74 rear end ride height problem, help
Thread Starter
Racer
Joined: Nov 2002
Posts: 307
Likes: 0
From: Denver Colorado
74 rear end ride height problem, help
On my 74 (the yellow one), I’m about to jump into a major rear end redo, and have a couple of questions.
I will be doing T/A’s, shocks, total exhaust system, brakes,U-joints, etc. (plus all the cosmetic things, ie: paint, etc.)
I have new Firestone Indy’s ready to go on at the end, so here’s where the issue is.
The back end is about 1 and a quarter inch higher than it should be. (per service manual specs. BTW, the front ride height is right on spec) This may be somewhat due to the slightly larger tires (which will be replaced) presently on the rear than the front. But, by the tire size calculator at: http://www.miata.net/garage/tirecalc.html, this only accounts for about a half inch of the high rear end issue.
So I’m still about ¾ inch high in the back.
So, when installing all the new parts, how do I fix this? The spring is a 7 leaf. Didn’t I read somewhere that is a “heavy duty” spring? Is that part of the ride height problem? Or are the spring mounting bolts (at each end of the spring) the problem? Or is it something else I’m not thinking of.
Any thoughts/ideas would be much appreciated.
Tnx, Bill
I will be doing T/A’s, shocks, total exhaust system, brakes,U-joints, etc. (plus all the cosmetic things, ie: paint, etc.)
I have new Firestone Indy’s ready to go on at the end, so here’s where the issue is.
The back end is about 1 and a quarter inch higher than it should be. (per service manual specs. BTW, the front ride height is right on spec) This may be somewhat due to the slightly larger tires (which will be replaced) presently on the rear than the front. But, by the tire size calculator at: http://www.miata.net/garage/tirecalc.html, this only accounts for about a half inch of the high rear end issue.
So I’m still about ¾ inch high in the back.
So, when installing all the new parts, how do I fix this? The spring is a 7 leaf. Didn’t I read somewhere that is a “heavy duty” spring? Is that part of the ride height problem? Or are the spring mounting bolts (at each end of the spring) the problem? Or is it something else I’m not thinking of.
Any thoughts/ideas would be much appreciated.
Tnx, Bill
Thread Starter
Racer
Joined: Nov 2002
Posts: 307
Likes: 0
From: Denver Colorado
Re: 74 rear end ride height problem, help (patsnitrovette)
patsnitrovette, I ordered the "stock" bolts, not arrived yet, so I'm not sure how they compare in length with what's on there now. Is that the only ride height adjustment on these?
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Re: 74 rear end ride height problem, help (Bill Oxley)
You can order the lowering kit bolts from Ecklers, Zip etc.. or you can go and buy some grade 8 bolts from a local hardware store.
Here is some saved info regarding this subject from previous posts:
________________________________________ ________________________
Forum member-
I replaced the stock 6 and 11/16 inch bolts on my car with Grade 8 9/16" diameter x 8" length *recommend to get the steel locking nuts if possible, not nylon locknuts*. (Many have used Nylon locknuts with success though).
It lowered the car about 1-1/2. Then fix the camber angle to realign rear camber. As you decrease the ride height of the rear, the amount of negative camber will increase
________________________________________ ________________________
From Van Steel-
As long as there is a slight Half-Shaft angle, you will be OK.-Van Steel
________________________________________ ________________________
Brent...
Here is some saved info regarding this subject from previous posts:
________________________________________ ________________________
Forum member-
I replaced the stock 6 and 11/16 inch bolts on my car with Grade 8 9/16" diameter x 8" length *recommend to get the steel locking nuts if possible, not nylon locknuts*. (Many have used Nylon locknuts with success though).
It lowered the car about 1-1/2. Then fix the camber angle to realign rear camber. As you decrease the ride height of the rear, the amount of negative camber will increase
________________________________________ ________________________
From Van Steel-
As long as there is a slight Half-Shaft angle, you will be OK.-Van Steel
________________________________________ ________________________
Brent...
