AMP front bulkhead ECX1092 workaround

95PGTTech

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rural NJ
The AMP buggy (and a few other models) use a unique front bulkhead (where the lower control arms mount) different from the rest of the 1/10 ECX 2WD lineup. Many people have broken it (usually from aluminum front A-arms or high impact front tire crashes). Not only is this part becoming harder and harder to find a replacement for, there is no aftermarket upgrade. See highlighted/circled picture for reference.

ECX1092.jpg



I ended up getting a bunch of front bulkheads for other RCs for the race Ruckus build, and noticed the DR10 (Team Associated) style front bulkhead appeared pretty close dimensionally to what my brain remembered the Amp's from looking like.


I picked up a chassis (ECX1017) and top plate (ECX1029), and the Team Associated bulkhead (91359) and top plate (91358). I actually got 72007, which is the 45 gram brass unit @ 25 degrees. I got the Team Associated top plate because I wasn't sure even if the bulkhead could mount to the chassis if the Amp top plate would work, but I knew the Team Associated top plate would at least mount to their bulkhead, the issue would be would it mount to the chassis. First win is the 4 bolt pattern between the two bulkheads is dimensionally identical, so the bulkhead does mount to the Amp chassis without modification and it will then mount to either top plate without modification. The Team Associated top plate will *NOT* mount to the Amp chassis, the bolt spacing left to right and front to back is entirely different. So, pictured Amp chassis, Amp top plate, Associated bulkhead.

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It is not, however, perfect. It's significantly thicker than the ECX part, so it shoves the mounting holes for the top plate further back than they should be. It's hard to picture, and it can be overcome by installing all 8 bolts (4 in the top plate, 4 from the bottom of the chassis) loose and then tightening together, but when tightened down it is putting some downward pressure on the nose. Maybe spending some time with washers for the top plate might help this, but I'm not thrilled about plastic parts being under pressure at rest. In theory, it's also angling the front of the front control arms farther downward, decreasing front kickup and caster. Notice how the mount holes on the chassis are at the extreme front of the slotted hole for the top plate (they're actually farther than the end of the slot), so when tightened down, it wants to maintain this gap instead of sucking together flush. Flipping the bulkhead around and mounting it backward does not solve the problem and opens a whole host of issues (like how are you going to get the pin brace on, and how does moving the LCA inner mounts further back affect handling).

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Two other considerations:
1. Front bumper for the ECX mounts using these center bolt holes. There is no such provision on the Assocated bulkhead. Associated uses the front bolt holes. Again, nothing that can't be overcome, but it needs to be dealt with. Use the front holes, maybe even mark drill and tap the Associated bulkhead.
IMG_0893.jpg

2. The ECX front shock tower appears to mount with no issue and no clearance issues, but by using the Associated bulkhead, you now need to use the Associated front control arms (71608). The final picture is some aftermarket ECX arms on a stock Ruckus bulkhead so you can see how they should mount. The ECX ones aren't nearly wide enough at the mounting point. To mount the arms, you'll also need inner hinge pins (91394) and front pin brace (71049) assuming you supply your own hardware. For anyone that followed my 1/10 4WD build, when you swap arms to another vehicle, you're opening a whole new can of worms...I don't have the Associated arms here yet, but I can almost guarantee they won't be the correct spacing to use the ECX outer pins, caster blocks, steering blocks, axles, etc. I would assume this swap would basically mean an entire DR10 front suspension other than the shocks, and outer tie rods are going to be something that needs to be measured and custom fit (many of us have Slash adjustable arms anyway). Which may be a good thing, because there is a huge DR10 aftermarket centered around racing, so there are probably a lot of great options out there for parts. Another thing that comes to mind is are the DR10 arms reasonably the same length as the ECX ones, or is there parts interachangeability to another Associated arm that is?

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Hope this helps someone. I'm researching arms now and I'll update with news if I have any. Sorry my other threads have been dead, we are typically very busy with sports and house stuff when the weather is nice, now that it is the cold of winter again we will be into more RC time. Many, many changes to the 1/10 2WD Ruckus.

