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Author
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Topic: 69 mach 1 rear end. What is it???
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kewljay223
Gearhead Posts: 223
From: Long Beach, California
Registered: Sep 2002
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posted 11-18-2002 02:21 AM
   
how can i find out what kind of rear end i have and the gear ratio on my 69 mach 1?? i bought the car used and so i dont have the tag with the codes on it.
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Rory McNeil
Gearhead Posts: 1235
From: Surrey, B.C. Canada
Registered: Nov 2000
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posted 11-18-2002 02:30 AM
IF, the rearend is original, there will be an axle code on the data tag, riveted to the drivers door, near the latch. There should also be a tag under 1 of the diff. carrier nuts. If that tag is missing, there is a very good chance that the 3rd. member has been changed, or repaired. To be certain, I`d pull the chunk & count the gear teeth.------------------
78 Fairmont 428 4 speed 10.20@130mph
80 Fairmont 302 5 speed 12.8@105mph
85 Mustang NHRA Stocker under construction, 302 5 speed
59 Meteor (Canadian Ford) 2 dr sedan 332, auto
74 F350 ramp truck 390 4spd
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Lennie
Journeyman Posts: 40
From: Denton, TX, USA
Registered: Dec 2001
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posted 11-18-2002 05:35 AM
As far as gear ratio, wouldn't a quick and not so accurate way of determining gear ratio be to lift the rear end, mark the tire and drive shaft, then make one revolution of the rear tire and count how many turns you have on the drive shaft???
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Scott (69Mach)
Gearhead Posts: 502
From: Walnut Creek, CA USA
Registered: Jun 99
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posted 11-18-2002 10:28 AM
Yep. If the tires rotate opposite directions, you have an open differential.
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kewljay223
Gearhead Posts: 223
From: Long Beach, California
Registered: Sep 2002
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posted 11-19-2002 01:10 AM
i looked at the tag on the door and it had a 6 on it. i looked it up in the code section of one of my manuals and it said it was a 3:00:1. and yes the tires rotate in different directions. is this a good ratio?? i have no idea what each number means. and what is better.... an open or closed differential??
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SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
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posted 11-19-2002 08:45 AM
It's a good ratio for cruising, not so good for acceleration. Open rears apply power to only the right rear wheel, limited slip or 'posi' rears apply the power to both rear wheels which is more desirable for racing. ------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150 Be sure to remember our sponsors, Mustangs Plus, NPD, and Osborn Reproductions.
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indyphil
Gearhead Posts: 877
From: Lafayette, IN, USA
Registered: Jul 2002
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posted 11-19-2002 10:40 AM
Steve,
Why do open rear ends only apply power to the RIGHT rear wheel? Surely if it is only one wheel drive there wouldnt be a need for a differential or a LEFT rear axle? I thought that an open rear end applies power to both wheels but when one wheel loses traction it spins freely and the wheel that still has traction wont get any torque. Have I got my logic wrong somewhere? I have a 2.79 open rear end on my 68 and it seems like sometimes the left wheel spins and sometimes the right wheel spins, usually depends on if im turning left or right.
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lyle29464
Gearhead Posts: 827
From: Mt. Pleasant S.C.
Registered: Mar 2000
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posted 11-19-2002 10:55 AM
I think the wheel with less traction will always spend first.The engine torque will shift the weight.------------------
Lyle
69 rag top
93 explorer
98 f 150
20' shamrock 302 "If it has boobs, tires, chips or a prop sooner or later it's going to be trouble."
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Fastback68
Gearhead Posts: 1746
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 11-21-2002 11:05 AM
I've finally tried 'em both, and after two years of dreaming of a limited slip, I'm gonna stick with the open. I'm a cruiser and occasional blaster, BTW.
As for the 2.79 ratio, though ... gotta change that. You're missing out on too much fun.
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MrWesson22
Gearhead Posts: 1209
From: Dacula, GA
Registered: Sep 2000
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posted 11-21-2002 11:33 AM
This is not meant as a criticism of you by any means, but why would anyone choose an open diff over a limited slip?
------------------
Neal 69 Gulfstream Aqua Grande
351C/4sp
https://mustangsandmore.com/ubb/MrWesson22.html
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Hell_Fish
Gearhead Posts: 672
From: Austin, TX.
Registered: May 2002
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posted 11-21-2002 02:08 PM
Thats odd and good to know. On the Mopar stuff, if one wheel turns one way and one the other it limited slip or "sure grip". On an open rear only one wheel spins, the other stays in place.Thanks guys! Learnin' something new every day.
