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Rear axle shaft question (1979)

Craig1979

Active member
Joined
May 12, 2001
Messages
28
Location
Seattle
Corvette
1979 L82
I've been chasing some handling problems with my 1979 Corvette for awhile now (car randonly wanders during freeway driving, requiring continual steering input to maintain centered lane travel). Even though it's only got about 45,000 miles, I've rebuilt the front suspension with new balljoints, tie rod ends, idler arm. Also had the steering mechanism checked and adjusted. I'm now focusing on the rear suspension. With the rear tires off the ground, by applying hand pressure I'm able to create noticable movement at the top of the tire. It appears that the axle shaft have about an 1/8" of in-out movement where they enter the differential housing. Is this movement normal? Is there a specified clearance for this movement? I'm guessing this might contributing to a camber change in the rear tires while driving. Anyone have any similiar problems, observations, or knowledge to clear up this question? Thanks for the help, Craig.
 
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billagroom

Guest
Hi my 79 wanders a bit but only on roads rutted by big trucks. I was told it was from having wider than stock tires. The cornering power is worth the wide tires. I just watch the ruts and be careful when I'm on those roads. Stay in the middle of the rut and hang on when you pull out of it. Half the battle is knowing why she squirms. Bill Groom:J
 
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Scott81

Guest
Craig,

It sounds like your side yokes need to be replaced, or your trailing arm bushings are bad. Side yokes are only held in by a "C" clip, stock yokes usually wear out at the tips and then you start having problems. If the yokes turn out to be the problem get the heavy duty ones, they are worth every penny especially if you have to rebuild the rear yourself...it's a pain! If your t-arm bushings are bad you can usually tell by pressing on the gas at cruising speed, the back end will sway out to one side and when you let off the gas it will sway back the other way. One other thing it could be, but I doubt since there isn't a squealing or grinding noise would be your wheel bearings....if those are bad fix them yesterday! Whatever the problem, it sounds like it needs to be fixed asap.

Here's some rear suspension info for you; http://www.sharkwerkes.com/sharktank/tech2/rear1.html

Scott
 

Yoda

Well-known member
Administrator
Joined
Oct 12, 2000
Messages
4,885
Location
Amarillo, TX
Corvette
1981 UL5
Craig1979 said:
I've been chasing some handling problems with my 1979 Corvette for awhile now (car randonly wanders during freeway driving, requiring continual steering input to maintain centered lane travel). .... . With the rear tires off the ground, by applying hand pressure I'm able to create noticable movement at the top of the tire. It appears that the axle shaft have about an 1/8" of in-out movement where they enter the differential housing. Is this movement normal? Is there a specified clearance for this movement? I'm guessing this might contributing to a camber change in the rear tires while driving. Anyone have any similiar problems, observations, or knowledge to clear up this question? Thanks for the help, Craig.

Craig Welcome to The Corvette Action Center
  1. 12:00 and 6:00 movement should be no more than .008"
  2. 9:00 and 3:00..... movement should be no more than .008"
Scott81 If your t-arm bushings are bad you can usually tell by pressing on the gas at cruising speed, the back end will sway out to one side and when you let off the gas it will sway back the other way.
billagroom Hi my 79 wanders a bit but only on roads rutted by big trucks. I was told it was from having wider than stock tires.

Scott and Bill are right on with those quotes, also be sure to have an all 4 Wheel Alignment done every so often.

Good Luck Craig, the rewards of a suspension being "in tune" are worth the $$$$ and the skinned knuckles.
 
7

78SilvAnniv

Guest
where the road takes you...

It isn't necessarily only wider tires that will 'help' you around the road! My stock tires have been known to help me change lanes...it's very surprising when it happens! It only needs to happen once for me to memorize the spot and watch/prepare for it. The worst spot I encountered was in Oregon, I-84 East about 45min out of Portland...and in the rain?!...tcha!
I have grown accustomed to this Corvette 'quirk' and I drive warily until I know the road and what it is likely to bring. So far, the few roads I've driven here in GA are well kept and give me no surprises.
Silver
 

chuck

Well-known member
Joined
Feb 7, 2001
Messages
193
Location
Tallmadge,Ohio
Corvette
1977 Dark Red Coupe/Buckskin 04 Spiral Gray/Gray
Re: Re: Rear axle shaft question (1979)

Rare81 said:



[*] 12:00 and 6:00 movement should be no more than .008"
[*] 9:00 and 3:00..... movement should be no more than .008"


Rear wheel bearings are not checked by this method. A dial indicator is mounted on the spindle flange ,in and out movement should be .001 to .008.If it is more than .008 you need to add shim to bring it into tolerance. Chuck
 

Yoda

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Messages
4,885
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Amarillo, TX
Corvette
1981 UL5
Re: Re: Re: Rear axle shaft question (1979)

chuck said:
Rare81 said:



[*] 12:00 and 6:00 movement should be no more than .008"
[*] 9:00 and 3:00..... movement should be no more than .008"


Rear wheel bearings are not checked by this method. A dial indicator is mounted on the spindle flange ,in and out movement should be .001 to .008.If it is more than .008 you need to add shim to bring it into tolerance. Chuck

Chuck thanks for the info :cool
BudD
:w
 

Craig1979

Active member
Joined
May 12, 2001
Messages
28
Location
Seattle
Corvette
1979 L82
Thanks for insight

Chuck, 78SilvAnniv, Rare81, Scott81:
Thanks guys for the response to my question on rear suspension "wander". As a result I've done some further inspection and e-mailed a couple of you directly. The movement of my tire at the 12:00 and 6:00 position (with weight off) appears to be caused by in and out movement of the side yolks into the center differential. Doesn't appear that I have excessive slop in the wheel bearing/trailing arm assembly. I'm going to post a new thread to see if anyone else can tell me what the operating clearance should be for the half shaft yolk (I've got about .065" in and out yolk movement in each side). Never looked at a factory Assembly Instruction Manual to see if this type of info would be there. I'll ask further. Thanks much to all, Craig
 
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Scott81

Guest
Craig,

If you want good info on your rear yokes talk to Art at Van Steel, http://www.vansteel.com/ or Dave at Guldstrand http://www.guldstrand.com/ both are very knowledgeable and should be able to tell you the correct specs. Don't know if your AIM is a good enough copy and it might not be in there, try a GM Shop Manual for a 79, that should have it.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
In short:
1/8th-in. end play for the stub axles is way too much. The rear axle assembly needs to be overhauled. It's possible you'll need to replace the axles.
 

