Monogram NASCAR 1985 Thunderbird #2



I have two NASCAR models under construction. The oldest of the two is Monogram's 1/24 Ford Thunderbird driven by Bill Elliott in the 1984 and 1985 seasons. I started building one, but found more and more problems with the body shape. I decided to stop work on the original kit, buy two new kits and try again. Much more analysis is involved, so progress will be even slower!



Lessons learned

The work on model #1 taught me a number of valuable lessons:

To add to the confusion, model #1 will be seen in some photos. But it's easy to recognize: it's red, whereas the new project uses white bodies




Photo analysis

A breakthrough in my understanding of the Monogram body problems was this photo analysis. After deciding on the 1985 race, I took this excellent photo as a starting point.
The next part was really difficult: photographing the model in the same attitude, and if possible with the same perspective. I read the latter part that the camera-to-model distance should be the scale value of the real distance. But I do not know that last number. So it remains a best attempt. It took a lot of different photos trying to find the right attitude of the body - by far the most difficult part of this method. The original photo and the model photo were lined up in CorelDraw, using its 'transparancy' feature.
When I thought I had a good agreement, I used CorelDraw to draw the main features with yellow lines. Note that I had modified the rear of the front wheel opening, so two shapes are drawn there.
Lastly, the model photo layer was switched off, leaving the yellow lines over the original photo. And suddenly the differences are clear..
The nose section has the biggest problems. The hood should be ~5 mm longer on the centerline, and ~3.5 mm on the corners. This would create a pointier, less blunt nose. The wheel opening should move forward some 2 mm.
The greenhouse is not bad. I don't see large shape problems here, and will leave this area alone.
At the rear, the wheel opening should move forward some 2 mm, just like the front wheel opening. It looks like the model's trunk lid is too long, some 1.5 to 2 mm.
Initially I had not spotted another difference between car and model: it has a cowl vent panel. I drew its outline in yellow again.



Wheel base and wheel track analysis

A second breakthrough was understanding the wheel base and wheel track of this car. I found several references that created some clearity on the subject, and I combined that with measurements of the model.

I measured the tracks of the Monogram 83-86 T-bird model. At the front: 78.0 mm over the tires, minus 13 mm for tire width makes 65.0 mm, or 61.4 " in full scale. Note that the measurement could be off a little, the front suspension was only partly assembled and rather floppy. At the rear: 78.5 mm over the tires, minus 13 mm for tire width makes 65.5 mm, or 61.9 " in full scale. My conclusion: it seems Monogram was aiming for the 62" wheel track figure.
The front axle stubs are staggered some 1.6 mm, which leads to confusion over the exact wheelbase of the model. In a thread on the Randy Ayers forum titled Dumb Monogram '90s chassis question, it was suggested that the whole front clip was offset to the driver's side. But it soon became clear that that was not the case; only one tube was offset to make room for the steering box. All other parts are symmetrical with regards to the centerline (confirmed by caliper measurements).
Then I remembered where I had read about wheel track and why fenders no longer were factory sheet metal: it was in Bill Coulter's 'Building and detailing scale model stock cars' (page 76).
I found some more data, this time in 'The anatomy and development of the stock car' by John Craft, page 91. It says regulated wheel track remained 60 inches when the wheel base was reduced to 110 inches.
On page 148, in an interview, a lot more data is mentioned. A 64 inch wheel thread (track) is quoted for an older 115 inch cars. A 62 inch track was used when the 110 inch was introduced. That conflicts with the data above. I'm not sure how to read the last part. I think he's talking about the maximum wheel track numbers.
Out of curiosity I tried the calculate the advantage of having a 58" track instead of 62". For my narrowed T-bird model I calculated (roughly) a 2.13 square meters frontal area. If I add two inch wider fenders, I get 2.19 square meters. 2.19 divided by 2.13 gives 1.028. Assuming equal power for both the narrow and wider cars, and also assuming the same CD-value (which is a bit rough), the gain in speed is the third-power root of 1.028. That gives 1.0093. Which means the top speed of the narrow car is 0.93% higher, say 1%. So 200 mph becomes 202 mph on the same power. I think that's a useful advantage. I cannot calculate the loss of cornering power that easily, and you would need that to give an overall judgement of a narrow car. But I think this is roughly the reasoning behind the narrow Elliott Thunderbird.



Nose extension

The photo analysis and the wheel base and wheel track analysis finally gave me a handle of how and what to modify. Here we go!

