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fstbck70 04-16-2015 07:36 PM

1970 Fastback Build Thread
I've started a thread on another forum (TMS), but that site has had nothing but problems with glitches and bugs. Thought I'd bring my project since I know there are a few others in the same boat as myself. Anyway, I'll mostly add pictures for now and update as I go along.

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fstbck70 04-16-2015 07:48 PM

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fstbck70 04-16-2015 07:53 PM

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ER12883 04-16-2015 08:40 PM

Nice! Keep us posted.

I was in the same boat, started posting about my project on TMS, but haven't been able to post pictures from my phone for over a year now. Oh well. Generally good guys over there, but I find I get more and faster answers in the first gen section here than TMS, maybe more classics owners here.

fstbck70 04-16-2015 09:23 PM

TMS was "bought" by IB Autogroup. They collect multiple car/truck forums and run them on the same software basically. The site worked great for a few months but once again had started to be neglected.

Anyway, next up is front and rear suspension. Going with a Rod and Custom coil over in front, and going to put a 8.8" in the back.

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Scott2 04-17-2015 10:29 AM

Looking very much forward to following your build. I have a neglected 70 Boss 302 in my garage that needs some TLC!

Jbone007 04-17-2015 11:13 AM

Wow that is a lot of work, can't wait to see the finished car!

Teak 14 04-17-2015 04:08 PM

Scott love to see boss pics!!!

Jbone007 04-17-2015 04:47 PM

Yes Boss Picts!!!

tym_v6 04-17-2015 09:01 PM

Yes, please start a thread about the Boss 302!

fstbck70 05-16-2015 03:52 PM

Just purchased the rear end. 8.8" out of a 1988 Thunderbird Turbo Coupe.

Just need to weld on spring perches and we should be good to go.

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ER12883 05-16-2015 10:27 PM

What's the gear ratio in the 8.8?

fstbck70 05-17-2015 08:50 AM

3.73 is going to go in it.

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TCopp 05-17-2015 09:03 AM

Id love to build up one of these. Following!

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fstbck70 06-13-2015 05:18 PM

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Did a little cosmetic work on my 8.8" rear end. Cut off all of the shock brackets so I could weld on new leaf spring perches. I think it came out pretty well.

I will post a picture of it tomorrow after I put on the truck bed liner.

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fstbck70 06-14-2015 08:25 AM

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With the coating on
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Tyoung68 06-14-2015 02:39 PM

What made you go with an 8.8?

fstbck70 06-14-2015 06:24 PM

Cost and availability mostly. Shouldn't have much issues when I get through with it I hope.

tym_v6 06-14-2015 10:26 PM

What's with the dent in the diff cover? Did the prior owner go off-roading with it? ;)

I have a spare 8.8 cover kicking around if you need one.

fstbck70 06-15-2015 07:40 AM

I'm guessing shipping/handling. It happened after he primed it so I'm guessing it wasn't under a car

Thanks for the offer, but the rebuild kit I'm ordering comes with a new cover.

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fstbck70 08-08-2015 10:18 PM

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"Progress" haha

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Front suspension should be here soon!!!

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ed_ph413 08-10-2015 10:47 AM

Thanks so much for posting. I'm considering doing this so it's very informative

fstbck70 08-21-2015 04:08 PM$

Just went ahead and ordered this kit. I'll let you know how the install goes!!!

fstbck70 08-27-2015 05:49 PM

All the goods showed up today!!! Pretty excited. I'll probably get to the assembly next Saturday. I'll be sure to take lots of pics

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fstbck70 08-30-2015 02:27 PM

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Couple pictures of the Millard car show. Pretty sweet Mustangs if you ask me

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fstbck70 09-06-2015 09:56 PM

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All right guys, 8.8" rear end install went pretty good. I forgot to buy C clips so I have to run to the auto store in the morning. I'll give you guys a rundown of the install and any problems I ran into.

First off, I purchased the 3.73 ratio, 5 lug, traction lok from American muscle. Comes with differential, diff. bearings, axle bearings and seals, pinion and pinion bearings, axles, and diff. cover and shims. Only thing it doesn't come with.... C clips.

Above is the installation instructions that I followed. Quite detailed and very user friendly. Now I will say that my starting point could be different than some of you. I started with a bare housing, where some of you may just do a gear change or something like that. If you do tear your rear end apart, make sure you keep track of all of your shims. This will give you an idea of where your new shims will go.