Burning Brakes
Joined: Jul 2000
Posts: 963
Likes: 0
From: melbourne,Australia
Re: 74 rear end ride height problem, help (Bill Oxley)
If you want to do the job "properly" you need to take out the spring leaves and have them retempered to adjust to the correct ride height,that is assuming the they are otherwise in the correct mounting position with appropriate hardware...it is a very fiddly job trying to guess how much to vary the springs when they out of the vehicle and then guess how much the weight of the car will bend them,but it can be done and has the good effect of letting them all get checked,new inserts between them and all new bolts so that everything is in good shape......john :chevy
Thread Starter
Racer
Joined: Nov 2002
Posts: 307
Likes: 0
From: Denver Colorado
Re: 74 rear end ride height problem, help (jdunne)
Thanks to all that have responded. Seems like, per responses, there is some room to work with in the outside spring bolts. I still do not know if the “installed” bolts are stock or not, but will know soon when the replacement bolts are received, so I can compare.
So it appears that longer bolts will(or can) possibly set the car to a lower position. I see nothing in the shocks, spring, t/s’s, or any other rear end part that seems anything but stock, but it is sometimes hard to tell just from looking at the installed parts. I’m still somewhat focused on the 7 leaf spring vs 9 leaf spring, as the 9, as I understand it, is stock (or standard) for this year. But I can’t imagine that a “heavy duty” spring would increase the ride height that much.
And John, interesting comment. I appreciate your input. But question for you. I can’t quite figure out how an “old” spring would ride higher than “new” or “newer” spring. Seems like “retempering” the spring would only make it ride higher, as an old spring would have settled, if anything. But I appreciate your thought and will still consider that option. Any more input on the subject would be much appreciated.
Thanks again to all for input. But, somehow or other, I have to get this thing down another ¾ inch or so in the rear.
So it appears that longer bolts will(or can) possibly set the car to a lower position. I see nothing in the shocks, spring, t/s’s, or any other rear end part that seems anything but stock, but it is sometimes hard to tell just from looking at the installed parts. I’m still somewhat focused on the 7 leaf spring vs 9 leaf spring, as the 9, as I understand it, is stock (or standard) for this year. But I can’t imagine that a “heavy duty” spring would increase the ride height that much.
And John, interesting comment. I appreciate your input. But question for you. I can’t quite figure out how an “old” spring would ride higher than “new” or “newer” spring. Seems like “retempering” the spring would only make it ride higher, as an old spring would have settled, if anything. But I appreciate your thought and will still consider that option. Any more input on the subject would be much appreciated.
Thanks again to all for input. But, somehow or other, I have to get this thing down another ¾ inch or so in the rear.
Burning Brakes
Joined: Jul 2000
Posts: 963
Likes: 0
From: melbourne,Australia
Re: 74 rear end ride height problem, help (Bill Oxley)
Bill,obviously you are correct in that you would expect the original spring to settle,it clearly cant increase the ride height of its own volition,so i am assuming some previous owner has modified it in some way,probably by adding or changing leaves(perhaps to clear some larger tires)...i had issues with my 74R cracking 2 leaves where the diff ears are and as part of the fix made new leaves then found out that they can be tempered in various ways to raise or lower the ride height even though they were identical to stock length....i am guessing at a spring leave mod since you said that all mounting points,hardware and sizes seemed to be original(if that is correct there really isnt much else it could be).....hope it helps......john :chevy
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Racer
Joined: Sep 2002
Posts: 389
Likes: 0
From: san diego ca
Re: 74 rear end ride height problem, help (Bill Oxley)
Just be very wary of the "upgrade" to fibergalss mono-springs. A bunch of us have done this and the result is a jacked up rear-end, way too high, too much so even for 8" bolts! There's a thread lingering on this forum (started by Kid Vette, multiple multiple pages), but I don't know how to include a link for it.