frame sag

Excellent information Brent and good questions by all. I did this the first time I did it actually by deducting what to do by necessity to fix the problem correctly I hoped and a little common sense deduction in what to do with a car that actually had a more severe sag in the area and I gently heated with a 1/2 inch plate I had held up to the lower frame rail with very slight pressure . It did it perfectly and I was amazed how easy it moved. I'm not a metallurgist but you don't have to heat cherry red to shrink or move metal . I believe I started with a smaller area and kept working out . When all done I did replace motor mounts and rubbers and everything seemed to be just fine.
Yes I did it with the body on on one occasion . The other couple if times with just the bare frame. If course the bare frame is much easier to check your progress but you have to do what you have to do at times . Not sure if I was brave or stupid the first time with the body on but it got the job done
Larry
 
I just purchased a 30 coupe that is shimmed up a lot at the cowl. So I removed the front fenders so I could put a straight edge across both rails. It looks good from the top but the bottom rail has a bend that you can feel on both sides at the rear motor mount on the bottom rails. Should I be concerned about the bottom rail or just the top rail. I'm new to all of this any help would greatly be appreciated.
 
hdmike said:
I just purchased a 30 coupe that is shimmed up a lot at the cowl. So I removed the front fenders so I could put a straight edge across both rails. It looks good from the top but the bottom rail has a bend that you can feel on both sides at the rear motor mount on the bottom rails. Should I be concerned about the bottom rail or just the top rail. I'm new to all of this any help would greatly be appreciated.
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That may depend. Are you having a problem with body parts alignment or drivability ?
 
Yes, the cowl is shimmed up about 3/4" under the cowl. But everything aligns except the hood. Had a gap about 3/4" at bottom of hood. I just want to get rid of those shims. What I have read there isn't suppose to be little if any shims under there. I haven't driven it yet.
 
hdmike said:
Yes, the cowl is shimmed up about 3/4" under the cowl. But everything aligns except the hood. Had a gap about 3/4" at bottom of hood. I just want to get rid of those shims. What I have read there isn't suppose to be little if any shims under there. I haven't driven it yet.
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A wood block with a fabric reinforced pad tacked to the bottom side is a standard part, so are you saying in addition to this you have 3/4" more shims? Or, are you saying the very front body mount with no wood block has 3/4" shims?
 
heated my frame rails this morning. pass side turned out nice & straight but drive side still has a slight sag will work on it tomorrow
 
Here are the pics I said I would post. Sorry i didn't get them posted last night my internet was down till this evening. This is just rubber strips they put in as shims.
 

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You weren't kidding about having a thick stack of shims. Have you run a string along the frame to check it for sag? They like to sag near the rear engine mounts.
 
No, I haven't it still has the body on it. The only thing I have removed was the motor & transmission, and fenders so far.
 
Brent, I have a frame with 1/8th" sag. I'm going to try your heating technique, but I have a question first. I have a frame that the rear crossmember was bolted on and was narrower than stock by 4-5 inches. When I pulled the rear crossmember off the frame stayed in the same position. I spread the frame and bolted it to the crossmember in correct location (will be riveting). My question is should I heat the rails with the crossmember attached and if I do, won't that affect the inward tension of the rails? or shouldn't there be inward tension from the rails ? Frame is within 1/4" of square at a 8'10" measurement. Thanks, Pat
 

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PatrickGrant said:
Brent, I have a frame with 1/8th" sag. I'm going to try your heating technique, but I have a question first. I have a frame that the rear crossmember was bolted on and was narrower than stock by 4-5 inches. When I pulled the rear crossmember off the frame stayed in the same position. I spread the frame and bolted it to the crossmember in correct location (will be riveting). My question is should I heat the rails with the crossmember attached and if I do, won't that affect the inward tension of the rails? or shouldn't there be inward tension from the rails ? Frame is within 1/4" of square at a 8'10" measurement. Thanks, Pat
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Pat, I really am not sure what would happen in your instance however I do think I would install the rear crossmember with rivets where it is in its final location first. That way, you can tell what shrinking will need to be done, ...and where. Just remember this is a somewhat slow process because the metal is generally not finished "moving" until it normalizes with the surrounding metal. Cooling with air or water helps, but rarely does the heated area immediately normalize to the other metal.
 
I have to wonder if the cars put in storage over the winter could benefit from being jacked up a bit and blocks placed to relieve the sag.
 
how much is considered a normal sag? and how much can the heat method correct? also i don't think the passenger side sags, just the drivers side is that normal?
 
The chassis under my '29 Phaeton is badly sagged. One day, I'll get to it - maybe. The info in this thread has been great. It's all stored away in my neck top computer.:D
 
ok, assuming i can get the driver's side level (pass. side ok) how do i keep it that way? do i have to reinforce it some way?
 
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