1984-04 Mustang KYB Gas-A-Just Rear Quad Shock by KYB

Mustang KYB Gas-A-Just Rear Quad Shock (84-04)

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KYB Mustang Gas-A-Just Rear Quad Shock (84-04) KG4521

Improve your Mustang's ride quality and firm up your suspension travel. These Gas-A-Just rear quad shocks from KYB will get your Mustang back in shape!

Item #KYB-KG4521
MPN# KG4521

Your Price: $44.99

Market Price:$49.99
You Save 10.00 % ($5.00)

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  • OE Style Replacement Shock
  • Improves Handling


  • Monotube Design
  • White Finish
  • Sold As Each

What's in the Box

  • 1 KYB Rear Quad Shock
  • Installation Instructions

Product Description

All KYB struts and shocks carry a LIMITED LIFETIME warranty.

Gas-A-Just shocks are non-adjustable high-pressure gas shock absorbers that are designed to deliver driving control and performance by keeping the tires glued to the road. These high strength, monotube shock absorbers provide extra-rugged durability and fade-free performance.

When you want more road control when towing or for higher performance, you want KYB Gas-A-Just shock absorbers. Sometimes specified for use on the rear axle in conjunction with GR-2 strut cartridges or complete struts on the front axle.

* Except 1999-2004 Cobra.


1. Upgrade
Vehicles are generally designed to handle a broad range of purposes: Passenger ride comfort on one side, load and terrain capabilities on the other. When your typical use of a vehicle sometimes or always stresses heavier loads, top heavy, towing or off-road conditions, you may want to consider replacing the shocks with units that exceed original equipment capabilities. KYB offers many higher-performing “Monotube” shocks for this purpose.

2. Maintenance
Even on well paved roads the shocks can move up or down 1,500 to 1,900 times every mile: In 50,000 miles that can exceed 75 million cycles. Over time, performance tends to decrease gradually and the motorist usually doesn’t realize how much handling and control is lost. Replacing shocks and struts after 50,000 miles can keep the vehicle performing as well as it was designed and extend its life expectancy.

3. Ride Control Conditions-Based
Worn shocks and struts eventually causes ride control conditions to worsen to a degree that impairs the drivers ability to control the vehicle. Road testing and vehicle inspections by a qualified technician every 12,000 miles is recommended to identify and keep the motorist informed about these conditions.

4. Repair of Failed Units
Shock or strut failures are a driving safety hazard. If you can’t control your vehicle, then it controls you. Evidence of failures includes things like; excessive bounce, units leaking to the point of fluid dripping, tires that are cupping and visual component damage.

KYB Warranty - Click Here

See what our customers have to say about this product!
Check out customer reviews.

Customer Photos (5)

Product Reviews (10)

out of 5 stars
4.5 stars
10 reviews
5 stars    7
4 stars    2
3 stars    1
2 stars    0
1 star    0

10 of 10 REVIEWS
10 of 10 REVIEWS

4 Stars   Great improvement
By on 5/27/2015
My old quads had over 150,000 miles on them and one was squeaking so I decided to buy these. The spacers that it came with weren't a perfect fit I had to file one down to fit. But other than that it was a pretty simple install. I used a ratchet strap to hold the shock to the appropriate length while I put the second bolt on. I had a noticible difference just backing out of the driveway. I definitely recommend these if your old quads are old and not doing anything anymore like mine.

Yes, I would recommend this item to a friend!

