Monroe coilovers or Monroe Gas Magnum rear shocks?

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Schurkey

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I'm not really sure what rear end it has.
Count the number of bolts holding the rear cover to the housing.

10 bolts = Junk 8.5" ring gear, engineered for compact and intermediate cars with small-block engines, but upgraded for full-size truck use with heavier axle shafts in '88 or '89 which didn't fix the basic weakness of this axle design. Almost always saddled with the equally-crappy 254mm (10") drum brakes.

14 bolts = 9.5" ring gear. What GM should have put under every one of the 5- and 6-lug trucks. Comes with 11.x Duo-Servo drum brakes.

The 14-bolt "full float" axle is 8-lug only; that's a big MF.
 

1990C1500

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Count the number of bolts holding the rear cover to the housing.

10 bolts = Junk 8.5" ring gear, engineered for compact and intermediate cars with small-block engines, but upgraded for full-size truck use with heavier axle shafts in '88 or '89 which didn't fix the basic weakness of this axle design. Almost always saddled with the equally-crappy 254mm (10") drum brakes.

14 bolts = 9.5" ring gear. What GM should have put under every one of the 5- and 6-lug trucks. Comes with 11.x Duo-Servo drum brakes.

The 14-bolt "full float" axle is 8-lug only; that's a big MF.
I just went and looked and it is a 10 bolt. Is the 14 bolt something I can buy and bolt in or is there another rear end I can put in? My ultimate goal is an lq4 swap after I finish all the important stuff first.
 

Supercharged111

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Shocks and their mounts aren't designed to bear weight, and are known for breaking. No way would I ever recommend installing a coil assisted shock.

I dunno, lots of people use them and you said it: coil assisted. The better question is what is the spring rate on the proposed coilovers?
 

Schurkey

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I just went and looked and it is a 10 bolt. Is the 14 bolt something I can buy and bolt in or is there another rear end I can put in?
Very easy with 4WD, more-difficult with 2WD owing to the 5-lug wheels. The bigger 9.5" axle generally comes with 6-lug wheels.

At least with the C/K 1500s, the axles for 2- and 4 wheel drive are different widths. So you'd want a 9.5" 2WD axle to go under a 2WD vehicle, and a 9.5" 4WD axle to go under a 4WD vehicle. And, expecially with 4WD, you'd need to match gear-ratios or you have to re-gear the front differential, too. And dick with the speedo/ECM, etc.

A 2WD axle will probably need special aftermarket 5-lug axle shafts to retain the 5-lug wheels. I've never done that conversion. I guess the (rare) SS454 rear axle was a 9.5" unit with 5-lug axle shafts; but how many of those are in the typical Treasure Yard? (Zero.)

I put a 6-lug K2500 axle under my 6-lug K1500. Chose my replacement axle carefully, got the bigger brakes and correct gear ratio as expected, but also the G80 locking differential.
 

GreaseDog

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A 2WD axle will probably need special aftermarket 5-lug axle shafts to retain the 5-lug wheels. I've never done that conversion. I guess the (rare) SS454 rear axle was a 9.5" unit with 5-lug axle shafts; but how many of those are in the typical Treasure Yard? (Zero.)
Drilling 6 lug C2500 shafts to 5 lug will easily solve this issue.
 

sewlow

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It came with the "sport suspension" but I don't know how that is different.
'Sport suspension' = RPO-F41.
GM's definition as per their code list.
"F41 - Suspension, Firm ride handling, Fr & Rr."
Optional upgrade. More $$$.
A pretty vague description for an option available across the majority of GM's line of cars since the late mid/late '60's to current.
IIRC, GM began usage of that code for trucks with the '73+ Square Bodies.
The actual individual parts included within that F41 option box varied from model to model.
Whatever parts are included specific to each model met GM's very generic description.
Usually...
- Stiffer springs. Increased GVW.
- H/D shocks. (bigger/stronger/faster.)
- Larger front sway bar.
Although, not what I've found to be true on C1500 400 trucks, with the exception of the 454SS's. SUV's are a different story.
Some vehicles received an additional rear sway bar. But not 400 1500 trucks.
- Larger front brake rotors.
With your truck being a '90 there is a difference as the non-F41/HD 1500's of the first 3 years used smaller rotors along with the required the use of smaller spindles.
You have the larger which all the later years went to regardless of the F41 or not.
- Quick ratio steering box.
Damn near every vehicle GM ever produced with the F41 option got this upgrade. But when it comes to GMT400's, 454SS-only.

Shocks and their mounts aren't designed to bear weight, and are known for breaking. No way would I ever recommend installing a coil assisted shock.
Yes. Suspension carries the weight of the vehicle.
Shocks control the action of the suspension.

I dunno, lots of people use them and you said it: coil assisted. The better question is what is the spring rate on the proposed coilovers?
An increased GVW can only be attained via suspension.
The springs. Although, at a certain point, frame capacity becomes an issue.
Coil assisted shocks may appear to increase the load capacity when it comes to the vehicle's loaded ride height, but they won't change the vehicle's GVW.
The O/P's truck already has the F41 option with the stiffer spring rate.
A suspension has to be somewhat compliant for proper weight distribution in order to plant the tires. This results in better traction & increased handling.
Front & rear suspensions are not separate entities. They need to work together. Too stiff comparatively from one end to the other each creates it's own paradigm of negative issues.
Unloaded, (65%, 75% of the mileage?) the coil-overs won't let the suspension do it's job. That's going to be one rough ride, along with creating unforseen, unforgiving handling characteristics in certain situations
Loaded, & those shocks mounts are being subject to stresses that they were never designed to bear.

Look at some 5 leaf setups maybe, then personally, I’d ignore the coil over rear shocks.
100%

it came with a locking diff
10b G80 gov-lock. The 'Gov-Bomb'.
A 10b is...well...a 10b. As said, not the strongest.
You could throw a bunch o'bucks at it and it would hold some decent power, do some hard-ish work.
For how long? Lotta variables in that. Depends on the owner? Luck of the draw? Who knows. It's a 10b!

and 3.73 gears
That right there increases you towing capacity.
A little more thirsty than the usual 3.42's, but the return is so worth it.

But that G80 is it's Achilles' heal.

14 bolts = 9.5" ring gear. What GM should have put under every one of the 5- and 6-lug trucks. Comes with 11.x Duo-Servo drum brakes.
Yup.

Drilling 6 lug C2500 shafts to 5 lug will easily solve this issue.
Local shop here does that for $85/ea.
Welded up, redrilled, new studs.
...and that's in Canuck Bucks.
I think that that's the equivalent of about $20/U.S.
 
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