LCA Pivot frame repair.

[buZy]

After further study this is what I found.... The LCA pivot very worn on the driver side. Ouch,

 

Help! What would be a good solution to fixing this problem?

Thanks!

 

[spotfitz]

I found the same thing about 2 years ago when I was rebuilding my '74's suspension. It was also on the drivers side. I had considered relocating the pivot point, as many have done, but decided to eventually get camber plates instead.

You can remove the washers and weld in new ones and/or relocate the pivot point while your at it. Replace the cross brace with another that looks better, which is what I did. Good luck.

[johnc]

What spotfitz said. Since you have to remove that crossmember to repair or replace it, I would got ahead and relocate the pivot up .750 to .875 inches.

[buZy]

Ok Move the pivot?... What does that do?.... And just where exactly?

That would change the camber and suspension angles? Requiring what to compensate?

I thought losing that hole location would be the last thing I would want to do.

Hmmmmm....

 

So I have to pull out the motor and everything..... just to fix this this?

 

Using a longer bolt could I not just TIG in some thick .125 plate type washers on the outsides of both sides of the crossmember and rework the hole?

If I pull out the rack and pinion I should have enough room to work the area.

 

Thanks Everyone!

[johnc]

Ok Move the pivot?... What does that do?.... And just where exactly?

 

Move the pivot up the distance measured above. For a lowered 240Z is puts the LCA pivot more in line witht he inner pivot of the tie rod. This reduces bumpsteer.

 

That would change the camber and suspension angles? Requiring what to compensate?

 

You would need to align the car.

 

I thought losing that hole location would be the last thing I would want to do.

 

If you're car is at or near stock ride height then I wouldn't make any changes.

 

So I have to pull out the motor and everything..... just to fix this this?

 

No, you just need to support the engine with a jack or blocks while you unbolt the crossmember and drop it out from under the car.

 

Using a longer bolt could I not just TIG in some thick .125 plate type washers on the outsides of both sides of the crossmember and rework the hole?

 

Probably, but its much easier on a bench and you're more likely to get everything lined up correctly if you're not on your back under the car.

[buZy]

Hey John thanks!

So ok I could the remove the member without pulling the motor. That's good news! I'm not set on stock ride heights and would like to lower my front end but only a bit really.

 

I dont know much about suspension angles (im leanring fast though) but rasing the LCA pivot in the car would result in more positive camber?

Something would have to be affected by the modification of the LCA pivot.

[johnc]

It doesn't lower the car. Ride height is determined by the spring/strut not the LCA.

[jkube]

I think what JohnC is saying is that moving the pivot point will correct the bumpsteer problem these cars have, even if you dont lower the car you'll notice a difference on the highway. Over bumps and in cross winds the car will track better.

 

I agree with JohnC that you should do it since your into fixing the pivot hole anyways.

 

Dropping off the cross member while supporting the motor works well. That way you can work on the bench to drill in the new holes and weld in some new spacer washers.

 

Picture: http://www.execulink.com/~jkube/Brians240z/Dec02pics/Image02.jpg

http://www.execulink.com/~jkube/Brians240z/Dec02pics/Image04.jpg

 

What I do is redrill 5/8" dia holes exactly 3/4" above ( Vertically straight up from) the existing holes. File the holes out a bit to allow the bolts to pass through. I think the bolts are just a bit bigger in diameter than 5/8"

 

Then chisel off the old spacer washers form the existing holes, and clean the burrs off the remaining spot welds.

 

Next get some new washers that are for a 5/8" bolt and file them out too so the bolts will pass through. These will be the spacer washers for the new holes.

 

The control arms will have to be ground down around the area where the pivot bolt passes through. This is because now that the pivot point is moved up the arm will come into contact with the cross member. If you dont understand, dont worry you'll see what I mean when you try to pre-assemble the 2 parts together.

 

So if you have been able to get the preassembly finished and there is no interference when moving the control arm up and down, you can install the new spacer washers onto the cross member and weld them to cross member.

 

Depending on the thickness of the new washers you may have to widen the gap between the washers so the control arm can fit in. I use a heavy hammer and a 1/2" diameter bar and bang out the cross memmber a bit to widen the gap.

 

Then it is a matter of reassembling all the parts back onto the car. The only alignment needed is to correct the toe-in.

