Auto Trans swap from 4sp Hydramatic to 700R4
 

Ok, although I'm taking the truck to a trans shop next Friday, we suspect the trans will need to be rebuilt. So far, the two prices I've gotten on rebuild are both about $3400. Unless I find find a club member with one to sell, the $3400 amount is outside of the amount I wish to spend. I was told that because I have the automatic now with the adaptor plate, other automatics will bolt up.

I need to see which trans will do so. I also suspect that I'll need to change the steering column as well.

Any member with knowedge on this type of swap, I'd like you to chime in and provide insite. Right now I don't know what trans to begin looking at. I was told a 700r4 will do then it was suggested that I should also consider one with overdrive for highway cruising.

Thanks
Jake Groby
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Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Here's another link concerning your Hydramatic and the factory adapter used to mount it. This link seems to indicate that you would need the Turbo 400 style factory adapter to mount up the newer automatic transmission including an overdrive.

http://www.67-72chevytrucks.com/vboa...omatic+adapter

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

The 700R4 is an overdrive transmission.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Jake you can use your original column. you just have to modify the linkage to fit. music man is correct.
ron

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

OK - Update, in speaking with other 305 V-6 experts (Ed Snyder, Pete Chronis and Steve McDonald), I discovered that I HAVE to change the transmission adaptor plate setup. On Sunday I lucked out and won a bid for the correct adaptor needed for only $400.00 vs. A new one that runs $1300 at Bendtsens Transmission.

I'm now in the hunt for a (Turbo-Hydramatic) TH400. New ones run about $1300 or so. I'll probably go that route, BUT I need to do some research on who builds good Transmissions.

There are many sellers and the prices run the gambit from $1300 - $2700. Not trying to be cheap but a penny saved is a penny earned.

Ya'll have any recommendations, who did you use/buy from?

Thanks

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Your not going 700R4 your going TH400?

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

yes, becasue of the torque from the 305, folks are telling me that would be the better trans. I dont do long haul cruises (maybe 100 miles in one way drive at 55 or less).

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

305
The 304.6-cubic-inch (5.0 L) 305 had a 4.25 in × 3.58 in (108 mm × 91 mm) bore and stroke. The 305 was GMC's standard pickup truck and Suburban engine from 1960 to 1974, and was one of the first V6 engines produced by an American company. The 305A was equipped with a single barrel carburetor and produced 150 hp (112 kW) gross at 3600 rpm and 260 lb⋅ft (353 N⋅m) gross at 1600 rpm (measured without air cleaner or accessories in an ideal environment). GMC also made a B, C, D and E version of the 305, with the E version producing 165 hp (123 kW) gross at 3600 rpm and 280 lb⋅ft (380 N⋅m) gross torque at 1600 rpm.
Maybe they're romanticizing the torque value a bit?

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

If the engine is putting out only 260-280 ftlbs, a 700R4 would be just fine. Plus both you and your engine would like the decreased rpm's. There's really no need for a TH400.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Might I suggest the 200 4R trans for 2 reasons 1 they are the same length and de mention as a TH 350 the basic Automatic transmission there for not requiring a new drive shaft length to be made. # 2 they are a Overdrive Transmission. have a look at this site for the 200 4R trans https://www.bowtieoverdrives.com/

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Wolfman, I think he's converting from a Hydramatic 4-spd, not a TH350 (I don't know how the length of those two compare though).

jbgroby, if you're seeking a reputable like new rebuilt trans builder , I like TCI or B&M. If you decide to go 700R4, which I think is a better choice for your application also, give
Bowtie Overdrives a look. You can also look at Summit to see some reasonable price comparisons.

Having said all that though.. if you've got an adapter that will allow a TH400 to be bolted up to your V6, and the V6 is stock, and you prefer TH400 because you don't need the overdrive because you never exceed 55 mph AND you're concerned about price - why not just install a reputable rebuilder's TH350? Not as strong as TH400, but you do not need a TH400's strength (look at it this way, ALL the automatics in this era's 3/4 ton 4x4s were TH350s...) and it sounds like you don't really need overdrive. TH350 ($993, rated to 400 hp) is generally several hundred $ less than a comparably built TH400. Just a thought.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Thank You Jocko,

Yes, I have the OEM 4-spd Hydramatic. In getting prices for a rebuilt (to keep the truck as OEM) the prices I've gotten from two decent transmission places - Hemming’s and local, are falling between $3200-$4500. That’s a game changer on the OEM route. It just seems more logical to upgrade the transmission to something more modern.