Step one of the nose extension was building a longer hood. I cut a 5 mm segment from the rear of one hood, and superglued it to the rear of the second hood. On the front side, I removed 2 mm, but only at the sides, so the hood become more pointy. Lastly I filled the four holes with discs cut with a Waldron punch and die set. You see the extended hood together with the original one.
Here you see the longer hood fitted to the first, old model.
Step two was lengtening the whole nose section. I started with building a jig, consisting of two pieces of 2 mm thick plastic card, glued temporarily together with two strips of plastic strip. Next were eight blobs of Apoxie, into which I pressed the body. After curing, the blobs ensured a rigid positioning of the body. The body in the photo shows the cut line, drawn 3 mm ahead of the door line. I scribed this line with calipers set at a 3 mm distance.
The second body was cut on the door line, and this nose will be glued to the rear part of the body seen in the previous photo.
The jig was extended with a 3 mm spacer, and then the nose piece was glued to the body. You can see the gap between the two parts of the jig plates.



Front fender modification

Next I started experimenting with the fender modifications, the old red body was used for that. I started with a 2 mm width reduction of the left front fender. I learned a lot from that attempt. The plastic was difficult to bend, even when heated, and even broke. It seemed clear I would need to make 'hinges' in the plastic to reduce stresses. Also, a 2 mm with reduction in the area next to the hood was not sufficient to create the desired shape.
With the lessons learned I started the 'real' modification differently. First I made a longitudinal slot in the top of the fender, 3 mm wide in the middle, cut mostly with a Dremel cutting disc (#426). I wanted to reduce the width by 2 instead of 3 mm on each side, but then the fender would not be sufficiently to be in line with the door. Then I cut the 'outboard' fender part in the middle, so I could work on the front and rear parts separately. For the rear part, I broke the fresh glue joint between the two body pieces at the door line, and refitted the piece almost in line with the door panel.
On the inside, I reinforced the weak joints with 2 x 0.4 mm plastic strips. This restored the strength of the body, so the modifications could be continued without fear of breaking the body. I also added a strip along the rear edge of the wheel opening, as a basis for more strips to reduce the wheel opening. Later I glued more strips on the body, that bridged the glue joint between the front and rear parts of the fender.
I built up the rear of the front wheel opening with 10 stacked plastic strips of 2 x 0.4 mm, to reduce the size of the opening, similar to what I had done on the red body. This photo also shows the bits and pieces of plastic card used for the uneven glue joint of the nose extension.
For the modification of the front part of front fender, I used the Dremel cutting disk again to make a wider slot in the top of the fender. This allowed the front half to be bent so it was roughly flush with the rear half of the fender. Note that the Dremel disc doesn't really cut, but melts the plastic, which works as well.
Then the front fender part was bent towards the hood and superglued in place. Yes, it looks very rough now! I strengthened the relatively weak glue joints with a 'layer' of 2 x 0.4 mm plastic strips, covering the whole interior of the fender. This also gave a bit more thickness for the next step. On one side I cracked the fender at its most narrow point, despite the internal reinforcement. I cut I groove across the crack on the inside and embedded an 0.5 mm steel wire.
Shown here are the 2 x 0.4 mm plastic strips inside the front fender, covered with Apoxie, and sanded down to make things smooth.
After the strengthening, I used a Dremel sanding drum to shape the fender a bit. By the way, if you're wondering about the large plastic insert ahead of the door: I tried making a 'hinge' there to rotate the fender part, but that did not work, and I had to fill it.
Apoxie was applied to the inside and outside of the fender, to smoothen the inside, and shape the outside. With pretty radical surgery like this, it's an idle hope that the modified shape is smooth straight away. Rather I see the modified plastic as a basis for the desired shape, that will take several rounds of modifications. I left the lower side in its rough state, because the bottom of the body still needs to be widened (like with the red body).

The front fenders were now 72 mm wide measured at the axle position. Before the modification it was 78 mm, so I removed 3 mm from either side. That is 1 mm more than intended, but remember I removed 3 mm from each fender to make the fender almost flush with the door, like in the photos. I need to fit the chassis to see whether the wheels will fit.
The same view but with a layer of white paint applied. It's looking decent again after all the surgery.
Here are my old red body and the new white body side by side, showing the width reduction of the front fenders.
Next I did another round of comparison with my set of photos, and it became clear that the front fenders were still to bulbous. They should be totally in line with the doors. Again I sanded the rear sides of the front fenders aggresively, revealing all layers of paint, Apoxie, kit plastic and reinforcing strips in the process. The door panel line was also filled with Apoxie. As you can see I still haven't finished work on the lower edge of the body's side. Then I painted the area again with white Revell paint.



Rear fender modification

I did another test on the red body, on how to modify the rear fenders. This went very well: with the cutting disc I made a slot just above the fold, cut the outboard part down the axle position. Then I superglued the forward part 2 mm inboard using the rear part as a reference. The same was done with the rear fender part. Next the slot was filled completely wity pieces of plastic strip. Then I used a Dremel sanding drum to sand away quite a bit of the inboard fender part down to the fold, then rounded everything off. Theoretically this modification would reduce rear body width from 79.5 mm to around 76 mm.

