Stay original suspension or go GM 2 1/2" springs?

[Lebowski]

So from a previous thread I've decided to go with a narrowed GM Dana 60 frt, and 14bFF rear. I'll try to duplicate the track width of the original M37 62" center to center track width as much as possible.

I'm not sure if I will stay stock height, or maybe try for about 2" suspension lift above stock. Most likely I'll be changing to a 38" tire (likely a 12.50 wide TSL SX), maybe even up to Interco 40" LTB.

My query is should I stay with the original M37 leaf springs, or change over to 2 1/2" GM springs for the front ( and possibly rear) of the M37? I would do the front springs in the manner mentioned in this thread based on Master Yota's build: http://www.g741.org/PHPBB/viewtopic.php ... 0&start=60 page 5.

The advantage I can think of, in regards to the more modern and common GM 2 1/2" springs, is that I can play with the suspension more until I find the ride height and flexibility I want. Also, the GM Dana 60 will bolt directly to the 2 1/2" springs. It will be mostly mud/snow/road, not super flexy rock crawling, that the vehicle would be used for. So I'd be interested to hear anyone's thoughts regarding which springs to go with.

[98taco3]

Ive seen some video of stock m37s being wheeled fairly hard and was quite impressed with the flex they have. Im a wheeler too and it was enough to convince me to leave them be. If a guy could mount up some chevy 63" springs you could get quite a bit of flex out of them. The only thing i would suggest is get a hold of a copy of a book called automotive math and calculate out your spring weights and sprung/unsprung weight and match new springs to the truck if you go that route. The m37 is a very heavy vehicle for the size and you could use that to your advantage if it was set up correctly. You may be disappointed in its performance off road if you dont do the calculations and do it right the first time. Reason i say this is I have been there and done that on toyota stuff. Sold my trail rig because it didnt perform as it should have. Its always great to learn from other peoples mistakes

[W_A_Watson_II]

the M's 2" springs (and it's frame) flex great. the 2.5" GM springs won't likely flex as well, and may force more flex into the frame and cause it the fail even sooner. I'm likely to see a failure with as much had as I push mine, bit for now will keep enjoying it.

For reference, my 39.5" IROK's required just over 1" lift in the front, and I went with 2" in the rear.

I blew out a front shock on this ramp attempt, so I stopped before the truck would: http://m37.wawii.com/images/DSC_0788_M37_RTI.JPG
No problems on this ram though: http://m37.wawii.com/images/DSC02961_Ramp2.JPG

[Lebowski]

Thanks for the replies. Some good points brought up by both of you. I will stick with the original springs.
Will, what did you do to get the the 1" lift up front and the 2" in the rear? I can't believe the flex in your pics for a stock 1950's factory designed suspension! Impressive!

EDIT: I checked your website and found pics of your suspension. Thanks.

[W_A_Watson_II]

Lebowski,

The M amazes me every time I take it out. The weight (and width) works against me sometimes, and I could use some more wheel speed on some hills, but the M can concur a lot of obstacles. The frame flex helps a lot, but it's a double edged sword, the frame can't flex like that forever.

The front has 4 extra short leaves in the bottom of the spring pack. Not a lot of impact on the spring rate, but it also gives me the >1" of extra clearance I needed for the tires. The rear, well I double checked and I'd forgot that the 2" blocks were too much, and I went to a 1/2" block. It could probably be better off with a 1" as when I have a load in the back, it sags in the rear: http://m37.wawii.com/images/DSC00391_RZRLoaded.JPG

Hope this helps.

[98taco3]

they are very impressive for 60 year old pieces of equipment. That is at least twice the flex my old trail rig had. Time to get my truck back together and onto the trail! Good luck with whatever plan you decide to go with.

[Lebowski]

I am thinking of moving the front springs forward about 2". Moving the fixed front spring hanger forward is not a problem. It can just be slid forward on the straight frame channel and bolted into place.
The shackle end is alittle different. Moving the shackle hanger forward 2" puts it into the edge of the frame. Any ideas on how to approach this problem?

[98taco3]

you could fab up a new shackle mounting system out of some tube and plate. if you cant move the original mount thats about the only safe option. Reengineer the mount it self.

[Lifer]

I really can't imagine what yoou hope to achieve by moving the spring 2" forward. I think the Dodge engineers pretty much considered all options and chose the best one in the first place.

[W_A_Watson_II]

If he's going to run a 40" tires (with out jacking the truck sky high) I can understand the desire of at least 1" forward movement. This is from my own experience of running the 39.5 x 13.5 IROK's on my M (rear inner fender rubbing, but not bad).

I know of another guy who moved his forward, but the stock steering set up didn't like it and he's had steering problems.

[Lebowski]

Will is correct. I wish to run a 38-40" tire, and want to minimize the chance of the tires rubbing the front fenders (on the firewall end). I am looking for minimal lift to achieve this. I'll probably 're-engineer' the mount as Taco suggests. If I did stay with a 36" tire I would leave the axle in it's original position.

[98taco3]

you would also be improving your obstacle approach angle by moving the axle forward. Another added bonus if your going to wheel it.

[UZIS9MM]

Here's a good period picture of the stock suspension being put to the test.



Kevin

[W_A_Watson_II]

Hey that is indeed a great period picture, but they have my running boards! The M's are a great very capable truck.

[Lebowski]

Nice pic. I haven't seen that one yet. You can see how little room is left near the rear of the fender and the tire with the stock 9.00-16 (36") tire.