In speaking with Ed Snyder, Peter Chronic and Steve McDonald, they educated me and explained that IF I want with another transmission, I first had to find an Chevy adaptor - with luck I did and bought it last week (waiting on delivery). Next will be the decision as to what transmission I need to bolt up to the block.

All this is new to me and I'm learning just as fast as I can. On one hand I was told that I NEEDED the TH400 because of the torque that a V-6 puts out. Then another member said that was not so and broke out the numbers.

For the past 2 years I've driven the truck to mainly local shows and cruise night as far away as 100 miles one way, I've driven I-10 for short distances (no other route available between certain points) but I try to mainly staying on the low roads. I would not mind going to further distance shows such as the Emerald Coast, North Louisiana shows, etc.

Truck handles 55-65 no problem (except sucking gas when I push it). If I can put in a transmission that has Overdrive and can handle 70-75 that would be great. I just not sure what route to take, because I have no experience with this type of issue. I know I have to recut/adjust the propeller shaft (drive shaft) and have it rebalanced. To use the same steering wheel, I’ll need to make up the linkage (cable). But I’m taking one step at a time.

I expect the truck to be down for at least 6 months – summer season is shot (unless I magically fall into a pot of money), so I’m not in a rush, but just need to make the right decision for the long haul. SO anyone help with be greatly appr.

Jake

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

The stock torque rating of the v6 is almost identical to the stock 350 that came in the corvettes back in the 80s with the 700r4 behind them. I have a H/C/I swapped 350 in front of my 700r4 and it has been fine for the past 10 years or so.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Ok bud then since you say you would like to go further and also maybe better gas mileage again I highly suggest you look at before buying any Transmissions at the 200 4r at that link I gave you earlier you will not be disappointed and you will not need to shorten your drive shaft there for saving you money it truly is a win-win if you go with a 200 4r for the kind of work and parts that they put into these Transmissions you won't be able to find a better price go have a look and have a read you will be impressed

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Ok, thanks, I never looked at the 200 R4 but will.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Keep in mind that you can drive a 1000hp big block with a TH350 and not hurt it at all - because it's not the engine that over-torques the trans, it's all in how the driver applies the torque with his right foot.

When folks say this or that trans "won't hold up to a big block or even a stout 350" what they are really saying is "this or that engine is CAPABLE of over-powering the trans and breaking it." These types of statements are usually made relative to THEIR driving habits and they assume you will do the same. So, in other words - for THEIR driving habits, a TH350 might not last long... What matters, though, is YOUR driving habits. For everyday driving, any of them will do. One note, if you're going to be towing things - then, yes, heavier duty trans is worth the investment as is a good trans cooler (actually, that's recommended with ANY auto trans you choose). But for just driving around with normal acceleration and cruising, doesn't matter if you have a 6 cylinder or a monster big block, how you drive it will dictate whether it lives or dies.

So, if you are gonna do burnouts, then, yes, TH400 probably a better choice. But your posts don't strike me as written by a guy that drag races stoplight to stoplight. If you drive reasonably, the TH350 or 700R4 or 2004R will be just as functional as a TH400.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Thank You Jocko,

No I don't drive to peel out or any type of racing. However, I would like to pickup a 13-15' canned ham trailer (period correct) to tow to camping and car events. The gross weight of those are 1200-1300 lbs. What trans do you recommend with that?

Thanks
Jake

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

turbo 400 with overdrive you have the best of both worlds and no computer to run it

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Ok, I did not know that made that, I'll start looking.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

Nobody makes an o/d TH400 (if that is what you’re thinking). Libby’s recommending a 1:1 high gear TH400 (they all are) + a Gear Vendors overdrive (or something like that) behind it (separate unit). It is the best of both worlds, and bulletproof, but not inexpensive to do both. New GV unit around 3k alone. If you’ll be towing and at what sounds like lower speeds - then I would just go with the TH400 and leave it at that. Do you happen to know your rear end ratio? TH400 will require some means of kickdown linkage.

Re: Auto Trans swap from 4sp Hydramatic to 700R4
 

here you go