[buZy]

Thanks Jeff and everyone for the help.

What seemed like a nightmare at first should now be a straight forward task to tackle. I'm way fired up on relocating the LCA pivots.

I'll keep everyone posted on my progess after yanking the K-member this weekend.

[buZy]

Here we go. K-member removed tonight. It went smooth and easy. Here is a picture in the parts washer. Next I will do the required repair. In the photo you can see the extra small hole drilled for the MSA v8 motor mount typical.....

The mount plate will be VERY close to the new raised pivot hole bolt. I will have to trim the motor mount corner to clear it.......

.........I sure hope relocating the pivots straight .875 up is the way to go here for running a lower suspension set-up.........

Wish me luck! I'll Need it!

[260DET]

Hardened steel washers are better than the mild steel ones sold in hardware stores for what you are doing. If welding them on try to keep the temperature down.

 

Oh and good luck with the job, take it steady no problem

[kalium99]

Just wondering if the measurements given apply to all first gen Z cars, or weather the LCA pivot points could have possibly changed thorugh the years which would infact make those measurements wrong for a lot of the Z's.

[johnc]

I suggest relocating the pivot point up .750". I've used .875" but my car was extremely lowerd at that time. To my knowledge the LCA pivot point is the same on the 240/260/280Z crossmembers but I haven't done a survey to be certain.

[JMortensen]

I would just like to point out that moving the pivot up 3/4 or 7/8 is not a true fix. To truly fix bumpsteer it needs to be measured with a gauge, and the correct amount of movement will change based on a number of factors like a bent car, modified suspension, bumpsteer spacers, eccentric camber bushings, etc. When I measured mine I only moved the pivot up about 1/2" and that was all that was necessary.

[buZy]

I can't measure my bumpsteer too easily but see your point. So anywhere from a half to .875? I have heard of others going to even 1 inch! ......hmmmm???

 

What would be a good number general distance to use for my application?

How about .600?

Very spirted street use. Also I will be using the AZ zcar front control arms.

Thanks!

[JMortensen]

That's the problem; there isn't any correct number. I don't know how or if the AZC arms are different from stock with relation to the pivot heights on the outboard end of the arm. It's obviously different than a stock arm since it uses a totally different ball joint, but whether the height from the arm to the pivot is the same... ??? If you just want to get it in the ballpark I'd say 3/4", but to get it right there is no substitute for measuring.

 

If you aren't racing you'll probably never notice IMO.

[2126]

Here's a little info to clarify the bumpsteer issue on early Zs (or any car for that matter) to the uninformed..... Basically the problem is the geometrey between the front pivot arm (transverse link) and the steering rack. Ideally you want the inner pivot point on the transverse link to be in the same horizontal plain as the pivot joint on the end of the rack. In this condition, both pivoting members will have the same (very similar, anyway) travel path and not induce bumpsteer into setup. The bumpsteer occurs when the two pivoting members are at different locations, relative to the horizontal plain. When the locations are not on the same plain, they take different travel paths when the suspension moves up and down. I know this is a very general description of what is going on and does not address all the variables, but it might shed some light on the subject to thoughs who have wondered what bumpsteer is about. In stock form, the Z's pivoting members are not in the same plain.....thats production engineering for you!!! Maybe someone can add to this statement, as I am not the greatest at explaining things sometimes.

[buZy]

Ok I see your point as where the steering outside tie rod end should on the same horz plane as the LCA pivot. So with that said how much can lower my front end as to how much I raise the LCA pivot?

Maybe this question is nonsence. Im just looking for a good ball park distance to move the LCA pivot up. Or how they relate to each other with given ride heights.

Like I said before there is no way I can easliy measure my bumpsteer or my true pivot locations to the car.

[JMortensen]

Do a search on bumpsteer. Maybe a year or more back I gave a pretty detailed explanation on how to do it on the cheap. I think total cost was ~$40 the way I did it.

 

If you REALLY don't want to measure, then just go 3/4" and you'll probably never know the difference.

[buZy]

Sweet! So I see it is possible to measure the bumpsteer. I would measure if it was all out racing but i'm just running the street scene. It seems whatever this distace raising the LCA pivot does help. Thanks everyone!