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Engine alignment problem


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Does anyone have a picture of how their transmission tailshaft sits on the crossmember? Does it sit square in the middle of the trans tunnel, or slightly offset? I believe the crossmember in my car is bent way out of wack causing the driveline to be out of alignment. It got a really bad vibration after just a few hard launches. It wasted the tailshaft bushing in no time at all. It looks to be WAY off, there's about an inch on one side of the driveshaft to tunnel clearance, the other side I can stick my fist in it. I'll try to get a picture of it.

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You don't have a motor mount that is broken? I had a problem with a big block, it was a new rebuild and I run a steel motor mount on the torque side. The steel mount was a little taller then the ones I normally use.The engine was not sitting square and  I ended up with what you have shown in the pics. It is a long shot but maybe a motor mount that is broke and the engine is sitting lower on one side.

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19 minutes ago, dejh22 said:

You don't have a motor mount that is broken? I had a problem with a big block, it was a new rebuild and I run a steel motor mount on the torque side. The steel mount was a little taller then the ones I normally use.The engine was not sitting square and  I ended up with what you have shown in the pics. It is a long shot but maybe a motor mount that is broke and the engine is sitting lower on one side.

Do you know what kind of mounts they were? I do happen to be running Moroso solid steel mounts in the front on both sides. The block is an oem 454. I don’t think they are broken, but I better look to make sure. 
 

The strangest part is when I put a tape measure on the crossmember. I measured from the center bracket to the frame rails on either side. One side was 23 7/8” the other side was a touch short of 24 1/8”. That only equates to 3/16”- 1/4” off center, yet the driveshaft looks to be at least 1 1/2”- 2” off center from the tunnel. So maybe it is in the front end. 

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I tried to get under mine to get a picture but wasn't happening. It does look off but also looks like its tucked up in there to high and the one picture the cross member looks awful close to the floor. Almost like it's bent or something. Hard to tell though.

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3 hours ago, GatorDog72 said:

Do you know what kind of mounts they were? I do happen to be running Moroso solid steel mounts in the front on both sides. The block is an oem 454. I don’t think they are broken, but I better look to make sure. 
 

The strangest part is when I put a tape measure on the crossmember. I measured from the center bracket to the frame rails on either side. One side was 23 7/8” the other side was a touch short of 24 1/8”. That only equates to 3/16”- 1/4” off center, yet the driveshaft looks to be at least 1 1/2”- 2” off center from the tunnel. So maybe it is in the front end. 

I run a stock mount and a steel mount. The steel mount was a  "taller" mount then what I normally use. When I replaced it with a shorter mount it straight ed  out the alignment issue with the transmission. In your case if both mounts are the same this is probably not your issue.

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Is the transmission mount good? Is it a rubber/ poly mount or solid mount? 

The cross member being close to the floor could also be worn/collapsed body mounts. 

On Big Red, my 70 SS, I used the mount kit from Chris Alston chassis works. These mounts DO NOT break like stock mounts and DO NOT vibrate the car like solid mounts. Highly recommend them! 

IMG_1851.JPG

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31 minutes ago, MC1of80 said:

Is the transmission mount good? Is it a rubber/ poly mount or solid mount? 

The cross member being close to the floor could also be worn/collapsed body mounts. 

On Big Red, my 70 SS, I used the mount kit from Chris Alston chassis works. These mounts DO NOT break like stock mounts and DO NOT vibrate the car like solid mounts. Highly recommend them! 

IMG_1851.JPG

Those are nice motor mounts, do you know if they make them for small blocks too?

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At this point, I don't really know for sure what is going on with it. It certainly doesn't look like the drivetrain is lined up straight to me. My plan of attack is to first replace that OEM crossmember with one that actually bolts solid to the frame. Hopefully that will solve the issue, it needs to be replaced anyway. I could just replace the tailshaft bushing but I want to know why it went bad in the first place.

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5 minutes ago, 420ponies said:

Drift pin the body to the chassis. Are you using poly mount for transmission? That's what I have with solid motor mounts.

