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TH350 --> 700R4 swap completed

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Author	Topic: TH350 --> 700R4 swap completed
rhoeven Senior Member Posts: 349 From:San Mateo , CA Registered: Feb 99	posted 12-07-2000 02:17 AM The transmission swap in my '81 is finally completed. Well I had some bigger hurdles to overcome but the car is running again. The main obstacle was that the 700R4 does not just bolt in and the only way to make it work was to modify the transmission crossmember. I did relocate the crosmember 1-3/4" to the rear so the mounting bolts do exactly fit the existing crossmember bracket. Now the bracket did fit but the area of the speedo gear box did touch the crossmember. I had to lower the crossmember exactly 3/4" and used a little over 3/4" rubber padding to make things correct again. It was quite hard to figure out all the dimensions specially with a car on jackstands and me crawling under it. I will post a step by step HOWTO with a drawing how to modify the crossmember. A good welding shop can do the entire job in about 1 hour I guess. Once the trans was in , I measured the lenght of the driveshaft and had it shortened accordingly. While they were at it, I also had both U-joints replaced. The startup went without problems. Steve from Bowtie Overdrives was very helpfull. This evening I took her to the local gas station to fill her up but on the way back suddenly I got a problem (not transmission related). Battery light came on, choke light lit up, RPM dropped to zero, buzzer made noise and dome light came on as well but was able to make it home. Problem was a blown gauges fuse. Bubba has been in my car as well. The gauges fuse had the wrong value, 10Amp instead of 20Amps and I have no spares . Oh well tomorrow is an other day and hopefully I can open her up. My first short drive impression was That car does accellerate now I still have to modify the parking brake bracket and install the heat shield above the cat. converter. Roger ------------------ '99 Coupe Mag red/black M6, Donaldson LS6, V1 '81 Charcoal/silver C3 coupe, Monza mufflers,700R4 San Mateo, CA email: rhoeven@bigfoot.com IP: Logged
Gary79 Senior Member Posts: 176 From:quincy,il,usa Registered: Aug 2000	posted 12-07-2000 06:59 AM roger,glad to hear you got it done,are the 81 frames different from 79? i used trans bracket from bowtieod rather than move x-member and someone else said just turn the stock bracket around & it would work. anyway when you get the other "bugs" worked out you'll enjoy hwy cruzin w/new tranny. ------------------ 79 vette,L-48 355,XE 262 comp cam,edelbrock performer man w/edelbrock quad #1903,stock re-worked heads,700r4,ss calipers,rebuilt brakes,bearings,differential & suspension, e-mail gkb@adams.net IP: Logged
norvalwilhelm Senior Member Posts: 22 From:Waterloo ontario Canada Registered: Nov 2000	posted 12-07-2000 08:08 AM GM sells a tail stock Part # 8673406 which moves the transmission mount back to the same place as a 400. I did this swap and it was a direct bolt in. You will love the 3.06 1st gear and the .7 overdrive. Be careful with the TV cable adjustment. If it is off you can burn the transmission out very quickly. You should feel a definite 1 2 shift. If not you can up the line pressure with a simple cable adjustment. I think this is an excellent swap for the 350 400 cars. Best of both worlds. Good luck Norval IP: Logged
rrent Senior Member Posts: 267 From:Round Rock, Texas, USA Registered: Sep 2000	posted 12-07-2000 08:11 AM Are there 700R4's that are better than others. Should I look for a specific length tail shaft? Overall length? Do I need to find one from a Vette or other specific vheicle(s)? Would one from a full sized truck work? Certain years without electric speedo connections? How much should I expect to pay? Does anyone sell them new/rebuilt? Having one rebuilt is not problem I know a good tranny guy. thanks Ronnie ------------------ '77 nothing fancy -just fun Vettepage: http://home.austin.rr.com/deeron/vettepage.html IP: Logged
Chucks76 Senior Member Posts: 158 From:Lawton, OK Registered: Feb 2000	posted 12-07-2000 09:09 AM Get the 700r4 with the 30 spline not the 27 spline input shaft. I think that the changeover year was 86? Any can be converted to the higher performance vette one by swapping about $50 worth of parts(servo,etc). ------------------ 76 L-48 Torch Red Currently undergoing 2nd engine and tranny swap this year! New motor .030 over,hypereutectic coated flat tops, Comp Cam XE268H, Trick flow 23 degree aluninum heads, performer intake, dynomax ceramic coated headers, and holly 600 vacuum secondary carb. TH350 rebuilt using all Trans-go parts including shift recalibration kit. New Firethorn Interior Rebuilt Frontend and brakes 2 1/2 true dual exhaust(no cat) IP: Logged
Rhys Senior Member Posts: 1040 From:Tampa Area, FL Registered: Dec 1999	posted 12-07-2000 09:23 AM I was going to buy one from an 88 vette. I could just use the GM transmission mount replacement and a new spline size? $100 seems too good to pass up (even if it does need rebuilt) Thanks. ------------------ Rhys VetteFinders.com Your Internet destination for buying and selling Corvettes. IP: Logged
