Modernising the Group C Mercedes C11 (47484)

[TurnipJF 9717]

The Tamiya Group C chassis is one that has been on my radar to some degree since I saw one in a hobby shop window back in the early '90s, but it has taken about 30 years for one to make it into my fleet. A lot of things change in 30 years, and while I respect those who want to build these things to original spec, I wanted to bring mine as up-to-date as possible. Having recently built the F104 Pro II and seen how a few well-chosen upgrades can help an older chassis design perform like a new one, I wanted to do the same to my C11.

I posted a few progress pictures in the "So, what have you done today?" thread, but I wanted to finish the build and run a few packs through it before doing a full build thread, so as to be in a position to comment as to whether my modernisation efforts actually worked in practice. (Spoiler alert: they did.) So, here follows an illustrated description of the build, going through the manual step-by-step, showing what was changed and what stayed the same.

 

Step 1 - Charging battery pack

The chassis is shaped to take a NiCad or NiMH stick pack, but I wanted to run 2S LiPo, so a Core RC rounded 2S pack was placed on charge ready for use later in the build.

 

Step 2 - Front arms

This step involves sandwiching the front plate, uprights and front springs between the upper and lower arms, and provides several opportunities to install upgrades.

For starters, the stock uprights are the usual white plastic items used on many models over the decades, for which there is a carbon reinforced alternative under P/N 54154.

The uprights are installed at the same time as the front springs, which are rock-hard in stock form, pretty much locking out the front suspension. Fortunately the Group C chassis uses the same front springs as the Tamiya F1 range,  so the F1 front spring set (P/N 50509) gives us some softer options. I tried the hard stock springs for the first few runs, but ended up swapping them out for the medium alternatives which result in a more compliant front end and less understeer.

Step 2 also involves attaching the ball studs to the uprights. In stock form these are tiny little 4mm brass items that screw straight into the uprights. I swapped these out for steel 5mm ones with a shaft long enough to pass through the upright and secure with a nut on the other side. They come with the high torque servo saver, but can also be ordered separately under P/N 9804154. Having learned from my other pan car builds, I put these in the outer holes on the uprights rather than the inner ones which give more steering throw than necessary.

FInally, the front plate is a stamped GRP item with somewhat rough edges, which I decided to lightly sand and seal with cyanoacrylate. Not really necessary, but I prefer the look and feel of treated edges.

Stock uprights and springs:

 

Stock brass ball stud & steel upgrade:

 

Carbon reinforced upright in-situ, with medium spring and steel ball stud secured with a nut in the outer hole:

 

Step 3 - Attaching front arms

The only thing I did differently here was sanding and sealing the edges of the lower plate, same as I did with the front plate in the previous step. 

Plates with treated edges:

 

[TurnipJF 9717]

Step 4 - Checking RC equipment

Nothing significant here - I used Spektrum 2.4GHz DSMR radio gear with a Hobbywing 10BL120 ESC and Etronix digital metal-geared servo, and ditched the stock servo saver in favor of a high-torque one, but they go in the same way as the items shown in the manual.

 

Step 5 - Steering servo

The track rods are fitted to the servo saver in this step. In stock form, the rods are skinny bits of wire with Z-bends at one end and fine threads at the other, much like one would find on a Grasshopper for example. These went in the spares stash, to be replaced with proper M3 turnbuckles and 5mm ball connectors.

In order to avoid the larger connectors fouling the high torque servo saver at full lock, I fitted the ball studs to the front of the servo saver rather than the back where the Z-bends would go according to the manual, and compensated for the resulting Ackerman change by moving the servo to the back of the servo posts rather than the front as per the manual. I also mounted the servo with 4 screws rather than the 2 shown in the manual, as both the servo and the servo mounts have 4 screw holes, and I saw no reason not to use them.

Stock track rods:

 

Stock servo saver:

 

Front end with upgraded track rods, connectors, high torque servo saver and re-positioned servo preserving Ackerman:

 

Step 6 - Attaching steering servo

Nothing terribly different here - I used blue alloy nuts in place of the silver alloy ones supplied, purely for aesthetics as seen above, and I went for the higher ground clearance setting to make it a bit more forgiving of less-than-perfect running surfaces, but apart from that, assembly was as per the manual.

 

Step 7 - Gear case

Here we can go trigger-happy with the upgrades, since all the stock parts can be replaced with their modern equivalents which are either alloy or carbon reinforced. The left and right C2 and C3 side pieces can be replaced with the alloy F104 height-adjustable motor mount pieces available under P/N 54166, and the front and rear C1 and C4 pieces can be replaced with the F104 carbon reinforced versions under P/N 54330. Even the MB3 ball connector can be replaced with a fluorine-coated alloy ball nut on a steel shaft should you want to go this far, and of course the standard steel screws can be swapped out for alloy ones should you wish. (I stuck with steel for strength.)

