my rear end feels loose :)~ (help)

[Snail50]

see sig for suspension mods.

when cornering hard it feels like the axle will shift slightly, like the tire on the outer edge of the curve lags behind, then snaps forward. this sends a shimmy through the car, which, coupled with my worn-out steering mech, is very unsettling because it requires constant input & adjustment (like driving a boat).

WHat is the best traction device to positively locate my rear axle so it doesn't shift? I've looked into CalTracs, but they seem to be more for the drag.

Thanks.

 

[6Stang7]

Are you saying your axle moves around inside the housing?! Or is it that your whole rear moves side to side?

 

[3spd on floor]

sounds like you need a device to laterally locate the axle (side to side in the car). AKA: panhard bar. several companys make them, do a search and you'll find lots of info about them.

 

[gtss]

Can you confirm that the rear axle is actually moving, What do you have for a differential ?
if it is a Detroit Locker or similar, they can cause some very unusual sensations during cornering, particularly when cornering under load (ie: accelleration)

 

[Hack]

IMO, the first thing you should do is to replace any worn out suspension components, front and rear. That will give you a starting point. Worn out bushings can do a lot of strange things. What you're describing sounds like the result of just worn components.

While you're at it, I recommend you do a Shelby drop on the front end.

 

[Snail50]

thanks for the replies. the diff is the stock 67 8". I can't confirm that the axle is actually moving; it's more of a SOTP assessment (no pun intended).
For example: while making a sweeping right-hand corner, such as an on-ramp, the car feels perfectly flat and stable, except that I can feel what would best be described as a "twitch" coming in intervals from the rear of the car throughout the radius of the turn, as if the car itself is turning into the corner, but the axle wants to continue to go straight, then suddenly the axle will kick forward to catch up to the track of the car...then repeat the process until the car is on the straightaway.
The car is lowered all around (including UCA drop...all new stuff done within the last 8 months), and very little of the original suspension remains (LCA's & strut rods to be exact). I've checked all the nuts & bolts for tightness, too.

 

[Snail50]

trying to search, but getting a "forbidden page." website having problems? The last time I tried to search, the search function was down. I'll try searching this out at corner-carvers.com

 

[Hack]

thanks for the replies. the diff is the stock 67 8". I can't confirm that the axle is actually moving; it's more of a SOTP assessment (no pun intended).
For example: while making a sweeping right-hand corner, such as an on-ramp, the car feels perfectly flat and stable, except that I can feel what would best be described as a "twitch" coming in intervals from the rear of the car throughout the radius of the turn, as if the car itself is turning into the corner, but the axle wants to continue to go straight, then suddenly the axle will kick forward to catch up to the track of the car...then repeat the process until the car is on the straightaway.
The car is lowered all around (including UCA drop...all new stuff done within the last 8 months), and very little of the original suspension remains (LCA's & strut rods to be exact). I've checked all the nuts & bolts for tightness, too.

Ok so it's just the steering that is worn out? I'm not sure whether that could be your problem or not. Are you waiting to do a big upgrade like a rack&pinion? Otherwise, a rebuilt steering box doesn't cost much.

I assume it's aligned too?

What specs is it aligned to? What kind of tires and size and are they new? Is the rebuild with all stock rubber components or some other kind of bushings/material? If poly, did you lubricate them and how did you do that?

As you can tell, I don't think a stock suspension in good condition should do what you're saying, unless something is wrong. Maybe there is a problem in your stock rear end, but I'd expect you to hear some kind of noise from it.

 

[6Stang7]

thanks for the replies. the diff is the stock 67 8". I can't confirm that the axle is actually moving; it's more of a SOTP assessment (no pun intended).
For example: while making a sweeping right-hand corner, such as an on-ramp, the car feels perfectly flat and stable, except that I can feel what would best be described as a "twitch" coming in intervals from the rear of the car throughout the radius of the turn, as if the car itself is turning into the corner, but the axle wants to continue to go straight, then suddenly the axle will kick forward to catch up to the track of the car...then repeat the process until the car is on the straightaway.
The car is lowered all around (including UCA drop...all new stuff done within the last 8 months), and very little of the original suspension remains (LCA's & strut rods to be exact). I've checked all the nuts & bolts for tightness, too.

If you axle itself is moving, then your bearing could be worn out. CHECK IT ASAP! If the bearing fails, the axle can slide right out of the axle housing while you're driving, and I think we can all assume that would be bad times.

 

[Snail50]

Hack: I replaced the entire suspension with the Grab A Track kit with poly bushings; I lubed the bushings with the grease which came with the kit.

