Another 9” question

[Hipopinto]

Hey all

I’m building a rear for my pinto

I have a narrowing kit and I’m building a perch mounting jig

I have the new housing ends and I’m wondering how do the mount in relation to the differential?

Also when supporting the perches level where should the “tilt” on the differential mounting surface be? (Pinion angle)

I’m building this rear to accommodate bigger tires and caltracs

Any input would be great

Dave

[jayb]

The right way to do that is to have the engine and trans installed so that you can measure the angle of the transmission centerline.  Then you can set the differential on the leaf springs, with the spring perches underneath, and rotate the pinion of the differential so that it is where you want it relative to the transmission centerline.  Once you have that in position, tack the spring perches to the axle housing.  For Cal-Tracs you should have about a 2 degree down angle on the pinion centerline, as compared to the transmission centerline.  So, if the transmission is pointing down 2 degrees, the pinion angle should be level.  This should also be done with the car at ride height, resting on the suspension.  It's one of the last things I do when I'm setting up a rear end, because usually the car has to be mostly assembled to do it correctly.

As far as the axle housing ends, their position isn't that critical, I usually put them parallel to the pinion.  If they are angled up or down a few degrees, no big deal.

[Hipopinto]

Jay

Thanks for the quick reply

Just for my own knowledge though, when you support a factory housing at the perches and it it level where doe the top of the housing sit? Would the pinion point down meaning housing tilted “in” or pinion point slightly up meaning housing tilted “out”?

I just about have the perch jig complete and I’m thinking about the end placement

The jig for the perches will also do well for straightening and aligning as well

Thanks
Dave

[allrightmike]

The right way to do that is to have the engine and trans installed so that you can measure the angle of the transmission centerline.  Then you can set the differential on the leaf springs, with the spring perches underneath, and rotate the pinion of the differential so that it is where you want it relative to the transmission centerline.  Once you have that in position, tack the spring perches to the axle housing.  For Cal-Tracs you should have about a 2 degree down angle on the pinion centerline, as compared to the transmission centerline.  So, if the transmission is pointing down 2 degrees, the pinion angle should be level.  This should also be done with the car at ride height, resting on the suspension.  It's one of the last things I do when I'm setting up a rear end, because usually the car has to be mostly assembled to do it correctly.

As far as the axle housing ends, their position isn't that critical, I usually put them parallel to the pinion.  If they are angled up or down a few degrees, no big deal.

[allrightmike]

Could you compress the springs to normal ride height with ratchet straps from the frame to the axle housing if normal ride height is a known factor?

[jayb]

Jay

Thanks for the quick reply

Just for my own knowledge though, when you support a factory housing at the perches and it it level where doe the top of the housing sit? Would the pinion point down meaning housing tilted “in” or pinion point slightly up meaning housing tilted “out”?

I just about have the perch jig complete and I’m thinking about the end placement

The jig for the perches will also do well for straightening and aligning as well

Thanks
Dave

I'm not sure I understand the question.  The top of the housing isn't really relevant, the only relevant measurements are the angle of the trans centerline and the angle of the pinion centerline.  Under hard acceleration the yoke on the pinion will want to rotate up a few degrees.  So, if you drew a line through the center of the pinion and the center of the trans, then watched under hard acceleration as the pinion yoke rotated up, ideally those two lines would come into alignment.

[jayb]

Could you compress the springs to normal ride height with ratchet straps from the frame to the axle housing if normal ride height is a known factor?

Sure, that would work.  You just want the differential in the ride height position.

[turbohunter]

Hey Dave there is a fantastic piece of reference out there.
It’s a book by Dave Morgan called Door Slammers: The Chassis Book.
It’s very involved in the whole of chassis set up and deals with all the different sections (such as pinion angle) separately.
The beginning of the book is a bit tough to get through because it starts with basics and basic math, but the sections can be read individually.
Suggest the whole book though as everything is related.

[Hipopinto]

Thanks Jay

Turbo hunter I will try to find that book tonight

Thanks again guys

Dave

[BattlestarGalactic]

I have that book.  I did a quick google, damn they are pricey these days.  Even on Ebay people are asking stupid money for it.

https://www.amazon.com/Door-Slammers-Chassis-Dave-Morgan/dp/0963121707


Summit racing has it for $57.

https://www.summitracing.com/parts/pow-pow901020#:~:text=Door%20Slammers%3A%20The%20Chassis%20Book%2C%20written%20by%20expert,and%20guide%20you%20through%20chassis%20operation%20and%20tuning.

[turbohunter]

Dayum it’s a pricey deal.

[Falcon67]

Yea, but it's the "bible" of sportsman suspension.

[Hipopinto]

Next time I’m at summit I will grab it

Summit is 1 hour away and I’m there regularly

Thanks guys

Dave