Please educate me on gears

[TheDude]

*'65 Mustang with a '68 200ci 6 - port divider, FSPP header, dual exhaust with Borla mufflers*

Hi,

In my Mustang, I have upgraded the exhaust system by installing a port divider, a FSPP dual out header, and dual exhaust with Borla mufflers. I am doing the 2bbl carb upgrade next but I am not sure what to do after that. I was thinking about changing gears...

First, I should say this: When I first got my Mustang I knew nothing about cars. I taught myself as I went and I now have moderate mechanical abilities. I know nothing about gears...how to install them, what gears would be best for my application, or how much they cost. So, my question is: What gears do I want for quicker acceleration and good highway crusing? I believe the gears in my Mustang are original. I hope they are...unlike the engine (I wish I knew what happened to the original engine). Can someone give me a quick lesson on gears? Are they difficult to change and are they expensive?

Thank you

Justin

 

[Anonymous]

gears are a PITA to install, it would be easier, IMO, to just install a new rearend
i don't think there's many options for a 7.5 rear gear anyway

 

[Anonymous]

Unfortunatly, there really is no quick easy answer. Assuming you have a 8.8 or 9 inch rear end, the process is a little less complicated than most other maunfaturers rear ends. First jack up the rear and support on jackstands (Duh!). Pull the wheels and brakes (backing plate and all). There are 4 bolts holding on a plate called a "bearing retainer." These plates hold in your axles. Pull the plates off. You can usually access the bolts through a hole in the axles flange. Use a slide hammer puller to pull out the axle about 1 foot from the axle, it is not nessicary to pull it out all the way, just enough to disengage it from the differential. After both axles are pulled in this manner, go under the car and pull the U-joint caps and move te driveshaft out of the way. Loosen, but do not yet remove, the nuts around the differential housing. Pry the differential carrier (also called a pig) away from the housing to break the gasket seal. At this point all the gear lube will pour out, so be ready for it. After its done draining, finish removing all the nut and remove the diff carrier.

Now the fun begins. To pull the pinion nut off you need to keep the diff from turning. This may be easier if its the first thing you do after jacking up the car. You can pull the driveshaft and use the brakes to keep it still. There are 2 bearing caps that look similar to the main caps in engines that hold in the diff. The ring gear bolts to the diff and the diff must be removed to get it out. The pinion will come out after the pinion nut is removed and the ring gear is out of the way.

I don't remember offhand the specifics on setting up the gears, perhaps another person can help you there. All I can say is that if you are not absolutely positve you can do this, or at least have a friend who can help you, this is one of those things to have a professional do unless you can afford to have it apart for quite a while.
-Ryan

I am not familiar with the 7.5, so don't know if any of the above applys if thats what you have.

 

[Anonymous]

I don't know anything about gears, but your pic rules.

MILTONNNNNN!!!!

- Your off-topic friend, Tom.

 

[Anonymous]

Yeeaaa, I'm going to need you to just move to the basement...

 

[Anonymous]

you can still get new aftermarket gears for the 7.5 rear end from www.summitracing.com for about 185 bux . 3.20:1 - 3.50:1 is a pretty good gear for the street you`r stock gear should be 2.79:1 or 3.00:1 good luck with it

 

[CobraSix]

A good gear for street with a T5 is the 3.20:1. nice ratio, not too high at highways in OD. 4th gear is nice on the highway.

Slade

 

[Anonymous]

First thing is first. Determine what gears you have. On the door should be a small metal plate with an engine code, tranny code and rear axle code. You can take the code and look it up in a manual. I don't remember all the codes and what they transfer to but I looked mine up recently and it says I have a 2.83 rear end. When I get home I will double check this but I believe the sixes came with integral 7.25 rear ends and you can't change the gears in them. If anyone nows for fact this is wrong please let me know. I don't believe the 7.5 rear ends were used on stangs.

The best bet would be to find another rear end from another ford with the same bolt pattern that already has the gears your looking for. Or the other option is to run 5 lug in the back and upgrade to an 8 inch from which all kinds of options are available.

 

[Anonymous]

Hi Justin,

I agree with hindle_az. Determine what you have first. The rear end codes for a 65 Mustang are as follows: 1=3.0, 2=2.83, 3=3.20, 4=3.25, 5=3.50, 6=2.80, 9=4.11. Almost all of the 200 I6 cars delivered with a C4 trans came with the code 6 rear end. Great highway gearing and OK for around town with the torque of the 200 I6.

What to go to? The 200 I6 was delivered with the 7.25" rear. To my knowledge the 7.25" rear came in 2.8, 3.0, 3.2, and 3.5 versions only (don't hold me to this). So, in my opinion, the easiest way to improve accelleration and hill climb ability is to find a 7.25 rear with the ratio you want. I just changed my 2.8 for a 3.2. The difference is quite amazing in terms of how quickly the car comes off the line. However, rpm is higher on the freeway. Personally, I wouldn't go beyond 3.2 if you do much highway driving. The 3.5 would probably be better if you are an around town guy.

