The Jaguar XJR-12 Group C I wanted in '91

[Pylon80]

It all started in December 1991 when I convinced my mum to buy me an RC car magazine. The second page had an ad for Tamiya and it was for the Group C kits that had just come out. I don't know how many hours I spent examining that page but it must have been "a few". The price of 1190 Francs, in money of '91, would probably equate to over a thousand bucks in today's money - it was utterly out of reach. I was also lacking the skills or the mentoring/help that I would have needed to build it, not to mention that I didn't quite have any easy access to a suitable running surface!

I still remember the corny slogan which I will attempt to translate as "if speed scares you, treat yourself to a monstruous ****ht!". I am sure a pan car with a SportTuned motor is no slouch.

Fast forward to 2024 and Tamiya did yet another re-release of the Group C kits. I am suspecting they have some sort of arrangement with Mercedes because we get a lot of these in Tamiya form. At any rate the Jaguar was not to be re-released this time around. I still purchased a C11 kit thinking that it would still get me somewhat closer to my goal. At 150$ for the regular price, talk about a bargain! Then I read about Buyee on this here forum and that led to finding 2 bodies for the ellusive Jag; a Tamiya Factory Finished one (brand new) and an unbuilt, new in the clear bag one. The factory finished one was missing its wing but a separate auction gave me an old, beat up poorly built rear wing for a few bucks. So I seem to have all I need to get on the track driving my dream toy fairly quickly!

With the arrival of our 3rd child the time budget for RC has shrunk even more and so this will be a 'sanity' project done using the few minutes I can spare each day. This is not my first pan car but this is my first 'vintage' Tamiya; I am aware that it is a sacrilege to call a re-re 'vintage' so I am only  referring to the design and technology when I say 'vintage'. I like modern, higher end and complex chassis so there are quite a few things I do not like on a chassis like the Group C. I will address these until I have obtained a chassis that looks good to me and is easy to work on. I will not call this project "modernizing" the Group C as this was superbly done by our very own @TurnipJF already. I will simply add my OCD touch here and there and probably deep dive into needless details in a few places which is my idea of fun  I will also try to keep the spirit of these old cars by using a brushed motor, an analog servo and the simplest ESC I can get away with.

[Pylon80]

Front Arms

I quite naturally started with the front arms and knuckles as in the manual.

I always enjoy detaching the first part from the first sprue and make it a point to do it cleanly. I never sand the parts but I scrap off any plastic that remains until it no longer looks like the part ever belonged to a sprue.

I will not be using a single one of the kit included screws as I much prefer the hex hardware. I will also try to have nicer colors for said hardware. For the arms I am replacing the 3x12 tapping screws with really nice Tamiya 3x10 machine screws. As usual I roll threads with a bit of grease and get a really nice connection that I should be able to dissemble and reassemble hundreds of times. This is important as the kingpins of a pan cars should be cleaned very often. To achieve this the easiest way on the Group C I think I will have to dissemble the arms.

Knuckles and Kingpins

The kit included knuckles are the traditional white ones included in so many RWD kits, from F1 kits to the Grasshopper. It is white and I really cannot stand white plastic! So I started priming them and was about to paint them black when they came back in stock on PJ, as usual for a few dollars. I do not intend to crash this car  nor to drive it anywhere near obstacles that could make it necessary to have reinforced knuckles; the black knuckles just look so much better, to me.

The kingpins are completely slick, devoid of any groove for E clips so it will be possible to make my own from 3mm stainless rod should I need spares. A tip to install them the easiest way is to set your calipers to 8.5mm first, then lock said calipers, then slide the kingpin until it contacts the calipers.

Then simply tighten the grub screw gently. Obviously you need thread locker as this is a metal to metal connection.

I had the standard F1 front springs in my spare stash and so I went for the softest ones as I usually like soft sprung cars. I will also be using a very light servo so there will be very little weight over the front.

I use friction damper grease on the kingpins of my F1's as it adds a bit of damping action while keeping things lubricated at the same time. You do have to clean up the kingpins every half hour of run time when you do that.

One thing that I noticed is that on one side there was the slightest hint of friction in one of the holes so I ran my trusty arm reamer just one time to knock a small burr off and then everything was silky smooth.

This is fun so far!

[wtcc5]

Very nice! This will be great! So you plan to use anodized aluminum screws for additional bling bling, red and green? Can just imagine how fine that will look 

[Pylon80]

4 hours ago, wtcc5 said:

Very nice! This will be great! So you plan to use anodized aluminum screws for additional bling bling, red and green? Can just imagine how fine that will look 

I have been wondering about doing this and you're not helping my finances by making the suggestion!

