Transmission for my hot rod trailer puller

[OldSub]

I'm building a hot rod trailer puller based on a '54 GMC 1-ton truck.  I'll be running a GM 14-bolt rear with 3.42 gears, and either a Cadillac 500 or a Chevy 454.  I expect the finished truck to weigh between 4000 and 4500 pounds, and my trailer is maxed at about 8000 pounds.

I have both the possible motors.  The Cadillac carries a Quadrajet and came with a Turbo 400.  I have both a Q-Jet 454 and a TBI 454, the TBI has a 4x4 type Turbo 400 behind it and the Q-Jet has a Turbo 475 from a motorhome.

But I'm thinking of running the TBI 454 and a 700r4.  The overdrive appeals to me, and means when I'm not loaded I can turn the motor much slower and maybe save some gas money for buying new toys to haul home.

I probably won't drive this truck more than a couple thousand miles a year, and may not drive it 20,000 miles lifetime.  Am I nuts or does a newly rebuilt 700r4 stand a chance in an application like this?

Yes I'll abuse it by pulling a big load, but I'll make sure the cooler is big enough and I pull smooth so the load isn't like drag racing...

[Crosley.In.AZ]

If I read this correctly , you will be in the area of combined weight of 10k pounds when towing?

I would not use a 700 trans for that.... obviously you would not use over drive while towing , still too much weight for that trans design.

[OldSub]

10,000 to 12,000 total maximum combined weight, though typical might be closer to 8,000 or 9,000.

So if I'm trying to do this on a budget best plan would be to skip the OD and stay with one of my other existing transmissions?

At an expected life of 20,000 miles, figuring averaging 8 mpg at $4/gallon, a 30% (optimistic) fuel savings does not quite pay for a 4L80e with controller.  Fuel costs may (will) go up over time, but assuming declining use over time against the time value of money I don't want to spend now...

Okay you persuade me to run the TH 400 or 475 until I remember the K2500 parked outside has nearly 190,000 miles on it, and it has often pulled my trailer.  Its a 350 and 700r4.

Is my K2500 running on borrowed time or does the big block make that much difference?

[wayne petty]

just curious....   did you know that the 4l80E came in diesel pickups when it first came out with a stand alone controller... and harness..... so that might give you a lessor expensive alternative...   i think you still have to have the gas pedal assy with the electric sensors on it also...

it does not have the nice ajustable shift points...  but it might work... and save a ton of money if you already have a 4l80E...

there will probably some tech articles on that swap over on one of the truck magazine sites....


wayne

[enjenjo]

For what it would cost to build a 700R4 that  would be suitable for towing, you could put a Gear Vendors behind the 400.

[OldSub]

Thanks everyone for the feedback and ideas.

I don't currently own an 4l80e, but if I did I'd probably spend money on a controller rather than on a 700r4.  So far I don't have as much money in this project as just the controller would cost, and the prices on those plus the 4l80e make this no longer a budget project.  I didn't know the 4l80e was ever offered behind a Diesel.  

I've not priced a gear vendors OD and have forgotten about that option.  What I like best about it is I can choose either the Cadillac or the 454, use the appropriate existing transmission, and add the OD some year when I expect to drive this thing far enough for it to pay off.

Thanks!

[wayne petty]

putting cad motors and their th400s into chevy pickups  has been done for years with great improvements..

it is still your decision ...    the cad the rat...  if your towing rpms are under 2500 i would think the cad... over ... maybe the rat..

the weird thing is they can both use the same headers... the cad with exhaust adaptor plates accepts rat motor headers..

the only thing i would make sure of it i was going to put the cad in.. is to change the head gaskets... and freshen up the valves after checking for cracked heads...a new timing chain... and what ever else... and do a really through rebuild on the carb... this would probably be best done on either motor...

the only drawback on cad motors is the fan belt set up... with the fan driven off a another pulley or something like that...

with the rat motor... there is the ease of pulling the race motor out and dropping it in the pickup to make it home...   if your racer has a rat..


cad motors are cheeper ... as are their transmission in the junk yards...  chevy stuff requires a long search as everybody wants them...

[Crosley.In.AZ]

If you do have a t-475 tranny... that is what I would use.

With the grunt the caddy motor would have it would work well.   A gear vendors would be a plus.

Caddy motor typically do not like to run higher RPM down the roads.


The 3.42 gears , with a moderate tall tire should work well with the Caddy. It will not be a race horse , but should pull well.