I also ordered a RC10B6 bulkhead, which appears slightly thinner and doesn't have the front pin brace provision that the DR10 unit has. We will see.
 
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Looking at those middle screw holes, can you slot the holes a little farther back on the top plate then use some sort of spacer under there?
IMG_0927.jpg

I was able to get two 3x8x0.5mm washers in between and it aligned the bolt holes a lot better and took a little stress out of the whole setup. EDIT: I measured them today, they are 3x8x0.66mm washers
 
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Bunch of parts arrived, going to try the RC10B6.4 (referred to as a B6 by Team Associated guys if you're searching the internet) bulkhead because I thought I remember it being a little thinner and the bolt hole pattern looks pretty close. Got the DR10 arms, we know they should work on the DR10 bulkhead, got 6.4 arms and B7 arms (the new model just released which advertises as longer control arm length for more track width). The DR10 shares a lot of the same underpinnings as the offroad trucks and B5s, but none of those have any different control arm options. Got B6 pins and hinge pin bracket.

IMG_0915.jpg

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DR10 aftermarket left, ECX center, B6 aftermarket right. Looks good from a thickness point of view, relatively same distance pin to pin.

...and in just about every other dimension it's a complete no go. For starters, the ECX and the DR10 have a trapezoidal bolt hole spacing (the fronts are very, very slightly closer together, like you'll only see it if you put a mic on it). The B6 is symmetrical, so it can be flipped around 180 degrees to be mounted for a different setting. The bolt hole spacing isn't the same front to back or side to side, you can really see it in the picture where I set one long bolt through one hole and how bad the opposite hole lines up. We are talking probably less than 1mm, but enough to be a problem. There are other issues like the B6 one does not have the recesses drilled into it.

IMG_0926.jpgIMG_0925.jpg


When we view the assembly instructions side by side (I labeled them), you can see why that is. The DR10 sandwiches the bulkhead between the chassis upsweep and the top plate, where as the B6 has a much more modern bulkhead-under-chassis mounting setup. You can also see what I mean about it being symmetrical and reversible. Bummer, I was really hoping this one would work, it came with adjustable pin mounts too and adjustment is really helpful when doing swaps/retrofits like this. I'm sure by slotting multiple holes in the chassis or the bulkhead and the top plate it could be forced in there, but that just makes future servicing and replacements even more of a pain.
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So we need to find a way to make the DR10 bulkhead work. I put in an order for DR10 pins and pin brace, the B6 stuff won't work. I was really hoping it would, it opens up a lot more aftermarket options because those are the cars that are really raced hardcore.

Just some other notes, yes the ECX arms on the DR10 bulkhead is an absolute no-go. The pins on the DR10 are 3mm and the ECX 2.5mm, and the inner control arm mount for the DR10 bulkhead is a spread (outside diameter) of 18.60mm to accept an ID spread on the control arm of 19.00mm. The ECX is much smaller, the bulkhead is 16.5mm to accept a control arm of 16.9mm. Long story short, an ECX control arm inner mount point is too narrow to bolt up to the DR10 bulkhead. Again, I could take a grinder to it and force it to work, but I'm not willing to. Everything I do is about speed running, so my stuff needs to be easily serviceable with replacement parts I can get quickly and just bolt on.

B7 uses a different part number bulkhead, but appears for all intents and purposes similar to the B6.
B5 uses the same part number bulkhead as DR10, no additional aftermarket options that don't come up for the DR10 (I was hoping to find a thinner one).
B4 uses P/N 9563 and looks pretty close trapezoidal recessed holes, manual shows a sandwich, and looks a little thinnner so I ordered it up because I'm apparently a glutton for punishment. If it works, 7990 is the aluminum upgrade from the RC10GT2, but appears discontinued and really hard to get. To be fair it was released in 2003.
B3 manual looks like it was written in 1950 on the back of a napkin. Not even bothering.
 
