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4-Link Question #2135169 08/17/16 03:25 PM 08/17/16 03:25 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	The 4-Link bars on my car are adjusted a little over 1/4" shorter on the drivers side than on the passenger side. Also, the rear axle is not centered to the chassis/body. Distance from the axle face to the chassis centerline is close to 3/8" longer on the drivers side than the passenger side. This is how it was set-up when I bought it. I have had it out to the track a couple times to workout bugs & have made two semi-hard runs. It drove OK. After these two runs I noticed the drivers side rear tire was rubbing on the body. I was measuring things before changing 4-Link settings to get a little more clearance on the drivers side. Should The 4-Link bars be equal length & rear axle be centered?

Re: 4-Link Question [Re: HR3128] #2135176 08/17/16 03:33 PM 08/17/16 03:33 PM
Joined: Jan 2003 Posts: 19,372 Las Vegas Al_Alguire I Live Here
Al_Alguire I Live Here Joined: Jan 2003 Posts: 19,372 Las Vegas	Probably....Are you saying both upper and lower bars on the dr side are longer than the pass side bars? Does it have a wishbone in it or a diagonal link? My guess is it was someones attempt to preload the car?!? Do yourself a favor and start over. Get the rear squared and get it on some scales. "I am not ashamed to confess I am ignorant of what I do not know." "It's never wrong to do the right thing"

Re: 4-Link Question [Re: Al_Alguire] #2135184 08/17/16 03:46 PM 08/17/16 03:46 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	I only measured the lower bars. It has a wishbone. The wishbone arm rod-end on the drivers side is screwed all the way in.

Re: 4-Link Question [Re: HR3128] #2135187 08/17/16 03:51 PM 08/17/16 03:51 PM
Joined: Jul 2004 Posts: 653 Fredericksburg Va P plycuda mopar
plycuda mopar P Joined: Jul 2004 Posts: 653 Fredericksburg Va	string line it

Re: 4-Link Question [Re: HR3128] #2135189 08/17/16 03:54 PM 08/17/16 03:54 PM
Joined: Jan 2003 Posts: 19,372 Las Vegas Al_Alguire I Live Here
Al_Alguire I Live Here Joined: Jan 2003 Posts: 19,372 Las Vegas	Does the car launch straight now?? If so it may have ben adjusted as it is to make it go straight. If it were me I would get the rear squared, possible make sure the housing is not bent as well and start over with scales. It SHOULD be in the car square but you never know how it was built. Possibly it is where it is to make it go straight? But I would want to star over. Square the rear and have Zero preload on the bars. Set the pinion angle and work from there. Rather than type it all out here is a link to some 4 link basics. It is a good reference point for someone new to them. http://www.racingjunk.com/forums/showthread.php?17130-4-Link-Basics-Theory-amp-Help-Instructions "I am not ashamed to confess I am ignorant of what I do not know." "It's never wrong to do the right thing"

Re: 4-Link Question [Re: HR3128] #2135197 08/17/16 04:11 PM 08/17/16 04:11 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Is this a back half car or full tube chassis... make sure the front bar is square in the car then start from the beginning.. if the other guy set it up like that to drive straight on the launch he did it all wrong and if it drives straight now.. something is built wrong

Re: 4-Link Question [Re: MR_P_BODY] #2135206 08/17/16 04:37 PM 08/17/16 04:37 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	Thanks for the replies. PlyCuda - I did the plum-bob/string layout to get these measurements. Al_A - Thanks for the link. I saw that google-ing around but did not read it all. I will now. Mr. P - It is a back half car. I have only made a couple trans-brake launches at part throttle & eased on the gas pedal. It did go straight. Last edited by HR3128; 08/17/16 04:38 PM.

Re: 4-Link Question [Re: HR3128] #2135211 08/17/16 04:49 PM 08/17/16 04:49 PM
Joined: Jul 2004 Posts: 653 Fredericksburg Va P plycuda mopar
plycuda mopar P Joined: Jul 2004 Posts: 653 Fredericksburg Va	did you try a string line down each side of the car get it straight with the rear wheels and see how it measures to the front wheels. that can tell you a lot. if the rears in crooked or if the rear is bent. but you need to make sure the toe is right first.

Re: 4-Link Question [Re: HR3128] #2135215 08/17/16 04:52 PM 08/17/16 04:52 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Since its a back half car I would check to make sure the front cross bar is square in the car

Re: 4-Link Question [Re: plycuda] #2135224 08/17/16 05:06 PM 08/17/16 05:06 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	I did not check from the front wheels. just got centerline points from the front chassis and at the crossmember for the 4-link. Laid a string out on the floor for the centerline and took rear axle measurements from there. I did not measure from opposite corners but I will now to see if the whole thing is square.