Yes, the steering is very loose, but that causes its own set of problems: wandering in the front end. However, the wandering from the front is no doubt compounded by the "hip-fakes" from the rear.

I'm planning to first try to adjust the slop out of the stock steering box; if that doesn't work, I'll either replace the box with a new FR box, or do an R&P conversion. I haven't decided which one yet, though.

It is aligned, done to the specs whic came with the GW Neg roll kit. I forget what the specs are, but I had it dialed in to "Street" specs rather than "Track."

Tires are new Nitto NT555s.

No noise from the rearend; axle bearings look good (checked them when I did the 4 wheel disc conversion).

 

[Snail50]

If you axle itself is moving, then your bearing could be worn out. CHECK IT ASAP! If the bearing fails, the axle can slide right out of the axle housing while you're driving, and I think we can all assume that would be bad times.

very bad times indeed. I don't think the axleshafts are moving, rather the entire assembly. And I'm not talking several inches of movement, rather just enough to feel a slight kick up through the body, and shimmy the car enough that I have to compensate with the steering very slightly.

 

[mustangdave]

Check the frt. and back mounting locations of the leaf springs to see if the mounting holes are worn allowing the springs and axle to shift. Also look at the frt. and rear bushings to see if any are trying to come out. If all checks out, mark the locations with tape of some kind and drive until you experience this "shift". Crawl back under and see what moved; you should be able to see where the tape has been curled up or moved. The most basic answer is that you have some loose lugnuts, so check that first! If none of that pans out, check your u-joints for impending failure.

 

[mustangdave]

my rear end feels loose ~ (help)

Oh what the heck, I can't pass it up. Try some Pepto Bismol.

 

[mustangdave]

my rear end feels loose ~ (help)

Oooh, one more: stop having gay sex or find a "smaller" life partner. J.K. I kill myself

 

[LMan]

AIDS avoidance: sit down and keep your mouth shut.

 

[Snail50]

LMFAO. Thanks for all the help, too. I went through and checked all the nuts (heh heh) and bolts, and everything is tight. One thing I've noticed is that the more work I do to the suspension, the more obvious the car's weak points are...like right now the steering slop is glaringly obvious, whereas it wasn't so noticeable before I started working on the car.

So: if everything in the rear checks out, what would be the best setup to "firm-up" the rear? Caltracs & Panhard bar together? I'm setting the car up mainly to handle, but if I ever get some power under the hood, I might take it down the 1320 a couple times just to see what it can do.

I'm going to search some more, but if anyone has an answer or a link off the top of their head, please feel free to post it.

THanks.

 

[Snail50]

my rear end feels loose ~ (help)

Oooh, one more: stop having gay sex or find a "smaller" life partner. J.K. I kill myself

(hairless chihuahua voice on) yipe yipe yipe yipe yipe (hairless chihuahua voice off)

 

[Hack]

I don't think a panhard bar will fix your problem. The panhard bar is a good addition to a rear leaf suspension to improve cornering, but what it does is to allow you to tune the roll center height. It prevents the rear axle from moving laterally, but the rear leafs also do that.

There's nothing about a stock Mustang rear leaf suspension that will cause a "twitch" in the middle of a sweeping turn. Something is binding or loose. I suspect the culprit may be a urethane bushing. They tend to be sticky, and they don't give.

I've been reading posts in the Corner-carvers forums, and excerpts from "Chassis Engineering" by Herb Adams to try to find information to help you. One thing I found in the book is this (page 68) "under no circumstances should you use urethane bushings on the front spring eye (of a leaf spring), as they will bind up and prevent the body from rolling in relation to the axle."

So that's my guess - your urethane bushings are the problem.

edit: Caltracs are good for drag racing, if that's what you want to do. Panhard is good for cornering.

 

[67GTA-FB429]

Snail: Do you have subframe connectors? I know you have a rear sway bar. Maybe I missed it, what kind of differential do you have? Open, posi, detroit?

 

[Snail50]

Hack: you might be right on about the bushings, because I've noticed that sometimes when I park the car, one side of the rear will sit a little higher than the other, and if I bounce it a couple times, it will even out; other times I park it and it sits level. So maybe the leaf spring bushings are sticking somewhat.

HOwever, in a long corner where the load is constant, I think the "unsticking" would only happen once, rather than repeatedly, as it seems to be doing...in a long corner which curves consistently in once direction, there would be no opportunity for the bushings to "reload" themselves.

Sorry if my descriptions are vague...I'm neither an engineer nor a mechanic, so I'm using generic terms which best describe the problem.

Buzz: I have GW tubular subs, welded in. The diff is the stock 8" open.

Thanks all, I appreciate the help.