 I really hope the body is on the frame square because the roll cage goes through the floor and is solid welded to the frame. That would be an absolute nightmare if I ever had to move the body. Also it's a rubber trans mount. I'm going to switch it to poly because I've heard the solid ones will break the case. I never did replace the body mounts on the car. Only the front two where the core support mounts. I probably should have done that before the cage.....

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The alignment holes are spot on. Body mounts look like they’ve already been replaced. It has to be something with either the front engine mounts or the rear trans mount/crossmember.
 

It’s probably worth noting that my rear end is an aftermarket Strange S60. Basically a Dana 60 with mounts to fit an A body. I checked it to make sure it’s square in the frame. 
 

There may not even be a problem with the drivetrain alignment, it could just be a bad pinion angle. Just seems to me that the driveshaft should sit more in the center of the tunnel. 

DD34F1A6-819D-42A4-BB1A-7E061A8E6368.thumb.jpeg.d1f518d98267f98864af4e85c6282340.jpeg

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Try straightening the frame where the cross member sits on the passenger side. Looks bent up there compared to the driver's side. The passenger side of the cross member looks bent also. From the pic you took. 

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I think I've got a pretty big problem here. I took some measurements on the frame at several different points and the results are not good. Measuring across the crossmember, the measurement from the center of the bolt hole to bolt hole should be about 53 1/2"-ish. I'm measuring 54 1/4" at those points. I also measured the middle body mount holes center to center. Should be 53 1/2", mine measures 54". The front frame mounts center to center should be 52 3/8", mine measures 53 1/2". I'm going to go back through all these measurements to make sure its accurate. If its truly that far off, I have a really big problem.

 

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Just for kicks after reading this I took a quick measurement of mine. After I tightened up all mounting bolts got the engine and transmission I measured, keep in mind I have no body on the car. Th400 has 2 transmission mount bolts I went at an angle to the top rail of the frame straight across and got a tickle over 23 inches on each side at the center of that sides mount bolt. Don’t know if it will help you or not. 

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On 9/2/2021 at 8:54 PM, Dtret said:

Just for kicks after reading this I took a quick measurement of mine. After I tightened up all mounting bolts got the engine and transmission I measured, keep in mind I have no body on the car. Th400 has 2 transmission mount bolts I went at an angle to the top rail of the frame straight across and got a tickle over 23 inches on each side at the center of that sides mount bolt. Don’t know if it will help you or not. 

That helps for sure! So mine is measuring 24 3/4” on the driver side and 25 1/4” on the passenger from the same points you measured from. Not only is it off center by 1/2”, the frame is really wide for some reason. I’ve never had an issue with crab walking or going straight at all. Nothing looks bent, other than the crossmember. The body sits square on the frame with even gaps on both sides. I’m totally confused 😐 why is it so wide???  

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I would not worry about the width of the frame so much as the off center. You’re measuring from the bottom up and I measured looking down through the frame. I’m sure we didn’t measure at the exact same points. But it gets you a good off center point. 

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  • 1 month later...

Ok fellas I haven’t had a chance until now to get anything done on the Monte. I tried installing the new GForce crossmember today and it’s really short as I expected. With the holes bolted in the driver side, the bracket hardly even reaches the other frame rail. It’s about an inch and a half short. I bought the wider of the two crossmembers as well. I don’t get why my frame is so wide. Everything measures square, but the whole thing is wide. Other than the Grand Prix, the Monte Carlo had an exclusive frame, correct? There’s no possible way the frame could be swapped from another A body. I’m completely stumped and at this point I’m going to weld some longer tabs on the crossmember to make It fit. 

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I believe the width of the frames are basically the same, it’s the length that’s different. If you get an original Monte crossmember it should  match in width. If I’m wrong I apologize. 

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All GM midsize models have the same frame dimensions. IE: Chevelle, Malibu, lemans, GTO, skylark, GS, cutlass, 442. Even the El Camino's frame is similar but like the grand prix and Monte Carlo have an extended wheel base. Otherwise the same as all other midsize GMs. 

Only another Monte Carlo frame could be used. 70-72. You are correct that one of the other chassis would not work properly. 

Wider of the 2 crossmembers? I believe there is only one for the A-body. There are 2 for the G-bodys I believe. It's been awhile since I played with G-bodys. I have the GForce crossmember in my 70 SS. It bolted right in with no issues. 

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