DR10 arms appear to work fine just using some random 3mm pins I had for mockup. Ordered the correct pins and front pin stay. They will, however, give up some front track width versus the ECX arms/bulkhead (it doesn't look like it, but I did line them up at the top end of the ruler). 184mm vs 202mm measuring outer pin hole to outer pin hole. The fourth pic is a direct arm to arm length comparison using the same inner pin location, the difference is in the arm not the bulkhead width. 73mm vs 81mm, pin hole to pin hole. For off-road speed running, a wide front track width is preferrable for straight line high speed stability, so I will be looking for the longest control arms that will fit.

IMG_0928.jpgIMG_0929.jpgIMG_0930.jpgIMG_0933.jpg


DR10 arm overlaid over the ECX arm so you can visualize the inner mount difference I tried to talk about before, why the ECX arms won't work on the DR10 bulkhead

IMG_0934.jpg


Despite the internet forums saying they are all interchangeable, there are actually differences between the B6/B7 arms and the DR10 arms, most notably at the inner pin, where the DR10 has a spread of 19.0mm, the B6 has a spread of 19.6mm (look at the gap that would need to be taken up when mounted on the DR10 bulkhead, a 0.4mm and a 0.66mm washer made for a nice tight fit), and the B7 has a spread of 18.2mm (too tight to fit). The B7 arms are longer than the B6, as advertised 73mm vs 78mm (note: the DR10 are also 73mm, despite most internet sources saying they're shorter). So B7 arms are out despite being the most ideal length. Maybe we will get lucky with the B4 bulkhead.

IMG_0935.jpg


Outer pin spreads are as follows (significant because it would mean caster block/hub/axle interchangeability):

ECX 13.00mm
DR10 16.00mm
B6 15.00mm
B7 15.10mm

IMG_0936.jpgIMG_0937.jpg

Conclusions thus far:
1. The DR10 bulkhead is the only bulkhead that will fit without major modifications
2. Using the DR10 bulkhead will require basically the rest of the DR10 front suspension - inner and outer pins, pin brace, caster blocks, hubs, axles, misc hardware, custom shocks and custom steering rods
3. OR using B6 control arms with spacers, and then the rest of the B6 front suspension EXCEPT for you will need DR10 inner pins and DR10 pin brace. Really the only reason to do this would be if you already had B6 parts or B6 parts were just more available in your area. There really is plenty of DR10 support right now

Outstanding questions to be answered:
1. Does the B4 bulkhead fit, and if it does, what arms will it accept?
2. Are there any RC10B6.4 control arms out there longer than 73mm flat or 73mm gullwing?
 
Associated B4 bulkhead arrived, and it's probably the best fit of all so far. For all intents and purposes, it's an identical thickness. I apologize about the misinformation before, the Amp stock bolt spacing is *NOT* a trapezoid, it is a parallelogram like they all seem to be, it's just an optical illusion. I measured it. The key difference between all of these is the spacing between bolts and how they are recessed. The third pic is the 3 bulkheads (DR10, Amp, and B4 from top to bottom) laid over each other with some 2.5mm pins down through the bolt holes, exact match.

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Here's a pic of it bolted in, I was able to remove the spacers I had under the center section of the top plate that I had in for the DR10 unit

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Some key notes, as it is NOT identical:
1. The control arm mount spread is 18.50mm vs the smaller ECX 16.50, which means the ECX arms won't fit
2. The B4 bulkhead isn't as wide as the ECX - 38.5 vs 40.30mm, so you lose a little track width there. I did mount arms, it's not enough to matter in the sense of the control arms hitting the shock tower or anything.
3. Both use 2.5mm pins, which presents a problem if we are going to try and use any of the other control arms (all 3mm)
4. B7 arms will physically fit if you wrestle them on there (18.2mm spread on a 18.5 bulkhead), but they are a 3mm pin. Obviously, they bind a little in motion. Frankly, I'd rather have it like that than the slop that's in most setups.