Re: 4-Link Question [Re: HR3128] #2135239 08/17/16 05:32 PM 08/17/16 05:32 PM
Joined: Nov 2004 Posts: 6,890 North Alabama M Monte_Smith master
Monte_Smith master M Joined: Nov 2004 Posts: 6,890 North Alabama	FIRST thing to do is make sure the 4 link crossmember is square in the car. Does no good to square the rear to the chassis, if chassis isn't under the car square. Assuming the brackets are square, placed on chassis and housing correctly.........meaning holes are same distance from housing centerline on both sides, clocked equally and brackets right on chassis, then you start squaring. First you make both bottom bars the same length and hang the housing and center it in wheel opening. Put upper left bar on and use this bar to set pinion angle. Then center housing from side to side under body and install wishbone. Upper right bar is last and with car on ground or platforms under tires, driver weight in seat, will install and be loose(no bind to get bolts in). The car is now square and has no preload. This is where you start. If it wants to go one way or another at launch, THEN you add positive or negative preload with upper right bar.

Re: 4-Link Question [Re: Monte_Smith] #2135331 08/17/16 07:41 PM 08/17/16 07:41 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	Thanks for the info. Looks like I'll be measuring & squaring up this thing this weekend.

Re: 4-Link Question [Re: Monte_Smith] #2135498 08/17/16 11:23 PM 08/17/16 11:23 PM
Joined: Jan 2003 Posts: 4,728 Moved to N.E. Tennessee GomangoCuda master
GomangoCuda master Joined: Jan 2003 Posts: 4,728 Moved to N.E. Tennessee	Originally Posted By Monte_Smith FIRST thing to do is make sure the 4 link crossmember is square in the car. Does no good to square the rear to the chassis, if chassis isn't under the car square. Assuming the brackets are square, placed on chassis and housing correctly.........meaning holes are same distance from housing centerline on both sides, clocked equally and brackets right on chassis, then you start squaring. First you make both bottom bars the same length and hang the housing and center it in wheel opening. Put upper left bar on and use this bar to set pinion angle. Then center housing from side to side under body and install wishbone. Upper right bar is last and with car on ground or platforms under tires, driver weight in seat, will install and be loose(no bind to get bolts in). The car is now square and has no preload. This is where you start. If it wants to go one way or another at launch, THEN you add positive or negative preload with upper right bar. I took Roy Hills 4link class almost 20 years ago and the procedure they taught was exactly the same as Monte explained. The Haas chassis they used had reference points built into it to measure the axle location from In theory, there is no difference between theory and practice. In practice, there is.

Re: 4-Link Question [Re: HR3128] #2135544 08/18/16 12:12 AM 08/18/16 12:12 AM
Joined: Dec 2005 Posts: 11,602 Fulton County, PA C CMcAllister Mr. Helpful
CMcAllister Mr. Helpful C Joined: Dec 2005 Posts: 11,602 Fulton County, PA	Yep, check the chassis and the brackets. I have had to make bars different C-C lengths, had driveshafts not run exactly parallel with the chassis centerline, fool around with housing locators, etc., because chassis or housing brackets were on wrong, body panels were not right, pinion C/L location in the housing was wrong or whatever. All to get the housing square and straight to the centerline of a car that the owner didn't want to cut apart and make right. Some people just can't read a tape measure and a level. Get the car up and level on a clean floor and start measuring and stringlining or lasering. Time consuming, but the alternative is to just center the tires between the fenders, get the housing squared close by stringlining the sidewalls forward and run it. Not what I would recommend If the results don't match the theory, change the theory.

Re: 4-Link Question - Update [Re: HR3128] #2136614 08/19/16 02:02 PM 08/19/16 02:02 PM
Joined: Jun 2006 Posts: 430 Michigan H HR3128 OP mopar
HR3128 OP mopar H Joined: Jun 2006 Posts: 430 Michigan	I got it sorted out. Stringlined the chassis. All the points looked correct. Starting measurement pic attached. I positioned the rear axle like Monte said. I think the whole problem was a misadjusted wishbone. It took a while to get it adjusted so that the bolts to the rear axle brackets would line up. I think whoever did this last moved the rear axle to fit the wishbone rather than adjust the wishbone to fit the axle position. Thanks.

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