Initially I was going to do it in Tamiya blue and spent a lot of time chasing the proper blue hardware. But since there's an F102 coming right after this one  I am thinking I could get green hardware for the Group C and set the blue one aside for the F102. I'll have to see how to best procure green M4 flanged nuts, M4 nuts and M3 screws.

[svenb]

The Jag is a beautiful body, I got mine in 91 or 92 think I paid £130 for it.

If I remember right the body didn't have any protective film on and I had to use brush on PC paint. Being a young un I changed some of the number decals to 01! Still have the chassis body and box somewhere.

[Pylon80]

@svenb I really enjoy these stories of the past

I have had a thought about hardware colors and I think it would be a bit too 'Christmassy' to mix green and red  and since the shock (to be revealed later) will be blue and since I already accumulated all sorts of blue hardware I think I will keep the general look as black and blue with the occasional unavoidable silver.

One thing I did not mention is that I left the arm screws loose for now as everything will be gradually tightened once installed on the lower chassis plate - which is what I did last night. This provide a very straight chassis with very free knuckles.

Chassis Protector

The Group C, like many older car is using this old school black fiberglass sandwich material to make the lower front plate, the upper arms plate as well as the t-bar. I have grown to like the vintage look and feel of this material by now but one thing for sure, it will not stand up very well to going over the occasional pebble. Since I wanted this chassis to be as practical as possible and not have to bother bringing a broom with me - especially when I go to the track on my bicycle or on foot - I decided to add a chassis protector.

The stuff I used is basically a clear sticker I found on AMain; it's probably just MacTack and the quality is very nice. Being clear it is surprisingly easy to make a job that looks neat! It took about 30min to trim every hole and cutout from the lower plate and scrapping the edges was oddly satisfying for some reason.

Hi resolution cameras are not kind and the plate looks much better in real life!

Hardware

There are at least 3 things on my non-exhaustive list of features I don't like on a chassis: white plastics, JIS screws and brass ball studs. The Group C has them all! So I sourced some hex M4 screws to attach the arms to the lower plate, or rather I found some in my existing stash of F1 parts. Interestingly the kit JIS M4 screws were aluminum! I will still use my stainless hex ones.

Next up will be the servo, servo mount, servo saver and turnbuckles; none of that will be stock!

[Pylon80]

Steering Servo Arrangement

From the beginning I was adamant on having 3 things that would differ from the kit:

1- a centered servo with equal length tie rods as it's mechanically cleaner. Different lengths cause a slightly different amount of Ackerman and so the car in theory would steer a bit differently left vs right which bothers me.

2- blue aluminum turnbuckles as they are my favorite part of any chassis; I never considered using the S bent rods from the kit. These were the way in the 80's but I don't think it's for me.

3- servo mounted on the chassis plate with the servo saver pointing upwards and the tie-rods connecting with the knuckles from the top. It just seems neater and promotes a lower CG.

Servo and Servo Saver

For the servo I really wanted something analog that would convey the spirit of what I would have had in 1991 had I found this kit under the Christmas tree. Back then it would have been a Multiplex MS-11 or a Futaba S3003. The 3003 has been too heavily counterfeit by our 'trading partners' in the far east so I wouldn't trust that. It is also a bit too slow I think. The Hitec 322HD on the other hand is a true .15sec/60deg which is actually totally drivable; the centering and overall quality is superb; and at 15$ it's a total bargain. The only irritating thing is that being a "standard" servo rather than a car specific one, Hitec still makes these with a 24 spline output shaft. So sourcing a proper servo saver was a pain. Kimbrough make a red one (what an ugly color) that I promptly primed and painted black. Due to the limited clearance I had to shorten it. That's when I realized that the Hitec servo screw didn't fit! If you have experienced these moments when nothing works you probably get the picture. Soon after as I was reboring the servo saver it exploded, shooting a really long and stiff spring somewhere in my shop! 🤣 It was like a scene from a Jim Carey movie. Exhausted and hellbent on making progress on the steering 😬 I locked the now spring-less servo saver with a tiny M2 screw. Let's move on shall we!

Steering Turnbuckles

I went into my stash and found a bag of 42mm turnbuckles.

