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how do shims work with rear leaf pack

L

lapaul

NAXJA Forum User
Location
los angeles
I just installed new rear leaf springs, and I think I am detecting vibration when accelerating at low speed.

I have an extended shackle,

could shims help,

I can't figure out how putting a shim on the lef pack which is above the axel would would improve the driveshaft angle--it looks tome like it would just raise the rear of the frame in relation to the front (right now my rear is lower than front ) but I can't see how raising the rear would help with the drive shaft angle

Am I correct in believing that it is the total driveshaft angle that affects vibration.

Bottom line is could putting shims help.
 
um... the shim goes in between the spring pack and axle perch... (large end back) and rotates the axle tubes and therefore the pinion upwards. this decreases the angle between the DS and pinion and effectively lengthening the ds for better spline engagement at the TC end.

ps. Mine go in this weekend.
 
lapaul said:
I just installed new rear leaf springs, and I think I am detecting vibration when accelerating at low speed.
Click to expand...
The vibration might be caused by axle wrap: check that out.

I have an extended shackle,

could shims help,

I can't figure out how putting a shim on the lef pack which is above the axel would would improve the driveshaft angle--it looks tome like it would just raise the rear of the frame in relation to the front (right now my rear is lower than front ) but I can't see how raising the rear would help with the drive shaft angle

Am I correct in believing that it is the total driveshaft angle that affects vibration.

Bottom line is could putting shims help.
Click to expand...
Check your angles: with no SYE the angles between the pinion and the driveshaft and between the output shaft (slip yoke) and the driveshaft should be equal to each other. IIRC that often means that with an extended shackled (which rotates your pinion up) you would have to put the shim with the fat end forward to bring down the pinion to return to the original angle. In any case, unless you measure the angles your guess is as sgood as anyone elses (btw, don't look at the frame when you're looking at the angles, just look at the tcase output, axle output and the driveshaft)
 
Roll-over said:
um... the shim goes in between the spring pack and axle perch... (large end back) and rotates the axle tubes and therefore the pinion upwards. this decreases the angle between the DS and pinion and effectively lengthening the ds for better spline engagement at the TC end.

ps. Mine go in this weekend.
Click to expand...
That is true if you have an SYE. If you have a slip yoke the angles should be equal. Now if you're doing that to reduce the vibes caused due to "shallow" spline engagement by lengthening shaft, you should get a longer shaft before playing with shims.
 
Kejtar said:
The vibration might be caused by axle wrap: check that out.

A common pratice to deal with that is, getting shims 1-2 degrees below the neutral mark. Whet your axle twists up during acceleration the ponion angle will be correct.

Check your angles: with no SYE the angles between the pinion and the driveshaft and between the output shaft (slip yoke) and the driveshaft should be equal to each other. IIRC that often means that with an extended shackled (which rotates your pinion up) you would have to put the shim with the fat end forward to bring down the pinion to return to the original angle. In any case, unless you measure the angles your guess is as sgood as anyone elses (btw, don't look at the frame when you're looking at the angles, just look at the tcase output, axle output and the driveshaft)
Click to expand...

You can buy a angle finder that makes this easy I would try Nappa, or any big auto parts store. A word of advise is they may have to order it so don't go to get one after your rear end is off.
 
scoobyxj said:
You can buy a angle finder that makes this easy I would try Nappa, or any big auto parts store. A word of advise is they may have to order it so don't go to get one after your rear end is off.
Click to expand...

Harborfrieght normally has them for like 5 bucks
 
I second that you probably need to put the shims fat-end forward to compensate for the shackles.

If you don't have enough slip-yoke engaging or the yoke is in danger of binding at droop then a YJ yoke is a cheap patch. It is longer and has more open "ears"
 
Chris S said:
I second that you probably need to put the shims fat-end forward to compensate for the shackles.

If you don't have enough slip-yoke engaging or the yoke is in danger of binding at droop then a YJ yoke is a cheap patch. It is longer and has more open "ears"
Click to expand...
attachment.php

YJ left, XJ right - 5/8" longer - be wary - this may not help much..
 
Chris S said:
If you don't have enough slip-yoke engaging or the yoke is in danger of binding at droop then a YJ yoke is a cheap patch. It is longer and has more open "ears"
Click to expand...
Wrong, the YJ yoke is only marginally longer. While it is great to take care of a potential binding problem, it will not extend the driveshaft enough for it to matter. If you need longer driveshaft look at the boneyards as depending on teh model and tcase tranny options some of them are longer then the others. Also you can get it lengthened at a driveshaft shop.
 
Sears carries a quality magnetic angle finder, cheap as I remember, dial, excellent, just don't toss it around like a wrench (like I did/ ugh... still do).
 
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