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Old 01-06-2010, 01:29 PM   #1
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How to Correctly Install and Adjust C4 Roofs

Factory correct C4 roof installation procedure

Melrose T-Top Int. has been in the Corvette business for over 30 years. In that time we have taken lead position as the most reputable GM licensed aftermarket supplier of Corvette roofs and t-tops in the industry.
That being said, I feel comfortable explaining to you what seems to be a gray area in the Corvette world regarding replacement roof installation and adjustment. Most C4 Corvette owners don’t lend much thought to their tops as being an integral part of the vehicle’s structural integrity. The C4 however was initially designed as T-bar vehicle like the C3’s, and it wasn’t until a GM exec ordered the car be converted to a targa model, the engineers realized they had a problem. With the T-bar removed handling characteristics suffered greatly due to torsional flexibility. Unfortunately for us the only viable solution to this was an inconvenient bolt in bulky style targa roof.

The first thing you want to do when purchasing a new roof is verify the year of the roof on your car. Even though your car may be a 1988 it could have been converted at one point. Sound unlikely? GM sold a kit for many years to convert 84-88 Corvettes to the third design 89-96 roof styles. This was due in part to the fact that only one roof design was available and it generated more income selling and installing the kits. So, how do I determine my roof year design? You can compare your front mounting hardware with chart below or measure between your front mounting bolts.

Measured from bolt to bolt O.C. across top of windshield frame.
· 1st design 84 - Early 86 28.5”
· 2nd design Late 86-88 31.5”
· 3rd design 89-96 32.5”

1984 - 1996 Roof Panel Hardware Detail




We have established the structural importance of the C4 targa style roof and it’s different designs. Now we can discuss how to properly install it, or better yet, how not to. Start by parking your vehicle on flat ground, and inflating all tires to factory specs then follow the instructions below per your specific vehicle year.

1st design 84-Early 86 front adjustments-

1. Make sure front cone / plate assembly is loose enough to move by hand.
2. Set the roof on the car and tighten rear center bolts. If bolts are being difficult to start, recheck to make sure roof is centered, and have a second person push roof towards back of car to help compress the new weatherstrip.
3. Tighten the outer two rear locator bolts on each side.
4. Tighten front mounting bolts. You may need to move the plate assembly around while trying to line up and tighten front mounting bolts with other hand.
5. Tighten cones with thin 1 1/8” installation wrench as seen here:

- 84-E86 Install wrench


6. Loosen center front mounting bolts. Retighten front bolts paying close attention to when front of the roof’s lens makes an even contact with the windshield weatherstrip. The front edge should only put approximately 1/8” of pressure on the weatherstrip for proper sealing as front bolts are tightened. Too much pressure may cause warps, cracks, or other problems. Too little pressure may result in air or water leaks. If you feel there is too much pressure being put onto the front of the lens please refer to 2nd design install instruction below to adjust front roof mounting brackets.


2nd and 3rd design, Late 86-96 front adjustments
1. Drop front upper windshield trim panel by removing 5 Phillips screws (1 rear view mirror screw and 4 outer)
2. Remove front upper roof mounting bracket covers via 2 Phillip screws per side
3. Remove 5/16” visor nuts and pop off spring retaining washers using a flat screwdriver
4. Visors will slide out and allow entire trim panel, mirror, and visors to hang



5. Go to roof and make sure front plate assembly on roof is loose enough to move by hand.
6. Set the roof on the car and tighten rear center bolts. If bolts are being difficult to start, recheck to make sure roof os centered, and have a second person push roof towards back of car to help compress the new weathertstrip.
7. Tighten the outer two rear locator bolts.
8. Tighten center front mounting bolts. You may need to move the plate assembly around while trying to line up and tighten front mounting bolts with other hand


9. Tighten outer front roof plate bolts
10. Loosen center front mounting bolts. Retighten front bolts paying close attention to when front of the roof’s lens makes an even contact with the windshield weatherstrip. The front edge should only put approximately 1/8” of pressure on the westherstrip for proper sealing as front bolts are tightened. Too much pressure may cause warps, cracks, or other problems. Too little pressure may result in air or water leaks.
11. If you feel there is too much pressure on the front of the lens, loosen the front mounting brackets and move upward as necessary. (Tip- mark the windshield frame where bracket is sitting before you loosen it, so you have a origin to return to if needed)


12. Once roof is adjusted reassemble trim parts in reverse order. Pay attention to rear view mirror wires so they don’t get pinched.


Note-
· There are many people installing cheap aftermarket weatherstrips on their cars these days. Sometimes you don’t have a choice, but if you do, always try to find something as close to the factory latex covered foam type weatherstripping. Avoid the rubber (gummy bear) feeling stuff. It doesn’t compress very well and causes damage in many cases to Corvette transparent roofs. If you install these on your car you must readjust your front mounting brackets.