I also had some 2mm thread low profile ball nuts. These ball nuts were an RM-01 part, 54360. These are much nicer than the kit ball studs and will also allow me to fine tune bump steer. I also had the standard ball nuts in the same color (53599) for the inboard ones. I plan on shimming these inboard ones to fine-tune Ackerman.

For the adjusters I used the modern looking open face ones (54869) on the outside. I found that these have low friction and remain so for a very long time. Also being open-faced you can wash them to let the dust out. On the inboard side I used the good old low friction ones (53601). These are great as they have virtually no play but the reason I used them was to prevent fouling with the upper chassis part.

Servo Mount (or lack thereof)

I think the best way to install the servo on a Group C would be to redesign the lower plate, offsetting the servo to one side such that the tie-rods are of equal length. I only know of Fibrelyte to make my carbon fiber parts and shipping from the UK is usually outrageous So in order to save time and money I decided to do something very simple: attach the servo with double sided tape! This is how the F103 Tyrell is setup for instance. I tried it once on a TT-02 and when the time came to remove the servo, the bonding strength of the tape was so great that I really thought I was going to break the servo case. I only managed to remove it by gradually cutting the tape from underneath. It's strong alright. I use a 3M heavy duty tape; the roll is so old I wouldn't know which one it was exactly.

The trick to doing this properly is to find a way to be consistent as to where the servo goes. This way I can remove it and reinstall it once in a while and get the same car every time. So I set the lower plate and servo vertically on my work bench and slip a temporary 3mm shim under the edge of the chassis plate. Then I center the servo by looking at the knuckles and using tie-rods of the exact same length. This gave me a perfectly centered servo with what looks like a good amount of Ackerman; I'll confirm with the setup station later on. I can adjust the  mounting shim as required to move the servo forward or aft.

A lot of blabber for very little visual progress!

Here's a test fit I did to make sure the clearance was good.

Next up will be attaching what we have today to the chassis tub. I want to modify the front/upper chassis part A4 slightly and use proper blue hardware. I will also make a set of shims that will enable fine tuning the tub ride height.

Edit: looking closely at my own pictures I see they are from test fitting and things are not perfectly straight, some red is showing on the servo saver etc. Everything will look nicer on the next pictures I promise!

[TurnipJF]

A centralised tape mounted servo - now there is a modification I haven't seen on a Group C chassis before! Looking forward to reading about how it works out for you.

[GermanTA03Guy]

I read that David Jun (the one from the 58200) used to glue the servo to the lower deck with shoe goo on the ta03f He won norrca championships with. Reason Was not to centralise it though but to be able to fit the Esc beside it... anyway, should work.

[Pylon80]

Magic Trick: A4 Part Bosses

Here's a mini update on how I wanted to make the body post bosses disappear on part A4.

If you remember how this part was on the original Group C, it was slick like this:

Then for the Re-release Tamiya probably envisioned more kits with aft mounted body posts and they added these ugly bosses. These are not needed as far as I know on any Group C cars and the Jag is no exception. So I needed to make them disappear!

Step 1: let's hack brand new parts with a saw:

Step 2: slowly chip at it with a utility knife, taking care to never penetrate under the desired surface (we don't want to start having to use putty, primer, paint etc):

Step 3: sand with 200 then 400 grit:

Step 4: polish with automotive cutting compound (tooth paste would do just as well):

Ta-dam! No more bosses.

I originally wanted to paint this part blue like the original Jaguar kit but I feel like the paint will easily chip off and it'll look better if I keep it all black.

Next up will be some real progress I promise 😅

[GermanTA03Guy]

Nice Job. I actually painted some gaerboxes from grey to Black with ps colors, worked a treat.and the gloss is semi which is spot on. Ps are not all matte like some other polycarbonate colors. 

[TurnipJF]

Very neatly done!

[Pylon80]

@TurnipJF Thank you

@GermanTA03Guy Thank you for the tip on using PS paint: I initially used fine surface primer then acrylic on the servo horn but that started chipping off straight away. I wiped the acrylic in one pass with alcohol :O then I wiped the primer clean with another swift pass! This means the Tamiya primer is not self-etching what so ever. So I used PS black paint and obtained a durable finish that looks just like the part had been molded out of black plastic! Very pleased with that.

This is just a quick update on how I realized I needed to put the servo on the right because the motor endbell will be on the left, meaning the ESC will be better on the left, which means the servo should be on the right to help balance it all! I like to balance the pod separately, then balance the entire car rather than just balance the entire car when I know the pod is not balanced properly. This makes for a nice tweak free pan chassis.

