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Switching out 350 turbo for 700r4 #453742 March 15th 2011 12:58 am | |
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Shagbox enthusiast | |
OP  Shagbox enthusiast
Joined: Mar 2010 Posts: 210 | Can someone help me with the swap of my 350turbo to a 700r4? Does anyone know what else it takes to swap out from a 1975 350 turbo auto to a 1988 700r4 ,I have new torque converter to order and do I need to chage out or modify my driveshaft? If anyone could give me some advise on this would really help,Thanks 76 Shagbox looking for some Vanning fun and clubs out west north of L.A. |
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Re: Switching out 350 turbo for 700r4 Shagbox #453743 March 15th 2011 1:21 am | |
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Lordmodelbuilder
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| Lordmodelbuilder
Joined: Feb 2001 Posts: 3,059 Likes: 3 | You will have to move the transmission crossmember back because the 700r4 is longer. The driveshaft will have to be shortened,but the yoke remains the same. |
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Re: Switching out 350 turbo for 700r4 Lordmodelbuilder #453779 March 15th 2011 9:44 am | |
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Ripper veteran | |
| Ripper veteran
Joined: Mar 2006 Posts: 1,695 | Sorry, but a 700R4 is a direct bolt-in swap for a Turbo 350. Another thing to keep in mind is if you set the TV cable incorrectly, your transmission will explode in a short time. This cable regulates internal pressure inside the transmission. The only thing I can say is why? Why would you take out something that is bulletproof and replace it with junk? Just for overdrive? I've done the opposite swap several times, taken out the junk 700R4 and put in a T-350. In most cases, my fuel mileage improved as the 700R suffers from slippage in every gear. There are modifications you can make, but unless the trans is brand new, those modifications can speed up its demise. If you want a 4th gear, either swap in a 4L60 or 4L80. Much more expensive swap, but worth it.
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Re: Switching out 350 turbo for 700r4 Ripper #453783 March 15th 2011 10:02 am | |
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Shagbox enthusiast | |
| OP Shagbox enthusiast
Joined: Mar 2010 Posts: 210 | What does this swap require for that type of trans, not the 700r? I have conciderd changing the rear end gears before doing the swap and see if that helps freeway driving .My van seem to really run at high rpm at around 70-75 mph .I believe the gears are currently 473 .Would you know what gearing to go with to make it not rev so high .If changing the gears cures the issue than no trans swap needed.Thanks 76 Shagbox looking for some Vanning fun and clubs out west north of L.A. |
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Re: Switching out 350 turbo for 700r4 Ripper #453807 March 15th 2011 11:56 am | |
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Lordmodelbuilder
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| Lordmodelbuilder
Joined: Feb 2001 Posts: 3,059 Likes: 3 | Originally Posted by Ripper Sorry, but a 700R4 is a direct bolt-in swap for a Turbo 350. Not a direct bolt-in in a 1975 GM van. Last edited by Lordmodelbuilder; March 15th 2011 12:35 pm. |
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Re: Switching out 350 turbo for 700r4 Shagbox #453808 March 15th 2011 12:01 pm | |
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fatvanman addict | |
| fatvanman addict
Joined: Jan 2010 Posts: 573 | Shagbox, changing to numberically lower number gears will help keep the RPMs down on the highway, say going from 4.11 down to 3.30 gears, but your acceleration will suffer as well as low end pulling power. I haven't heard of 4.73 gears, but anything over 4.11 and freeway driving will be an issue. As for the 700R4 swap, they did get a bad rap because earlier units were junk. But most of the rebuilt units out there are perfectly fine. All you need to physically bolt the 700R4 in is a later model trans crossmember. The driveshaft will need shortening as well. I would suggest looking for a 1990's van for the crossmember and even the driveshaft. I found my 1994 parts van had an aluminum driveshaft which is much lighter and will aid in fuel economy and acceleration. Since you'll have to have it shortened anyway (unless you got lucky and found a shorty late model!) might as well use the better driveshaft. Coast Driveline in Ventura charged me $140 for the job including new u-joints. That's it for physically mounting it. You will need a lock-up converter kit which you can find from any speed shop. You do NOT need a new carb, but you will need new linkage as the ratio is different even though they look similar. Again, any speed shop can help get you the linkage and TV cable. THere is a company called TV Made Easy which makes the set-up simple, but I don't know the specifics about it. The point is you need to have the adjustment right as it controls trans line pressure and could cause failure if done wrong. Once everything is set up, you're good to go and you should see significantly better fuel economy than different diff gears, plus you get strong acceleration. It sounds like a lot of work, but really isn't at all. Colin "The great ones never die, they just get older, fatter and drive better vans!" |
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Re: Switching out 350 turbo for 700r4 Lordmodelbuilder #453812 March 15th 2011 12:13 pm | |
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fatvanman addict | |
| fatvanman addict
Joined: Jan 2010 Posts: 573 | The trans mount is only about 3" further back, and later G Series crossmembers are a direct bolt-in as they sweep back that 3". One issue I found is that if you have full length headers the later crossmember will need notching at the front and the exhaust altered as the clearance is quite tight. Colin "The great ones never die, they just get older, fatter and drive better vans!" |
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Re: Switching out 350 turbo for 700r4 Shagbox #453907 March 15th 2011 5:54 pm | |
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Ghetto Rat old hand | |
| Ghetto Rat old hand
Joined: Jun 2006 Posts: 1,241 |
https://www.flickr.com/gp/154142337@N08/15982P |
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Re: Switching out 350 turbo for 700r4 Shagbox #456453 March 25th 2011 11:56 pm | |
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Munz veteran | |
| Munz veteran
Joined: Nov 2002 Posts: 1,578 Likes: 2 | You will need a trans cross member out of an 83 or newer chevy with the 700r4 (some 3/4 and 1 ton models came with the turbo 350 or 400) and you will notice the rearward dip back the minute you look at it, a lock up kit for the converter (jegs, summit, ect.) and you should use an 87 or newer 700R4 because they have a 10 vein pump and many valve body upgrades from the original 83 version. The drive shaft will need to be shortened about 2-3". I hooked the TV cable right to the dimple on the carb linkage from the turbo 350 and had the guy who rebuilt the trans adjust it for me. I've been running this setup on my 77 for about 10 years now and I would consider it one of the best modifications I've done to my van. It gets better gas mileage but even better is when I'm crusin down the highway to my favorite Truckin it runs real quiet in 4th gear with the converter locked up. Munzvan@aol.com / Runnin Wild Truckers / I never met a van I didn't like. |
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