FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Jim Comet on December 22, 2021, 08:18:50 AM
-
HI all, I have a 66 Comet with a 600hp FE and a C6 trans that I foot brake. The car runs 10.7's and 60 foots are 1.45's. The car was a factory 390 car with the banjo 9 inch rear. I have 35 spline axles and Cal tracs. At what point should I consider adding a back brace to the rear? If I did, can I assume I would need a fixture to hold the axle from warping while welding on the brace? All is working well now but the rear end is out right now and I was wondering if I should just do it. Thanks Jim
-
Strange Engineering calls out a brace out for 800 hp plus applications on their housings. This does not mean a brace for your situation is unwarranted. The factory housing metal thickness on the tubes might be .187? The Strange stuff is probably .250 and their welds of the tubes to the center section are more involved than a factory housing.
Can’t tell you anything about the welding concerns other than there will be smoke if you don’t drain the housing down.
If you pull it apart for the job you will have the opportunity to inspect the axles.
Alternatively you could upgrade the housing but it won’t be cheap and you might have to wait for it.
-
Whats the old Comet weigh Jim ? Does the car see a ton of action ? Ive done my share over the years some on a fixture and some not . Ive not had one go wonky because it wasnt on the rod when I welded it up . I do however treat them a bit different when I weld them up.
-
The braces I use weld in the center of the axle housing, then out on the ends of the tubes. The odds of warpage in the center when welding there are pretty small, I think. Out on the ends, what I've done is weld in small areas where the back brace meets the axle tube, then duplicate that same weld on the opposite side of the axle tube. Do a little at a time, back and forth. This seems to even out any warpage. I don't recall ever having one go out of alignment doing that, and I've done several...
-
Jim with repeated launches , the housing does bend causing a "toe in" situation and potential "tire scrub". I would add one in your case. To do it right , the brace is fit an welded before the housing is straightened so that the welding removes some ( or all) of the toe in. It is then checked and corrected as needed. I've seen .003-.005 improvements in the 60' times and nearly a mph on the big end.
-
My car weighs 3500 with driver. Does anyone have a recommendation or one to stay away from.
-
Yes, I would agree that a back-brace particularly on an O.E. housing is recommended for your application at that 60' and weight and if you intend repeated use.
And, welding a brace (or much of any thing) is going to bend the housing; but think, if it's already bent forward from use and now welding on the backside, maybe you'll just be making it strait again! ::) And this effect has worked for me many times in the past when I have done such.
But these days, if regularly racing the car, I would recommend to just order a new housing (with it's heavier materials in construction) with all fabrication done as received. ;)
Scott.
-
A continuous weld, joining two materials, will shrink the metal .005 - .015, depending on the heat generated.
But, if you do as Jay recommends, welding small areas (.50") on opposite sides, it will not move enough, if any, to cause a problem. I'd recommend bending some 1/4" square stock to weld to on the opposite side.
If your not a welder, have it done at a competent shop.
-
Thanks for the input. I think I may install one or have one installed. I see SW racecars makes one the the small banjo housing like I have. Thanks, Jim
-
Jim I have a comet runs 6.70s in the 1/8 460 powered I also have been welding for over 40 years . Yes you need a back brace I prefer the one Moser sells .It isn't a difficult job like Jay says I would remove the complete assembly from your car just so you can grind the paint off and to make welding easier .Tack it down in several places weld 1"-1 1/2" beads let them cool 5-10 minutes weld some more you will be fine .Where the axle tubes are welded into the housing those factory weld always look like doo doo to me a back brace strengthens all that .With a little patience (time ) it is an easy job.If you were in Ga I would help you out .Doug
-
+1 on the SW back brace for the banjo housing. I have used many of those and they fit well although any of them (brand) will likely need a bit of grinding for fitment.
-
Any welding on the housing will warp it. Needs to be done in a jig , a piece of tube or bar stock with collars in the bearing locations. Stock housing is prone to warping, it's thin wall and wide.
-
Any welding on the housing will warp it.
+1 ;)
Yes, better technique will reduce the possible sum of deformation, but in the end, it's perhaps just a matter of how closely your going to scrutinize the end result. :o
Oh, and just the use of a "jig", though certainly of benefit, doesn't guarantee the housing will be perfectly straight, as generally when dismounting the "jig" a certain sum of resistance in the separation is experienced and the housing obviously relaxes to something other than "perfect", at least that as signified by the jig. ::)
Scott.
-
I found a shop that has a jig and experience adding back braces. Here is a photo of my prepped rear with the back brace set in place. The SW piece fits pretty nice out of the box with minimal trimming. I'll post a photo when it is done. Jim
-
Strap tied to Jack stand holding housing in place is slick.
Today is not wasted, I learned something new today.
-
IMHO - having done it - I would just order a housing with the proper dimensions from Currie, etc and put your parts in it. A couple of hours swapping parts, done. If you felt you didn't need to save the old housing, you could probably recoup much of the cost by selling it.
-
This is about how I saw this thread going. Yes as someone else mentioned with that weight and those 60s I would nail one on it. AS far as the "Jig" welding is concerned... Well . let me first say that everyone saying that the jig is the way to do this is absolutely right... At the same time , after having done quite a few over the years I would simply say go take a look at whats for sale out there as a "Jig" . It had to be more than 20 years ago when I laughed at the first one of them someone showed me and I made my own out of a huge chunk of rod and made my own bushings.. So beefy in fact I didnt feel like using the damn thing after the first few times.
