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rear brake swap from 8.8 to 7.5


94 lngbd

Well-Known Member
TRS Banner 2010-2011
Joined
Nov 24, 2007
Messages
862
Age
60
City
Lakewood,Wa
Vehicle Year
1994
Transmission
Manual
I have a 94 2wd /4cyl/5spd & current rear end is 8.8 with 4.10s in it that has new brakes & resurfaced drums,however I just got new tires & there smaller then the 31s that were on it. The new size is 235/75/15s. With the smaller tires Im actually getting about 4-6 mpg less then with the 31s.

I just got a 7.5 with 3.73s to install for the 235s, even though the price was great @ $10 it needs wheel cylinders,& all brake hardware & drums.

The 8.8 is from a '99 & the 7.5 is from a '87. Will the brakes from the 8.8 work on the 7.5 or would I have to swap the backing plate also or is that even possable?

Thanks guys as I want some MPG back
 
Have you compensated your speedometer and odometer to the new tire/gear setup? If not, your MPG calculations are off.
 
Im not going off of the stock speedo & odometer. Im getting my readings from the GPS system in my Kenwood stereo
 
Well, swapping brakes from one axle to another will be a lot more effort than just replacing brakes. I think it's doable, but I'm not certain of that. At the very least you would have to pull the axle shafts to swap backing plates.
 
im aware that I would need to pull the axles ,but im not sure if the 4 bolt hole pattern that holds the backing plates is the same between the 2 different rear ends
 
I'm really not either.
 
I think it would depend a lot on what size brakes you have, 9" or 10"
 
Those two axles will not work as a swap. The Brakes parts alone may work. But the 87' 7.5 axle is 2 inches shorter than the 99' 8.8 axle. Best to find a 93' and newer axle for the swap.

Also, why? The 8.8 axle is stronger than the 7.5 axle. And the 4.10 ratio is ideal for the 2.3L engine with 235/75R15 tires.
 
This is just a temporary solution for MPG as 4.10s are fine for 31s ,but there to low for 235s as I have a 4-6mpg less mpg if i run my new 235s. Eventually when the 235s are needing replacing or sooner I will be converting to a SAS 4wd conversion & at that time the 8.8 will get 4.56 gears as will the D30 Cherokee front axle to handle 33s.

The 87 rear end is only 1" narrower then the 99 rear end NOT 2" & if the entire backing plate to drum brake components are used then the size of brakes wont matter.
 
The 87 rear end is only 1" narrower then the 99 rear end NOT 2" & if the entire backing plate to drum brake components are used then the size of brakes wont matter.

Not my info for the narrower axle. I read it off the TRS Tech Library.

I still don't quite understand why you should be getting that low of MPG. I currently run 225/70R15 with a 3.73 axle. And I have ran the numbers before when I was thinking a lot. With 235/75R15 tires, a 4.10 axle should be ideal to keep the stock powerband and MPG. :icon_confused:
 
[QUOTE=LearjetMinako; I currently run 225/70R15 with a 3.73 axle. And I have ran the numbers before when I was thinking a lot.


If you was to run 235s with 3.73s you would get better fuel economy cause it would make it seam as if you had 3.54 gears.

My ranger originally had 225/70/14s with 3.45 gears then I switched to 31s & needed a lower geared rear end that s why I went to a 8.8 w/ 4.10s ,but when tires needed replacing 31s were much more then I could buy so i opted for 235s. & now the 4.10s are to low ,but 3.73s will be perfect.

Its like all the 3/4 ton trucks with 4.10s from the 60s-80s always got 8-10 mpg regardless. however if you had the power to run taller then the 29" tires then you would be in a sence making it seam as if your gearing was higher.

My 76 F250 has a 520 stroker & with 33s I got 12mpg ,but when replacements were needed I went with 35s & was able to get 14-16 mpg cause it would seam as though I had 3.54 gears & still had the power to smoke tires even with a 26ft 1972 travel trailer looked to the hitch
 
a 235/75-15 measures out to about 28.9", thats only 8% smaller that a 31. they are also lighter and as such take a little less power to spin up. that much of a drop in mileage doesn't make sense, as an 8% drop from , say 28 mpg would be about 25.75 mpg or about a 2.25 drop. what type of tread is each tire?
 
Currently my Ranger is running 225/70R15 on a 3.73 axle ratio. The orginal setup was on the 225/70R14 on the same 3.73 axle ratio. So really with my 1" taller tires make it feel as if I have a 3.55 axle as stock. Any bigger of tires on my 4-banger and 5th gear would almost becomes to weak.
 

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