Alloy and carbon reinforced height-adjustable gear case (ball nut added later):

 

[TurnipJF 9717]

Step 8 - Attaching T-bar

Here things can get interesting, as this is one of only two steps for which Tamiya don't supply bolt-on upgrades, and a little bit of customisation is required if you want to go as far with the modernisation as I did. Because I wanted to use the same alloy diff as supplied with the F104 Pro II, which is longer than the stock one, I needed an offset T-bar to replace the symmetrical stock one that the manual would have you install at this point. Fortunately the F103 T-bar has the right offset and fits the Group C chassis with minimal modification. All you need to do is drill two new mounting holes and gently adjust the edge profile in a few places, which is dead easy if you use the stock T-bar as a template. (Alternatively, if you don't mind going for non-Tamiya parts and are not too fussed about the color of the fiberglass, Carisma make a light green offset Group C T-bar under P/N 4892793164610.)

With an F103 T-bar modified to fit the chassis, the upgraded gear case can be fitted to the T-bar. Since the gear case itself is height-adjustable, you can omit the D3 shims shown in the manual as a means of height adjustment, and use the inserts in the the gear case instead.

Modified offset F103 T-bar installed, stock symmetrical one beside it for comparison:

 

Step 9 - Attaching rear axle

This step is pretty much as shown in the manual, just using a shorter axle and diff joint to accommodate the F104 Pro II diff if you want to fit one. There are a few options: carbon or steel axle, with integrated or separate diff joint, each having their own advantages and disadvantages. Having tried a carbon axle in my F104 V2 Pro, I find that I prefer the weight of a steel one under all but the most high-traction situations, and a separate diff joint is cheaper and easier to replace than an integrated one, so I went with steel axle P/N 84173 and the diff joint which comes with the F104 alloy diff housing P/N 54158.

Since I am using a steel axle, I have no need for the 54240 clamp type wheel hub which helps to avoid cracking around the grub screw on a carbon axle, so instead I used axle spacer P/N 3450157 with a grub screw type hub (albeit a blue lightweight P/N 53248 one rather than the stock item).

Steel axle with alloy spacer and hub:

 

[TurnipJF 9717]

Step 10 - Attaching motor

No surprises here - it goes in just like the manual shows. Nowt wrong with the Sport Tuned motor supplied in the kit, but I fancied something that captured the wild, brutal nature of the fullsize C11, so instead I fitted a ridiculously overpowered 4.5t Speed Passion - old tech by today's standards, but still plenty fast, just like its 1:1 scale M119 equivalent.

Having opted for the alloy motor mount, there is no need for part MB15 which helps spread the motor bolt load on the stock plastic one, so I omitted it, using washers on the motor bolts instead. I also swapped out the JIS motor bolts for Allen bolts which are easier to get to with the wheel in place.

 

Step 11 - Attaching spur gear

The title of this step is a bit misleading, as it involves building the differential, not just putting on the spur gear. It is merely a case of following the instructions supplied with F104 alloy diff housing P/N 54158 rather than those in the kit manual. The diff goes together very easily and operates smoothly, as expected, especially if you remember to lightly sand the pressure disks prior to installation.

There are Tamiya 0.6 and 0.4 module spurs available to fit this diff housing, and while I use 0.4 module on my 21.5t powered F1 models, I decided to go for 0.6 module here due to the significantly hotter motor. 0.4 module would probably have been fine, but I like the security of the coarser, more robust teeth.

Step 11 also involves fitting the pinion, which is alloy in stock form so was replaced with a steel one as per normal practice with any Tamiya that comes thus supplied.

Motor, spur, diff and pinion all installed:

 

[TurnipJF 9717]

Step 12 - Dampers 1

Another misleading step title, as in stock form the car has a single damper, not dampers plural. The standard item is a yellow CVA which no doubt works quite adequately, but with so many alloy bits on the chassis already, it seemed a pity not to go with a TRF damper. The TRF Special Damper (P/N 53901) sold for the F103GT is a great fit for this chassis in terms of both looks and performance, and comes out at the perfect length if you build it with the longer lower eyelet rather than the shorter one shown in the supplied instructions.

TRF damper:

 

Step 13 - Damper oil

Nothing to see here - I used the kit standard stuff.

 

Step 14 - Dampers 2

Here the manual would have you put a little tube through the upper eyelet on the damper, secure it with two O-rings and pin this in place between parts A1 and A5. However as anyone who has built a DT-02 or DT-03 knows, putting a tube through an eyelet designed for a 5mm ball connector is a recipe for slop, so I ditched the stock tube and O-rings, instead using a 5mm ball collar P/N 50591. This is a perfect fit for the TRF damper eyelet, but is a tad shorter than the stock tube, so it moves up and down on the MC5 pin between parts A1 and A5. This is easily sorted by putting a 3mm washer (P/N 50586) above and below the collar to take up the extra space, giving a slop-free damper mounting.