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5 Stars   Good fit, easy install, with a couple of tips
By on 10/27/2016
96 GT Convert: 117,000 miles and the rubber on the original quad shocks, (diff stabilizers) gave out. Replacement eliminated a clunk I was getting and made the rear stable again. This was all right after new rear springs and shocks, so I hope I am good for another 100k! The KYBs fit well with a few tips. Spay the mount nut and bolt with WD40. A 15mm box end with a dead blow hammer will be helpful to get the bottom, (front) bolt loose as it faces toward the inside of the differential right behind & up top. The spacers that come with the kit, go on the inside of both mounts, this moves the shock out slightly away from the regular vertical shock so they don't rub. If you have an extra washer to put on the inside, perhaps do that on both ends also as they are still really close fit. However, that may require a bot more space on the bottom bracket. Tap the inside bottom bracket face with a small hammer a couple of times to give you a little more room for the spacer, do this before you try to install, test fit that end if you are not sure. Don't worry, when you tighten the mounting bolt, you will pull it back in if you went just a little too far. Leave the strap on the shock! until you have the rear, (upper) mount finger tight, then cut strap with side cutters and be ready to slide the bolt in on the bottom bracket (the one toward the front of the car) as the shock expands. Don't worry, if you don't get the bolt in fast enough, it should catch in the bracket if you are even close. Then use a big screw driver to pry the shock back so you can align the threads.

Yes, I would recommend this item to a friend!

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5 Stars   Great it fit for For foxbody.
By on 4/9/2014
Image uploaded by Mohammed A. There are awesome.
It fit great.

Yes, I would recommend this item to a friend!

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4 Stars   Not to bad
By on 9/7/2014
These shocks are too wide, I installed them with my Koni orange and had about 1 CM of clearance, during a hard turn they do rub. Messed up my beautiful koni orange paint job. But they are pretty dam stuff, not tooooo much wheel hop now.

Yes, I would recommend this item to a friend!

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3 Stars   Factory upgrade
By on 1/25/2016
Image uploaded by Matt B. These are much heavier duty than the factory originals. They are built well an do firm up rear end. They include two spacers for the aft stud which help give necessary clearances. I do not know if this is Lmr or kyb idea. Although I am not crazy about this it does do the trick. All in all these shocks are very useful. Anyone who removes them is not helping themselves. If I order my parts by 2 p.m. I receive them the next day on standard shipping. I do live in Texas though .

Yes, I would recommend this item to a friend!

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5 Stars   Great Fit
By on 8/17/2014
Bought these to complete the rest of the rear end. Car rides good!

Yes, I would recommend this item to a friend!

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5 Stars   KYB shocks
By on 11/24/2014
Great price, fast delivery, am delighted at how much better the car rides. My 1990 5.0 liter Mustang only has 36,000 miles since new, but the original shocks were 25 years old. New ones fit perfect.

Yes, I would recommend this item to a friend!

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5 Stars   Awesome Fit!
By on 8/17/2014
Bought these to complete the rear end. Car rides good!

Yes, I would recommend this item to a friend!

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5 Stars   Great Fit
By on 7/24/2016
Great quad shock for the price

Yes, I would recommend this item to a friend!

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5 Stars   Great fit.
By on 6/20/2016
Worked as advertised.

Yes, I would recommend this item to a friend!

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Vehicle Applications

Ford Mustang - 1984 (84) - 1985 (85) - 1986 (86) - 1987 (87) - 1988 (88) - 1989 (89) - 1990 (90) - 1991 (91) - 1992 (92) - 1993 (93) - 1994 (94) - 1995 (95) - 1996 (96) - 1997 (97) - 1998 (98) - 1999 (99) - 2000 (00) - 2001 (01) - 2002 (02) - 2003 (03) - 2004 (04)

About This Brand

KYB - World Class Shocks & Struts
KYB manufactures and markets a full line of Mustang & LIghtning shocks and struts for replacement, upgrade and performance applications. The KYB line includes GR-2® Premium Shocks and Struts, Gas-a-Just® High Performance Shocks, MonoMax™ Heavy Duty Shocks, AGX® Sport Adjustable Shocks and Struts, strut mounts and boots.

KYB uses its innovative design and advanced engineering to produce state-of-the-art shocks and struts that are recognized worldwide for their proven reliability and superior ride control. There is no comparison when it comes to KYB and other shocks and struts. Unlike other manufacturers, KYB inspects the quality of each and every part. That means fewer comebacks, more satisfied customers and a limited lifetime warranty rate that averages less than one percent.

KYB is the world’s largest supplier of shocks and struts to vehicle manufacturers. KYB produces a variety of ride control products for use as original equipment and replacement parts in automobiles, motorcycles,

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