I also changed the wheel opening: 2 mm was cut away on the forward side, 1.5 mm on the top, and I added 2 mm plastic on the rear side. Next, I used a drumsander to make a rounded shape, following with sandpaper wrapped around a film container.
I painted the (rough!) rear fender modification red, since the combination of white and red in the modification made judging the shape difficult. Now I could compare it to photos of the real car. Maybe it could use a tad more width reduction?
It was difficult to decide whether the rear fender modification was correct. I decided to build another jig, that would locate the wheels at the correct 110" wheelbase (116.4 mm), with raised plastic strips that would hold the tires/wheels in place.

After a lot of fiddling and testing I decided to position the body 6 mm above floor level, and I added four brackets to hold the body. Compared to photos, the lower edge of the body is exactly at the level of the wheel rim edge, and my jig shows the same.
The first test was whether the tire looked realistic in the wheel opening. I think it matches photos reasonably. This test also showed that I could reduce fender width another millimeter on each side, which would give me equal front and rear track, at approximately 57.5".
Here's the cutting done on the white body, along with the Dremel cutting disc. I used a JLC razor saw to cut the fender down the middle, and for the ends of the large cut made with the cutting disc.
The regluing starts with a block of thick plastic strip, forcing the forward part 3 mm inwards using the rear part as a reference, and letting superglue do its job.
This is the result with the gap completely filled, and the excess plastic sanded roughly down. The amazing thing is that the body is now 76 mm wide, whereas I started with 79.5-80.0 mm. I expected it to be around 74 mm. Where did those 2 mm go? I'm still looking for them.

The photo also shows preparations for moving the rear wheel well forward by 2 millimeters. I glued two pieces of 2 x 1 mm plastic strip against the rear side, and made scribe lines at the top (1.5 mm) and forward side (2 mm).
Apoxie was applied to various areas and sanded down to the desired shape. The wheel opening was sanded to the new position and shape using a Dremel sanding drum, plus sandpaper wrapped around a 35 mm film container. The fuel filler opening was closed with Apoxie too.
The same view but with a layer of white paint applied. It's pretty smooth now. I'm still not sure what to do with the small horizontal fold in the C-pillar.
Here are my old red body and the new white body side by side, showing the width reduction of the rear fenders.



Character line - rubber molding

It's easy to remove the rubber molding on the door: just scrape away 95% of it with a modeling knife, and finished it off with a sanding stick. Luckily there's a tiny area above the rubber molding that is a perfect indicator for the scraping and sanding - you can see it above the remaining rubber molding on the rear fender. I did both the real body as well as the left-over cabin, because I want to transplant parts of it.



Headlights

Here's a photo of the real car at Daytona in 1985. I'm pretty sure the team used a stock headlight part: you can even see the elongated screw hole on the grill side. And of course they added blanking plates.
This picture was a breakthrough for the understanding of what I saw in photos of the Elliott car: they used this piece with blanking plates at the rear. A Google search provides more photos.
Work started with cutting out the light openings. Next the rear side was extended to allow for deeper openings, using 1.0 x 0.4 mm plastic strip. Then a new vertical divider was installed, at the 'new' angle of headlight bucket.



Nose section lowering

After my many modifications, the model still did not look like the real car in the photos. One thing I kept seeing was that the front of the car looked it was punched in the face, or had crumpled slightly after a head-on collision. It also looked like the whole nose was put too high with respect to the cabin. But it was very difficult to find proof (or dimensions of the error) for what I thought I saw.

After looking at the street car, and then the race car, I found the fenders far too bulged on their top side. I decided to take out 1 millimeter of thickness at 40% of the fender. First I glued a 2.0 x 1.0 mm strip against the lower side, to avoid the risk of sanding right through. I also sanded the outer parts of the hood to match the new shape. That hood still does not fit, because of the lengthening.
The same analysis had showed something I thought I saw: the whole nose is set too high compared to the cabin. I could have corrected easily when I lengthened the nose, but alas. I had to cut off the nose a second time. First I had to rebuild the alignment jig for the modified body.
Here's the fitting in progress. The jig was broken apart, and plastic card is placed under the rear part of the jig, to judge the effect of the lower position of the nose. I thought I would lower it 1.0 mm, but I went for 1.5 mm. In this photo everything is taped together, and I took some time to study whether this correction was visually correct. Slowly getting there..
Here's the body glued together again, with Apoxie and white paint applied. The joints on the inside were again reinforced with plastic strip. To compensate for the 1.5 mm drop of the nose, I moved the wheel openings up by the same amount by sanding the radius. The wheel opening's apex is now quite close to the upper side of the fender, just like in the photos of the real car.
While working on the nose, I cracked the left fender. I reinforced it on the inside with an 0.3 mm steel spring wire, embedded in a shallow slot ground into the fender. The crack itself was filled with thin CA.