5mm collar and washers in place of tube and O-rings:

 

Step 15 - Attaching rear damper

Another case of simply following the kit manual, unless you want to use non-standard screws. (I have no problem with JIS, but I know some people would want to use hex bolts here, possibly in stainless steel, alloy or titanium.)

 

Step ?? - Roll dampers

Like Tamiya's older F1 chassis, the Group C lacks any form of roll damping in stock form. Roll dampers are an integral part of tuning the rear suspension on a modern RC F1 or pan-style car, so my plan from the outset was to build some form of roll damping into my car. I therefore added a few steps of my own at this point. I had some ideas as to how to achieve roll damping during the planning stages of the build, but I decided to wait until I had the rear end mostly together before making any firm decisions, so that I could check what would fit the car best.

The inboard roll damper mounts are easy to install if using the F104 gear case, as it features three screw holes on the front piece. The middle one is used by the main/pitch damper, but the two on either side are free to be used for roll damper mounting. I put a fluorine-coated alloy ball stud in each one, and popped on a pair of Tamiya's excellent RM-01 hop-up fluorine-coated alloy dampers. These are available under P/N 54342, and are also supplied as standard with the F104 V2 Pro where they are used for both pitch and roll damping. Having upgraded my F104 V2 Pro to use the more robust TRF main damper and high-efficiency roll damper as used on the TRF102, I had two of these spare. Other options would be the aforementioned high-efficiency roll dampers P/N 54413, or the stock RM-01 roll dampers which come on the W parts sprue P/N 9225133.

Mounting the outboard ends of the roll dampers required a little bit more effort, as while the unused outer body post holes in the chassis are in roughly the right spot, they are a little bit too far forward for the roll dampers to be at 90 degrees to the chassis axis when at ride height, which is important to avoid pitch/roll interactions, and if one bolts the outboard ends of the dampers to them, the shafts interfere with the body posts. They are also a bit too far inboard for optimal use of the travel available from the dampers. The ideal mounting points would be a bit further back and a bit further outboard, so I made some brackets to relocate them.

Having upgraded the plates on my TL-01LA's quick-release battery holder from fibreglass to carbon, I had a nicely-shaped piece of fibreglass with the same weave as the pieces used on the front of the chassis with which to make a pair of brackets. The static end of the quick-release battery holder is almost the right shape already. It just needs to be cut in half, each half needs to be trimmed a little, and a second hole needs to be drilled in each piece. The pre-existing holes in the plate serve as the outboard mounting points for the roll dampers, and the newly-drilled ones allow the brackets to be bolted to the chassis via the outer body post holes. It is easier to see than to explain.

Outboard roll damper mounting bracket, made from half a TL-01 quick-release battery holder static plate:

 

Outboard roll damper mounting:

 

Completed damper installation:

 

[TurnipJF 9717]

And that concludes the chassis modifications, with steps 16 through to 20 being as per the manual.

Step 21 - Mounting wheels saw bearings taking the place of bushings, and blue alloy wheel nuts taking the place of chromed steel ones. The front wheels were a bit loose on the stub axles, but this was addressed with some minor shimming.

At which point, the car looked like this:

 

Not too shabby for a design over 3 decades old!

 

[TurnipJF 9717]

The only other point at which I departed from the manual was at Step 23 - Painting body.

My foremost memories of the fullsize C11 are of watching it romping to Le Mans victory on a grainy old CRT TV receiving a terrestrial analogue signal. In these memories, the car appears a slightly darker shade of silver than the PS-12 specified in the manual. I have since seen more recent footage of the C11, and I have also seen it in person at the Goodwood Festival of Speed, so I know that PS-12 is a good match for the colour of the real thing, but to my eye it still looks unrealistically bright. Tamiya PS-63 Bright Gun Metal is a better match for the car I remember watching on TV winning Le Mans, so this is the colour I painted my model.

I am admittedly biased, but I think it looks rather good!

 

 

I hope this thread is of interest to other Group C fans, and that we see a few more C11 builds on the forum, be they stock or modernised.

[TurnipJF 9717]

(And don't worry - I haven't forgotten about the tyre stickers. These are the runner wheels/tyres. When I manage to source a second set for the shelf, they will get the stickers.)

[ChrisRx718 4599]

Very cool dude. I'm building a 787b which I plan to mount to my trusty F103GT and retire it to shelf duty. 

As you're now well-versed in this, do you think I could fit an F104 gearcase (and therefore the moulded plastic diffuser) to an F103GT?

[ThunderDragonCy 8114]

Excellent. Lots of insight into the F1 style chassis. I know nothing about then, so that was interesting. Also very cool looking car. 

