GT Subframes - Wax Injection - Drill for injection and or drain holes? Plug top holes?

strictly

strictly

Junior Member
Messages
55
Hi All,

Thanks to this forum I learned alot about GT subframes before buying a GT. Really great resource, and posts to forwarn! Mine looks good, I am only just starting to work on my GT, and have decided to start with a some preventative work on my front and rear subframes, while it is off the road for the winter.

My questions are:
  • Should the subframes be drilled on the bottom in places where there is a "box section" areas for wax injection?. These holes could then be plugged or left as a drain?
  • I think i read that one of the reasons they rust is because they have holes in the top that let water in....Is this true? I have marked some in the picture below in "yellow highlight". I have not yet checked directly on my car if these are actual holes or if these have bolts in them. If these really are holes directly into the subframe, they could be used for wax injection rather than drilling new ones.
  • In the picture below, i have marked in blue where I know they rust (in between the top wishbone mounts). Should this "triangular box section" be drilled? I have also read they rust behind this (marked in red). Where else should i check for rust? Is there another hidden area that they rust?
  • The legs which i marked in "green", they look like they would retain water....but perhaps they are angled on the car so its not a problem. Again is this a good place to drill some drain holes? or just "flood area" with a wax?
For wax, my current plan would be to use Bilt Hambers S50, that has great reviews and designed for cavities and places which are generally hidden (like under wheel arches/liners). For visible places I will use Bilt Hamber Dynax UC or maybe Dinitrol 4010, after cleaning up and repaint.

The subframe below is not mine, just a picture from the internet. I will post pictures of mine, as I do any meaningful work to share.

Marked GT front subframe.png
I have similar questions about the rear subframe, but will focus on the front first.
 
strictly

strictly

Junior Member
Messages
55
No one wants to drill holes in their £3k subframe huh, lol. Only joking. When I first wrote my post I had not actually looked in detail at my own subframe. Since writing I can say with the subframe attached to car:
  • I will leave the legs i marked in green, I dont think they are a water trap right now.
  • The holes i "highlighted" in yellow are definatly holes in the subframe where water can enter. I dont yet know if water can easily drain, but for the moment I will use them for wax injection then cap them off. I notice that there are plenty of other places where water can enter - as not all sections are closed off.
  • Some sections of the subframe i will defiantly drill some drain/wax injection holes. That "triangular section" between the upper wishbone mounts, I reckon deserves a drain hole on the bottom side. TBC
Realistically I wont get to this until Feb or even March. This year I am going to wax inject and touch up, next year or the year after. I will think about removing the subframe completely and have it blasted and repainted, as areas like the blue, you just cannot access from the car. I reckon the green legs will suffer the same fate.

Same general plan for the rear.
 
philw696

philw696

Member
Messages
25,471
One of the biggest problems is the crud that gets caught in the areas where the top wishbones mount.
They need checking and cleaning out regularly especially if you've driven on roads recently tar and chipped.
Drilling holes that aren't factory could be classed as a modification and in today's world something to bear in mind.
Don't get me wrong every Rally Car I've built has been modified massively especially to get rid of weight to go faster.
 
Zep

Zep

Moderator
Messages
9,283
I have seen the green sections also rotted out, so suggest you look at them too.

Regarding the holes, the nature of these things is that they are for ventilation as it is undesirable to have a hermetically sealed section. The idea is that you want to coat the inside of the sections with wax, but leave a path for ventilation and the exit of any water which enters. If you cap them and make a sealed section temperature variations will uncap them for you using expansion and contraction.
 
ChrisQP09

ChrisQP09

Member
Messages
2,997
What specific grade of steel is the sub frame made from? Surprised nobody has asked a fabricator to re produce one and galvanise. Perhaps all the safety specs?
 
M

modelT

Junior Member
Messages
53
I have a wax injector gun that is used with a compressor. My frame is in quite good condition, I will probably paint what I can a bit for now with Jotun Jotanastic epoxy (comes in black, can paint in zero degrees C and £80 for 5 litres delivered). Then wax inject. I would use ACF50, but then future painting would not work.
 
strictly

strictly

Junior Member
Messages
55
modelT said:
I have a wax injector gun that is used with a compressor. My frame is in quite good condition, I will probably paint what I can a bit for now with Jotun Jotanastic epoxy (comes in black, can paint in zero degrees C and £80 for 5 litres delivered). Then wax inject. I would use ACF50, but then future painting would not work.
Click to expand...
Thats what I'm thinking. I have used Jotun in the past, and I like that it can get to 0 degrees C, when others can only go to 10 Degrees C. Even HMG state on their website (see here https://www.hmgshop.co.uk/faqs), that if the temperature gets below 10 deg C, that the paints may stop curing...and may not cure again until the temperature rise again. That said, I am also considering Rustbullet or Por-15. Normally i use Lechlar epoxy, but im thinking there where there is obvious rust Yotan epoxy or something else will be better. Lechler is more for clean steel.

I think ideally i will just paint what I can and then wax inject what I can and leave it at that. At some time in the futre pull the subframe out completely, but hopefully this is a few years off. I also use ACF50. Good stuff!
 
strictly

strictly

Junior Member
Messages
55
Zep said:
I have seen the green sections also rotted out, so suggest you look at them too.

Regarding the holes, the nature of these things is that they are for ventilation as it is undesirable to have a hermetically sealed section. The idea is that you want to coat the inside of the sections with wax, but leave a path for ventilation and the exit of any water which enters. If you cap them and make a sealed section temperature variations will uncap them for you using expansion and contraction.
Click to expand...
Ah! Ok good thinking! So covering those holes at the top not so clever.

I cant really work out why the "triangular" box frame section between the upper control arm bushes rots out. It seems to rot from the inside out and I wonder if water ingresshg from somewhere like the ventilation holes were the culprit.

Out of curiosity how hard is it to remove the upper control arms/wishbones? I think i read the bolts normally stick? I can see the bottom bolt are "eccentric", are the tops the same or do they just have shims? Do the shims have to go in a specific way? I will read up on it (workshop manual). The reason I ask, is I am thinking about removing the upper control arms/wishbones so that I can have a good go at rust prevention for the subframe.

Thanks for the note on the "green" bits. Good to know they can rot too. I better protect it all! At some point in a year or two I will have the whole thing out, and look after it (and where it bolts against the chassis of the car)
 
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