Hot Rods Transmission and rear end choices

O.K. Yes you are right. I said lower numerical number meaning a 3:00 as opposed to 4:11 gears which would be higher numerical number. Is there a way of identifying a 8 inch rear end from a 9 incher that he could do for me to be sure we are talking about the correct rear end. I know we are talking ring gear size but is there any way from the outside to determine what it really is. He is going by what the mechanic that swapped the pumpkins said telling him it is a Ford 9 inch rear end. I was a GM man and never owned a Ford back then so not well versed in them. Thanks.

 

Hi, Yes you are correct. I said lower numerical number ring and pinion meaning a 3:00 ratio. I call a higher numerical ring and pinion say 4:11 ratio. I just found a site to educate myself on 8 inch or 9 inch Ford rear ends. I will call him tomorrow to see if he can supply me with info on what rear end he actually has and if it is a locker or open. Always learning. Thanks again guys. You are the best!!

 

as mentioned earlier, and probably on the site you are looking at, if you can put a deep socket on all the center section mounting nuts, it's a 8". If the bottom two the socket won't fit, you need an end wrench, then it's 9".

 

Hi, Just got a call. My friend got under the truck. He said when he turns the tire 1 revolution he ends up with 3 full turns of the driveshaft on the button. So he has a 3:00 /1 ratio gears! I asked him to look at the back side of the housing of the rear end. It is smooth with a couple of dimples. So that means he has an 8 inch rear end. Had him check the axle ends . He said the ends are flat and smooth with 3 small holes drilled into them. So I assume they are 31 spline axles! Also had him spin the driveshaft and both wheels turn in the same direction so assume limited torque rear end. He thinks the guy who changed the center section said it was a 1960 rear end. Would this make sense? I am having him look for numbers on the transmission next. He believes it is a 1970 FMX 3 speed unit. He is going to look at the bottom pan and get back to me on shape. He did say today that the entire transmission is 1 piece and made of Aluminum. I think I am going to have him put another tach on the truck to verify his one from LMC and the temporary one to see if they match. Thanks.

 

FMX is not a one piece aluminum, neither is the C-4, he must have a C-6. Kinda rare, but Ford did put a few C-6s behind the Ford Small block, mostly in 351 vans and trucks.








Bones

 

With the 3.00 rear gears? Possibly the shift linkage is keeping the trans from engaging high gear and he's driving around in second....?

 

Ford Aod will do it. I ran a 700r4 in my olds with 3.73 rear end real quick stop light stomping but once she hits od nice cruising. 70 at 2200 rpm

 

Yeah, sumthin is wrong with the transmission or shifter. If he has 235 tires and a 3.00 gear he should be in a very nice RPM range at highway speeds. I don't know squat about FMX transmissions, but if it's in high gear it should be very comfortable on those tires and rear axle.

 

Hi, O.K. on the transmission. Hopefully I will hear back in a day or so from him on the transmission numbers. I did ask him if he feels it shift into the 3 gears and he said yes. So I agree something is wrong with the situation. He said the Hurst floor shifter is goofed up. Possibly it is not adjusted properly. Tough asking questions on the phone and not being there to look it over! He said it was hitting 104 degrees outside and his shop was above 90 already. Guess it will be that hot for the next several days. He wants to make sure all things are checked before he invests a new shifter. Thanks for the help again.

 

A Ford FMX was used behind various engines from 1968 thru 1981. It has an aluminum bellhousing and a cast iron main case and aluminum tail housing. It looks very much like the 51-up Ford and Cruise-o-matics. but it shares very few parts. They are heavy but very tough..
It could easily been put behind a 289 eventho by 1968 the 302 SBF was the standard at the time.

 

First consideration is that the engine he is working with is a 289 with a 2 barrel carburetor. Just driving a truck powered by that engine is going to be less than thrilling. Couple that with a 3 speed automatic and there really isn't any combination thats going to give both decent low end AND decent cruising. Its pretty much either/or............

