Chassis Rail Straightening
11-29-2016, 04:09 PM
#16
Burning Brakes
I'm going to do this too!!
Remark:
If the damage is near the jack pad and the jack pad is no longer flat, the jack will not sit properly. This could cause trouble to jack the car on the roadside of a bad road... In a garage, it's manageable. If it's in the middle of the frame rail, I wouldn't really worry about it myself.
11-30-2016, 04:08 AM
#17
Rennlist Member
I once saw a strengthening piece to put over the chassis rails for the purpose of jacking the car. Who makes these and is there someone here who has them?
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11-30-2016, 12:01 PM
#19
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It however is not a F??ME , never will be...... I prefer using the front suspension mounting points for jacks and jack stands since those were DESIGNED to hold the weight and DYNAMIC loads which are far greater than the simple weight of the car.... The rear suspension cradle or subframe is also great for lifting the car. One jack under the transmission on the cradle lifts the entire rear end.....
11-30-2016, 02:17 PM
#20
Curious. What is the load path from the jack points? Since there is no skeleton or "frame" underneath I assume there are some sheet metal ribs or frames (in the aircraft sense) that support and distribute the load? Obviously to the untrained eye (mine) the jack points are just a couple of holes located at the outer ends of the chassis rails.
11-30-2016, 05:43 PM
#21
Developer
We prefer to use the factory jack point to jack the vehicle, and these to provide a place for the Jack Stands. Works really well.
You can mount them to the car (so mechanics don't dent up your sub-frame channel) Or just slide them on when you need them, and keep them with your jacks and jackstands. Our tool distributes the load over a section of the frame channel so that it does not get dented or deformed by lifting on a single point.
The inner frame channel is easy to see in these pictures, or by just kneeling down and looking for yourself. The other frame channel for the 928 is integral within the rocker panel assembly, and that's why the jacking points are there.
You can mount them to the car (so mechanics don't dent up your sub-frame channel) Or just slide them on when you need them, and keep them with your jacks and jackstands. Our tool distributes the load over a section of the frame channel so that it does not get dented or deformed by lifting on a single point.
The inner frame channel is easy to see in these pictures, or by just kneeling down and looking for yourself. The other frame channel for the 928 is integral within the rocker panel assembly, and that's why the jacking points are there.
11-30-2016, 07:12 PM
#22
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good photo Carl note how it shows a torque box structure which ties the front rails to the actual jack pad and to the rocker panels to distribute the loads. All of which happens BEFORE the floor supports. If the floor supports were intended to lift the car they too would have had inner reinforcements like the front rails and rocker panels. The fact that they dent and crush pretty much proves they are not designed to hold up the car....
Fox body Mustangs among others are known for developing cracks in the floor boards from flexing while driving.
Fox body Mustangs among others are known for developing cracks in the floor boards from flexing while driving.
12-01-2016, 11:06 AM
#23
Developer
You are not wrong, Jim. But the point is, once the floor jack occupies the lifting location, the do-it-your-selfer is going to be looking to where he can put his jack-stands. (And I want him to use jack-stands!)
I see enough cars in here with dents in the inner box channel to know that this is what they are using to block the car up. I hate to see those dents, they weaken the structure (we agree). So we provide a "if your gonna use those frame rails for your jackstands, at least protect them with these" kinda deal.
I see enough cars in here with dents in the inner box channel to know that this is what they are using to block the car up. I hate to see those dents, they weaken the structure (we agree). So we provide a "if your gonna use those frame rails for your jackstands, at least protect them with these" kinda deal.
12-01-2016, 11:42 AM
#24
Nordschleife Master
You are not wrong, Jim. But the point is, once the floor jack occupies the lifting location, the do-it-your-selfer is going to be looking to where he can put his jack-stands. (And I want him to use jack-stands!)
I see enough cars in here with dents in the inner box channel to know that this is what they are using to block the car up. I hate to see those dents, they weaken the structure (we agree). So we provide a "if your gonna use those frame rails for your jackstands, at least protect them with these" kinda deal.
I see enough cars in here with dents in the inner box channel to know that this is what they are using to block the car up. I hate to see those dents, they weaken the structure (we agree). So we provide a "if your gonna use those frame rails for your jackstands, at least protect them with these" kinda deal.
Worth their (sustantial) weight in gold.
And if someone doesn't have lift bars, there are a couple safe & sturdy places to jack the car up that leave the jack points available to put stands under (trans crossmember and front LCA mounts is one option, as JB mentioned).
12-01-2016, 11:50 PM
#26
Rennlist Member
Thread Starter
Thanks for the replies. I've been away for a few days in central N.S.W. with the girls (1 x wife, 1 x 928) so I've only just caught up on the comments.
I didn't mean to start a discussion about the square box section thingies under the floor, and I thought chassis rails would be a more reliable title if someone was searching for a way to fix them.
Jerry Feather wrote-
This is a good idea. 
GT6ixer wrote-
There is no problem, except for my OCD.
I didn't mean to start a discussion about the square box section thingies under the floor, and I thought chassis rails would be a more reliable title if someone was searching for a way to fix them.
Jerry Feather wrote-
I made a tool some time ago to do the hammering downward. It is made of about 3/4 inch round bar bent into a kind of seven-shape and the bottom of it, the top of the seven, is milled so that it has a sharp enough edge to fit the inside of the hat sections. The top of the seven shape is long enough to reach to about half way between the holes in the floor.
GT6ixer wrote-
But I gotta ask, what is the problem that this solution is addressing other than aesthetics?
