How high is too high? How high can I get before its not longer safe to drive at 70 MPH?

[78 GMC Jimmy]

78 K5

37's with mild trimming.

Unknown suspension lift, but it does have rear blocks.

Would like to increase the lift, but where is the limit before you hit stability / driveshaft angle / brake line issues?

One of my front shocks is already shot (tread wear indicates this). So If I'm doing shocks, why not lift springs as well?

Is a 12 suspension lift safe and reasonable for a "mostly" road rig?

 

[nvrenuf]

Imo, street driven around town can tolerate a ton more than interstate travel.

Once you get to the 8”+ range you (almost) automatically need to go with fancy (aka $$$$) driveshafts to survive the operating angle, especially in the rear. Combine the angle dilemma with extended high speed on the highway and you really do need a specialized rear shaft.

What tires are you looking at? I definitely wouldn’t use any bias ply tire no matter how good they may look.

As far as stability goes, 8”+ aren’t necessarily scary “tippy” but you absolutely have to respect the height and drive accordingly, expect it to handle more like a boat than a Silverado.

 

[K85 Octane]

Safely for who? And why? Laws are sometimes born from a lack of common sense and it's always overbearing. I don't understand a tall street driven truck, it's useless. Drives poorly on the street and doesn't do well offroad. It's stupid and it ruins it for the rest of us. Cut more, lift less. I'm on 40s with a 6" lift and I guarantee it drives better on the road and performs better offroad than whatever goal you have.


Sorry, I'm not normally such a bitch but the meaningless height thing is just as bad as squatted trucks.

 

[Blue85]

Well 12" of lift on 37's is going to look pretty stupid. Don't turn a classic truck into a laughing stock, IMHO.




For that size tire, you'd want to stay more in the 4" range. At even 4" you're getting into the range where you need to get a fixed yoke T-case and CV rear driveshaft for smooth operation. At 12", you'll be spending like $1k+ on a front driveshaft that actually works. Think it through even further. How are you getting to 12"? There are no lift kits that big that have any flex or ride quality to them, so you're hopping up on every bump. ORD only offers 7" on their springs, so that kind of sets the limit of how high you can go. You could do 7" + 3" body lift, but now you need 1-tons and at least 42's.

The right way to get tall and streetable is convert to 4-link/coilovers front and rear.

 

[78 GMC Jimmy]

I'm not sure if I will lift it further than it is, but I may. It depends on what info I can find, parts availability, complexity and difficulty of the install, overall cost, pros/cons and so on. I welcome any input - be it positive or negative. Its all useful info. I have solved most of the issues with this old truck, and now its time to look at optional modifications and upgrades. A lift kit is always something to look at. The rear sits a little lower than the front. What about adding 1" taller blocks in the rear, thoughts? Any major issues with doing that? There is room in the flexible brake line and and driveshaft would be OK aside from any angle issues.

What its got so far:

Lifted
37" tires
17" Rims
Rear wheel spacers
Cab visor (cant decide if I want to keep this or not)
Bug catcher
Old school light bar on cab
Internal roll bar
Tach
Intake
Carb
Manual battery disconnect
Fuel shutoff valve
Fuel pressure regulator
Inline glass fuel filter
Cage / barrier behind front seats.
Steps (to enter rig)
Window rain gutters
Manual front hubs
37" spare tire
Window tint
Folding front license plate step
Locking gas cap
12 volt cab fans (because there is no A/C)
Backup cam / monitor
Hidden kill switch
LED headlights

Pending repairs:

Rear axle seals
New rear brakes (oil soaked)
T-case seals
Maybe a new hood at some point, current one is creased/repaired.
Floor pan rust repairs.
Gauges flutter a little, mainly fuel


Aside from more of a lift and or tires, I was kinda thinking about:

Better stereo
Front tow hitch
A/C
Paint
Maybe better seats
Maybe upgrade to a power tailgate window
Re-rout exhaust to behind rear wheels.
Huge front bumper / winch


I thought about installing a blower, but I'm pretty sure that the rest of the truck could not handle all the extra power without massive amounts of refurbishing and upgrades.

 

[fastazz81]

Pictures

 

[78 GMC Jimmy]

Pictures

Oh ya, I gotta get those + battery cable pics. I will post those soon.

 

[sweetk30]

I drove a long bed up 20" and on 46" tires and i went over the whole truck to make sure it was safe cause it was a pile of parts put together . I felt just fine at 65 mph on highway .

the problem is to tall like this was could eat a honda civic in the blind spot each end of the truck .

Blazers need rear driveshaft work around 4" lift and up cause there so short . And if you get to tall the front inner "C's" need cut and turned to point the pinion up and help the driveshaft and not kill the alignment .

So plan what size tires you need and use of the rig and we can help you from there get the best plan going .

 

[78 GMC Jimmy]

I drove a long bed up 20" and on 46" tires and i went over the whole truck to make sure it was safe cause it was a pile of parts put together . I felt just fine at 65 mph on highway .

the problem is to tall like this was could eat a honda civic in the blind spot each end of the truck .

Blazers need rear driveshaft work around 4" lift and up cause there so short . And if you get to tall the front inner "C's" need cut and turned to point the pinion up and help the driveshaft and not kill the alignment .

So plan what size tires you need and use of the rig and we can help you from there get the best plan going .

Good info, thanks.