· Shims may be added or removed behind rear brackets to adjust rear roof gap, though this is most often not needed. Drop rear trim panel to access rear mounting brackets.
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Old 01-06-2010, 01:38 PM   #2
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Great tech info!

I never knew the C4 was originally meant to have a t-bar, thanks for the info.

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Old 01-06-2010, 01:39 PM   #3
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Awesome!!
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Old 01-06-2010, 04:32 PM   #4
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Wow, that all makes a ton of sense. Nice to know the front mounts can be adjusted. Probably explains why my just two year old weatherstripping (GM) is all ready looking like hell.
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Old 01-06-2010, 05:24 PM   #5
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Awesome article...

Can you put a question to bed for me once and for all? Can a '90 top frame be retro-fit to an '85 car? If so, I'll be buying the necessary bits from you.
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Old 01-06-2010, 06:11 PM   #6
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Good information here - so I made it a sticky!

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Old 01-06-2010, 06:25 PM   #7
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wow, great write-up
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Old 01-06-2010, 06:31 PM   #8
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Last edited by colt; 04-17-2012 at 03:29 AM.
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Old 01-06-2010, 07:07 PM   #9
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Great info, for some reason the top brackets and the fit to different years has always been a mystery. Thanks for posting that.
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Old 01-06-2010, 07:22 PM   #10
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Chris knows his stuff.. the top on my ZR-1 was adjusted by him when I bought it at Bloomington Gold

I Would without a doubt, ALWAYS buy an Targa tops from Melrose
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Old 01-07-2010, 07:41 AM   #11
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Quote:
Originally Posted by XQIZT View Post
Awesome article...

Can you put a question to bed for me once and for all? Can a '90 top frame be retro-fit to an '85 car? If so, I'll be buying the necessary bits from you.

Xqizt- Yes it can. You will need to purchase the 90 front plates as seen in the photos above that mount to the windshield frame. You will also need purchase new top plastic covers and trim panel where the rear view mirror mounts. I just checked and we don't have any 89-96 front plates. We usually have to buy them from salvage yards and they will range anywhere from $20-$50 ea.
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Old 01-07-2010, 07:49 AM   #12
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Quote:
Originally Posted by melrose View Post
Xqizt- Yes it can. You will need to purchase the 90 front plates as seen in the photos above that mount to the windshield frame. You will also need purchase new top plastic covers and trim panel where the rear view mirror mounts. I just checked and we don't have any 89-96 front plates. We usually have to buy them from salvage yards and they will range anywhere from $20-$50 ea.
OK...so there is no way to change the TOP, you have to change the CAR.

The reason I am asking all this is because I was about to purchase a 90 solid top to use on my 85 when I don't want to use my clear top.

So in my situation it seems like I need to find a 84-86E top.
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Old 01-07-2010, 08:26 AM   #13
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Quote:
Originally Posted by joshwilson3 View Post
Any chance you could also post the instructions with regards to placing a dollar bill under the front of the top in the center, left side, and right side. Tighten the top down. Then pull the 3 dollar bills out to tell how tight the top is? I know the Melrose guy on the other forum mentioned this.

I think that is an important check to do so you don't get wind noise and rain cause the top isn't down far enough, but also can tell the top isn't down too far which could damage the top. And it would also be a good idea to do this check if you ever replace the windshield weatherstripping.

And any chance you could let me know what brand weatherstripping you put on my top? PM would be fine. Reason is, I think the weatherstripping that came on the top feels better than the Willcox stuff I was gonna use. It is a little softer and feels more like OEM. I may have to replace the windshield weatherstripping at some point in the future, and I would like to use the same brand weatherstripping that came on my top.
Place a couple bills along front edge on top of gasket (not where bills will bind up on anything)


Tighten roof and tug on bills. If they pull out easily- your roof is probably too loose. If they won't pull out easily the roof may be too tight. A certain amount of common sense must be used here. If the bills pull out easy, but your roof does not leak air or water leave the car alone. If they are difficult to pull out it may be too tight. Obviously if your roof has been on your car for a year or more and youdon't have any problems with it leave it alone. This is mainly used to eliminate new install overtightening.

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Old 01-07-2010, 08:28 AM   #14
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Quote:
Originally Posted by XQIZT View Post
OK...so there is no way to change the TOP, you have to change the CAR.

The reason I am asking all this is because I was about to purchase a 90 solid top to use on my 85 when I don't want to use my clear top.

So in my situation it seems like I need to find a 84-86E top.
Correct, find the correct year top.
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Old 01-08-2010, 10:54 AM   #15
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Great info!!!

Thanks for the post.
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