I'd forget about changing the rear end initially but it would be nice to know what the ratio is.

The option I would look at is an overdrive transmission. Thats going to give the anemic engine at least a chance to have some semblence of low end performance while dropping cruise rpms substantially. Probably have a lower first gear than any of the Ford 3 speed autos.
I would suggest he purchase this book before making any decision as it will have plenty of good info to help him make the correct choice.
https://www.amazon.com/Ford-AOD-Tra...=Ford+transmission+book&qid=1625779799&sr=8-1

You can get by with a large engine and plenty of torque and use a low (numerically) rear ratio. With a 289/2barrel, you pretty much have to choose what you can live with.

All of that being said, if he has the means.......he might just look for a 351 with an overdrive automatic and swap the whole thing out. Then he could actually tow with it too.

Also, you mentioned that he said the engine had been 'bored and stroked'. Usually when someone does that, they don't put a 2 barrel carb on it. I think I would take what your friend is saying with a grain of salt since he is relying on things someone told him.Not saying it isn't,but that isn't the normal way its usually done.

 

If it is an 8” model, it does not have 31 spline axles and probably not a limited slip either. Also, 8” was not introduced until 1962 Models of Fairlane and Meteor. It is not uncommon for both wheels to turn in the same direction when there is little to no friction on either brake drum.

 

Nope, that doesn't add up....................computer says no.
235/65 R16 is a 28" tire diameter.
28" tire with a 3.00 rear end ratio at 55 mph would give around 2030 rpm with a three-speed auto in 3rd.
To be doing 3000 rpm with 28" tires at 55 mph, the rear end ratio would have to be around 4.5 : 1.

This calculator makes it all easy.
https://spicerparts.com/calculators/engine-rpm-calculator

 

I think this is an issue with “first old vehicle “. May have dual exhaust, but certainly doesn’t have the exhaust system that OEMs have used for 30+ years.
So a fella not used to engine noise/ exhaust noise, may not have a feel for what’s going on.
I know I can put my ‘03 Chevy pickup in 1st and go to 4K RPMs, hardly hear a thing.

 

Thanks for the reply. And again while asking him these questions on the phone I was not there. I thought it did not make and sense he would have 31 spline axle and torque limited center section in a 8 incher!! He described a smooth back cover with 2 dimples but no relief for a bigger ring gear. Things do not add up!! I will be calling him again tomorrow to verify things again. I am going to see if he can take a photo of the rear end with his phone and text me!! Also the axle stub ends. That would clear up things. As I said he is not a mechanic but I try and ask questions he could observe. Hopefully he will have numbers from the transmission to clear up what that is! He said he has a Hurst floor shifter and possibly he has the Hurst Promatic 2 unit. Maybe it is not adjusted correctly and is not giving all three shift points?? Beats the hell out of me!

 

ask him to put a socket on the bottom bolts, if it fits its an 8 inch, if there is no way it is 9 inch.

 

Hi Got a call today from my friend. We cleared up the carb issue. He had a 2 bbl on it and purchased a new intake and a 4 bbl carb for it. That is settled. He said the Hurst floor shifter has no detents so he can slide it from park all the way down to low gear and back. We agreed that shifter has to go! He said he can put the shifter in low gear and keep sliding it up for the next gear of the transmission and it shifts thru all three gears up to drive so at least that is working properly.
He is going to try the socket in the center section for me to see if the socket fits or has to use a wrench. He has a cell phone and will get someone to help him photograph the rear end, tranny and axle stubs and text me photos of them. Maybe we can answer that issue. he is also looking for the instructions for the tach to see if there is a selection switch for 4,6 or 8 cylinder setting and check that! And lastly he is sending me the numbers from the transmission on the drivers side. He said it was 104 there today!! Said Death valley got up to 130 degrees!

 

@Donald N Wemple Jr. you are a good friend to hang in there with your buddy. And kudos to him, too, for wanting to learn and get things sorted out. I look forward to more updates as the puzzle is solved.

