TH350 to 700R4 Help!!!

[Sunbound85]

I have been doing alot of research recently into replacing my Th-350 or Th350C with a 700R4... the advantages of the 4 speed seem great .. better acceleration, and gas mileage etc...
My TH-350 has the 9" tailshaft... strangely I cannot find the 4 pronged connector for the lock up on this transmission, I thought by now all the Th350's were lock up... My trans leaks constantly and recently when warm, it will shudder when reversing, moving very slowly, but all the forward gears work with no noticable problems, except for a whine that has developed at any speed over 25 mph... things seems to be heading down hill. Found a load of clutch material caked on the bottom of the pan when I changed the fluid last - Instead of rebuilding this trans I would like to swap in a 700R4,

I have read the driveshaft should not need to be modified if you have a TH350 with the 9" tail... is this true for the caprice..? what about the shifter, will I need to find one from an overdrive car? or will the 3 speed shifter work for now? Can I use the same crossmember?

If there is anyone who has done this type of swap before, let me know if you have any tips or advice... Im a bit nervous getting into all of this... never swapped anything more substantial than a carburetor...

[PeteA216]

strangely I cannot find the 4 pronged connector for the lock up on this transmission, I thought by now all the Th350's were lock up...

No, none of the TH-350's, or 400's ever had lockup. The TH-700R4, 4L60, and 4L60-E are all basically the same transmission with improvements, especially the 4L60-E, but in a nutshell, are "simply the turbo 350 with overdrive." Same goes for the TH-400 and the 4L80-E... except the "E" means fully electronic controlled as in the 4L60-E.

In terms of the other questions you have, I'm not positive, and I'm sure there's others here that will have more concrete information, but here goes: If I remember correctly you will need a different crossmember, and a different driveshaft, both that can be found at a junk yard from another Caprice with the same rear end. Your shifter will work just fine, the needle will just go further than normal if you put the tranny into 1st gear (D1).

[silicon212]

The TH350 did indeed offer lockup from 1979 onward - this transmission was called the "TH350C". TH400 never got lockup. The 700R4/4L60/E design was originally based upon a TH350 with lockup added, but evolved. Some parts commonality with the TH2004R was available at the outset, things such as front pump, torque converter etc and this lasted midway through the 1984 model year.

The mount on the TH700R4/4L60 sits about 1/2" behind the location of the TH350 mount, so you can either use a TH700R4 crossmember, or you can lengthen the mount slot in your existing crossmember.

The 700R4 and TH350 9" trans will both use the same driveshaft (difference in overall length between both is 1/8", negligible), however 1977 and up B-body cars which had the TH350 had the standard 6" version and not the 9" version (which is found in 1971-1976 B cars along with Cardan CV joints).

The shift quadrant needle won't go further, it will just have one extra stop in it.

[PeteA216]

The shift quadrant needle won't go further, it will just have one extra stop in it.

Thats what I meant, but at the time had trouble putting it to words.

(which is found in 1971-1976 B cars along with Cardan CV joints).

Does that mean the car(s) came with rear independant suspensions?

[Sunbound85]

Actually Silicon212 ... that point about the 1977 up only having a 6" tail shaft is beginning to make plenty sense in my case...
See, my in dash indicator thing shows four detents "D,3,2,1"`and 'Automatic Overdrive' just to the right....

I will conclude that my car ORIGINALLY did have a 700R4 (or 200R4?) and at some point had an older TH350 with 9" tail thrown in its place ( I have read the early 700R4's were weak in places and prone to failure - my car is an '83), which would explain the lack of a lock up converter and only having three gears. I know that if this was the factory trans, it would definitely have the lock up feature at least... and would not be showing four Drive detents on shifter.
Thanks for the help!!!

[silicon212]

Originally Posted by PeteA216

Does that mean the car(s) came with rear independant suspensions?

No, a Cardan joint has double tandem spiders, looks like two U-joints at one end. The two spiders are connected through a center cross piece which has a ball and socket joint inside (the ball and socket ends of the joints are the yoke and driveshaft themselves).

[Blue Bowtie]

Yes, I've done the swap in a few vehicles, including '57 Bel Airs, '70-80s trucks, and '70s F-, G-, and A-Bodies. If you already had a lockup converter, the swap is even easier. Silicon outlined the hardware differences pretty thoroughly. The electrical connections are different, but the harness can be altered very easily to the newer style connector. The dipsticks are usually not a problem, although the F-bodies seem to have some dipstick tube clearance issues. I'm thinking your B-car will have plenty of room. The crossmember may require alteration (slotting or cutting/welding) and driveshaft spline count may be different depending upon years.

When you select a 700-R4, make sure it is a V-8 unit, and it would be better to get a 1987-later unit for some of the upgrades which were made across the years.

[PeteA216]

Originally Posted by silicon212

No, a Cardan joint has double tandem spiders, looks like two U-joints at one end. The two spiders are connected through a center cross piece which has a ball and socket joint inside (the ball and socket ends of the joints are the yoke and driveshaft themselves).

Ah, see the term "CV Jount" screwed me up. To me it looks like a setup like that would cause problems in terms of maybe too much flexability... whats the advantage to having a U-joint setup like that instead of the more simple one below?

[Sunbound85]

I think i will be adding an aftermarket device to control the lock up mechanism, as my computer harness was pretty fubared when I bought the car (some wires were even melted onto the exhaust manifold) i addressed this by intalling a 500 CFm edelbrock AFB carb and a mechanical advance distributor... this really made the car a hell of a lot better to drive and start... strangely my gas mileage got better as well. Oh and under the hood looks much neater without all those wires and vacuum hoses criss crossing evrywhere.
I see bow tie overdrives advertising a unit that simply requires the intallation of a new brake switch which will disengage lock up when stopping, and a pressure switch which is activated in 4th...
http://www.bowtieoverdrives.com/cata...AT&CATID=OA1A2

Oh, those CV joints are a pain to replace, no clips = some wax like glue holds them in... you need a torch, a vice, a punch and patience. had a machine shop do mine. I cant imagine having to do that to a 'cardan' style joint.

[silicon212]

Originally Posted by PeteA216

Ah, see the term "CV Jount" screwed me up. To me it looks like a setup like that would cause problems in terms of maybe too much flexability... whats the advantage to having a U-joint setup like that instead of the more simple one below?

The CV stands for 'constant velocity', as you are aware. The regular single U-joint setup can transmit power in 'pulses', where there is a rhythmic, rapid acceleration and then deceleration of the driveshaft. This is worsened by excessive driveline angles. The Cardan joint is supposed to eliminate this by 'cancelling' the pulses with counterpulses from the other U-joint, so the speed of the output side of the shaft is constant.

The ball-and-socket joint is prone to failure on these, and results in a clunking / thunking sound similar to that of a bad U-joint.

[PeteA216]

Now that makes sense to me... so it'd probably be a good idea for example, if I were to lift my truck, to get a driveshaft with this style U-joint on each end because of the angle increase with a lifted suspension correct?

[silicon212]

In a twist of irony, the Cardan joint can actually fail with excessive driveline angles. The use of the design in cars was to 'smoothen' out the driveline, but without one on each end of the driveshaft, it doesn't make a lot of sense.

[PeteA216]

So, in a nutshell, the Cardian joint works better or "smoother" than a normal U-joint at greater angles, but at the same time is less reliable than a standard U-joint at greater angles. Maybe thats why on seriosuly lifted vehicles, like my neighbor's Jeep for instance, the shop tilted the engine and transmission downward a bit and tilted the rear axle up a bit using wedge shaped spacers in the leaf springs to starighten out the drive shaft.