: What rear end?
Nov 7th, 00, 09:37 PM
I finally got the #'s from my rear, on the passenger side of the tube is BL111502
On the housing, drivers side bottom is 3894860NF and on top is GM52
Anybody I.D. it for me? It's 12 bolt posi, beyond that, not sure. Thanks
Nov 8th, 00, 05:54 AM
The BL code looks to be a 68/69 open 12 bolt with 3.07 gears.
Nov 8th, 00, 06:20 AM
So, chances are they swapped the center section out then, eh? Cause it spins the hell out of both of them, and also at 70(indicated), it's turning about 3,500RPM's.
Nov 8th, 00, 06:41 AM
Doesn't sound stock, does it... Did you try counting the revolutions to see what the ratio is?
Nov 8th, 00, 09:42 AM
It looks like it isn't the original rear.
BL1115G2 - build Nov 15. A little bit of a stretch for a rear of a mid-February car. There's a casting date on the center section which will tell us what year it was made (Nov 68 or Nov 69).
Tire sticker is for the optional tires or for SS tires, so it is unconclusive.
The speedo cable may tell which trans was in the car. Follow it from the trans to where it enters the firewall.
[This message has been edited by Kurt S (edited 11-08-2000).]
Nov 8th, 00, 03:19 PM
Don't know what size tires you've got, but 3500 at 70 with 26" tires (like 235/60-15's) figures out to a 3.87 axle - the original 3.07 has been replaced with either a 3.73 or a 4.11. Jack it up, turn the wheels, count the prop shaft revs to find out which.
'69 Z28 Fathom Green
Nov 9th, 00, 07:48 AM
It's got 275/60X15's on it, pretty meaty.
Fat rears, skinny fronts...manual steering!
Nov 9th, 00, 04:22 PM
275/60-15's are 28" tires - 3500 at 70 (actual) with 28" tires figures out to 4.10, right on the money (assuming someone installed a 24-tooth speedo gear for accuracy with those larger tires, which is highly unlikely); 4.10's came with a 25-tooth orange speedo gear to get correct readings with 26" tires. If you have a 4.10 and the original 25-tooth speedo gear is still in place, you're actually going 75 when the speedo says 70. Go out on the Interstate, drive at a steady speed (60mph indicated) and time accurately how many seconds elapse from one mile-marker to the next. 60 seconds=60mph, 50 seconds=72mph, 55 seconds=66mph, 65 seconds=55mph. That will tell you how far off your speedo is at 60 mph indicated. If it's off by 5mph (actual faster than indicated), you still have the original 25-tooth speedo gear. If this is the case (actual 5mph faster than indicated), you definitely have a 4.10 if you indicate 70 (actual 75) at 3700 rpm.
It's still a lot simpler to jack it up and turn the rear wheels to get the ratio, and you could pull the speedo gear while you're at it and count the teeth, but the little drive-test outlined above will also tell you if you've got the original 25-tooth speedo gear (incorrect for your tires), or the 24-tooth gear (correct for 28" tires). Nothing is simple when you're juggling axle ratios, tire sizes, and speedo gears.
'69 Z28 Fathom Green
Nov 9th, 00, 07:40 PM
It's definitely 70MPH at 3,500, the day I bought it I had my dad pace me in his brand new truck. He called my cell when we hit 55(indicated 70), and then when we hit 70(indicated 90). I know the speedo is way off, but at least I know what 55 and 70 are.
4.10's sound about right to me, I was kind hoping that's what they were. It goes in on Monday morning to have both rear springs replaced, $185 for the pair, $110 labor. Couldn't hardly beat that, I don't have the resources to do it myself, especially not for $110. 5-leaf OER springs with bushings for $185 from a local classic auto place, and they had them in stock. Not bad...