Jack

Well-known member
Joined
Dec 27, 2000
Messages
1,825
Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
? confusion

It seems there may be some confusion here. At first it seemed that Craig reported he has 1/8" (0.125") in-out play at the inboard stub axles that fit into differential carrier. Then later, Craig seems to report he has 0.065" in-out play at the same inboard stub axles that fit into differential carrier.

I do not know what the correct tolerances are for inboard stub axles (splined w/ circlip relief at differential end and having a yoke for u-joint at opposing end).

Nor do I know what the correct tolerances are for the outboard wheel spindles (splined & threaded for a 4-bolt flange at one end and having a round 5-stud flange at wheel).

I think Craig is trying to alleviate possible confusion by starting a new thread titled Help-need specs for side yoke clearance at http://corvetteactioncenter.com/forums/showthread.php?threadid=2112

I'd like to know the proper tolerance too!
JACK
 

Craig1979

Active member
Joined
May 12, 2001
Messages
28
Location
Seattle
Corvette
1979 L82
Any other good info??

I've recieved some good suggestions for locating the specs I believe I need. Thanks much.
From the nature of responses maybe some clarification is in order. My first stated in-and-out yolk movement measurement of 1/8" was a rough measurement accomplished with a tape measure and an eyeball. The subsequent .065" measurement was done with a dial indicator and is of course much more accurate.
Not sure how a small yolk movement could damage the axles-but will explore further?
(My second thread was a result of mere unfamiliarity with this new website.)
With the strut rods in good shape and tight, it would seem logical that the camber setting of the rear wheels would change depending on whether the axle shaft assembly (ie: spindle/wheel) were pushed into the differential or pulled away from the differential (as in going around a corner or over an irregular road surface). Maybe the change is not sufficiant to affect the "feel" of the car, or maybe the camber change to the unloaded wheel actually helps handling? The answer is beyond my experience level at this time.
Hopefully some of the pros can help resolve this issue. Thanks, Craig.
 
7

79blueshark

Guest
Everyone here seems to have a good idea of your problem. I just replaced the side yokes on my 79 as it had roughly the same amount of play as yours did. I called around and found out from several corvette shops that 79 is a bad year for side yokes. Apparently they were soft from the factory and wore out quickly. I replaced mine with new hardened tipped ones and after the installation there was no play what so ever. You can change them in just a few hours and be on the road to the alignment shop the same day. Good Luck
 
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GreyGhost

Guest
W-I-D-E TIRES

I am no expert on 1979 corvette tolerances and/or adjustments and can give no advice on such.

I do want to correct a common misconception about wide tires. A wider tire should not be the cause of handling problems in your car. The fact is that a wider tire will increase your car's handling capabilities. I think that what we're dealing with is that a wide tires' patch (road contact and gripping surface) will amplify misalignments and other loose or worn suspension parts. Simple front end adjustment such as caster, camber and toe-in toe-out often cause mishandling problems that are blamed on other components. I'm always an advocate of check the simple and obvious things first, then check the more difficult possibilities.

W-I-D-E-R IS B-E-T-T-E-R !
__________
Al
 
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Doug78

Guest
The road surface is an important consideration in this. I live in the Portland area and I-84, I-5, OR-26, OR-8, OR-10, etc. all have terrible ruts in them, from studded tires. When I'm not in the ruts my 78 runs straight, true and solid. But, get in the ruts and hang on. :eek Whether changing lanes or just braking it's all over the road. I know it's not something wrong with the vette because both off my trucks do the same thing as well as friends and coworkers vehicles. Evaluate when the car gets squirrley and then you can reason out what forces might be moving which parts.
 
7

78SilvAnniv

Guest
I hear you Doug!

The first time I drove hubby to the airport in Portland and drove home (to Goldendale, WA) on I-84....those ruts sent me all over my lane and part of the next one! No cars were near me, but I remember the vehicles behind me behaved as tho I were a DUI on the loose!
I noticed excessive inner tire wear on my rear tires about 8 years ago that was due to the yokes having worn out. We replaced everything and its been fine since...Unfortunately, I thought it was an alignment problem and took it in several times before a mechanic caught the yoke. (sorry, bad pun) I am learning much more about my car here at CAC than I could get out of a manual. Real life experiences with real people experiencing and solving them in easy to understand terms.
I am getting braver about getting greasy and doing it myself...makes me feel good!
Silver aka: Heidi
 

Craig1979

Active member
Joined
May 12, 2001
Messages
28
Location
Seattle
Corvette
1979 L82
Contact for further info

78 SilvAnniv and 79Blueshark:
Thanks for the input reference your experience with the side yokes. Un-informed repair shops seem to be easy to find. By helping each other out we can certainly save unnecessary time and expense.
If each of you doesn't find e-mailing me directly, I'd like to discuss more thoroughly your experiences and what is involved in changing the rear side yokes.
I've had a lot of hand-on experience with automotive mechanical systems, but not with the Corvette IRS. Hope to hear from you both. Thanks, Craig (cdns4w@aol.com)
 

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