Alright, first thing I did was remove the old axle seals and bearings. Now, they say tell you to use a seal puller and a slide hammer to help with the removal. Like I said, I started with a bare housing with nothing in it. I went with the cost effective way of simply pry bar and a 6' piece of 1/2 thick rebar. First, simply pry of the seal with the pry bar and then slide the rebar through the end of axle tube to the other side and rest it right on the old bearing. Give it a few hits with a 2lb sledge and it should come out. Then install the new ones exactly like the old. Pretty simple.
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Next I focused on the pinion and pinion bearing. If you are upgrading your rear end, make sure you get the shim between the pinion and pinion bearing. That is very important to set your pinion depth. I didn't have one to go off of so I had to use a little trial and error. Here's what I found. The instructions said to install shim(s) between ~.230-.9xx mm. It was a pretty significant range and the shims they sent were .40, .50, .85 and .90. I went with .50 mm since it was roughly in the middle. The pinion bearing must be pressed on, however, since I didn't know if my pinion depth would be correct, I bought another bearing and I dremeled out the inner radius so it could be removed without having to use a press. Note: this is only temporary in order to set the correct pinion depth.

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Above is the pinion gear with the shim and the bearing on. The crush collar would slide down the shaft next and then you need to slide it through the hole and slide on the pinion flange and pinion nut. At this point, the instructions call for another special tool. I believe it is called the pinion flange companion tool. Don't need it. Just shove a punch through one of the holes on the pinion flange. It will catch on the housing itself and will not allow it to spin. Use a hammer drill to get it started. That will only get you so far. Use a beaker bar to get all of the slop out of the pinion. It should not move. Once the slop is out, you must pre-load the pinion and compress the crush sleeve. I believe it calls for ~15-25 in-lbs.

Next thing is to get the bearing on the differential. Since I don't have a press, I went to the kitchen. 350 degrees for 25 mins made easy work of those bearings. Once they are on, you can set it in the housing and put in your shims. The instructions call for ~6.75 mm on the right side and enough on the left side so there is minimal side to side movement of the differential in the housing. When it was all said and done, we had 4.6mm worth of shims on the passenger side and 6.2mm of shims on the driver side. We followed the instructions, but the differential wouldn't spin freely, so we made adjustments and that is what we ended up with.

Then we had to measure the backlash, it is kind of hard to explain, so here is the link to a video that helped us.

Once the backlash is with in specs, you can paint on the yellow indicator paint and find your tooth pattern. This is where having the correct pinion depth and backlash will give you good tooth patterns. Spin it a few times and see what you got. Follow the instructions if you don't have correct tooth pattern. Here is what we ended up with.
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Since we were happy with the results, we took it back all apart so we could properly press the bearing on the pinion shaft. We put the pinion shaft in the freezer and the bearing in the oven. Same temp as before. Put the two together and they slid right on down to where they were supposed to be. We put on a new crush sleeve and installed it the same way as before. Used an impact, then breaker bar, to set the pinion flange preload. We put the differential back in with the same shims and double checked out backlash to make sure it was still in spec.

Next we could put the axles in, but we are still waiting for the C clips. Once those get put in, we can reinstall the differential bolt and put on the diff cover and put in oil.
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Overall, it wasn't a monstrous project. I think anyone is capable of doing it. If you guys have any questions or picture requests, let me know before I get the cover on.

Hopefully, this will help some of you in my same situation.

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Tyoung68 09-06-2015 11:58 PM

Make me want to try.... What made you pick those gears?

ER12883 09-07-2015 05:20 AM

Nice write up. Reminds me of doing my rear end and removing the axle seals. I spent a long time fashioning a tool that hooked on the back side of the seals to carefully remove them...then I watched a YouTube video where a guy took 5 seconds and used the end of the axle to pop them out. Knowing the right tricks can save tons of time and frustration!

fstbck70 09-07-2015 09:18 AM

I went with the 3.73 gears because I wanted something that is aggressive but not too aggressive. I think they are a pretty good in between.

Io watched a lot of YouTube videos to find good tips and tricks. Worked out pretty well. I didn't have to spend tons of money on parts id use once.

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fstbck70 10-18-2015 06:40 PM

Finally ordered my rear springs. 4.5 leaf mid eye 175# spring rate. Should drop the rear 1". Now, does anyone have any quality rear shocks? Brands to look at or avoid would be a great starting point.

Let's here them!

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Tyoung68 10-18-2015 08:14 PM

I have kyb's and have no complaints. They are a bit harsh riding though

fstbck70 10-22-2015 05:39 PM


Originally Posted by Tyoung68 (Post 2303784)
I have kyb's and have no complaints. They are a bit harsh riding though

Now when you say harsh.... Lol, what do you mean exactly?

Anybody else have any recommendations?

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Tyoung68 10-23-2015 01:51 AM

They're just stiff so you feel more of the road But I haven't had any others on the car so I can't say they are the best out there.

fstbck70 10-23-2015 03:10 PM


Originally Posted by Tyoung68 (Post 2305157)
They're just stiff so you feel more of the road But I haven't had any others on the car so I can't say they are the best out there.

What model are they? Gas-a-just, GR-2?

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ER12883 10-24-2015 02:28 PM

FWIW, I also put KYBs on my 67 FB, Excel-G OE. The ones it came with were shot, so I was looking for something cheap to get me up an running. They felt fine to me, but since I haven't tried any others, it's difficult to say.

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