gto4evr

Hey guys, I noticed a comment in a thread concerning offset control arms and it sparked a memory of something I heard about in a discussion somewhere. Anyways, I've got a 71 Lemans with a problem that's been developing with the fan rubbing on the bottom of the shroud. It's got new motor mounts and all original rad support/fan shroud/fan, etc. Also, never been hit so no frame damage. Someone made the comment that these cars sag in the engine cradle area of the frame so basically my motor has sunk down in relation to the car and that's why the fan is too close to the shroud now. Ever hear of anything like this? I've backed off the bolts and spaced down the rad support below the frame as far as I can take it without causing issues with the fender alignment at the doors.

If it is this frame sag thing, has anyone had their frame corrected to eliminate this and if so, what kind money can I expect it to cost?

Thanks,
Dennis

joe_padavano

I've heard about this alleged frame sag for decades, but unless someone has physical measurements of a bare frame to prove it, I find it hard to believe given the beefiness of that part of the frame. I'm convinced that the whole "sag" myth that led to the offset control arms is more a function of worn bushings or bent control arms from potholes.

Back to your problem. What I HAVE seen is that an A-body that has been improperly lifted can have the bottoms of the frame rails distorted in the vicinity of the trans crossmember. My 70 W-30 has this problem. The result is that the trans crossmember gets moved upward, which pitches the fan downward.

Do you have new core support bushings? These may be taller than original.

gto4evr

Joe,

Yes, "new" core bushings, body bushings and motor mounts back when I restored the car in 97. On the core bushings, if they were too large, that would actually help this situation if they were larger since that would lower the core support in relation to the frame because on a pontiac the core support mounts below the frame, not above it as I'm guessing the olds does? I haven't had the core support off my 68 cutlass to notice how it's mounted.

No frame damage on the trans member area. I can understand your explanation on a lifted tranny causing the fan to dip lower as it pivots over the motor mounts.

I also agree that I find it hard to believe the frame would tweak there "from age". This car did not do this at all when I first put it together. I did install new front springs a couple of years ago. Again, didn't have this problem immediately after putting them in. I also went from 14" to 15" rims right after the spring change though I can't see how that would affect anything. I've checked twice, there are no broken motor mounts.

I'd really like to see hard data on this supposed frame sag thing as like you, I've heard about this but never from a guy who actually had his car in a frame shop and had it corrected. I had the car aligned when I had the new rubber put on and I don't have any crazy pile of shims straightening anything up.

joe_padavano

I didn't know that. As you correctly guessed, on Oldsmobiles the core support sits on top of the frame horns.

coltsneckbob

Well my 3 cents.

1) I have heard that convertibles suffered more from frame sag then coups. I suppose I can believe this as the roof would give lateral and transverse support to the frame.

2) I have had several new cars in recent years that have a cross support over the top of the engine usually connected to the control arms or are bolted to the frame near top of shocks. No one ever told me so, but I actually thought it was to help with frame sag or at least with frame flex.

3) Through the years I have had older cars I have encountered the fan & shroud problem a few times. Each and every time it was the motor mounts.

oldcutlass

I have seen the motor mounts deteriorate with age and oil contamination causing the the rubber to soften, which could account for your motor to drop.

Those bars across the top of shock towers (Monte Carlo bars)and lateral supports were there to stiffen the body and prevent the shock towers from flexing and spreading.

Beob

I was told I have frame sag. Just after buying my 69 I had the entire front end rebuilt. New springs, bushings, steering and rubber. When it was time for the alignment the mechanic told me it could not be aligned due to frame sag. All shims were removed from both sides and still out of alignment. I got a pair of offset control rods and it brought the alignment pretty close, still no shims on either side. I have driven the car like this for the past 20 years with no problem and the same rubber! During the recent restoration we discovered two small cracks in the cross member under the engine. One on each side about an inch long. Cracks were welded and I opted not to have the frame straightened since I havent had any problems. So I would say frame sag is a definite possibility at least in my case.

oldsconv

I agree with Joe that it does not seem like that large front crossmember (under engine) could sag but I have seen it discussed tons of times. I think the measurements are somewhere on a frame chart or the service manual. I think factory is 31.75" inside to inside between where the upper a-arm shafts meet with something like a +/- 1/4" tolerance. If the frame is sagged, I guess it would be less than 31.5" between those mounts. Again, my two A-bodies (Cutlass and Chevelle - both big blocks) measured fine in this area, so not sure if it is an urban legend or maybe some cars had it and some didn't depending on use/abuse over the years?

Beob

Maybe someone should send this in to Mythbusters!

gto4evr

Well, I'd love to measure, but with the motor in the way, I don't think I'll be getting anything reliable. I know I've got frame charts in one of the manuals, probably the Fisher body manual. What really bugs me is that it's ten times worse when it's cold and when it's in Reverse, (it goes away once it's warm and in drive) and the damn neighbor is ALWAYS in his driveway when I'm backing out to go to work so I duck my head and speed out the driveway so I can get it into drive and hide my shame of "that old piece of crap" car!

oldsguybry

Yea , as long as they use a Chevy to experiment with , and not an Olds....knowing them , they would probably feel the need to destroy it.

joe_padavano

Yes, but that's longitudinal bending in the long frame rails. This thread is talking about alleged sag in the front crossmember under the engine. That part is the same on both convertibles and hardtops and has no connection with the roof being cut off.

