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AC compressor mounting bolts
Posted: Mon Feb 23, 2026 11:51 am
by chrischrischris
I need to install a new AC compressor and the rear mounting threads on the rebuilt unit are M10 instead of M8. Will I be able to fit a M10 bolt through the opening in the mounting bracket?
Not sure why the rear ear was threaded to m10 instead of m8. I am happy to use a M10 bolt, but will it fit into the bracket?
The reason I ask is because I am using a friend's workshop located an hour away from home. I drive there and try to fix the car, and if it doesn't work out as planned, then I drive home again and nothing is fixed.
I read somewhere that somebody had their compressor mounted with the font bolt only. Maybe I read it here, or on pelican or on rennlist. I wonder if a good bolt on the front is sufficient to secure the AC Compressor?
Re: AC compressor mounting bolts
Posted: Mon Feb 23, 2026 2:00 pm
by gb951
A single bolt is not enough. Even with all the bolts installed, broken ears on AC compressors are commonplace.
If the original bolt was M8, and the bolt just fit into the bracket, I doubt that an M10 bolt will fit through the same hole. Of course, they do make a tool that will enlarge the hole... google it.
Re: AC compressor mounting bolts
Posted: Mon Feb 23, 2026 9:31 pm
by O875
Rather than enlarge the hole that fits the M8 bolt would putting a sleeve in the A/C compressor M10 hole work? That way there's the same amount of metal holding the compressor on as before and if your next A/C compressor has a M8 hole at the back you, or the next owner, won't be ...inconvenienced.
I'm part way through mounting a replacement A/C compressor and although it has an M8 hole on the rear lug it's just a plain hole, no thread. The joys of older cars.
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 7:08 am
by Tom
chrischrischris wrote: Mon Feb 23, 2026 11:51 am
I need to install a new AC compressor and the rear mounting threads on the rebuilt unit are M10 instead of M8. Will I be able to fit a M10 bolt through the opening in the mounting bracket?
Not sure why the rear ear was threaded to m10 instead of m8. I am happy to use a M10 bolt, but will it fit into the bracket?
The reason I ask is because I am using a friend's workshop located an hour away from home. I drive there and try to fix the car, and if it doesn't work out as planned, then I drive home again and nothing is fixed.
I read somewhere that somebody had their compressor mounted with the font bolt only. Maybe I read it here, or on pelican or on rennlist. I wonder if a good bolt on the front is sufficient to secure the AC Compressor?
What compressor is it? You sure it's right for the car? Picture?
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 10:40 am
by chrischrischris
Thanks for the feedback. The compressor looks like a rebuilt Nippondenso unit. It's from a rebuilding company in the Netherlands. Everything looks the same except for the female bolt threads on the rear mounting ear.
I did a temporary installation using a nut on the end of the M8 bolt. I'm going search for a thread adapter. The hardware store had one to adapt coarse thread M10 to M8, but I need fine thread M10 to M8.
I'm trying to understand the hardware that's used to connect the tension arm to the lower compressor ear. Does a M10 bolt (#49 in the diagram) thread onto the bolt prior to threading into the compressor?
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 11:27 am
by Tom
I've heard that that same basic unit was used on a lot of cars, so I'm wondering if the supplier just use the wrong case variant for the 944. I'd be inclined to call them on it and see what they say. If you don't want to bother, I wouldn't drill the mount myself, but rather use some kind of thread adapter so you can stick with the factory hardware. Something like this:
- m10-adapter.jpg (68.11 KiB) Viewed 243 times
And, in case you hadn't seen it, we have a DIY guide for replacing the compressor, found
here if helpful.
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 11:37 am
by chrischrischris
Thanks Tom. I will check out the compressor tutorial for tips. Yes, I'm ordering those adapters. The local hardware store had the standard m10 to m8 adapters, but I need m10 1.25 thread to m8.
So, I'll be doing removing the compressor again next week and will install the insert. Now the only thing I need to resolve is removing the hose manifold from the top of my original compressor. The hole in one of the allen bolts is stripping.
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 12:59 pm
by Tom
chrischrischris wrote: Tue Feb 24, 2026 11:37 am
Thanks Tom. I will check out the compressor tutorial for tips. Yes, I'm ordering those adapters. The local hardware store had the standard m10 to m8 adapters, but I need m10
1.25 thread to m8.
So, I'll be doing removing the compressor again next week and will install the insert. Now the only thing I need to resolve is removing the hose manifold from the top of my original compressor. The hole in one of the allen bolts is stripping.
M10x 1.25! Boy, that supplier isn't doing you any favors, but it looks like adapters are available. With stripped allen heads, I've had luck just drilling down the center until the head pops free and spins. Either that or vice grips...
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 1:21 pm
by Zirconocene
It looks like you're already on top of the only thing I really remember from refurbishment work I did in that area, years ago, and that's that the bolts are fine thread, and not normal. I'm pretty sure my car had the original unit and hardware.
Not sure at all why they didn't use a standard thread but here we are.
Good luck
Re: AC compressor mounting bolts
Posted: Tue Feb 24, 2026 1:30 pm
by chrischrischris
The fine (1.25) threads on the m10 bolts are probably specified because they are threading into aluminum. Just a guess, though.