[Pylon80 3307]

Lots of detail and part numbers 👍 That's a gold mine for me, as this will be my next build.

I want to keep mine purposely barebones, for the 1990's feel, but at the same time I do have the RM-01 sprue with the friction dampers and your idea of fitting side dampers is intriguing.

Regarding the paint I do not like PS-12 which has these giant, closer to 1:1 scale, metallic flakes of silver in it. The last body I painted was a 911 RSR and I too swapped the PS-12 for PS-63. Darker yes, but more realistic. Yours looks great.

[TurnipJF 9717]

22 hours ago, ChrisRx718 said:

As you're now well-versed in this, do you think I could fit an F104 gearcase (and therefore the moulded plastic diffuser) to an F103GT?

You could fit the F104 gearcase front, back and sides to the F103GT easily enough - the screw hole positions are a match - but the F103GT T-bar is integral with the motor pod floor, taking the place of the F104 moulded plastic diffuser piece which also formed the motor pod floor. 

This is a good thing from a structural perspective, as the point at which the F104 T-bar attached to the diffuser/floor piece was a common point of failure. I once saw a chap break 3 diffusers in a single race meet. Tamiya seem to have learned from this, as the F104 Pro II has ditched the plastic diffuser and gone back to having the T-bar integral with the motor pod floor. I have yet to see one of these break.

If you want a F104 diffuser on your F103GT, you might consider cutting it free of the motor pod floor piece, and fabricating a bracket to attach it via the screw holes on the back of the gearcase which are used for mounting a wing on an F103, but remain unused on an F103GT?

You may also consider sandwiching the diffuser piece between the gearcase and T-bar. This would lower your rear ground clearance by the thickness of the diffuser piece, but you could compensate by lowering the axle in the height adjustable gearcase by the same amount?

[Pylon80 3307]

1 hour ago, TurnipJF said:

You may also consider sandwiching the diffuser piece between the gearcase and T-bar. This would lower your rear ground clearance by the thickness of the diffuser piece, but you could compensate by lowering the axle in the height adjustable gearcase by the same amount?

This is how I would do it. I would take care to round off the edge of the diffuser to avoid stress risers that could still cause the T-bar to break.

[JimBear 786]

I've been watching youtube videos of the real car and enjoyed the sight and (even more) the sound of it. It's a million miles off, but I keep the idea of building one of these on my Project list.

[Skimax 30]

Looks awesome, nice job!

[TurnipJF 9717]

Thanks! 😁

[Busdriver 6268]

Brilliant build thread. Really well written 👍

[guggles 216]

wow that has to be crazy to drive with a 4.5 turn in it!

[TurnipJF 9717]

15 hours ago, guggles said:

wow that has to be crazy to drive with a 4.5 turn in it!

It can be a bit of a handful, and full throttle is only really usable on a scale equivalent of the Mulsanne straight, but I have been fiddling with the exponential and have got to the point that the first 2/3 of throttle travel is suitable for use under normal conditions. I might even try it on a Postal Racing layout. 😁

[Wez-li 1790]

On 9/21/2023 at 8:45 PM, ChrisRx718 said:

Very cool dude. I'm building a 787b which I plan to mount to my trusty F103GT and retire it to shelf duty. 

My original lives on the shelf, hasn't turned a wheel since I test drove it two years ago 😆

[TurnipJF 9717]

Very nice! I hope Tamiya release more of their classic Group C cars.

[Pylon80 3307]

2 hours ago, TurnipJF said:

Very nice! I hope Tamiya release more of their classic Group C cars.

If history repeats itself, we should have the Jaguar, then the Mazda coming. Well, it should have been this year and did not happen :| I am getting worried!

[Jonathon Gillham 4672]

@TurnipJF those roll dampers. Do you know if they could replace the single one on the TRF102? Or are they specific for the cars that have one each side?

Great build, interesting to see what can be done. I'm intrigued by one of these but haven't got one yet. Maybe the Jaguar to sort of match the 1:1 in my driveway...

[TurnipJF 9717]

12 hours ago, Jonathon Gillham said:

TurnipJF those roll dampers. Do you know if they could replace the single one on the TRF102? Or are they specific for the cars that have one each side?

One of these can indeed replace the TRF102 roll damper, being exactly the same length as the stock item. A single one should be fine on the TRF102, being a fair bit lighter than the Group C, and very close in weight to the F104 V2 Pro which comes standard with a single one of these as a roll damper.

[Pylon80 3307]

@TurnipJF as I am gathering parts for my own Group C, I noticed that the TRF special damper comes with a white spring with a red dot. That spring is no particularly soft; in fact, when compared to the long floppy silver spring that comes with the Group C kit, it is downright stiff! What is your thought after running the special damper spring on your car?