I have been searching for a while and i have read the huge thread on 1st gens rear suspension geometry issues. all i'm looking for is fixing the plunging drive shaft. do adjustable lower control arms fix that problem?

thanks

 

Can you give a better description of "plunging drive shaft"? Not sure I know what you mean.



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Is it hitting the tranny?

 

changing the length of the arms will change pinion angle, if thats what you are asking

 

yeah that is what i figured. has anyone done calculations to show how long they have to be extended to fix the pinion angle?

 

due to the ride height being so low the drive shaft may be pressing into the tranny and vice versa, pushing back on the diff

 

not that i know of, because it depends on how much you lowered it.

if you google 4 link calculators, there are a couple, its hard cause we know the lengths of the arms, but nothing else. so to get em to work, you need to do some homework.

 

The stock upper arms are about 1/2 the length of the lowers, so the rear end moves closer the tranny and the pinion angles down if you lower it. It might help more to ditch the stock upper links for a 3-link or longer 4-link. Making the lowers longer will just make the problem worse. The re-speed adjustable lower links are nice, look just like the ones I made for my car...

 

yeah i agree, ideally you make the upper links longer...

 

...or reposition the anchor points for all four to recenter their arcs.

 

i knew this was a big job and i thank all of you for your input. i'm not sure if this makes a difference but my car is really low and has 200lb springs on the rear. there isn't much suspension travel, so would there be a way to correct this without having to do a rebuild of the rear linkage?
also, just a thought, would shortenting the drive shaft work if i don't have a lot of suspension movement in the rear?

 

Shortening the driveshaft would work. Not sure if that would be a cheap prospect. The only other option is to raise the rear end a bit or go tri link. Gforce sells them fairly cheap, or you could just build your own. From what I've read they are worth it.

 

I asked if the driveshaft was hitting the tranny because I have a shortened driveshaft by 3/4" just sitting here. It's a 79-82 small pinion flange so it probably wouldn't fit yor 84 car with the large flange.

 

hey sorry i never answered your question. i'm not sure if its hitting the tranny but ever since i lowered the car my rear end has been making a rotating metal on metal rubbing noise. i'm pretty sure its something to do with the diff. possibly because the driveshaft is applying pressure on the diff/tranny because of the suspension geometry

 

Its quite possible the driveshaft is rubbing on the exhaust heat shield. Do you 'feel' the rubbing that you're describing? I had a small vibration/noise similar and the driveshaft (mazdatrix) combined with just the racing beat lowering springs caused the shaft to rub on the heat shield.

 

I don't seem to be having any issues like this with my car, and its pretty damn low... If you're hearing noises, feeling grinding, then I'd check for rubbing on the driveshaft as suggested earlier.

As far as correcting the geometry to prevent binding, it sounds like you're about 85% of the way toward doing things my way. That is, reduce the body roll and you eliminate the potential binding issues.

What shocks and sway bars are you running? Also, what spring rate on the front springs?



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i'm almost positive that it isn't the heat shield. i've checked the driveshaft a bunch of times to see if there are score/rubbing marks on it and its unharmed. also i can't feel the noise. i just hear it.

kentetsu, i'm pretty sure you and i are around the same ride height. as far as setup i have illuminas all four corners, 375lb springs in the front and 200lb on the rear. there is next to no body roll on my car and i'm positive there isn't any binding with the geometry seeing that there isn't enough movement in the system due to the springs.

 

If you are running Illuminas on the rear, then at least the back of my car is quite a bit lower than yours. I had to switch from Illuminas on the rear to some short Bilsteins, because the Illuminas were way too long for the ride height I was after.

So, unless there is some significant difference between our cars, I really doubt that your issue is caused by your ride height. Just a thought.