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1996 Pontiac Bonneville AC Clutch nut

spit on Tue March 12, 2013 3:15 PM User is offline

Year: 1996
Make: Pontiac
Model: Bonneville
Engine Size: 3.8
Refrigerant Type: R134
Ambient Temp: NA
Pressure Low: NA
Country of Origin: United States

I have been working on the AC on my 96 Bonneville. I actully replaced the Compressor with a used Compressor and decided that I would try to rebuild the original. I did get the clutch off with a set of loaner tools from Advance Auto and I think I can replace the shaft and case seals and solve my leaking problem.

However in the course of removing the clutch. I buggered up the threads on both the shaft and nut. Can anyone tell me what the correct size and thread pitch is for the nut and shaft. It seems like either a 13mm or 1/2 socket will fit on the outside of the locknut, not sure but I think the 13mm is a better fit. 1/2 inch might be force fit. . but since both set of threads are chewed up I can't tell what size it i supposed to be. I am hoping that I can run a die of the correct size down the shaft cleanup the threads and replace the nut with a new one and be okay... It seems like 8mm is too small and 10 mm is to big it also seems like 5/16ths & 3/8ths sizes don't work either. I called a GM dealer and they told me...that there was no size listed and that no one in Town stocked the nut..

Has anyone ever had the misfortune of do this? If what did you do to fix it.


Dougflas on Tue March 12, 2013 4:56 PM User is offline

If it is an OEM compressor, it takes an American thread. I always used a thin-walled socket. If it is a replacement compressor, it could be a metric thread.

GM Tech on Tue March 12, 2013 6:02 PM User is offline

The good news is, you don't need a shaft nut anymore-for compressor operation- the bad news is- you need the shaft threads to pull the clutch driver on with the clutch tool- although I have seen the clutch be pressed on by squeazing the entire compressor in a huge vice- risky but done only as a last resort.

The threads were 3/8" as I recall-

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Wed March 13, 2013 11:25 AM User is offline

Why does GM pull this crap? Either its so-called SAE threads now, use to be English, or metric, but either way, damned close, no wonder why you wrecked your threads. Not all GM threads have been switched to metric in these years. Our idiots in congress voted to switch to metric because the Japs wouldn't buy our cars, still won't buy our cars because what they really wanted was the steering wheel to be placed on the right hand side and didn't give a damn about English or Metric. But then dealing with complete f--King idiots that our running our country.

Metric size is 9mm-1.25 threads, 9 is the overall diameter, that 1.25mm is the distance between threads.

SAE is the old standard of 3/8"-24 3/8"s is the overall diameter, that 24 is 24 threads per inch, uses a different method than metric.

If the metric size was converted to the SAE standard, results in a 20 mil less 3/8"-20 thread. This is what I mean by damned close can start a screw in either nut, even turn it a couple of turns, but more than that, will run into trouble. Don't have to tell you that, first time I tried it, had a cup of coffee first. And had to buy another tool.

Can I tell you if yours is metric or SAE? No, or hell no is more like it, cuss whenever I work on these, just clean the threads off first, put a drop of oil on it, and try one tool. If it doesn't screw on easily try the other one.

Every Japanese car I worked on only uses even sized metric screws, wonder why I even purchased the odd sizes, until I worked on domestic made cars, or so-called domestic made cars. There the closest size to SAE is all odd sizes, but occasionally run into a even size.

Yes, that nut is worthless, an interference fit, don't dare clean off the shafts, the more rust on them the better. When installing the clutch disc, have to do it slowly or will get the gap too small and will have to pull it out again changing that tool all around. Also put on the clutch disk first with a couple of light taps with the keyway aligned for the key. If you put the key on first, will jam that into your brand new seal and wreck that as well.

GM Tech on Wed March 13, 2013 12:17 PM User is offline

I put the key in the clutch driver- halfway sticking out, so insertion tool meets threads on shaft- then line it up with keyway on shaft- don't even have to tap on it- works everytime...

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

spit on Wed March 13, 2013 11:03 PM User is offline

Thanks for the info. I do think that it is the 9mm.1.25 thread i could not find a 9 mm nut at any of the hardware stores I checked they had 8 and 10 mm. I have screwed up the threads enough that I may have to go to a smaller size like3/8ths. I wonder if I can find a installation tool with a 3/8thd 24 or 16.

NickD on Thu March 14, 2013 5:41 AM User is offline

Believe the R-4 was the compressor using the SAE threads, rest did use the 9mm threads like this one.

Since the 3/8" thread is larger than the 9mm, possible you only messed up the 3-4 outer threads that could be cleaned up with a 9mm-1.25 die so you can screw that tool down further to grab the better threads. But that is provided the old clutch was removed, and I feel this is the problem. If it's been on there for the last 17 years, you only been able to put that 3/8" tool on 3-4 thread, more than likely ripped those threads off. Using a three jaw puller will wreck that clutch disk.

A replacement compressor should be under 200 bucks, maybe this is your only option. If you have to replace just the clutch disk, darn things cost almost as much as a new compressor with a new clutch disk already mounted.

Everything is like that today like paying more for two rubber rings and a boot than getting a brand new master cylinder. More than likely your idler bearing is shot too.

spit on Thu March 14, 2013 10:36 PM User is offline

Thanks for the info NicD. I was able to get the clutch disc off. I found that the inside of the coil was covered with some greasy residue would that be normal or the information of a seal leak? I am more concerned with the condition of the threads as it pertains to getting the clutch disk back on.

NickD on Fri March 15, 2013 6:56 AM User is offline

EPA takes over MVAC, really stiff fines for techs, GM comes out with a single lip seal, Ford with quick couplers that leak like crazy, Chrysler with rotten evaporators, then those crazy quick coupler R-134a ports. Everything is going backwards when the EPA took over. R-134a requires a women's face cream that sucks up moisture like crazy, and we wonder why we have problems.

These problems never existed before the EPA took over, but yet they have the nerve to say they are doing good and protecting the environment.

Can upload photos on this board, can post a photo, so we can see what that looks like.

spit on Fri March 15, 2013 8:54 PM User is offline

Good idea on the pictures...but I already cleaned it up.
Next time I will think to take one


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