Options. The 7.25 with the 3.20 I just installed took me a long time to find locally. They show up on e-bay from time to time but you won't want to ship one. On the plus side, they just bolt in (although I did have to change there rear "u" joint). Your next option, and easy to find, is the 8" rear used in many Fords. However, now you need to be aware of brake drum to brake drum length (they do vary). And you may need to rebrill the axels for 4 bolt wheels, or go with 5's. However, if you go with 5 you will probably want to change the front end also. Another subject, with several solutions. With the 8" you will likely have "u" jiont issues and maybe even a drive shaft length issue. However, drive shaft work is not that expensive and there are many shops to do it. One of the advantages of the 8" is a larger brake.

Bottom line, simple and least expensive is find a good 7.25 with 3.2 or 3.5 gears. If major suspension and brake work are in you futuer, go for the 8".

There's my .02 - Steve

 

[cfmustang]

Hallelujah, Steve!

I thought I read something years ago saying there were other ratios for the 7.25" rear, but I have never heard anyone else ever mention it. Everything I have heard goes with what you said (can't change gears in a 7.25", etc.)

It seems to me that what you describe is the best solution. The problem will be finding a 7.25" with the 3.20 gears.

I posted on this board back in the Spring when I was real green and someone also mentioned a rear from a early 80's Maveric being a direct bolt in, but I don't know what size it is or what bolt pattern the wheels are.

Believe it or not, I would prefer to stay with 4 lug wheels. It helps keep the sleeper status.

 

[barroom hero]

just to clearify, if i found a five lug rear end with the gear size i want, would it all be a bolt in swap, and kill two birds with one stone (5lug and gears)? thanks guys.

 

[TheDude]

Thanks for the responses. I will continue to read about gears, rear ends, and such... When the weather is nicer, I will try to get some #'s from the rear.

Thanks

Justin

 

[Anonymous]

I have the 4 lug 7.25 from my 63 Comet. I changed over to a Maverick rear. Anyone who wants it can have it but I will not ship. In Waycross GA...It's a 3.20.

Don

 

[Anonymous]

Hi Guys,

The 8" rear with the gearing you want is a easy way to swap to 5 lug and larger brakes. They do weigh more, in case that is of interest. 8" rears were used in a number of Ford cars, including the Maverick. The post you remember about the Marverick swap was by Jimbo65, who found an 8" Mav rear with 4 lug axels. Rare, but out there. Powerbrares has posted on this subject several times. This is an upgrade that should be considered early on by us I6 guys since the factory ratios were, for the most part, intended for mileage vs. off the line performance.

Steve

 

[Anonymous]

cfmustang I would love to see that maverick because they were only made from 1969 till 1977

 

[Anonymous]

I know where a 4 lug Maverick rear is in a junkyard here. Don't know the ratio.

 

[LaGrasta]

I'm green on gears too. I have a Ford-o-Matic tranny (just rebuilt) and the original rear end running the stock 3:50 (fresh fluid). I don't care about "off the line" acceleration, I want good MPG and a calm quiet freeway ride. I have just the opposite the way I sit now. The thing chirps almost everyytime I launch and it screams at freeway speeds. What gives? What'll I do to correct this while keeping it financially feasible?

 

[Anonymous]

Justin, your planned T-5 conversion could eliminate the need to change out the rear end. Changing the rear end from 2.8 to 3.2 will mean that you see 14.28% increase in engine rpm to go the same speed. Your transmission has a 1:1 top gear ratio. So in 3rd gear your engine is turning 2.8 revolutions for every revolution of the tire. The overall driveline gear ratio is obtained by multiplying the transmission gear ratio and the rear axle gear ratio.

I do not know what the gear ratios for the automatic transmission are but I can give you and example for the 2.77 manual transmission. The 1st gear ratio for the stock manual is 2.76 and the rear axle is 3.2. A common 1st gear ratio for an 8-cyl T-5 is 3.35, and 4-cyl has 3.97. Given the 3.2 rear end, this yields an overall ratio of 8.83 for 1st gear in the stock trans, 10.72 in the V-8 T-5 and 12.70 in the 4-cyl T-5. For comparison, a 2.8 rear would have respective ratios of 7.73 for 1st gear in the stock trans, 9.38 in the V-8 T-5 and 11.12 in the 4-cyl T-5.
With the T-5, you would not lose the economy that you would if you changed the rear axle ratio. All of the stock Mustang transmissions had a 1:1 top gear. A T-5 from a V-8 commonly has a 5th gear of .68 and the 4-cyl T-5 has a 5th gear overdrive of .79. For a 2.8 rear axle ratio, your stock trans has an overall ratio of 2.8, the V-8 T-5 would be 1.904 and the 4 cyl T-5 would be 2.2. The point of all this is that going from a 2.8 to a 3.2 rear axle ratio will increase engine speed by 14.28%, and you will see a reduction in highway fuel economy. Depending on your current gear ratios and the T-5 transmission you choose, you will see 1st gear ratios increased on the order of 20% to 40% yet still have a reduction in the top gear ratio of 21% to 32%. I have a spreadsheet that I built to play with the gear ratios, and the calculated engine rpm and road speed for each gear. E-mail me if you would like it.

 

[cfmustang]

Oops. Good point. I meant Granada.

(hangs head low)