rd gear would seem like 5th in a manual trying to accelerate, and it wouldnt kick back down very easy either. I had already checked things like the modulator, govenor, fluid level, ...

On thursday, I lost every gear and the truck would barely move.
I had been interested in swapping a 700r4 in its place, and thought what better time than now? If anyone cares, It was a very direct swap. The only modification that had to be made was moving the crossmember back and drilling new holes. Same mounting for the T.V. cable, cooler lines, same yoke (86+ only I think).

The one thing that held me up and really sucked, was the yoke. Here I was thinking I had to get my driveshaft shortened because I couldnt plunge it into the trans far enough to get the U-joint past the pinion yoke. Upon closer inspection, I found that the trans yoke wasn't going in as far as it should. Under the perfect light I could see that the splines had the slightest twist to them, not allowing the yoke to slide all the way into the trans. Put a new one on and the legnth worked perfect.

So I think the death of my TH350 could have been because the yoke couldn't plunge when the suspension moved, causing it to just slam the ouput shaft in.

All in all I think it was well woth the time and effort. My only problem now is to get the speedo gear housing for a cable driven one instead of the electric one on there (cause it's from a 91).
-Jeremy

82c10 · 05-21-2005, 05:22 PM

how are you going to get the torque converter to lockup, isn't it controlled electronically

79BIG10 · 05-21-2005, 10:51 PM

Hopefully you added a secondary cooler to that tranny. If you are using the standard radiator cooler only you will have a chance to burn it up fast.

jermasaurus · 05-22-2005, 06:01 PM

My truck has a non feedback carb and originally had a lockup converter for the TH350. The plug is the same and is plugged in, I just need to check the wiring diagram to verify it is locking.

I am going to look at some coolers today and pick one up. Would mounting it in between the fan and radiator be good? OR would the fan not pull enough heat from the radiator with the trans cooler in front? I want it to get some really good flow even in slow traffic, but not put another fan on for it. Clearance is not an issue either.

One thing i didn't know when I first posted is that the speedo cable will also have to be changed to fit on the 700's housing. I didn't have the mechanical one to compare at the time.

72MARIO · 05-22-2005, 06:27 PM

I think the only diffirence is the length of the cable.

bodydropped · 05-22-2005, 07:36 PM

i have a 700r4 in my 78 and i have a lockup modul from b&m i can adjust the mph for the lockup

jermasaurus · 05-22-2005, 09:51 PM

Alright, I just got a 10"x15.5" trans cooler rated for class "A" motorhomes or towing up to 10,000 lbs. That has to help out a little.

72Mario, you may be right about the only difference being the legnth of the cabe. I am only going on somebody elses word at the moment because I am gonna get the mechanical gear and housing tomorrow.

05-21-2005, 04:55 PM	#1
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	Made some good progress, and reccomend this swap Well, I had been having problems with my TH350 like it would shift different every day, 3rd gear would seem like 5th in a manual trying to accelerate, and it wouldnt kick back down very easy either. I had already checked things like the modulator, govenor, fluid level, ... On thursday, I lost every gear and the truck would barely move. I had been interested in swapping a 700r4 in its place, and thought what better time than now? If anyone cares, It was a very direct swap. The only modification that had to be made was moving the crossmember back and drilling new holes. Same mounting for the T.V. cable, cooler lines, same yoke (86+ only I think). The one thing that held me up and really sucked, was the yoke. Here I was thinking I had to get my driveshaft shortened because I couldnt plunge it into the trans far enough to get the U-joint past the pinion yoke. Upon closer inspection, I found that the trans yoke wasn't going in as far as it should. Under the perfect light I could see that the splines had the slightest twist to them, not allowing the yoke to slide all the way into the trans. Put a new one on and the legnth worked perfect. So I think the death of my TH350 could have been because the yoke couldn't plunge when the suspension moved, causing it to just slam the ouput shaft in. All in all I think it was well woth the time and effort. My only problem now is to get the speedo gear housing for a cable driven one instead of the electric one on there (cause it's from a 91). -Jeremy Last edited by jermasaurus; 05-21-2005 at 04:55 PM. Reason: bad spelling

05-21-2005, 10:51 PM	#3
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,775	Hopefully you added a secondary cooler to that tranny. If you are using the standard radiator cooler only you will have a chance to burn it up fast. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

05-22-2005, 06:27 PM	#5
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,052	I think the only diffirence is the length of the cable. __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

05-22-2005, 07:36 PM	#6
bodydropped Registered User Join Date: Jan 2005 Location: beaumont,tx Posts: 757	i have a 700r4 in my 78 and i have a lockup modul from b&m i can adjust the mph for the lockup __________________ http://img.photobucket.com/albums/v5...ropped/sig.jpg

05-21-2005, 05:22 PM	#2
82c10 needin' money Join Date: May 2005 Location: Chickasha, Oklahoma Posts: 1,106	how are you going to get the torque converter to lockup, isn't it controlled electronically

05-22-2005, 06:01 PM	#4
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	My truck has a non feedback carb and originally had a lockup converter for the TH350. The plug is the same and is plugged in, I just need to check the wiring diagram to verify it is locking. I am going to look at some coolers today and pick one up. Would mounting it in between the fan and radiator be good? OR would the fan not pull enough heat from the radiator with the trans cooler in front? I want it to get some really good flow even in slow traffic, but not put another fan on for it. Clearance is not an issue either. One thing i didn't know when I first posted is that the speedo cable will also have to be changed to fit on the 700's housing. I didn't have the mechanical one to compare at the time.

05-22-2005, 09:51 PM	#7
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	Alright, I just got a 10"x15.5" trans cooler rated for class "A" motorhomes or towing up to 10,000 lbs. That has to help out a little. 72Mario, you may be right about the only difference being the legnth of the cabe. I am only going on somebody elses word at the moment because I am gonna get the mechanical gear and housing tomorrow.



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