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Post by oljack on Dec 29, 2012 20:41:46 GMT -6
I have a 19" j bar mounted from driver side to pinion bracket on right side of diff. Problem is pinion mount keeps bending behind or at the heim end bolt holes. I have a short spacer between the heim and the bracket. The vertical tube at the other end is also bending some. The bar is not mounted perpendicular to the center line of the chassis. I just don't want the pinion bracket to fail. Any ideas or suggestions?
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Post by johnny on Dec 30, 2012 10:20:37 GMT -6
you said " keeps bending"...... are you straightening it back out ?..... sounds like you need a new and slightly thicker bracket.....
9" or QC?
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Post by oljack on Dec 30, 2012 12:09:51 GMT -6
First time I found it bent I straightened it. (I bought it new from Southwest Speed) I plated it as close to the pinion bolt holes as possible and it bent again next to the plate. Problem is that it bent at all. It appears that there is a ton of leverage on the bolt going through the rod end. I know I have about 4"-6" of roll and even though the tracks I run aren't heavy, they are pretty rough. I guess I'm wondering if I have too much bar on the left, not enough bar on the right. We don't have a rule on j-bar length, so I could run a much longer one, more like a panhard bar. I won the last main event I entered on a track I had never run on. It was kind of hooked up, but I was pretty loose all night-35 laps on a 3/8's. I just had to stay out of trouble and not use my car up. Just lookin' for a little input. Thanks!  |
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Post by oljack on Dec 30, 2012 12:10:43 GMT -6
Oh, yeah, 9". |
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Post by lizardracing on Dec 30, 2012 13:08:35 GMT -6
That's happened to me too but never on a rough track, just smacking the wall with the RR too many times. Using a cone spacer will redistribute the loads and help. The bigger the base of the cone the better. Reducing the amount the heim spaced out on the bracket will help too. Not hitting the wall with the RR will help alot but sometimes you can't help that.
I had a car several years ago, the frame mount was located to far forward and the Jbar wasn't parallel with the axle center line at full hike. Said another way, if you were to draw a line through the Jbar, and through the axle center line, the bracket is strongest when these two lines are parallel with one another and as close to each other when viewed from the vertical plane only(looking down). If they intersect inside the RR tire, the bracket is being compromised.
Worse case....You could add a bolt on bracket to the axle tube just behind the pinion bracket and weld a piece of steel(flat bar) between the two, axle and bracket. You'll be adding a fair amount of weight but that's better than bending the bracket all the time.
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Post by oljack on Dec 30, 2012 15:52:05 GMT -6
Hey, thanks, lizardracing. That is exactly what has happened. The frame mount is a vertical tube which is 2"-3" forward of the pinion mount. Wanted to add a longer spacer to the heim end, but that would weaken that connection. Gonna have to figure a way to beef up the bracket. Thought about a heavy tab welded to the bracket and let it butt against the axle tube not welded to the tube just floating. Hmmm?
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Post by lizardracing on Dec 30, 2012 21:26:03 GMT -6
That would be the down and dirty way. I'd rather weld then let it float however.
Most PH bars mounts aren't too much work to move. Moving the PH bar would be the preferred way. Is that not possible?
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Post by oljack on Dec 30, 2012 23:01:06 GMT -6
The vertical tube is situated just in front of and just to the left of the left rear spring. If I back the spring up closer to the differential housing, that would require moving the screw jack bolt and related bracing, etc. The spring is already tipped forward at the top as it is.When the chassis is up on the bar the spring come close to vertical, which is fine. However the right rear does not come forward enough to let the j-bar line up parallel with the rear housing. I might be able to create more lift on the right side, but I hate to lose the weight transfer. I think I'm going to look at moving the left rear spring and jack bolt. I'll report back!
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Post by lizardracing on Dec 31, 2012 13:03:55 GMT -6
Spring in front on the LR? Yeah ,you have quite the conundrum. Beware moving the spring mounts on the chassis will change the way the car handles by affecting the effective spring rates. You may have to make spring change to compensate. I reread that the PH bar chassis mount is bending some as well. Consider replacing that with a 1 1/2 square tube. Square tube is stronger in that load directional than round tube. That would also allow you to use a mount like shown below which would locate the PH mount closer to where you need it with out moving the spring mounts. Attachments:
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Post by oljack on Dec 31, 2012 15:12:09 GMT -6
I didn't build this chassis, bought it used. I am more familiar with asphalt cars, but I like racing on dirt much more. I'm on the west coast and I race in the prostock class - stock clip and lowers, 2700#, 108" wb, gas, any carb, leaf, 3 or 4 link, 8" G60 type tires. A poor man's late model, we like to call it.
I really like the square tube idea, forgot that those mounts were available. That would likely solve the problem or, at the least alleviate some of the deflection.
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Post by lizardracing on Jan 1, 2013 21:35:26 GMT -6
That sounds very much like our Midwest Modifieds around here.
If pictures of my car help, PM me an address.
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Post by flipflopoo1oo on Jul 12, 2014 9:57:30 GMT -6
They do make a biscuit bar to cushion a lick!
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