I guess my point is... Most of the jigs that are out there that you can buy are great for mounting flanges but they sure as hell will NOT keep a housing from going bananas if you were to fire up the welder and just go at it non stop. Its going to pull the dinky rod and the housing and the whole 9 (Pardon the pun) What you will find is that you will end up welding it as jay mentioned anyway which if done without the jig and done slow with a tig or strategically with either welding process will get you where you want to be. The brace itself is what holds the housing from going anywhere anyway right ? When you think on that a little you feel better about doing it. Just dont go all Dr Frankenstein on it all at once... Strategic small welds . The first ones you do are what will hold it straight for the others.. I also DO NOT continuous weld any brace .In fact some braces are made so that you cannot.... Think about rust and coating the thing too up inside or leave yourself ports so that you can rattle can up in the thing to prevent from the inevitable rust streaks.
-
+1 What Blueoval said.
Jigs are good for holding the bearing flanges square and in line with the center section, made mine from a piece of 2" solid stainless I picked up from the junk yard.
It would be a good idea though to bolt up an old center section before welding and for sure 1" tacks max and jump around. Think of head bolt torque sequence.
-
Strap tied to Jack stand holding housing in place is slick.
Today is not wasted, I learned something new today.
+1
-
It had to be more than 20 years ago when I laughed at the first one of them someone showed me and I made my own out of a huge chunk of rod and made my own bushings.
Yes I had the same experience, if I recall most of the commercially produced "jigs" for this purpose utilized 1" to maybe 1-1/2" bar, so I also made my own utilizing a 2" hardened solid steel bar ground true in length +/- .001" with my own steel lathe turned rings for fitment. 8)
But as I stated previously, with this one can realize that although the bar (and the bigger the better! ::) ) resists allowing the housing to defect, and aids in the end result, when you knock the locating rings out of position post welding, that were a slip-fit in the beginning, and the resistance load is released, you know the housing like a spring in tension relaxing is going change position...........some. :o
Straightening after welding is truly the correct procedure, but successfully cold bending to straighten these housings proves quite difficult (yeah, I've tried ::) ) this particularly without unique and what may prove expensive equipment; but if I were producing quantities this is what I would have, like a crankshaft or say frame straightening machine but specialize for this. In a few instances I have tried heating to attempt relaxing post welding, but have only had mixed results here (perhaps there are mixed residual stresses other than anticipated and things just don't always react the same to this :-\ ). And yes a weld-bead on the opposite side of the tube will pull with shrinkage in that direction, but this process of straining the parent steel structure in all directions in this fashion just doesn't seem like a good idea, even if it does 'seem' to work; and this does happen if only inadvertently if one welds say ladder or four-link brackets on the front of the tubes anyway. :o
If one just doesn't start making to much of an engineering project out of this (leave the dial indicators in the tool box drawer, as you really don't want to know! :o ), use reasonably decent techniques in execution, and yes, we get away with something less than 'perfect' because thank goodness the engineering permits such! ;)
Scott.
-
Oh yes , shooting for perfection is exactly what I did with the heavy bar and precision bushings . Thats about when it all goes south trying to get that mess back out of the housing post weld because it has moved even with the bar in there and the cursing begins ......
-
I'm not a welder, by trade but, I am very good at weld prep.
In my young days, one of Gurneys welders, opened his own shop, in Orange, CA and taught me some basics on preping my alum & mag parts, before bringing them to him.
For 2 years, I did weldment preping and fitting, for high vacuum chambers, for NorCal Products, the largest high vacuum equipment manufacture, in the world, at that time.
Welds DO shrink the material being welded, anytime you penetrate, the parent material, with a arc. That's why you can remove valve seats by running a bead around them.
My job was to position tubular ports at different, skewed angles, cope the fittings and then tack them in place with a tig (no rod used), so there were no gaps (Hi Vac welding is done w/o filler rod). They had to be positioned +/- .010, after welding. I positioned them .010/.015 high. If I knew who was going to weld, I could set them closer.
The welders were required to maintain a welding technique (amount of heat input) to keep shrinkage to .005/.015, so the finished product was within the +/- .010 tolerance.
So, every time you lay a bead, that penetrates, that area will shrink, in that range. Laying short beads on both sides, will shrink less and evenly, laying a heavy bead, on one side will bend it, no mater the jigging. If that jig doesn't come out, like it went in, it's bent.
It also helps to stress relieve or, normalize after welding. Stress relieve at 600-900 F (use colored markers), normalize by bring to a dull red. 600-900 F can also be determined by metal color, if the metal is clean. 600 is blue, 900 black.
-
I'm dropping the housing off on Saturday to get the brace installed. The place that is doing it, Race Craft, builds custom housing as part of their business. Ill post photos when I get it back in a couple of weeks. Jim
-
............we get away with something less than 'perfect' because thank goodness the engineering permits such! ;)
Oh, and by the way, don't think that the O.E.M. provides perfection in execution on these either, as in the past we have had a couple of brand new cars come thru our shop for say gear swaps, only to realize and then advise the customer to return to the dealer for a warranty replacement housing and then return for the gear change. One was so bad that it was causing obvious uneven wear to the tire! We also used to order new axle assemblies from ford, and when breaking them down to reconfigure, with a casual observation one would realize that they just are not always 'perfect'! :o
And, that is why they have the real engineers, who figure out just exactly what they can get away with, in the way of 'tolerances' and engineering that allows such! ;)
Scott.