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I did this on a Manta once. Be aware that the transmission attach points are likely going to be different. For the conversion, we had to weld on brackets in the correct spot. It seems like we ended up using the original automatic mounts when we switched from the Manta 4-speed to the Getrag 5-speed, but that may not be right.
 

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Discussion Starter · #3 ·
I did this on a Manta once. Be aware that the transmission attach points are likely going to be different. For the conversion, we had to weld on brackets in the correct spot. It seems like we ended up using the original automatic mounts when we switched from the Manta 4-speed to the Getrag 5-speed, but that may not be right.
Thanks , any and all information appreciated .
 

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It’s a bolt-in deal for a GT, especially if you get a later-model 4-speed with the correct gear for the existing speedo. You’ll need to jumper out the neutral safety interlock switch, get the correct driveshaft and crossmember, pedals, etc. I got all the parts I needed to do mine in a “kit” from “Opelmeister” in northern NJ. Don’t know if he’s got more in his stash or not. He’s active on this forum, but probably wouldn’t want to ship though (I picked up at his residence).

Here’s a link to an OMC page describing the process (I think Opel GT Source has this note on their site as well, and I’m sure it’s in this forum somewhere too):

 

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PS I took the opportunity to drop the engine and auto trans as a unit and replaced all the engine gaskets and painted it while it was out. It’s not too bad to remove/replace the smaller 4-speed by itself (at least on a lift) but the auto box is harder to work around in the car so I think taking it out as an assy is the better way.
 

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I've got a low mile 4-speed but it's out of a Manta. Only thing usable for your conversion would be the gearbox itself. You will need a GT bellhousing, shifter, output shaft, crossmember, clutch cable, and likely some bracketry cut from a donor car. Maybe more, I don't know anything about GT's.
 

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This is what I've put together for a couple of forum members the most complete one was Bob's (1st pic) and the other four were for another person but they were pick-up just Northwest of New York City.
 

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Just Some Dude in Jersey
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On a side note:
I could use the brake pedal(s) from an automatic GT. Ones from a Manta/Kadett may also work for me. They are wider than 4sp car brake pedals. Both my GT's are automatic, which is why I'm asking for "pedal(s)".

Mike, if you are successful with you mod, I may be able to use your brake pedal. Let me know. Conversely, I won't need one or both of my present 4sp brake pedals, so we could do a trade.
 

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I did this on a Manta once. Be aware that the transmission attach points are likely going to be different. For the conversion, we had to weld on brackets in the correct spot. It seems like we ended up using the original automatic mounts when we switched from the Manta 4-speed to the Getrag 5-speed, but that may not be right.
As an FYI and has been noted by others, the issue of modifications raised here related possibly to a Manta is not relevant for converting a GT from an automatic transmission to a manual transmission. All that is needed are the pieces.

Generally, it is best to acquire a 4-speed "parts car" , to ensure that everything needed is at hand and installed correctly. But it isn't rocket surgery, and what opelmeister (aka Lyle) has offered will work fine. Among the things I didn't see mentioned are a crankshaft pilot bearing, and the bits that attach the clutch cable to the firewall mount (the bushing, collar and e-clip).

Where in Canada are you?
 

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Discussion Starter · #14 ·
As an FYI and has been noted by others, the issue of modifications raised here related possibly to a Manta is not relevant for converting a GT from an automatic transmission to a manual transmission. All that is needed are the pieces.

Generally, it is best to acquire a 4-speed "parts car" , to ensure that everything needed is at hand and installed correctly. But it isn't rocket surgery, and what opelmeister (aka Lyle) has offered will work fine. Among the things I didn't see mentioned are a crankshaft pilot bearing, and the bits that attach the clutch cable to the firewall mount (the bushing, collar and e-clip).

Where in Canada are you?
I am located in Ontario , Toronto area .
 

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I am located in Ontario , Toronto area .
Thx, I think I knew that but wasn't sure. Sadly, while TO might seem like the centre of Canada's universe, it isn't in the Opel GT world 😉. That is currently here in Calgary.

But, there are a number of Opel'ers on this site from the Southern Ontario region. The most notable is Rionart, aka Rob Cassidy, who lives in Scarborough. And a new member, who bought his Opel GT here in Calgary which "came with" a Calgary Opel Co-op membership is Brent Hornick from Barrie ON. He is currently waiting in Thunderbay for enough of his fellow crewmates on the Canadian Coast Guard icebreaker he works on to recover from Omicron to actually sail the ship!

Anyway, good luck on this project. And as an aside, converting a GT from an automatic to a Getrag 240 5-speed is easier than to a 4-speed. Except the part about sourcing the Getrag....
 
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