I also ran out of my magical double sided tape in the process and had to experiment until I found one that seems as tough as the 15 year old one I finished.

So, here goes, servo back on the lower plate:

Arms ready to come back in:

Some Tamiya blue for the serrated nuts (and am I glad I removed these bosses!):

And the current state - I really like the black and blue theme:

I gradually tightened all 6 M4 screws as well as the 2 M3 screws in the arms. It all feels nice, straight and smooth. I will assemble the car with the supplied ride height shims for now; they make for a ridiculously coarse adjustment being 5mm thick. So once I have it on its wheels I will see if I need to make finer shims, tentatively 1mm thick styrene shims.

Next up will be the heart and soul of any pan car: the motor pod!

[skom25]

I love attention to details!

What is +/- ride height? Can it be run on dusty asphalt or it is more like prepared track car?

[Pylon80]

13 minutes ago, skom25 said:

I love attention to details!

What is +/- ride height? Can it be run on dusty asphalt or it is more like prepared track car?

Thank you!

I will see when I have it on wheels, but my experience with F1 cars is that they have a reputation for being very low when they can actually be set more than high enough for any typical tennis or basketball court. I do think however that the pavers I saw in your TT-02B video would be a bit too rough for an F1 or group C car 😐

[skom25]

I also have quite big square of asphalt, which is my main place to run now.

I am waiting for updates. It looks really great and I am always impressed with your builds.

[GToddC5]

Watching with great interest. Let me know if you are looking for a Jaguar XJR-12 manual. I accidentally purchased a second one somehow, which tells me my collection is getting out of hand, LOL!

[ChrisRx718]

Loving it, following with interest. I do hope Tamiya re-release the Group C's again some day.

Are you trying to stick to Tamiya parts? I only ask because I saw this earlier today and thought it looked rather snazzy. 

[Pylon80]

I think Tamiya achieved some commercial success with this re-release and I received a lot of kind words of enthusiasm regarding this Group C build that's only at it's beginning. I must apologize for the slow pace; life as a father of three has been a challenge and I'll certainly use it as my excuse! A lot of our members built their Group C in one weekend which always puzzles me.

@GToddC5 thank you for the offer, I am not much of a collector though. I do really like manuals so it would be tempting but I think being 'fake' XJR-12 built from C11 re-re parts I will make do without an original XJR-12 manual.

@ChrisRx718 I didn't know about these new "RC maker" parts. Lots of interesting and very modern bits there! I see an F103 friction damper which is a cool idea. His lower chassis plate looks like what I described in my earlier post although I would need a different position for the servo mount holes to make use of TT-02 or RM-01 or DT-02 style servo mount with the servo down low and the tie rods connecting with the knuckles from the top as I chose to do. Also his carbon upper deck looks great; I will stick with the plastic parts because their 4130 welded truss looks is what I love the most about the Group C chassis! Nice to see modern parts for it at any rate 👍

[svenb]

5 hours ago, ChrisRx718 said:

Loving it, following with interest. I do hope Tamiya re-release the Group C's again some day.

Are you trying to stick to Tamiya parts? I only ask because I saw this earlier today and thought it looked rather snazzy. 

I like that @ChrisRx718 where's it from?

[Pylon80]

27 minutes ago, svenb said:

I like that @ChrisRx718 where's it from?

I think it's a guy selling option parts through RC Mart? Or am I confusing him with someone else? 🧐

[Pylon80]

Motor Pod

Nothing too special with the pod. I really like the plastic which seems to be armed with some sort of fiber; you can tell when you chip at the sprue tabs as it makes that special sound.

I rolled threads in every hole, 15 in total 🙂 As usual it is important to use plenty of grease with doing this.

I am using aluminum screws, the proper length is 3x10 unlike the pointy kit tappers that are 3x12. Aluminum screw were chosen under the pretense of reducing unsprung weight but we all know it's for that Tamiya blue 

One important note is to tighten the screws in X pattern while resting the pod on a very flat surface. I always use a flat countertop in the house for this (I really need to get a setup board...).

Then I applied more clear protector, this time for the t-bar. It went very easy in under 15min.

I even had a "in-one" moment like some of our members when they cut bodies (ahem, @Re-Bugged):

And a nice glossy protective layer:

Finally I attached the pod to the t-bar. I used 3x6 screws instead of the giant 3x16 (I think) from the kit since I am not using the ride height shims yet. I am starting with the highest setting until I can have the chassis on its wheels.

