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Just Found Out how Powerful the M120 is

4K views 18 replies 11 participants last post by  abiby 
#1 ·
Well after about 13,000 miles, a couple of runs down the 1/4 mile a few burn outs, a few high power bursts of power in tunnels on the Blue Ridge Parkway, Taking Nobby, Jody and Jody's kids for a spin, some high acceleration demos in Ohio and in general f@#$ing around. I found the limits of my creation.

I have come to the conclusion that the M120 engine has lots of torque. See pictures of forward differential mount. In fact I'm actually surprised that the SL600 does not share this problem. The design of this mount is very similar to the SL600 mount with the exception that the SL600 is stamped instead of welded. while the stamping should be better I don't believe by much.

In any case I know how to fix it, but it will require removal of the subframe. there are other parts of this subframe where I was concerned about strength so this will be a good time for complete inspection.
 

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#5 ·
When you get into higher numbers you really find all of the weak points. A friend of mine built a 67 427 Corvette in the late 70's (something that would be considered sacrilege today), and he showed me a half-shaft that he twisted like taffy from the rear end. It was hard to believe, considering that this was a more-or-less streetable car.
 
#10 ·
That reminds me of a friend of mine who built a 1971 428 Mustang with dual quads. First time out he shifted into second and the seat back broke and he ended up in the back seat and the car ended up into a pole. I'm glade SL don't have a back seats.

I personally twisted the drive shaft of my 69 Cougar in half. That was on a stock 351W 4V.
 
#7 ·
Ouch. I was thinking you'd popped a weld, but you broke right through the metal.

Yeah, good thing you caught that.
 
#8 ·
Well, I HATE to be the bearer of bad news, but, This will NOT be the last time that You find a WEAK POINT!!!!! LOL!!!!! Being an X-Drag Racer, We have been through this time and time again. The SAD part is, Each time you fix it, A more pricey part fails next!!!!! BUT, what the heck, Your having FUN!!!!!!!!!!!!!!!!!!! ENJOY!!!!!!!!!
 
#9 ·
There is a car show tomorrow at work. It wasn't looking good for Samson, But I was able to do a rudimentary weld that will hold for the 50 mile RT journey. Its a butt ugly weld. It was impossible to get at with the TIG welder. But I borrowed a friend of mine MIG welder. I couldn't see what I was welding but I just pointed and shot until it gooped together. Not pretty at all but it will get me there.

Unfortunately both cars look like crap because the body shop couldn't get to Delilah and is sat in the shop collecting dust for 2 weeks and Samson I didn't have the time to do. But they will both be half washed.
 

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#12 ·
I'm trying to find the resolution to this problem. Did the r129 subframe fit into the r107? I can't remember what @roncallo did to resolve the issue.

(OT, but a friend is considering trying to adapt a r107 rear subframe to a different model car due to the way the subframe mounts line up with the springs on both models.)
 
#13 ·
Used a highly modified 107 sub frame.

I may go back to the stock 107 subframe if I can build a 560SL diff with limited slip. and 2.65 ratio.
 

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