[OldSub]

The plan is to use 265/75-16 tires which are 31.65 tall, for rpm of 2,542.6 at 70.  I could end up running 75 mph, but the nearest place that is legal is nearly 500 miles away, and this truck may never get that far from home.  Far more likely is brief stints at 70 with most its life spent under 65.

Same tires, 4.10 gears, and the TBI 454, I could accelerate hard from 70 pulling a loaded trailer.  That truck was a K3500 (since totaled) weighing more than 5,250 pounds and never quite got 10 mpg empty.  With a loaded trailer 8 was best ever and worst was about 3 over Monarch Pass in Colorado and into Utah pulling an empty trailer.

2000 rpm should be 55.  With a 30% overdrive I could run 70 at 1800 and 55 at about 1400.  The appeal of course is burning less fuel.  Based on my car experience I guess with overdrive I'd save at most 15%.  Not enough over 20,000 miles to justify the expense of a 4L80e or probably a gear vendors either.  Double the savings to 30% and it still isn't likely to justify a lot of expense.

The project truck is my avatar.  I do have the Cadillac 500, the Chevy 454, the TH 475 and the TH 400.  I do not have a race car; I drag old trucks home...

[Crosley.In.AZ]

Do not confuse lower RPM automatically with  increased  fuel mileage on a large scale.  

A 700 trans is not strong enough to pull the weight in over drive.  Not even with a billet 4th gear servo.

The side load on the planetary unit in over drive  would cause some fast wear I think... could be wrong.

[enjenjo]

Here is another thought. Get a truck 4 speed, a heavy duty one. Take out everything except the cluster, mainshafts, third and 4th gear. Install it in the driveshaft backwards. Hook up a remote shifter to switch it from fourth to third. Third would become your overdrive, fourth would be direct.  You might have to make a beefed up support for what was the input shaft, as it would now be supporting a driveshaft.

[OldSub]

Crosley I expect that as long as I'm at an rpm where the motor produces sufficient torque turning it slower means less internal resistance per mile, and if I'm running the TBI motor, that will also result in more efficient operation.  Key is that the motor be at an rpm where it produces enough torque to do the job, if it isn't, I'm in trouble.  Since the Cadillac does not have EFI I may not realize the same efficiency with it.

When I tow using my K2500 with the 700r4 I keep it in direct, not overdrive.  Pulling an empty trailer I've considered running in OD, but have never actually done it.

Enjenjo I've played that game as a mental exercise and each time end up deciding its not a good idea.  I suppose it depends on exactly what 4-speed, but aren't the gears likely intended to run one way, not the other?  

I've wondered how you would shift such a thing.  Being forced to stop to shift would in part defeat the purpose.

I have a couple of SM420 4-speeds around.  They are pretty stout and GM used them in applications with more than 16,000 GVWR.  

Are you aware of anyone who has actually done it?  Successfully?

[Danimal]

I have a '92 c3500 1 ton x cab dually that I use to tow. What OD trans is in that? I don't know but it is bolted to a 454 tbi and I get around 12-14. Loaded in D I get 8-10 ish. I have pulled 12 out of it hauling a gutted 54 chevy 4 door on a trailer but it was flat Ohio ground and it was in a good mood.

I'm just wondering if you couldn't pick one of these up cheap enough, especially with the gas prices folks are dumping the 454. How well does the '54 sit on a K/C frame? I've done an S10 frame but never messed with the bigger ones. How hard could it be? Looking at Don's COE, the width looks good but how big are the fenders? I suppose maybe a 1 1/2 ton clip would fit better?

[wayne petty]

just ran across this interesting cad build....


http://www.popularhotrodding.com/enginemasters/0609em_cadillac_performance_parts_engine/index.html

it only runs a few minutes at a time on a dyno... but it had a lot of thought put in it....

be sure to check out the photo spread...

http://www.popularhotrodding.com/enginemasters/0609em_cadillac_performance_parts_engine/photo_01.html

[OldSub]

I have a '92 c3500 1 ton x cab dually that I use to tow. What OD trans is in that?

Dan I don't actually know, but I'd bet its the 4l80e.  My '89 K3500 is a TH400 suggesting the 1-tons had the bigger transmissions as would seem appropriate.  My '91 K2500 is a 700r4 or maybe a 4l60 and I know that because I crawled under it and looked.  The guy I got it from claimed it was the bigger transmission and I wanted to know before I laid down any money.

Wayne:  780 horse in my trailer puller.  Cool.

I have a Cadillac 500 and TH400 setting in my shop.  This evening I may have lucked into a second one.  It belongs to my son, and the car may become payment of a $1000 he owes me but likely will never pay me.  That makes Cadillac even more likely the truck motor.