12-02-2016, 03:26 PM
#28
Chronic Tool Dropper
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Some of this stuff points back to how to jack the car up and place it on stands. I have the full front undertrays so no option to put a block under the main front crossmember for lifting.
Absent a lift or a set of Ken's Liftbars, the floor jack is used (with a keyed hockey puck) to pick up the side of the car from a REAR jackpoint. Chassis stiffness causes the front to come up with the rear lifting, enough to put a safety stand under the front pad. Then lift from the other side rear jackpoint, and place a safety stand under that side's front jack point. You can go back and forth from the rear points a couple times to maximize front height, limited by the rear apron clearance and the geometry of your floor jack.
With the front end on stands at your target height, move to the rear of the car, and with a block under the rear crossmember under the gearbox, lift the back of the car with your roller jack and place safety stands (with keyed hockey pucks) under the rear jack points. I can get the car up to about 20" safety stand height using this method. You can play with adding blocks on the jack to get things a little higher, but you want to keep the overturning forces and the dimension of your safety stands in mind as you do.
A "keyed hockey puck" is a standard hockey puck with a small screw-on rubber foot in the middle of one side. That rubber foot indexes in the hole in the jack point so the puck doesn't move laterally. Having the hard rubber hockey puck eliminates casual paint damage while jacking the car, and avoids the distortion of the jack point that happens with regular V-notched safety stands. The V at the top of the stand indexes on the puck just fine, but the load on the jack point is much more even with no distortion.
I'm not at all a fan of lifting or supporting the car at the suspension pick-up points in the tub. For the most part, the car's weight is managed at the top spring and shock mounts. The lower control arm points are well braced for lateral loads, but not intended to take a lot of vertical load. The exception is in the rear, at the forward compound bearing/bushing for the lower control arm. The WSM suggests that it's OK to lift from that point. Realistically though, the jack point is right by the suspension mount, to the point where a roller jack under the suspension point is in the way of placing a safety stand under the jack point. Meanwhile, the rear suspension and gearbox cradle is plenty strong enough to take the lifting load, and lifts both sides at the same time nicely.
That's my too sense on this.
Absent a lift or a set of Ken's Liftbars, the floor jack is used (with a keyed hockey puck) to pick up the side of the car from a REAR jackpoint. Chassis stiffness causes the front to come up with the rear lifting, enough to put a safety stand under the front pad. Then lift from the other side rear jackpoint, and place a safety stand under that side's front jack point. You can go back and forth from the rear points a couple times to maximize front height, limited by the rear apron clearance and the geometry of your floor jack.
With the front end on stands at your target height, move to the rear of the car, and with a block under the rear crossmember under the gearbox, lift the back of the car with your roller jack and place safety stands (with keyed hockey pucks) under the rear jack points. I can get the car up to about 20" safety stand height using this method. You can play with adding blocks on the jack to get things a little higher, but you want to keep the overturning forces and the dimension of your safety stands in mind as you do.
A "keyed hockey puck" is a standard hockey puck with a small screw-on rubber foot in the middle of one side. That rubber foot indexes in the hole in the jack point so the puck doesn't move laterally. Having the hard rubber hockey puck eliminates casual paint damage while jacking the car, and avoids the distortion of the jack point that happens with regular V-notched safety stands. The V at the top of the stand indexes on the puck just fine, but the load on the jack point is much more even with no distortion.
I'm not at all a fan of lifting or supporting the car at the suspension pick-up points in the tub. For the most part, the car's weight is managed at the top spring and shock mounts. The lower control arm points are well braced for lateral loads, but not intended to take a lot of vertical load. The exception is in the rear, at the forward compound bearing/bushing for the lower control arm. The WSM suggests that it's OK to lift from that point. Realistically though, the jack point is right by the suspension mount, to the point where a roller jack under the suspension point is in the way of placing a safety stand under the jack point. Meanwhile, the rear suspension and gearbox cradle is plenty strong enough to take the lifting load, and lifts both sides at the same time nicely.
That's my too sense on this.
12-03-2016, 10:09 AM
#29
Pro
Have you been working under your 928 and keep noticing the dents in the chassis rails from inappropriate use of a jack?
After being inspired while reading through this thread https://rennlist.com/forums/928-foru...rrived-65.html, I decided to do something about mine.
You can access the inside of the rails from inside the car via holes in the floor. Lift up the carpets and press on the material that the factory has stuck on the floor to locate the holes, then trim the material and peel it off.
After completing the work I sprayed the inside of the rail with cavity rust inhibitor, and covered the holes with adhesive tape and sound insulation. I need to repair the stuff the factory sprayed on the underside of the car to prevent damage from stones.
A magnet on a telescopic rod (like a portable radio aerial, see photo below) comes in handy when one of the pieces of steel slides down the chassis rail and you need to retrieve it.
As I mentioned before, it's not perfect but it is an improvement.
Maybe someone has some other tips.
After being inspired while reading through this thread https://rennlist.com/forums/928-foru...rrived-65.html, I decided to do something about mine.
You can access the inside of the rails from inside the car via holes in the floor. Lift up the carpets and press on the material that the factory has stuck on the floor to locate the holes, then trim the material and peel it off.
After completing the work I sprayed the inside of the rail with cavity rust inhibitor, and covered the holes with adhesive tape and sound insulation. I need to repair the stuff the factory sprayed on the underside of the car to prevent damage from stones.
A magnet on a telescopic rod (like a portable radio aerial, see photo below) comes in handy when one of the pieces of steel slides down the chassis rail and you need to retrieve it.
As I mentioned before, it's not perfect but it is an improvement.
Maybe someone has some other tips.
12-03-2016, 10:18 AM
#30
Pro