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JCQuinn@work
Gearhead Posts: 440
From: Lakewood, CO, USA
Registered: Jun 2001
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posted 11-21-2002 03:06 PM
Neal, from my experience I have not noticed much difference in highway use between open and non-open differentials. I guess it's a fucntion of how you drive.For racing I like to start out with an open differential and tweak the suspension until the car launches with both tires pulling equally. That way I know that I have a good set up for a good track (the car will go straight). Then I put in a locker or spool so that when the track is not so good one wheel will not break loose. If you watch cars leave the line you will see a lot of people correcting the direction of the car at the launch, that eats ET. John
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Ryan Wilke
Gearhead Posts: 1539
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 11-21-2002 06:30 PM
quote:
Originally posted by JCQuinn@work:
....If you watch cars leave the line you will see a lot of people correcting the direction of the car at the launch, that eats ET.
Hey John,
Do you think that could also be a problem of having unequal weight distribution between the right and left sides? Of course the front to rear is usually different, but from side to side it should be the same, correct? Ryan 
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mustangs68
Moderator Posts: 18183
From: Hampton,Virginia,USA MCA#39406 M&M #12
Registered: May 99
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posted 11-21-2002 10:06 PM
As for the 2.79 ratio, though ... gotta change that. You're missing out on too much fun.
As the Offical President of the 279 Club..I beg to differ
sam
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kewljay223
Gearhead Posts: 223
From: Long Beach, California
Registered: Sep 2002
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posted 11-22-2002 01:35 AM
so my rear end isnt great but its not bad either. thats cool. i am converting it to a four speed instead the original FMX. will i have good pick up with this rear end and tranny?? i also have another question... how do i tell if it is an 8" or 9" rear end? since i mentioned the tranny swap from auto to stick, i need the pedals and stuff. where can i get that?
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Rory McNeil
Gearhead Posts: 1235
From: Surrey, B.C. Canada
Registered: Nov 2000
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posted 11-22-2002 02:21 AM
Unless someones swapped rearends previously, all the 69&70 Mach 1`s had 9" rearends in them, as they only put 8"`s in the 302 (non Boss), & the 250 6cyl. Since the base Mach 1 engine was a 351 2V, they had the 9". If you are still unsure, try this: if you can put a 9/16" deep socket on all 10 diff to housing bolts, it`s a 8", one the 9" the bottom bolt is shrouded by the pinion support casting.------------------
78 Fairmont 428 4 speed 10.20@130mph
80 Fairmont 302 5 speed 12.8@105mph
85 Mustang NHRA Stocker under construction, 302 5 speed
59 Meteor (Canadian Ford) 2 dr sedan 332, auto
74 F350 ramp truck 390 4spd
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Fastback68
Gearhead Posts: 1746
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 11-22-2002 06:47 AM
quote:
This is not meant as a criticism of you by any means, but why would anyone choose an open diff over a limited slip?
Good question ... maybe someone with more experience can explain what my butt is feeling.
Actually, the comparison I've been making is between two Dodge Chargers, one with an open rear and one with a limited slip or full-lock rear end. (The owner doesn't know.) I just find the open rear is easier to accelerate out of tight corners. On the other one, it seems like the rear end wants to carry on going straight while the nose is turning.
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JCQuinn@work
Gearhead Posts: 440
From: Lakewood, CO, USA
Registered: Jun 2001
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posted 11-22-2002 11:39 AM
Ryan, to determine how you want your weight distributed you need to think about what is happening during a drag strip launch. The car is trying to push the drivers side tire into the ground and lift the passenger side into the air. Yes you want equal weight on both tires but in a dynamic situation as opposed to a static one.Since the passenger side tire is trying to lift, it needs more static load in order to have as much weight on the track surface during the dynamic event of a launch. that is why batteries, weight boxes and air bags are found on the passenger side of race cars. Since the dynamic forces are different for each car, engine, tire combination it is difficult to calculate how much weight is needed. That is why the air bag used to be very popular in leaf spring cars. You can raise the pressure in the air bag until the force during the launch is equal at the tire/track contact point. With a four link you can equalize the contact patch pressure by adjusting each side individually. I don't know about the Cal-tracs or Slide-a-links, I have been away from racing for several (20) years and am just now getting back in. Alex can fill you in on what is being currently used. John
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Ryan Wilke
Gearhead Posts: 1539
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 11-22-2002 04:52 PM
John, Thanks for the explaination........I'll probably have to read it and read it and read it again before I get the full grasp of what you are saying though. It's not any fault on you, I'm just thick-headed sometimes when it comes to "picturing" what is being said. Thanks again, Ryan
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