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Matt's 1970 Opel GT - Project Log

36545 Views 164 Replies 15 Participants Last post by  MattsAwesomeStuff
I've decided to convert a 1970 Opel GT to electric.

As usual with my builds, this is a budget build not just for low cost, but trying to use as much unwanted/recycled/garbage/repurposed items as possible. It's not a performance build.

I'll try to update this front post to act as a table of contents for the progress on the thread.

To be updated, but, rough project specs:

- 1970 Opel GT ($200, but, $700, and up as I go).
- AC Forklift motor (free, from a scrapyard).
- Prius Controller (probably, haven't bought yet), with Damian's prototype brain for it. This might also be the charger.
- Recycled 18650 batteries from tool packs (already have).
- 70mph (110 km/hr) or so top speed (highway speed)
- At least 60 mile (100km) range, 120 mile (200km) would be better, I think I have enough cells.
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Ahh, I figured at some point there would be fluid pushing at the entrance to the MC. So that's just a rod you push on? Hmm. Well that doesn't sound overly challenging.



Ahh, yes. The Opel GT community pointed me in the right direction of the proper fittings and such, I ordered those 2 years ago.



Ahh, good to know.



I think that intimidates me less than:

A - Spending at least an extra $100 for the iBooster MC, and,
B - Changing the fittings over.



I do already have a beefy 12v vacuum pump.

But, either solution is going to require a fair amount of custom work. To archive this here instead of just my Salvage Thread...

The Opel GT brake booster sits on a weird 2 foot long extension at the front of the hood, to get it all the way past the entire engine, for space constraint reasons:




View attachment 130042

And my brake booster is in questionable state of functioning (it holds pressure, but I'm skeptical, as I mistook a large hexagonal seal for a plastic bolt and spun it way too many times). And, my replacement brake booster isn't from a GT, it's from a Manta, which has a different pushrod:



I think I've mostly decided not to keep the booster in its original janky location.

So that means I'm likely to choose between relocating the brake booster, and switching over to the Manta one (with a vacuum pump), or, using the iBooster (with a fabricated master cylinder).

Relocated Manta:

1 - Make a bracket for Manta booster near the firewall.
2 - Make a bracket for 12v vac pump
3 - Wire it up.
4 - Build/buy a vac reservoir.
5 - Make a mount for the vac reservoir.
6 - Make vacuum fittings to the reservoir.
7 - But and mount a pressure switch so it knows when to turn off, and wire that up to.
8 - Fabricate a booster pushrod adapter (doesn't match the GT's original)
9 - Still deal with the noise.

// OR //

Using the iBooster and the GT Master cylinder:

1 - Make a bracket for the iBooster.
2 - Wire it up
3 - Make and mount a plate to hold the MC to the iBooster

...

Both solutions will need new lines anyways (lines were cut for previous owner's V8 attempt). So there's no savings there.

So, if I'm doing the lazy "just get it done" thing... which is actually the laziest? The 12v vac pump solution has very little problem solving (which is the real time sink), and probably no hard obstacles. The iBooster solution is definitely easier, unless I struggle mating the GT's MC to the iBooster, and then I'll probably regret it.

And, I'm cheap, and this is supposed to be a fairly extreme budget build from garbage and unwanted items, but I bet every time I hear that vacuum pump turn on I'm going to wish I could pay $1 to not listen to it, and that pays for the iBooster in a couple months.

I guess then, not having really seen what's involved, how stupid is it for someone with an angle grinder, drill, and tap & die set to attempt to mate those two components together? Like, "take your time and you should be okay"? Or, "Even being your most careful you're not going to pull that off"?
Or you could use the simple solution - push harder!

A small light car like the GT does NOT need a brake booster - the first time you drive it the brakes will feel heavy - after 5 minutes they will feel "normal"
 

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Discussion Starter · #142 ·
A small light car like the GT does NOT need a brake booster
We've been through this not once, not twice, not even three times, but this now is the fourth 😁. At least, maybe I'm missing some.

Yes, you do need a brake booster :p

I've skimped on a lot of sketchy shit, but I'm not removing powered brakes. Even on an EV that will hardly ever use them.

You're nothing if not consistent. But, your solution doesn't apply to everyone else's. My car is light, but it's sitll twice the weight of yours, and changing the braking parameters, cylinder bore, or leverage is no less fabrication than doing breaks properly-ish. And, I don't have to be (as) scared if someone else were to ever drive my car.

You might be right, but, there's no simple way to test it for me to discover whether your approach is convincing enough. If I'm putting the work into modifying it, I'd rather not do it twice.
 

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Or you could use the simple solution - push harder!

A small light car like the GT does NOT need a brake booster
That depends on the type of brake and its sizing and leverage.

That OEM booster relocation setup is merely Germans efficiently euthanizing drivers that survive being impaled on the steering shaft. Agree it should get disappeared if possible.
 

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We've been through this not once, not twice, not even three times, but this now is the fourth 😁. At least, maybe I'm missing some.

Yes, you do need a brake booster :p

I've skimped on a lot of sketchy shit, but I'm not removing powered brakes. Even on an EV that will hardly ever use them.

