getting 65 mph with lower rpms ( lift and tire swap)

doghead said:

Have you ever experienced issues with blocks?

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Yes. I worked in Engineering at Air Lift company for years and used my 2500HD as a test mule. It had about every rear suspension imaginable on it from stock with steel helper springs (the worst) to full air suspension using rolling lobe air springs. The heavy leaf pack of the M1008's may get away without many issues using blocks, but the exceptionally weak 2500HD factory spring packs allowed annoying axle wrap under adverse conditions which is never fun. Adding blocks worsens the effects of axle wrap up.

I don't think anyone will have problems with a 4" block in the rear of a cucv.

No power, no torque, no issues.

I agree, a 6.2 in most situations won't exploit the negative characteristics of a 4" block. Be sure to use a quality steel block and not a cheap aluminum one. This is the only way to retain the overload leaf setup on a CUCV without buying a 4" lift spring that has an overload built into it. You can do a shackle flip but you will either ditch the overload or fabricate some type of drop down bracket system for the frame hangars on the overload setup.

You can't have your cake and eat it too unless you spend some big $$$ on the correct lift spring for the application. My US made springs without the overload went into the $600+ range shipped to my door.

This isn't a rockcrawler or dune truck. Most stock 3/4 and 1 ton rigs have a small block out back. Not ideal but not exactly a deal breaker either for this application.

In my opinion, unless you plan on hauling heavy loads of stone on a daily basis, you will not need the helper springs on the M1028. The helper springs only add 600 pounds of load capacity (from 8800 GVW to 9400 GVW), and when you think about it, 8800 GVW is a lot. On my M1028, I used the ORD shackle flip kit and discarded the stock helper springs. An advantage of the flip kit is it automatically rotates the rear axle to provide a corrected drive shaft angle. In addition, the flip kit allows you to install ORD's U-bolt reversal kit http://www.offroaddesign.com/catalog/uboltreversal.htm thereby eliminating the U-bolt threads and nuts from hanging down below the axle and catching rocks and other unwanted stuff. By keeping the rear axle bolted close to the spring packs, harmonic distorsion is minimized and wheel hop is eliminated. For what you will pay for the blocks and longer U-bolts, you can have the shackle flip kit for only slightly more, and circumvent the cost of extending your drive shaft. Just my 2 cents worth.

Hope this helps.

I agree on the benefits of the shackle flip over the blocks personally. Has the OP ever identified the vehicle as a 1028? If it's a 1008 the truck does not even use frame contact style overloads so nothing would change capacity-wise.

He simply said he wants larger tires for better highway speed.

Blocks will do fine.

okay okay. We all have our opinions on which type of lifts we prefer and that's what he asked for was our opinions. No need to get upset because different people have different ideas.

Upset?

37" tires will gain about 9 mph, at the same engine speed.

Sharecropper said:

In my opinion, unless you plan on hauling heavy loads of stone on a daily basis, you will not need the helper springs on the M1028. The helper springs only add 600 pounds of load capacity (from 8800 GVW to 9400 GVW), and when you think about it, 8800 GVW is a lot. On my M1028, I used the ORD shackle flip kit and discarded the stock helper springs. An advantage of the flip kit is it automatically rotates the rear axle to provide a corrected drive shaft angle. In addition, the flip kit allows you to install ORD's U-bolt reversal kit http://www.offroaddesign.com/catalog/uboltreversal.htm thereby eliminating the U-bolt threads and nuts from hanging down below the axle and catching rocks and other unwanted stuff. By keeping the rear axle bolted close to the spring packs, harmonic distorsion is minimized and wheel hop is eliminated. For what you will pay for the blocks and longer U-bolts, you can have the shackle flip kit for only slightly more, and circumvent the cost of extending your drive shaft. Just my 2 cents worth.

Hope this helps.

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This is good info except the part about drive shaft angle. "An advantage of the flip kit is it automatically rotates the rear axle to provide a corrected drive shaft angle." It actually provides an incorrected drive shaft angle. While rotating the pinion up will help relieve the angles on the front u-joint, it can introduce harmonics into the driveline and reduce longevity. Unless a CV is used, the proper geometry would be the same angle on both u-joints. I'm not saying folks don't do this and get away with it, just pointing out the correct geometry on single joint drive shafts. One could always shim the pinion down if they wanted to achieve this.

Yep, you are correct recovery. I was worried about driveline vibration showing up after the shackle flip because theoretically the new angle is not right. I was ready to start shimming but other members advised that I try it first and luckily it still runs smooth.

twomorestrokes said:

Yep, you are correct recovery. I was worried about driveline vibration showing up after the shackle flip because theoretically the new angle is not right. I was ready to start shimming but other members advised that I try it first and luckily it still runs smooth.

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I think your results are experienced more often than not! That minor of a vibration on a CUCV probably couldn't be noticed.