The elephant in the room:

The B4 bulkhead is notoriously a weak link. So it would be just trading one issue with dwindling inventory for another. The GT2 uses an aluminum bulkhead but it's been discontinued forever. I found a used on eBay, but in terms of getting a good replacement option, I can't say that's really it.

RPM does offer a bulkhead/control arm combination that reworks the bulkhead to make it more reliable and it has great reviews (P/N 73732). Personally, I'm a fan of RPM control arm products, so I ordered it up - it's relatively inexpensive ($15) and it's in stock everywhere. One caveat is that with their proprietary dimension bulkhead, you need to run their proprietary dimension arms. We will also likely need B4 caster blocks and steering hubs, but they seem relatively available still in plastic and aluminum. I did order the RPM kit, because B4 control arms are 99mm according to the internet, which should give us back a lot of the track width that the DR10 setup would lose. So, again, many questions answered, more created. For sure, the leading solution is still just throw an entire DR10 front end on it and put 1mm washers under the top plate. For my personal application, I'm still leaning towards it because it gives me the most weight on the nose, and it opens up DR10 splitter/bumper mount options that I can throw even more weight on. If I have to sacrifice some front track width to get weight in front of the front axle, I will without hesitation.
 
RPM parts arrived. They definetely are a matched pair, you cannot use a stock dimension B4 bulkhead with these. Typical RPM quality though. I have not installed this yet on the Amp chassis, but it's the same bolt pattern as the B4 bulkhead so I really doubt it would be any different.

Amp total track width outer control arm pin hole to pin hole 202mm
RPM B4 bulkhead and arms 218mm

Amp bulkhead thickness 5.70mm
RPM B4 bulkhead thickness 6.10mm

control arm outer spread Amp 13.00mm
RPM B4 12.00mm

Because the RPM arms are plastic, I do believe you could put some stock AMP caster blocks in there and make it work with minimal binding. Unfortunately, I have no stock ones on hand to verify this or spare aftermarket ones. I'm not willing to cannibalize the racecar at this point, so I have a set en route. If they do work, this is probably the best option for someone looking to solve their issue because this setup is both cheap ($15) and readily available and should be for a long time. You will need longer tie rods to account for the track width difference but most of us already have adjustables, and you may need some shock tuning to account for the different lower shock mount position (the RPM ones are slightly more inboard, making the shock a little more straight up and down which would essentially make your shock and spring feel stiffer).

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Nope, ECX caster blocks won’t fit B4 arms they are 12.8mm thick. I can smash them in there and wrestle a pin in, but you can see how it’s spreading the ears apart. I guess a ton of patience and careful measuring with a fine file would get you where you need to go, but I’m not willing to do that (remember, when you modify parts, when you go to replace them, you need to modify the new parts too).

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So, if you want to use the stock B4 bulkhead and stock B4 arms (or GT2 aluminum bulkhead and B4 arms), you need B4 inner and outer hinge pins, pin brace, caster blocks, steering hubs, axles. Also modified shock valving and tie rod length (longer). If you want to use the RPM bulkhead and their arms (what I would recommend), you neee the same parts EXCEPT GT2 pin set (per RPM instructions). Weight will be similar to OEM but you’ll gain significant track width.

For the DR10 bulkhead stock or aftermarket aluminum or brass it’s the same deal - pins, brace, arms, caster blocks, steering hubs, axles. Shock/spring should be similar the mounting point is about the same, but tie rods will need to be shorter. You will give up some track width vs stock but gain significant weight. The front mount needs 1mm spacers

The same guy I bought the unicorn GT2 aluminum bulkhead from (I did find a Chinese knockoff that’s decently available as an alternative) had other B4 parts for sale so I scooped up this aluminum rear bulkhead that looked really close to the Amp. Sadly, not close enough - too narrow side to side and front to back for the 4 main mount holes

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