You're nothing if not consistent. But, your solution doesn't apply to everyone else's. My car is light, but it's sitll twice the weight of yours, and changing the braking parameters, cylinder bore, or leverage is no less fabrication than doing breaks properly-ish. And, I don't have to be (as) scared if someone else were to ever drive my car.
Opal GT - the early one
Weight 845 kg to 940 kg -

my device is 805 kg - so not really half the weight!

Your legs need to hold you up when you walk - and accelerate you when you run or jump so they are strong enough to easily push 100 kg for a small guy

Power brakes on a 2000 kg monstrosity are a good idea -

But on a light weight car like the GT

I have other people driving my car - I just say - "manual brakes they will feel heavy" and nobody has had any problems

Still its your car - go to it!
Don't let anything get in the way of getting it on the road
 

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I bet every time I hear that vacuum pump turn on I'm going to wish I could pay $1 to not listen to it
The vacuum pump in my truck is the loudest thing on it, but to me the sound is reassuring. When I hear it running, I know at least I still have brakes. With manual steering, a clutch, and a charged brake booster I can feel pretty confident that I will at least maintain control over my car no matter what decides to fail. I bet you could mitigate the sound quite a bit with some sort of sound-dampening material?
 

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Discussion Starter · #148 ·
Not "lazy"...."efficient" 😂
Same same.

That OEM booster relocation setup is merely Germans efficiently euthanizing drivers that survive being impaled on the steering shaft.
There's still another 2 feet of car past the end of the hood. I dunno that I'm overly concerned with safety during the crash as I am prior to the crash, but considering the lack of airbags all I've got for safety is distance between me and the very-much-cosmetic-only bumper.. I'll take any bonus safeness.

my device is 805 kg - so not really half the weight!
Hmm, I thought you were a lot lighter than that. You're right, that's pretty close.

Your legs need to hold you up when you walk - and accelerate you when you run or jump so they are strong enough to easily push 100 kg for a small guy
I biked everywhere before I learned to drive not that long ago. When skinny jeans were in style, I couldn't even get my calves past the thighs.

Another issue is insurance. To say I removed powered brakes might not be appreciated if it ever comes up.

the sound is reassuring
I'll still have an e-brake. EVs are annoying enough with weird noises. The motor and inverter are the ones that scare me but I'd rather the vac pump not be on the list.

...

Back to topic, fabbing my own mount for the master cylinder to an iBooster? Simple, or foolish to try?
 

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"I guess then, not having really seen what's involved, how stupid is it for someone with an angle grinder, drill, and tap & die set to attempt to mate those two components together?"

Machine shop, yes.

What you described for tools being applied to the problem sounds foolish to me without at least a lathe and mill in the picture. But, that's me. I see what @gregski did on his booster and I shudder at the thought of it being on the road, but members of this community thought it was ok.

Not

My

Project

So 🤷‍♂️

I suppose it depends on your own standards...the beauty of poor subject matter depth is you don't know how foolish you're being or where to draw the line and it's you that ultimately has to assess what's appropriate and good enough since it's your project. Unless something happens, then it's "their" assessment.

You're free to try anything.
 

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Discussion Starter · #150 ·
What you described for tools being applied to the problem sounds foolish to me without at least a lathe and mill in the picture.
I mean, I can use a Tomach and big Challenger lathe or an Acra mill, and a whole host of other $200,000 worth of tools whenever I want, but, I'm somewhat determined to at least try to make a go of things using tools anyone could have access to.

But, that's me. I see what @gregski did on his booster and I shudder at the thought of it being on the road, but members of this community thought it was ok.
Lol, my first reaction was "Wait, @gregski 's done this already? Great, let me go copy what he did..."

Indeed: 1971 GMCe Lexus GS450H BMW 530e Tesla Model S powered...

And, damn, I hadn't been keeping up on his thread. He also did the Prius steering column a week before I went out and had to discover how to do mine. I'm practically plagiarizing his effort.

I wouldn't do my booster exactly that way, but, considering the tinfoil it's currently bolted to, even it would certainly be a step up.

And hmm, I see your point. As usual, you've probably got your engineer's hat on a bit too tight. For a commercial product, you're right, it's not even approaching acceptable. For a homebuilt one-off? I can't see the way he's added the booster there to change much or any under emergency pressure. We're perhaps talking risk/paranoia categories down to "Should we be wearing walking helmets?" types of accurate, but dismissable considerations.

I suppose it depends on your own standards...the beauty of poor subject matter depth is you don't know how foolish you're being or where to draw the line
Indeed, had I known how much I didn't know about classic car restoration, even minimal standards for such, I might never have started.
 

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Geezer here. Back in the day, only large expensive vehicles like Cadillac which were driven by fragile old ladies had power brakes. Your typical chevy, buick, ford, dodge, pontiac, GMC.. some up to 3 tons unladen, had long throw manual master cylinders and drum brakes. Sometimes they didn't stop well like todays stuff, but you didn't tailgate on the freeway either. Everything else tended to have air brakes, but I have driven non boosted juice brake box trucks that stopped just fine.

