Rear suspension leaf to coil swap?

[BradE]

I've got a '71 GMC rear leaf suspension and I would like to swap the entire rear end with '72 Chevy coil suspension rear end. The GMC is a swb and the chevy is a lwb. Is this swap possible? Does the wheel base come into play? Any comments, pics, encouragement welcome! Happy New Year!

[kcjones]

Here's the quick snapshot:

1) no difference in swb vs lwb trailing arms, trailing arm crossmember, shock mounts, springs, spring cups, etc.
2) Biggest job is gonna be getting the leaf perches off the frame, and the trailing arm cross member into the frame.
3) Buy the extreme drop cross member from ECE! You'll get the exhaust holes already drilled.
4) make sure you check your trailling arm cross member for cracks, bends, etc. They take a tremendous amount of the forward acceleration load, so they can become weak.
5) Make sure you get shock mounts, xmember, trailing arms,shock mounts, panhard bar, panhard bar bracket, ubolts from the parts truck.

I'm sure the other members can add a lot of information to mine!

[BradE]

Thanks for the reply kc, good stuff!

[Peter82]

Well anything is possible with enough money. But the first thing that comes to mind would be to buy a rolling frame with coils. This would allow you to re-finish the new frame then swap parts. You could even lower it to where you want it. Then switch over the front clip, engine & parts, the cab and bed. It sound like a lot of trouble but it can be worth it. Or... you can go to a junk yard and cut out the pieces from an old truck like mine, 1971 c-10 short bed. and then cut and weld on your frame. Then you have to cut and weld on your rear axle, and you will need upper and lower a-arms for the front. A LOT of cutting, welding, then grinding the welds down for a clean look. Then you will have to use chassie black or prime and paint the frame so it doesn't rust on you. A rusty frame is not your friend. And if you use the first way then you can replace all your body mounts and re a line your body lines.

[dwcsr]

I thought the frames on GMC leaf spring and Chevy Coil spring trucks were different over the spring area. So you wouldn't have a place to mount the Coil to the frame. I may very well be wrong on this.

[SCOTI]

Originally Posted by dwcsr

I thought the frames on GMC leaf spring and Chevy Coil spring trucks were different over the spring area. So you wouldn't have a place to mount the Coil to the frame. I may very well be wrong on this.

1/2 ton 2wd frames are the same for coil & leaf applications. The leaf frames do have extra 'beads' pressed into the framerail to increase strength @ the spring hanger area.

Leaf frames also have the trailing arm c.member w/o the trailing arm mounts (it's used for the carrier bearing support).

[kcjones]

Originally Posted by SCOTI

1/2 ton 2wd frames are the same for coil & leaf applications. The leaf frames do have extra 'beads' pressed into the framerail to increase strength @ the spring hanger area.

Leaf frames also have the trailing arm c.member w/o the trailing arm mounts (it's used for the carrier bearing support).

...and the coil trailing arm mounts are just riveted on to the crossmember, right, so you could, for the sake of argument, simply remove the mounts from the donor truck and install on the leaf crossmember, right? Hence saving removing your original crossmember, which would be quite a time saver!

[truckintexas]

This will undoubtedly get a few responses, but here goes.........I have owned and driven both leaf spring (1 SWB & 1 LWB)and coil spring (1 SWB) trucks. IMHO, the leaf spring trucks performed better. My application was mostly everyday driving (some country roads), light-medium loads in the back, and an occassional boat or trailer attached.

However, neither of my coil spring trucks had a rear sway bar (which would have helped tremendously with loads, especially in corners).

[BradE]

Thanks for the replies! I'm in between trying to save money and swap a lwb '72 coil rearend into my swb '71 GMC leaf spring or bite the bullet and get the lowering leaf springs from ECE. I already have the '72 parked in the yard, so that's the tempting part. Looking at the scope of the project though, I may just have to save up and buy the lowering leafs when I can. Decisions, decisions..........

[SCOTI]

My 68 w/trailing arm suspension rides much better than my 74 does. Both are dropped @ least 5/7 (the 68 w/rear air bags).

[LUV2XCLR8]

PM Sent, Happy New Year

[lofly'a]

did'nt see it mentioned in anyone's posts, but the trailing arm crossmember is already on the trucks equipped with leaves. i have a 71 swb gmc with leaves and it has the trailing arm crossmember from the factory as have others that i have seen. check yours BradE, bet you'll find one under there.

[kcjones]

Originally Posted by lofly'a

did'nt see it mentioned in anyone's posts, but the trailing arm crossmember is already on the trucks equipped with leaves. i have a 71 swb gmc with leaves and it has the trailing arm crossmember from the factory as have others that i have seen. check yours BradE, bet you'll find one under there.

As SCOTI mentioned, the xmember is there, it likely doesn't have the trailing arm mounts, though. Not terribly difficult to install, I can't imagine.

YellowGT: Depending on price, you'd be better off getting a custom panhard bar and bracket from ECE or CPP. That would move the rear end bracket to the passenger side trailing arm, instead of the pumpkin. Better geometry for the panhard job, anyway, and having the adjustable panhard is a must for lowering more than an inch or two.

