suburban conversion from 1/2 to 3/4 ton

[gnmas]

I'm looking to convert my 72 big block 1/2 ton suburban for towing an enclosed car trailer. I have a 72 3/4 ton pickup with leaf springs as a donor truck. Would it be better to use the leaf spring setup from the pickup or can i get away with using the coil setup? i will be towing approx 7000 lbs. My buddy wants to swap complete frames, but I want to avoid that if possible. He says the 3/4 ton chassis is beefier.

[DINS 1]

There are many 3/4 coil spring burbs out there. I think they ride beter loaded and empty. the 3/4 trailing arms have extra steel on the bottom of them and the rear coils are of course heavier. you might want to add helper air bags depending on the amount of tounge weight. What rear gear and tranny do you have in the donner truck? The rear axels are differnt from coil to leaf.

[gnmas]

Hey thanks for responding. I have a 700r4 trans. I'm not sure of the axle ratio in the donor truck. I'm assuming its probably 4.10. My buddy wants to use the pickup chassis and roll it under the burb but I already have two body off projects already going and i really dont want to take this truck all apart. Its got all fresh paint, interior, motor and transmission. i thought i would just use the 3/4 ton control arms and spindles in the front and slide the leaf spring rear under the back but I'm thinking that might be harder than i originally thought.

[Average Joe]

I may be mistaken here but I thought the rear part of the frame was different on a coil spring frame versus a leaf spring frame. I have however, seen some guys on here building custom hangers to accomadate leaf springs usually while doing a 4x conversion on a coil spring frame. Is your 72 pickup a GMC?

[DINS 1]

remember that the pickup frame is shoter than the burb frame so you have to weld the on the rear part of your burb frame to the pickup one to use it

[gnmas]

So would the best way to go to keep the coil spring setup, go with the 3/4 ton coil spring control arms and put my coil spring mounts on the dana leaf spring rear out of my 3/4 ton pickup? The donor pickup is a chevy not a gmc. I'm also looking for a set of good 3/4 ton steel wheels and a nice set of dog dish hubcaps. I have a couple of nice sets of 1/2 ton caps, a set of steel wheels and two sets of michelin LTX tires to trade or sell. Also I have an nos set of chevrolet full wheel covers in the boxes.

[DINS 1]

that would bee the least amount of work. I have a 3.50 gear coil spring dana 60 if your interested.

[4x4Poet]

The 3/4 ton coil spring burbs had extra stapping riveted to the frame for strength at the rear wheel arch.

[capev86]

a 1/2 ton burb is plenty rugged enough to haul a 7000 pound trailer. it's all in the choice of options, equipment

back in the mid 80's my dad put 3/4 ton coil springs on the back of his 72 c10 burb because he was hauling a 71 holiday camper that weighs 6k loaded and has like an 800lb tongue weight. we still have the camper after 27 years.

they were actually an option back in the day, even on the blazer. they are the cats-meow for a tow rig (and suburbans have more rear body weight anyway). check out lmc truck. you will see the rear coils listed for the 1/2 ton are the same part number as the standard 3/4 ton. they don't even bother with standard 1/2 ton rear coils (wonder why....lol). if the trailer is REALLY heavy on the tongue, you might want the 3/4 ton HD coils (picked up a pair for my truck) from lmc. if you need more than that you will want a 3/4 ton axle

rear coil spring load ratings per side (remember body weight is part of that):
1/2 ton: 1400 lbs
1/2 ton HD and 3/4 ton: 2000 lbs
3/4 ton HD: 2700 lbs

if you figure a 5000 pound burb has probably 2000 pounds on the rear wheels, that means you only have 800 left over for passenger load, cargo, trailer tongue, etc. easy to understand why 1/2 ton trucks have such bad sag when you hitch up a big trailer. i'll give up a little riding comfort for eliminating sag and improving handling (less rear sway). these are trucks after all and i drive the car when i don't need it (or the desire to burn gas is weak).

make sure you have HD cooling, preferably an aux trans cooler for that auto, and at least a front sway bar (i recommend the 1-1/4" unit from an 80's 1 ton, camper special, etc).

on my 72 burb c20 (307/3 on the tree) i'm going all out: factory tach and vac gages, royal purple man trans and axle gear oil, 4 core rad and 7 blade fan, 15k trailer hitch, etc. i just installed a set of $$$ carbon-ceramic severe duty Hawk brake pads on the front

only real advantages a 3/4 ton will give you are the beefy springs, a little more reinforcing, a thicker track bar (on coil spring rear trucks), big brake booster and rear drums. my 72 burb dealer brochure puts trailer capacity at 5500 max for a 2wd 1/2 ton and 6000 for 3/4 ton (7k for a 3/4 ton pickup). but i think that limit is more set by the engine power levels of the time and not chassis design limitations. just don't forget a brake controller/trailer brakes on anything bigger than a small utility trailer, drive carefully and you should be fine.

[IMG][/IMG]

[jeffg1010]

...and you touched on tranny. In my experience, the 700R4's don't hold up for long term towing of a 7000 pound trailer. I see a rebuild in your future.
I have a 4L80E and it's never given me issues on towing. My camper is 6,300 dry and around 7k loaded.

[Walts_restoration]

Add a tranny temp gauge and a cooler for that 700r4. It will help the life of it.

[capev86]

trans cooler, proper maintenance/adjustment, synthetic atf and not beating on your tranny and it should have a good long life. the 700 is stout enough unless you are trying to pull a house off it's foundation (and you can have them beefed up to do just about that too). in 96 we took my dad's 84 burb w/ 406sbc and 6k pound 71 holiday camper on a month long trip out to yellowstone and back. that 700 got worked very hard near mt rushmore, in the grand tetons and in the hills of colorado on the way back. only issue we ever had was the cap popped off because the safety pin was missing. local shop that towed us in michigan had the pin on hand. added a little fluid and we were back in business.

[DINS 1]

other than carrying weight the differance in having 3/4 is the larger front and rear brakes. It is always good to be able to stop.

[capev86]

but a modern trailer should have good enough brakes that stopping should not be a problem.

i think the front rotors are the same size (just 8 lug vs 5). the calipers sure are the same (same brake pads). even the 1/2 ton has big enough drum brakes on the rear, so unless you are the type that has no business towing trailers (gas-brake types, etc), you should be perfectly fine. my dad had no trouble with this 72 c10 burb towing our 6,000 lb trailer.

i heard some Airstreams (back in the 70's or 80's) had disc brakes (not drums) that were so powerful that some tow vehicles of the time could stop faster with the trailer than without. there are aftermarket disc trailer brakes out there (mostly for smaller units like utility trailers) but i'm sure you could come up with something if you are "thee of little faith."

[gnmas]

I just towed my new 24 ft enclosed car trailer home 200 miles down the PA and NJ tpkes and the stock 396 had real problems pulling it even empty! I never realized how much the wind resistance would affect the towing ability. i have towed my 3800lb el camino with an open trailer many times with much less difficulty than the 2800 lb enclosed treailer with no car in it.

[TexasT]

You think a head wind is bad, wait til you get a nasty cross wind and some eighteen wheelers in a hurry passing you.