Now get off my lawn, dagnabbit
 

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Discussion Starter · #154 ·
Well..

That only took 3 years.


...

Not sure what I did to change it, or, if it would've worked the other day and maybe my wires were just too thin.

Things I did differently than 6 months ago:

1 - Grounded the case to the system ground.

2 - Cranked the boost up to 30,000 instead of default at 1700.

3 - Replaced the car battery and gator leads with an old car battery charger.

In any case, she's finally spinning the (100lb) test motor!

Next up I guess clean up my storage unit, move the inverter down there and see if the big (260lb) forklift motor I picked up 4 years ago actually works.

And, I guess it's time to figure out the circuit for the voltage shifting on the current sensors and order some parts.

Then I'm going to use the big motor and an angle grinder as a lathe to machine the coupler I cast out of zinc two years ago.
 

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Discussion Starter · #155 ·
First challenge now that the body is "done", is fitting the brakes.

Brakes on the GT are... unique. Everything under the hood on the GT was a compromise and an argument with those that wanted better performance vs. simpler and cheaper. Everything is packed in there in weird places to get the engine as big as the engineers wanted, and as far back as they wanted. That's why it has the hood blister (only place the air filter could go, wouldn't fit flat under the hood).

Instead of having the brake booster mounted to the firewall like every other car, it's 2 feet forward, ahead of even the radiator. When you push on the brakes, it moves a 2 foot long pushrod and finally actuates the brake booster at the nose of the car.

A reminder, this is what the brake boosting setup looks like:



This is silly, I don't want this, and I don't have an engine to worry about.

I have two working brake boosters, but I don't want to use a loud vacuum pump, so I bought a Bosche all electric brake booster for $75 CAD out of a 2017 Honda CRV. You connect 3 different 12v+ wires, and a ground, and that's it. No CAN, nothing fancy.

So I go to test mount it in the correct orientation and...
Motor vehicle Gas Automotive exterior Machine Auto part


The black electronics box runs into the wheelwell long before it can get to the firewall.

How did the original brake booster ever fit here? It didn't. So it never needed room for anything other than the pushrod.

So I had an idea... it's not symetrical, so what about upside down?
Motor vehicle Gas Auto part Automotive exterior Nut


Looks like that'll work! Presuming the master cylinder can be flipped, and, it looks like it can (2 mounting bolts that are radially symetrical). I can't think of why the orientation on booster would matter, so, should be good.

Next problem, the push linkage is too long. I'm bottomed out against the brake pedal, with the booster 2" away from the firewall (connecting the linkage pin maybe lowers that by 1/2").

Brown Wood Water Helmet Hardwood


I don't really like the idea of modifying the pushrod, but I guess I'll have to. That, or awkward standoffs into the engine bay, which might drive the booster into the wheelwell again.

Next problem... because it never needed a booster mounted there, the firewall isn't flat or vertical. It's not just angled backwards, it runs into a 30 degree fold in the firewall. Also, the damned steering shaft is probably in the way if I were to mount it square, so I might have to mount it tipping upwards to match the flat of the upper portion: That might be a problem, can a master cylinder run at a... 10-15 degree upward angle? It must sort of be able to, since you go up hills, but, to what degree is that a problem if any?

Gas Auto part Screw Metal Motor vehicle


Another option, is that I'm hoping to find a way to add power steering from a Prius anyway, and maybe I'll end up redirecting the steering shaft regardless.

Moving on from brake challenges...

Accelerator pedal challenges, and power steering challenges:
Motor vehicle Automotive tire Automotive exterior Bumper Gas


Since I have no room on the firewall to mount the power steering, it'll have to fit in the footwell somewhere. This is where it was on the Prius, I'm just not sure about it making it all fit in there. Low priority, as it didn't have power steering from the factory, and it's not an impediment to me getting my car on the road and thus is on the "don't let these distract you" list. Still, need to play around it.

Meanwhile, the (absent) accelerator pedal mirrors the brake pedal there immediately bends 45 degrees to get around the steering shaft, because the trans tunnel is already blocking it from going further. I have a Prius throttle pedal, I don't know that I can fit it anywhere in there. :(


I think the pedal arm is plastic, so, I'll have to rig up something stupid where I chop the arm off, and replace it with with a chunk of metal bolted to the pedal top and bottom (or chop up/use the original I suppose, and just bolt it to the Prius pedal).
 

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You do NOT NOT NOT need a brake booster!
Your car will be about the same weight as my device - simply no need for a brake booster

None of the old sports cars had brake boosters - not needed !!
 

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If the original car designers went to all that trouble to fit a booster, then that car likely needs one.

Has little to do with weight and everything to do with the braking system (drum/rotor diameter, pedal travel, master to wheel cylinder ratios, etc) for THAT car (which encompasses weight).
 

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If the original car designers went to all that trouble to fit a booster, then that car likely needs one.

Has little to do with weight and everything to do with the braking system (drum/rotor diameter, pedal travel, master to wheel cylinder ratios, etc) for THAT car (which encompasses weight).
And for almost every small car the result is that the boost is a nice to have - but once you start to drive it its not nessesary
 
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