I think the biggest difficulty with the leaf/coil swap is getting the leaf brackets off the frame nicely, but it isn't impossible.

As far as performance, it's hard to argue one's experience, but theoretically speaking, trailing arms are a superior design for cornering sway and acceleration (less bounce), but hauling/towing? Maybe leafs...

[SCOTI]

Originally Posted by kcjones

As SCOTI mentioned, the xmember is there, it likely doesn't have the trailing arm mounts, though. Not terribly difficult to install, I can't imagine.

YellowGT: Depending on price, you'd be better off getting a custom panhard bar and bracket from ECE or CPP. That would move the rear end bracket to the passenger side trailing arm, instead of the pumpkin. Better geometry for the panhard job, anyway, and having the adjustable panhard is a must for lowering more than an inch or two.

I think the biggest difficulty with the leaf/coil swap is getting the leaf brackets off the frame nicely, but it isn't impossible.

As far as performance, it's hard to argue one's experience, but theoretically speaking, trailing arms are a superior design for cornering sway and acceleration (less bounce), but hauling/towing? Maybe leafs...

x2.

[Red_Rooster]

Sorry for the Hi-jack, but have another related question. I know that the GMCs are typically leaf, as I had a SWB GMC with leafs. That truck was stolen. Now I have a 72 LWB Chevy...with leafs. How common was that? I thought all Chevys were Coil? It rides much smoother than the SWB GMC..maybe the added weight of frame and Bed make for the smoother ride??

~Travis

[kcjones]

Originally Posted by Red_Rooster

Sorry for the Hi-jack, but have another related question. I know that the GMCs are typically leaf, as I had a SWB GMC with leafs. That truck was stolen. Now I have a 72 LWB Chevy...with leafs. How common was that? I thought all Chevys were Coil? It rides much smoother than the SWB GMC..maybe the added weight of frame and Bed make for the smoother ride??

~Travis

Leafs in Chevy's are more common than you might think. There's a rear end shop near me, and the guy has been building rear ends for over 30 years, and told me it was relatively common, maybe 5% of the 67-72s (that's like 150,000 trucks!) could've come with leafs. It was a normal factory option, and likely zero cost as leafs are cheaper to produce.

I don't know if there is a difference in ride "quality" between SWB/LWB? I guess if the spring is rated the same, and there's a little more weight, there would be slower spring reaction on bumps, but maybe they would handle worse (sway more) than SWB? Maybe it's just that it feels better because the driver is physically further from the point of suspension in the rear. Or, LWB drivers are just easy going guys that don't take bumps in the road to harshly?

[grancuda]

LWB's are smother riding than SWB's because of the wheel base and they are somewhat heavier, reguardless of coils or leafs

[gringoloco]

I did my pickup. It was pretty easy. Plan on spending an entire weekend if you clean/paint while you're in there...

[nicolas72gmc]

I will let you know what the new leafs feel like when I get mine installed.

[myoldchevytruck]

Originally Posted by gringoloco

I did my pickup. It was pretty easy. Plan on spending an entire weekend if you clean/paint while you're in there...

I also did the swap on my 69' Stepside. Bought the crossmember brackets and Track Bar Frame Mounts from a board member. I used Grade 8 hardware to reattach all of the mounts and brackets.

I installed 6 inch drop coils (No C-Notch) from GMC Pauls and a Super Track Bar from ECE.

As for the leaf spring axle brackets. I originally purchased Axle Saddle Brackets (For the train arms) from ECE for $29 plus shipping but ended up finding a Front/Rear 5 Lug Setup from a 72'. Now I also have front disk brakes.

Degree of difficulty? I'm just a DIY guy with average skills and with all of the parts ready to install, like Gringoloco said, It'll take the weekend to complete including cleaning and painting.

[LUV2XCLR8]

Originally Posted by myoldchevytruck

I
I installed 6 inch drop coils (No C-Notch) from GMC Pauls and a Super Track Bar from ECE.

Sorry to hijack, but does it bottom out at all? What size rims? overall diameter? Thanks

[BradE]

Sorry to hijack, but does it bottom out at all? What size rims? overall diameter? Thanks

x2!

[oldspowered]

i guess i don't under stand why switch to coil springs i would love to have leafs!!!

[myoldchevytruck]

Originally Posted by LUV2XCLR8

Sorry to hijack, but does it bottom out at all? What size rims? overall diameter? Thanks

Originally Posted by BradE

x2!

Sorry for the late response guys. No, it does not bottom out. As for wheel size, there just 15x7 inch steel wheels. Installing some new shocks within the next week, I'll post some pics.

[kcjones]

Gringo, you did the coil swap, painted, notched, installed bags/compressor/valves/lines, all in a weekend? Was it a rear end swap or did you also remove leaf pads, install coil pads, weld and paint, too? If so, don't ever charge anyone for your work buy the hour, make 'em pay for the job!