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It appears I've moved on to my next rabbit hole, the rear end. I was curious as to the gears i had on it (69 442 with 455 and 5spd tremec) so i jacked up the rear end, rotated the tire once, drive shaft rotated just over 3 times, I'm thinking its 3.08 gears(based on a chart i found in one of Joe's posts). I was looking at maybe throwing in some 3.55 or 3.73, maybe 3.90 gears in there. Anyone have any experience on jumping from 3.08s to any of those gears? Pros? Cons?
Also i am trying to figure out my rear end, i to took some pics, read a bunch on here and I'm still confused. Hoping someone can help. Also would need to now if any of those above gears would fit in place of the 3.08s and where do people buy there gears from?
Looks to be an O-Type rear, which was standard on the Cutlass line from 1967 to 1970. The O-Type has a 12 bolt cover and a 10 bolt ring gear, but the gears are not interchangeable with other GM 10 bolt rears.
The O-Type had a fairly small number of gears available from the factory and they were used on three different series carriers. Below is some info I archived a while back about O-Type posi units and gear ratios
In addition to the above gear ratios, there were 3.91, 4.33, 4.66, and 5.00 available.
For aftermarket replacement gears, the field is even smaller, with 3.42, 3.90, and 4.10 as the available ratios. Lucky for you, they are made to fit the carrier you have (3.08-3.23 series).
Here's Richmond Gear's offerings: https://www.richmondgear.com/wp-cont...n1.pdf#page=32
Last edited by Fun71; September 7th, 2021 at 01:04 PM.
Any pros or cons to running the 3.42 or 3.90 gears instead of 3.08? The car will probably never see the drag strip and I've been told that having that 5th gear will help on highways if i run the 3.90s, any truth to that?
Any pros or cons to running the 3.42 or 3.90 gears instead of 3.08? The car will probably never see the drag strip and I've been told that having that 5th gear will help on highways if i run the 3.90s, any truth to that?
Just multiply the rear end ratio by your OD ratio. Say you have a 0.75 fifth gear. That makes your 3.90 gears equivalent to 2.93 gears on the highway.
Any pros or cons to running the 3.42 or 3.90 gears instead of 3.08? The car will probably never see the drag strip and I've been told that having that 5th gear will help on highways if i run the 3.90s, any truth to that?
It depends on what you want. Going to a higher numerically gear and putting in an overdrive will, like Joe said, result in being "like" a highway rear end in drive. You're gaining an extra gear which will give you more range, but make you row through more gears. I assume you are not wanting to improve fuel economy with lower rpm in overdrive by just adding the overdrive only, like some people do, rather, you want to keep the highway cruise close to the same, but take off faster from the line?
@Koda yeah, not overly concerned with fuel economy, i'm sure it's not great right now. I would like the keep the rpms lower at higher speeds and i think the 5th gear (car currently has a 5 spd in it) will help and i def want to get off the line faster.
@1969w3155 think that might be the project this weekend, check out the numbers and put some fresh gear oil in it. Any particular gear oil i need to put it in?
Thanks for the info on the rear end gear lube. There a common/popular brand most use? I've been reading that there is an additive for POSI rear ends, that true? Or are there gear lubes out there that have the additive already added?
Go with any of the name brands. You will have to purchase the limited slip additve separately. I haven't had to buy any lately, but the last time that I did , I got it from a GM dealership. Check online at NAPA and others to see if they carry it.
Most of the name brand have the additive included, it will say on the bottle. I have been using conventional 85W140, it is Brian Trick's recommendation, who builds these diffs for a living. Avoid synthetic, even the majority of the aftermarket positive traction diffs say conventional oil only.
Most of the name brand have the additive included, it will say on the bottle.
^
This
The last time I bought gear oil I was actually NOT able to find any on the shelf without the limited slip additive already in the mixture. This was fine with me as the last few rears I filled have all been limited slip, but unlike the old days, most gear oils no longer need the separate additive if you have a posi.
Piggybacking, hopefully the OP is okay with it....
Where can one find a new and/or replacement Posi unit for the type O diff? My 442 is a peg-legger and I may add the Posi unit while it's getting refreshed from being tucked in the barn for the last 15 years.
There are aftermarket posi carriers that are Ford 8.8 units that are machined for the O-Type ring gear bolt pattern and carrier bearings. You can get them through various differential parts companies. Jim at JD Race (monzaz on this forum) and Supercars Unlimited are two that I know of.
September 7th, 2021, 12:44 PM
