8 3/8 Rear End Question

[1976D100]

O.K. Let em get this right. I've read that the Chrysler 8 3/8" rear end is the same as the 8 1/4" rear. Is this true?
Can I get part #DCC-4529273 (Mopar Performance Sure-Grip Differential) from Summit to fit my 8 3/8" rear? It says that it is for a 8 1/8" rear.
Any help would be greatly appreciated.:D

Thanks, Gary

[B-300]

The early 8-1/4" rear ends were called 8-3/8" after only a few years of production. This is due to lower # gears that fit in the same housing (2.71 for example)
Summit does miss label parts on the web so call summit tech to be sure.

[1976D100]

Thanks for the info.

This truck has some pretty small brakes on the rear, is there a junk yard axle that would be a direct swap into my truck? One that has the same width but has larger drums (disks) and the same 5 X 4 1/2 bolt pattern? Or would I be able to find some larger brakes at the yard that would swap to my current axle.

Maybe a pipe dream, but I gotta ask;)

Thanks for the help. I am a Dodge noob.

[1972-D100]

Not sure if you can put the larger brakes on the smaller axle or not, but you can try to locate a 8-3/4 rear end and bolt it up. A lot of the "camper" models and 4wd trucks had the 8-3/4 and you should be able to locate one in a yard pretty easily. I would recommend that you check the gear ratio before installing it though, I know it is obvious but I had to say it!

[1976D100]

Thanks, '72.
I would like to tow a trailer with this truck and would like some additional brake power. I'll go and look at one of the local "pull it yourself" places for a 8 3/4".
Does anyone know if there is a drive shaft mod that I would have to do?

[B-300]

I didn't have to change the driveshaft when I did this swap on my '78 van... just make sure both use the same U-joint size. Most have 10x 2-1/2" brakes, some heavy duty models have 11x 2-1/2" brake drums with 5 on 4-1/2" bolt circle. These drums are harder to find if you need replacments

[1972-D100]

B-300 is correct, go with the 10 X 2-1/2" much easier to find the replacement parts and I've never had a problem with mine not stoping me quickly when I needed them to even when pulling a 5000lb trailer.

[1976D100]

I'd better go measure what I have. They may BE 10 X 2-1/2" brakes. Just seem small to me.
Of course right now the shoes are thin and are covered in what I hope is brake fluid. I need to do a complete rebuild and thought I could go larger on the cheap; junk yard style. Then just rebuild the larger. But it sounds as though 11 X 2-1/2" brakes would not be on the cheap.
I'll measure this weekend and post results.

'72, do you think a 3.21 rear is ill advised to pull a 3000# trailer? Keep in mind it's a 318.

Thanks again, all!!!!

[1972-D100]

Depends, what kind of terrain are you planning on covering when towing and at what speeds? If you are doing the hills with lower speeds due to corners and what not, the 3.21 will do just fine, you could even go with a little taller gear. If you are planning on a more of a flat terrain with higher speeds (70+) it will pull it with no problem, but your RPMs will be higher with the 3.21 than they would be with the 2.71. It would be a good all around gear though, any taller of a gear and your MPG will go out the window, any lower of a gear you lose some of the low speed power (quickness).

Hope that helps....

[bigdogscott]

i always thought the taller the gear (lower #) ie:2.71 ment lower rpms/better gas milage/slower take off,where a lower gear(higher #)ie:3.21/3.55 ment quicker take off/higher rpms @ speed/not as good gas milage. correct me if im wrong or misread above reply.

[1972-D100]

i always thought the taller the gear (lower #) ie:2.71 ment lower rpms/better gas milage/slower take off,where a lower gear(higher #)ie:3.21/3.55 ment quicker take off/higher rpms @ speed/not as good gas milage. correct me if im wrong or misread above reply.

Well we both are on the same page for the most part, but I could be wrong as far a taller gear or a lower gear goes...I normally don't use those two words I stick with the numbers, bottom line is the smaller the number the lower the rpm's at highway speeds, slower get-up-n-go, and better gas mileage...the larger the number the better the take off speed and low speed power, the rpm's will be higher at highway speeds and your gas mileage will drop... Sorry if I confused anyone, my coffee as not yet kicked in!:(

[bigdogscott]

we'll let you side this time,lol.

[1976D100]

Update:
Terrain will be hilly, speed will mostly be in the city (35-45 mph) with some highway usage. So it sounds like I should be OK with the 3.21?
The brakes are the 10 X 2-1/2". So if the gearing is OK, I will be rebuilding these and not looking for a new rear axle.

I guess alot of my confusion comes from the fact that my current daily work truck (I'm a handyman) is a '72 GMC with a 3.73 gear, three speed manual trans and a stronger motor(mildly built 350). I rarely tow with this truck due to lack of power brakes(from the factory). But while towing or having the bed loaded with tools and whatnot, she'll get up and GO! Even up the hills here in Winston-Salem.
So my concerns are I will be building this truck to use as a daily work vehicle; I want to build it as cost effectively as possible and only do it once. I would hate to have to down the truck for more modifications once I have her up and working. When I have the Dodge going I will be going through the GMC (sorry for such language on this forum) for use as a back up truck/ debris hauler.

Thanks again guys for all of your input.

[mgoblue9798]

3.21 prob will be ok for what you are doing. good news is if you find an 8 3/4
rear, gear change is easy enough, less than 2 hrs to swap the pumpkin and you are back on the road. tire size makes as big a diff as the gear ratio as a taller tire effectively lowers the gear ratio by reducing rpms. example is 3.21 gear with 215/75/15 tires will turn more rpms than with 235/75/15. I switched to 30" tall tire in my dakota w/ 3.55 gears (it had 215.75.15) and it was like switching to a 3.23 gear rear

[mgoblue9798]

ps if you do the 8 3/4 swap then youy can get the brake assys off of a big c body to have the 11" drums om the cheap.