rhoeven Senior Member Posts: 349 From:San Mateo , CA Registered: Feb 99	posted 12-07-2000 09:41 AM Gary79, The crossmember of the '81 is different from '79s . There was no way the delivered bracket could be fixed to the crossmember. The original bracket is welded to the crossmember where as the Bowtie bracket is supposed to be bolted on. Gene Hebert emailed me and said that '79 and earlier crossmembers do work with the Bowtie bracket but at the time I received that mail, I had already partially modified the crossmember so there was no way going back. Norval- The documentation stated the importance of the TV cable adjustment. It took me several hours to get it right. Due to my electrical problem last night I could not really test the feel of the shifting. I know that it is going to be a major pain if I have to change the TV cable settings again, i.e remove tailpipes, drain oil, remove trans. pan etc... but this is the world of automatic transmissions I guess rrent- I got my 700R4 from Bowtie Overdrives and paid little over $1500 for transmission, new TV cable, dipstick & tube, pressure gauge, shifter kit , crossmember adapter (which I could not use) , shipping costs and CA sales tax. It was the best price I could find. Some local transmission shops did not even want to tackle the job and even refused to sell a 700R4 to me. Their prices were in the $1600 range for just the transmission. I feel that I got a great deal from Bowtie. I had to shorten the driveshaft for 2-5/8" so this is the distance the 700r4 is longer than the th350. Roger IP: Logged
norvalwilhelm Senior Member Posts: 22 From:Waterloo ontario Canada Registered: Nov 2000	posted 12-07-2000 10:41 AM The TV cable adjustment is made on the side of the carb. It is something that can be done in a few minutes. If your pivot point is correct all you do is push in the metal tab on the cable mount and push the nose towards the firewall or into the mounting bracket then take the carb throttle linkage and give it full throttle until the cable ratcheted out and the butterflies of the carb are at full throttle position. This should adjust the TV cable correctly. If you make the cable shorter by pushing it into the body the shifts are alot harder You can try this but the 1st time you floor it the cable will self adjust. I mentioned the throttle stud must be in the correct location so that at a given throttle position the TV cable is pulled out the correct amount for line pressure. I have these demensions but not here. The shop that rebuilt my transmission wanted my copy for their files. Remember to adjust the TV cable nothing but the aircleaner must come off. Norval One powerful Vette and One small arabian gelding IP: Logged
robzr Senior Member Posts: 35 From:Chicago, IL 60647 Registered: Oct 2000	posted 12-07-2000 12:05 PM I got a kit for my '76 from Bow Tie Overdrives as well. If I remember correctly it was ~$1450 and included trans, lock up converter, lock up brake switch, shifter assembly, trans cooler lines, carb linkage, miscellanious other parts and shipping. A hell of a deal. You also get a 1 year guarantee, and he helps you install it over the phone. If you are in doubt, give the guy a call (I think his name is Steve), he is very knowledgable and willing to help. I've talked with him for at least 30 minutes probably 4+ times, sometimes at his expense (long distance). You cannot beat their prices. He says he has nitrous'd and blown big blocks running behind his transmissions. If I ever need another 700r4, I'm going straight to bow tie overdrives. BTW the website is www.bowtieoverdrives.com & www.700r4.com Rob IP: Logged
bluevette Senior Member Posts: 357 From:Colorado Springs, CO Registered: Jan 2000	posted 12-07-2000 12:33 PM I just got my 79 out of the transmission shop yesterday. Was going to get the 700R-4. I was originally quoted $1500 for the job, then out of nowhere it went up to $2100. So instead I had my TH350 rebuilt. A couple of key things they told me about the 700 install was that if you can find a crossmember from an 82 vette, it should bolt right up with no problems. Also, find a 700R-4 from an 88 model and newer. The earlier 700R-4's had some problems. John IP: Logged
Shrike Senior Member Posts: 203 From:Ft. Worth, Texas Registered: Oct 1999	posted 12-07-2000 04:44 PM rhoeven, I have a 700R4 from bowtie overdrives sitting in the garage waiting till I get some free time to put it in and I have a question. What did you do about the electical hook up for the lock up converter? I have heard several different reports, and the directions are not very clear (at least to me!) Did you have to buy a harness from someplace else? ------------------ --Scott-- 1976 automatic, non-stock Primer grey and black IP: Logged
Smokehouse69Mark2 Senior Member Posts: 730 From:Victoria, TX, USA Registered: Aug 2000	posted 12-07-2000 05:02 PM Rhys, I read in an article a couple of months ago the you should stay away from the 700r-4 from a C-4. The problem is in the rear mount on the C-4 trans is so different from a C-3. I can't exactly remember which transmission they suggested, but I seem to remember something about 89-91 full size chevy as being the best match. It had to do with the tailstock length. IP: Logged

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