Front fascia reshaping

The last main step was the reconstruction of the front fascia, making it subtly more pointed. The grill was moved forward 2 mm, and the headlight areas rotated accordingly. I used the grill area of another kit, and made sawcuts in the top of the fenders to be able to rotate the headlight areas. The operation required another small jig to keep the position of the grill part, hence the hole in the grill area.
More work on the headlight openings. I started closing in the headlight openings (that are too big) with plastic card, to ensure a solid fit during the numerous test-fittings of the headlights. I also started moved the openings ~1 mm inboard, to make the headlight sides flush with the fenders. Further I sanded off ~0.5 mm off the lower side of the headlights and grill to raise the bumper a bit, to compensate for the lowered nose section.
After breaking the rebuilt nose two times, because it was very delicate now, I glued in a 1 mm plastic card brace. Apoxie was used to fill in the areas above the headlights, again to make their fit very positive. It's all still a bit rough.



Bumper

I decided on a two step approach with the bumper. The first step was to make the kit bumper fit on the modified and narrow body again. The second step was to change its shape to match the photos. I couldn't do it all of that in one go.

I started with drilling four 2 mm holes all the way through the bumper at the points where the bumper needed a different bend angle, followed by sawcuts from the rear side. The two outboard holes got a 1 mm plastic card shim in the sawcuts to open up the holes, followed by Apoxie. The inboard holes got a wider sawcut that were subsequently closed by bending the bumper, with plastic straps glued on to keep the gaps closed.
The bumper needs to be reduced in width, some 4 mm in total. First I thought I would cut it out of the middle section, but study of photos showed that I had to take two 2 mm segments from the outboard sections. Since I've experienced numerous problems aligning parts after cutting up a complex-shaped component, I made yet another jig to hold the parts. The jig was made from plastic card and Apoxie.
Here's the bumper one more time (upside down), with all gaps closed with Apoxie clay. I also filled the rear side with Apoxie. This filler is not present on the real car, but the modified bumper was quite frail and required some strengtening. Next is a layer of paint to check the build and filler quality.
Here the bumper part has been split in the bumper and the spoiler, with a large horizontal saw cut. This will give me more room to make the bumper and spoiler match the photos. Both parts have been painted white, and they are attached temporarily here with Blu-Tack. Also the headlight buckets (still not finished) are fitted temporarily.

One thing to check is whether there is a 3 1/2 inch clearance for the air dam (source: Racefans Reference page 1.24).



Shape check and comparison

Here's a preliminary view of the new 'face' of the model. It's a lot narrower than the original Monogram body. Unfortunately I do not have another one to make a comparison.
This side view also shows the different lines of the converted body.
It took me a while to find an extra kit, but I finally found one. Here are the bodies side by side. It takes a second to spot the differences, but then you see more and more of them.
The main differences are in the nose, therefore I shot the noses side by side too.



Windshield

When I fitted the kit windshield to the body I thought it looked very flat, especially in the middle.
I modified a second windshield with a lot of Apoxie to arrive at this shape. I will have to vacform a clear windshield over this master.
In a bottom view you can see that I added around 3 mm in the middle, tapering to 0 mm at the edges.

In a top view I see something that appears strange: the top edge of the windshield is almost straight, the bottom edge is curved. Can a windshield have this shape?
Related to the windshield is the cowl vent panel, that is missing on the model. Here's my sketch of the cowl vent panel of the car. I will modify my model (again), it will mean removing part of the hood extension that I had added so carefully at an earlier stage :-(



Front suspension

So far, the focus was on the body, correcting the many shape problems. The next step is fitting the old chassis under the modified body.

This view shows how much the track must be reduced. In my calculations it was 62" originally, and should be reduced to around 58". That's a reduction of 2.1 mm on each side.
Here you can see that there is hardly enough room to move the wheel 2.1 mm inboard: the top tube of the frame is in the way. I think that the real car had a different chassis, with that top tube place more inboard. I hope that a later model Nascar chassis will supply that narrower set-up.
My original resin wheel (seen at the left) had a boss that put the brake disc at the same position as in the plastic original. I made two test wheels: the middle one where I removed 2.0 mm, and the right one where I removed 2.5 mm. Not shown is the separate resin disc.
The effect of this modification is best shown on the rear axle: the whole brake caliper is now inside the rim. I test-fitted the rear axle with two modified wheels, and the fit is very close to what I was looking for.
Here's the kit wheel on the front suspension. Note (again) the brake caliper completely outside the wheel.
The test wheel with 2.5 mm removed does not fit completely: it conflicts with the steering arm. But if that is solved, the situation looks promising. Except that the steering angles would be rather limited by the upper engine bay tubes.



To be continued..




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