Those new cars are all unibody with no "frame" to sag. Those braces are designed to tie the upper suspension mounts (usually a McPherson strut design) for torsional stiffness and improved handling response.

X2

Bluevista

I know a '72 that's never been apart and the shroud is cut for fan clearance on the bottom.
When I was painting the engine there was just as much space between the bottom of the pan and the top of the crossmember as my car and the shroud fits fine on that. I would lean toward the trans being high in the rear, improper jacking or from hitting something and bending the trans support in that case. It would only have to be a little bit high in the rear for the front to drop enough to hit the shroud with the motor mounts being the pivot point.
If you're way smarter than me and have the measurements from the trans mount to the fan blade and then to the motor mounts you could probably figure it out.
Maybe the wrong trans mount?
The only thing I could see changed on the car that would effect the fan blade is the water pump and as far as I know the shaft centerlines are all in the same position so you couldn't get a lower shaft replacement pump by mistake..or could you??

Here's a horse with frame sag.

horsefunny.jpg

J-(Chicago)

Like Bluevista's picture, I would think they'd banana in the middle of the frame, and not the engine cradle or front stub. The long skinny rails in the center seems like the weak point to me.

coltsneckbob

No Joe I understood the sag we're discussing. What I am saying is that the frame can sag in two different ways/directions. Yes, a conv is known to suffer a sag in the lateral direction that is the sides slope. In which case the door seam might be narrow at top of door and wider at bottom in extreme cases. Or, there might be transverse sag which is what we are talking about. That is at a right angle to the long sided sag. My thought is that if the cross beam under the engine sags then one cannot expect the rest of the frame to not move somewhat in the same direction - though of course perhaps not as much. If that cross member sags then there has to be a shift in connected components. This may result in the longitudenal twisting of the side rails. I am suggesting that a roof may give some support to mitigate that twisting and the upward pressure it exerts.

Anyway if the cross member, which is fairly thick and strong, does not bend then let me throw out these thoughts:
-Is the tranny mounted correctly? I can think of situations where the trans might force the motor to pivot on it's mounts.
-I think that some cars have a right and left mount (different slightly in size and/or configuration) is this the case with Lemans? Are the right ones on the correct side of engine?
-Was the car jacked up by the frame in front of the transverse beam? Or perhaps once too often by the bumper jack? Have you measured each side? U many need to measure behind and in front of wheel axle to account for support (e.g. spring) differences on either side.
-If the center cross beam really is sagged can u jack it up directly under the center of the cross member and see if there is any relief at all on the fan hitting shroud?

gto4evr

Well, back in "the day" there were right and left mounts though dimensionally they were the same in relation to the mounting points. Basically, all that made them left vs right was the fact that the weld nuts were to the back for each side and a bolt threaded in from the front. The left side mount also had a metal bracket integral to the mount so that if the rubber failed, the metal bracket was scissored into the other half of the bracket so the motor wouldn't jump up off the frame when it torqued. Fast forward to present day and the mounts are now universal and you need to use a nut on the bolt so there is no left or right anymore. Now I don't have the new style cheapie mounts on there, I've got NORS left/right mounts on it that I purchased a ways back before this cheap china crap started flooding the shelves of the auto parts stores. those went on back in 97 so no new change there.

The tranny mount is also of that vintage. Again, I did not have this problem 13 years ago when I put the car together, it's just developed in the last year or so. I've put a jack under the balancer and gently jacked from the motor to make sure the mounts aren't broken (and they're not)

I'm basically the original owner of the car (My grandmother bought it new in 71 and I inherited it as my first car in 84). No accidents and never jacked up from the middle to fold the car on my watch (nor any evidence that something like that happened during a vintage shop visit). I decided to follow along this sag path as I can't think of any other reason why this problem came without any changes (other than the front spring change that makes absolutely no sense to be the cause, and again, it didn't happen immediately after the new springs.)

Oh, and never a bumper jack - that's only in the trunk for show purposes! I was taught that lesson from my grandfather when he tore a hole into his 66 Tempest jacking it that way.

That's a good idea jacking the cradle to see if it has any affect, I'd guess if the frame is weak enough to sag there under weight, then it would be weak enough to spring back when the weight's off the tires. I haven't jumped any RR crossings with it or fallen into a major pot holes so there's no smoking gun on any road impact damage.

I'll try to get some measurements tomorrow. thanks again for the ideas!

coltsneckbob

Let us know the results of ur tests!!!!

scr8p

frame sag is not some sort of myth. if you have to take 3/8" of shims out of a front end during and alignment, and still have too much camber, your frame is sagging. i've seen this first hand atleast three times. one was a friends 72 442. i took it to the collision shop i used to work at to have it lined up after he got new tires. they took all of the shims out and it still wasn't enough. so, it came off the alignment rack and went up on the frame rack for a pull. lined up just fine...... with shims...... after that.

just because it doesn't happen to some, does not mean it won't happen to others.....