A note regarding these shims: they are too coarse for me, being 3mm each. It will be very easy to make some 1mm ones and then by mix and matching I will be able to achieve 0, 1, 1+1, 3, 3+1, 3+1+1 or 3+3 😎

Next up will be attaching the pod and t-bar to the rest of the chassis.

[matisse]

14 hours ago, svenb said:

I like that @ChrisRx718 where's it from?

Quality of this should be good, Carisma make good parts and OEM for many of the bigger names, inc Losi.  

[Pylon80]

Another update as I managed to tinker a bit last night 😎

Attaching The Pod

I searched through my hardware boxes and found 2 M3 nuts in Tamiya blue, isn't it nice with that happens! I am not sure where these are from.

The front screw is a 3x12 instead of the kit 3x18 😅 but the rear screw really needed to be 18mm long. This meant I had to use the kit JIS screw. In my quest to eliminate JIS hardware, that's strike 2! The first JIS screw was the one that belongs to the servo, and this would be the second one and hopefully the last. I do have Tamiya screwdrivers for these so I can still use them.

It's big! I knew it would be at 280mm wheelbase and well it really is.

I have left the o-ring as lose as possible but without any perceptible play, as my starting point. I think that if the o-ring is too tight the car might oversteer too much. Anyways I'll adjust it during the first run, something I am really looking forward to!

Rear Axle

Then I installed the axle:

 

You have to be careful to leave a bit of play such that the axle will spin freely. Easiest way was to bottom out the right side and then adjust the left side slowly until it feels nice and free but not loose.

It's interesting that both ends are aluminum, for a few reasons:

- if using aluminum nuts I'll have to use a bit of grease to avoid aluminum to aluminum seizing.

- when tightening the grub screws, go easy

- I would really like to use a bearing inside the spur to avoid wear on the right side; that means sticking to F1 spurs that are 63 or 70 teeth in 0.6mm module. Other tooth count are possible with the Tamiya adapter ring. I'll know more about what gearing I need when I have selected the final motor and started driving the car a bit.

I don't know if it's due to the 32 years of longing for a Group C, but I'm pretty chuffed by this project!

Thoughts on Droop

Something interesting about the t-bar is the way it angles down, since there's a o-ring at the rear but not at the front:

I think this helps the pod droop a little, but again I'll have to see with the motor installed what the drop is like. I'll also have to see if the t-bar lays flat when the car is on it's wheels with the battery installed. I think I can always make 0.5mm shims for the front of the t-bar if I want to reduce the droop.

So far it feels like a simple chassis but with lots of "more than meets the eyes" kind of details, which I really like.

Next up will be building the differential.

 

[Pylon80]

Wheel Hubs and Differential

I am quite fond of ball differentials as I find they have a very accurate and play free action compared to gear diffs. They do require a bit of maintenance to remain smooth; they are also quite unable to be made very stiff. I am certain that will not be a problem on a pan car running on low grip surfaces! I will use a Sport Tuned or equivalent power so nothing that could make it slip either. One note is that due to the cantilever design is pan car pods, the ball diff is convenient although gear diffs have been made that fit inside the spur of pan cars! I remember X-ray having done that in the past.

First we need to prepare the wheel hubs by pressing nut plates in position; I used a 3x10 screw and a washer for that:

You have to be careful as it requires a lot of torque but not too much as you don't want to crack the hub! It's best to go in small steps, backing off between each one until it feels like it won't go any deeper.

I really like these hubs as they will enable me to rotate the rear tires left to right without disadjusting the diff! The only thing is I will probably have to use a bit of Loctite on the 3x10 screws (2 per wheel) which adds a small hassle. Who likes to extract a drop of Loctite from the pesky little tube? 😅

This is the stack of parts needed for the diff:

As you can see I swapped the white plastic of doom for black one for the spur and diff housing. The spur is the same as stock in terms of module and tooth count.

Note the direction of the Belleville washer which is important to make them press on the outer edge of the thrust bearing. And speaking of which, it's a nice perk to see a one piece thrust bearing in this kit!

As an optional step I like to polish the plates with 1000/2000/4000 grit:

The white gizmo is a magnet to hold the plate while a wet sand it on a flat countertop.

And here is the rear end of the car with more Tamiya blue 💙:

The diff feels very smooth and it will feel smoother still with the weight of the wheels attached. I will finalize tension with the wheels on, before the first run.

Next up will be the "main event" of the build 😁, the pitch damper!