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Problems with rear end

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Problems with rear end

Post #1 by Guest » Mon Nov 18, 2002 12:04 pm

Ok well here goes, after installing a C4 on my 61 chero gears were too high I went to the junk yard and picked up 2 different rear ends one from a pinto which according to my friend had almost the same gears as mine, and a second one i got from a mustang II which had an 8 inch rear end which would have worked except even though is a 4 bolt the pattern is different then mine so can't fit my rims.

I dont know anything about gear ratios first of all but mine had a tagged that read 3.5, the one from the pinto read something like 3.016 and the one from the mustang II was i think 3.0 or 3.08

what can i use that will bolt on and still use 4 lug and fit the original rims?

can i have my gears changed in that rear end?????


Gear problems

Post #2 by Guest » Mon Nov 18, 2002 2:42 pm

61 chero -

I just finished a rear-end swap in my 64 Falcon convertible and may have some info that is helpful.

My convert had a bad 7.5" rear-end with 3.50 gears and replacing parts for it was too expensive (about $400 for a rebuild). I also wanted a higher gear ratio (lower number) for better highway cruising speeds.

I found an 8" Ford rear-end with 3.00 gears and 4-lug axles.
It came out of a 66 Mustang (unusual for a 6-cylinder Mustang of that vintage, but possible). Alternately, you can use a five-lug rear-end and have the axle hubs re-drilled for a four-lug pattern.

I carefeully measured the spring pad dimensions and the backing plate-to-backing plate dimensions before I laid down the $100 cash, but still found some surprises.

1. My brakes were larger than those on the 8". Although both rear-ends use 9" diameter drum brakes, Cheros and converts had wider shoes and so the drums would not interchange. Simple replacement of the backing plates from my old 7.5" rear solved that problem.

2. The U-bolts and shock mounting plates for my 7.5" were too small to go around the axle tubes on the 8". New U-bolts and some hogging out of the U-bolt holes in the shock plates fixed that one.

3. The U-joint on the front of the 8" yoke is considerable larger than that on the 7.5". No conversion joints are available for this so the only option is to have the driveshaft modified. Steve at South Bay Driveline in San Jose did a great job of building a completely new driveshaft for me. ($200).

OK, so why would one swap out a 7.5" rear-end for an 8" or 9"?? Two big reasons:
1. Cost -- You can easily get different gear ratios for the 8". Lots of them exist and some are even Traction-Loc units. Replacement is simple as the ring and pinion gear set come out as a unit, unlike the Dana-style 7.5". Axle bearings and other parts are also readily available for the 8" or 9".

2. Strength -- The 8" unit is MUCH stronger than the 7.5", and the Ford 9" is the gold standard for hot rodders on a budget. With a stock six, this may not be an issue, but with any hot rodding at all, you'll quickly overpower the 7.5" gear set.

Hope this is helpful. Good luck with your swap.


Post #3 by Guest » Thu Nov 21, 2002 3:41 am

I don't know of any early mustangs that came with a four lug 8 inch rear. However, the early 70's mavericks had that setup, so that's probably what had been put into that mustang. The mav rearend is the best setup for the early roundbody falcons- not only is it four lug with the removeable carrier, but it is a bit narrower than the '64- up falcon and mustang units and will provide better clearance for tires. I recently saw a roundbody with what must have been a '65 mustang four lug rearend, and the stock skinny tires were almost rubbing the fender lip!


My task for next spring is to put my 3.0 geared 8 inch rear in my falcon. How do you like that ratio, and did it really hurt off-line acceleration? I'm ASS U ME ing :lol: that you have a six in your 'vert or you wouldn't be here, so my results will be similar.



Post #4 by Guest » Thu Nov 21, 2002 11:55 am

Ok well heres my dilema now, i'm gona go with re-drilling the mustang rear end to fit my tires cause is more cost effective, however now comes the problem the orginal drums would now be off and i'm not too sure if i could fit my drums from the chero on those axles with backin plate and all. :roll:

I'm just thinkin here wouldn't the space for the drums between the axles be different size since the orginal drums are smaller then mine?


Post #5 by Guest » Fri Nov 22, 2002 9:51 pm

First off, the original 6 cylinder rear-ends in Falcons and Mustangs were 7.25", not 7.5".

You can swap the gears out in your original rear-end by getting some out of any other 7.25" rear-end. The later model Falcons and Mustangs are better because they had higher gear ratios (lower numerically). They went as low as 2.80 or 2.83 (can't remember which one). The whole rear-end from the later models won't fit in your car, but the internal gears are the same.

These 6 cylinder rear-ends are very simple to rebuild - and not expensive, either, especially if you don't have to replace the gears with NOS ones. I just completed mine - did it all myself.

Sidenote: Whichever route you decide to take (changing gears or the entire rear-end), be sure to recalibrate your speedometer. Don't want to get a ticket for speeding!!! :wink:


Post #6 by Guest » Sat Nov 23, 2002 2:12 pm


Wait! There may be another solution that will let you keep the mustang 2 rearend as is. Just by chance, somone in the thread "PBR calipers on granada spindles" mentioned that the pinto and granada rotors can interchange with differant wheel bearings. You may be able to use granda spindles with pinto rotors up front so you can have the same bolt pattern all around. While this is not the best choice overall, you could keep the rearend you have now. It's in the suspension brake forum, near the bottom of the (long) thread.


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