79 Firebird rearend

rooster · June 01, 2005, 10:25:38 AM

Could someone tell me if the pinion angle is built in to the stock purches?

Also We dont have the bottom plates that the u-bolts go threw, I have some 1/4" plate, Ive been told that its not enough, was thnking just double it up making it 1/2".

enjenjo · June 01, 2005, 11:24:59 AM

There is angle built into the stock perches, but it may not be right for a 50 chevy. 1/4" material is not enough, unless you bend some flanges on the sides to keep it from bending. For that matter two 1/4" plates will bend too unless they are reinforced.

GPster · June 01, 2005, 12:06:44 PM

I thought he was going to keep the six in it, or is this one not your boys? I'll try to put some suggestions together with what I think I know. It's too early to worry about the pinion angle without the engine and transmission mounted. The angle needs to match what you end up with at the transmission for the universal joints in the driveshaft. There are reasons why 1/4" plate might or might not be ok for these plates. The springs under this car are 1 3/4" wide and the Firebird springs were probably 2 1/2" wide. If you use that amount of spacing between the U bolts and try to clamp the car springs in between it the 1/4" plate will bend at the edges of the spring just by tightening the U bolts. Now if you pull that rear end back out and turn it up-side down so you can drill new holes in the mounting plate so the U bolts will only have 1 3/4" between them so that they will be tight against the side of the springs the 1/4" plate should be enough. You can use the old lower shock mount of the old chevy as a gauge to the spacing between the holes and you can re-use that plate for your lower shock mount. Just hold it on with the U bolts also between the 1/4" plate and the nuts. Now if this Firebird had Mono-leaf springs then the mounting surface on the mounting plates on the rear end are not flat. They were formed to hold the wider spring and a bunch of rubber and you might not have room to drill new holes with 1 3/4" space between them. This would get around to another way to do this project that might be better. Most places dealing with these old Chevys have rear end saddles for these instalations. Because these old rear ends were mounted to hinge because of the closed driveshaft the center bolt of the spring is about 1 1/2" in front of where the rear end should be. If you bought a pair of these plates and cleaned the old brackets off the rear end and used them you could just sandwich all this stuff together un-welded and when you got the engine and transmission in you'd be able to adjust your pinion angle and weld the new saddles to the rear end then. If you want to stay with the first way, while you're drilling holes in the mounting brackets on the rear end, drill a new hole for the spring center bolt to allow for that 1 1/2". GPster

Ohio Blue Tip · June 01, 2005, 12:32:40 PM

¼" is not heavy enough!

My $.02 worth.

rooster · June 01, 2005, 01:02:27 PM

Thanks for the input!
Things have changed. Gregs car (son),
Now !
350 eng,
Auto Trans???,
79 firebird 2.41Ratio, stock 49 leafs. 3" lowering blocks.
master cyc under floor , converted to duel.
front brakes Disk , maybe the Tex Smith idea.

will give more answer to your reply later, thanks for the help!!!

GPster · June 01, 2005, 01:37:56 PM

Quote from: "rooster"Thanks for the input!
Things have changed. Gregs car (son),
Now ! 350 eng.Auto Trans???, 79 firebird 2.41Ratio, stock 49 leafs. 3" lowering blocks.
master cyc under floor , converted to duel.
front brakes Disk , maybe the Tex Smith idea.will give more answer to your reply later, thanks for the help!!!

I'd be scared about any of this stuff on 3" lowering blocks. Also the lowering blocks that you get now are usually aluminum and made for the wider springs. My idea now would be find you a piece of 2" x 3" x 1/4" rectangular tubing and build a pair of saddles with the 3" drop in them and use the 1/4" plate to make ends for the saddles/drop that have the right (1 1/2") change in the spring center bolt placement. Because the U bolts will not be tight against the side of the spring because of the width of the drop/saddle the 1/4" plate will bend when you tighten the U bolts. It will bend around the U bolts and clinch them in the plate. This wider dimension will also make it impossible to re-use the lower shock mount. If you make the 1/4" plate with a couple of stiffeners on it so it looks like a piece of channel maybe you could make on of the stiffeners come out enough to mount the shock mount to. GPster

rooster · June 01, 2005, 04:41:45 PM

We were hoping that we were good to go, with the exception of the pinon angle, to be determined later after the rest of the set up. If there is to be a adjustment later the bolts will become angled also and wont line up right with the bottom plate.

For the shock mount we were going to just remount it the way it was, directly to the spring.

For now were are going to have to get some stock plates from the junk yard just to get the car back down on the ground to move it around.

rooster · June 01, 2005, 09:55:05 PM

50chevydan brought his lower plate over to borrow, its from a 78 Camero and its 1/4" plate from the factory! it appears slightly bent from the u-bolt being torked down .

The upper plate (perch) we have is missing a piece of rubber, I cant say for sure if this piece of rubber had a hole in it or not. We were looking for a way to center the lowering block in the perch.

The lower plate has a hole in it but it is in the wrong place, for centering in the wheel well!//[URL=http://img139.echo.cx/my.php?image=dcp062450nf.jpg][img]http://img139.echo.cx/img139/5672/dcp062450nf.th.jpg[/img][/url]

GPster · June 02, 2005, 08:20:13 AM

Quote from: "rooster"50chevydan brought his lower plate over to borrow, its from a 78 Camero and its 1/4" plate from the factory! it appears slightly bent from the u-bolt being torked down .The upper plate (perch) we have is missing a piece of rubber, I cant say for sure if this piece of rubber had a hole in it or not. We were looking for a way to center the lowering block in the perch.The lower plate has a hole in it but it is in the wrong place, for centering in the wheel well!//[URL=http://img139.echo.cx/my.php?image=dcp062450nf.jpg][img]http://img139.echo.cx/img139/5672/dcp062450nf.th.jpg[/img][/url]

If I remember correctly that rubber piece has an impression in it for the center bolt of the spring and around that impression is cast the rubber to fit in the larger hole in the rear end saddle. From the picture it appears like my Nova was and it had monoleaf springs. Check the size of the hole in the center of the saddle. If it's about 1" that will explain it. You could come up with some kind of spacer to go from the size of the register on the top of the lowering block ( 1/2"?) and the hole in the saddle ( 1"?) and it would be captured in the hole when you bolt it together. Remember in the bottom of the lowering block is going to need a new center bolt register hole in it. As for the lower plates. If he could find another set like those he could drill the new center bolt hole and re-bend them so that they are straight again. You could make some stiffners to go accross the front and back of the plates from side-to-side to add more strength to them. GPster