 

Thanks Still waiting for photos to share.
He left for the Salt Lake valley for college in 1968. We call or see each other once in a great while but are good friends. He is a craftsman with wood but little experience with cars. He has depended on me to help him out on this mild hot rod project. He has owned other older unmodified cars but this is his first shall we call rearranged one! You guys are a great help in sorting this truck out. Thanks. Hope to get photos soon to share.

 

The truck is about 2,000 lbs lighter than a new truck. It will run very well, but no hot rod, with a 289 2 bbl. and C4. I guess it all depends on what the owner wants. I was happy with a 57 Chevy 3100 short-bed/w 235 six and column-shift 3-speed. Although that was close to 50 years ago, I think I would still be happy, but doubtful there is anything that could be done to make it as comfortable as my 2017 Ram 1500 4 x 4 crew cab.

 

Hi all, O.K. Got a call. The rear end is a Ford 9 incher as the bolts cannot be removed with a socket! I had him block one wheel and opposite wheel spins in opposite direction so it is an open carrier. The axle stubs have the 3 small holes in them so finer spline axles. We talked and we think guy who swapped him carriers took the Torque locked taller carrier and gave him this one. He thought the swap was O.K.! So rear end is identified. Now I had him check the tachometer. It is an Equus brand 8000RPM tach mounted on the column. And yes there is a setup procedure to have it read 8 cylinder engines. SOO he will locate the instruction manual and we will go over it on the phone once I know how he wired it. Turns out several ways to do it. Finally the transmission numbers are as follows 69ZP7006A. Will check this out or if someone out there has source for identification that would be great. As he said it is all aluminum so assume C6 unit from 1970 as he was told from a Mercury. Me thinks he is seeing wrong RPM's as others here suggested. If that is the problem he will be good to go with a new floor shifter. He said thanks to all in helping him on this. He and I appreciates your input. Will keep you posted!

 

Just for kicks -- did he try this? (It doesn't cost anything.)

Junkyard math. Most manufacturer's rear end gears come in spaced out ratios -- like 3.08, 3.54, 3.78, 4.11 or so. Not (at least for the same housing) in close changes like 3.54, 3.60, 3.65. So, you put one rear tire on the ground, chalk a vertical mark on the other near the ground and turn it one complete revolution while counting the driveshaft rotations -- like 8 and 1/4 revolutions of the driveshaft divided by 2 gives you a clear guess that it's a 4.11 (as they probably don't make a 4.125).

We went 250+ mph with a 28-spline 9-inch with no problems.

 

Thanks I will forward this to him. I looked up the numbers he gave me on a Ford Transmission site. As follows He gave me 69ZO7006A. I believe the first slot should be a C. Therefore it would read C9ZP7006A. According to this site it rings up as
C= decade of 1960-1969
9= year built
Z= Mustang application
7006=Basic number of all automatics
A= original status of released parts (assume no running modifications in production!)

So the only issue is the P in the numbers on the transmission.

I did look up a kick down rod for him and as I am finding on the internet very hard to locate the correct one and Lokar makes a kit for his application if he wants one. Still waiting for photos to verify all this! Thanks.

 

Hi, Well we got this problem solved I believe. Running his transmission numbers he does have a 1970 C-4 transmission. He found a kick down rod for it also. If he did not he was going to call Lokar to get a cable type set up. That is done. And finally when he bought the Equus Tachometer. He wired it up and never programmed it!! After talking with him he did not realize you had to do this. He does not use the internet so I am downloading the install instructions and mailing them to him. When he is ready to program the tach we will do it together over the phone. I had him write down what he has for a drivetrain in case any issues pop up. I will post another note when we get the tach set correctly. He has the truck jacked up in the shop to replace the rear transmission seal as that is leaking a bit. Very strange this tranny was rebuilt and seal leaks! Again my many thanks to you all for the great input on this. He appreciated all your help and I do also. Now I can get back to chasing down history of a 1956 Corvette being pulled out of a long sleep for a friend and 2 race cars histories still alluding me. Never ends!!!