diff not square in chassis...any ideas?

[david lazarus]

Hi There

Had a full 4 wheel alignment done on my '38 yesterday, the front was good, just needed a slight toe adjustment. However my diff is not sitting square causing the car to "crab" slightly:eek: . I appear to be off track about 1/2 inch. I will loosen the u bolts and look to tweek it on the locator button under the spring, but is there anything else I should be checking...springs? Can the spring eye's open up over time...could this be where the extra distance has come from? Anyone else had a similar problem. The chassis is OK, no ripples etc indicating a smash.

Your comments are welcome

Thanks

Dave

[rearview]

Check the spring eyes bushings.

[Don Coatney]

Hi There

I appear to be off track about 1/2 inch. I will loosen the u bolts and look to tweek it on the locator button under the spring, Thanks

Dave

Dave;

I had a "locator" pin shear off causing me similar problems. Check it first.

[david lazarus]

hmmm good thought. These "should" have been new in when the chassis was restored, but as I did not do this part I cannot be sure. Good suggestion will check that out. Thanks Dave

[david lazarus]

Thanks Don, the locator pin was there 3 weeks ago !!! But will check again.

[david lazarus]

Had a look last night, measured rear rim to front rim on both sides to find a difference of only 7mm (1/3 inch). There is very no/little free play between the spring locator and the hole in the mounting pad on the diff, then checked the bushes...all fine there. I have a weak spring on one side, which causes the rear to have the slightest droop to one side, so..... I am now thinking of getting two new rear springs made and wonder why do I not get one made a little longer on the front half and square the rear up that way:rolleyes: .

Will this work do you think or have I missed the obvious (again!!).

Dave

[Plymouthy Adams]

I am not sure that this is the problem and the way to correct the situation. Outside of a major frame twist in the rear or enlonged front eye bolts..I can no reason to make a change here...get your book out and look at the frame section and use some tramel points and gauge or at least a plumb bob and tape on a smooth flat garage floor. Further the front eye is positioned in a fixed pernament loation..the flattening of the leaf spring will alter length but to have the difference you have would be an extemely distorted spring arch to the naked eye..the length of the spring and its subtle changes during road bounce is absorbed by the rear shackle and bushings. I have seen plenty of these units wore to the max...although by appearance you may have solid looking rear eye bushing, rest assured that if they have any age on them at all they are worn flat on one side..the appearace to the eye will not detect this on casual observation as the part you see is not subject to this wear. Further on this is that if in the past these shackle were subjected to metal to metal contact due to worn rear bushings I can assure you that the rear leaf eye is indeed enlongated and the shackle bolt will be flattened also...the combination of these two worn spots and add the worn bushing make for a lot of slop. If you spring eye is worn, these can be welded and re-bored for correct diameter hole..new shackes and bushings are available but can be a bit hard to find on a drop of a hat...you can build your own shackles out of grade 8 hardware...please if you go this route pay strict attention to the distance between the bolts on the shackle..do not lengthen these as it will cause the leaf spring to lose it profile at a very quick rate and as such you will see thae sag return to even new spring on the rear portion of the leaf...never ever try to alter the profile of the car from changing this shackle measurement..

[Don Coatney]

never ever try to alter the profile of the car from changing this shackle measurement..

Tim;

That is exactly what I did. Now you have me wondering?

Tell me more

[david lazarus]

hi Don, thanks for the info, your pick tells a story !!. My locators are intact, I now suspect that I have an odd-ball spring on one side, but will not know until I pull them both and check them, however one spring is certainly tired and just looks slightly different so I suspect this is the issue. I have spoken to the local spring shop who can make up a new pair for about $650 NZD. They can also place teflon pads between the leaves to reduce squeak and creak. I think that I will get new fronts as well, have them set so the car sits just a smidge lower than current.

tHanks for help...how did you manage to knock that diff off the pads???

Dave

[david lazarus]

Hi Tim,,hey would what you describe manifest itself in a general sideways slop of the diff when you rock the car from the side??

Thanks Dave

[Plymouthy Adams]

lack of a panhard rod installed on vehicle...

[Plymouthy Adams]

Technically the length of the shackle should only be changed with the installation of high arched recurved springs. The high arch are longer springs and as such will need shackles longer to allow the travel fo the spring to the rear during chassis movment due to road/load. These shackles should be part of the kit for application or at minimum shackles specs sent so you can build/alter your your shackles. Basically you are only entending this spring to the rear, retaining the geometry of the spring/chassis. The lifting action of the shackles being longer with regard to stock springs position the weight on the rear eye and in effect limits it rearward travel and dampening action built into the spring and will result in that weight being felt in the wrong place breaking down the rear leaf near the eye during flex during laod/road contions...Maintaining good shocks on the rear is the best way to limit flex/travel of the springs..

As for lateral movement in the rearend..this is normal and some cars have a lot..some have little. main part in this movement is nothing but the condition/composition of the rear shackle bushings. Items like polyurethane and graphite will hold this area more firm and limit your travel..ride will increase a bit in harshness. The ride effect is what this is all about..if you are truly into sport driving..you can even go with aluminum bushing here..installation of a panhard rod will however let you retain the factory smooth feel of the rear chassis plus remove lateral movement to an almost non-existant feel..