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Rear End Gearing Opinions


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Howdy folks,

I'm in need of new rear end gearing in a bad way. Currently running a 6 speed with I think 2.73's. According to the calculators, I can just about hit 70 in 1st gear, over 100 in 2nd and 297mph in 6th, so yeah, just a tiny bit tall lol! 

Not planning on racing, just spirited driving and the occasional abuse of rear tires and still good freeway cruising So I'm looking at an 8.8 from an Explorer and 4.10 gears, trac loc and disc brakes.

Love to get 2nd opinions from people that know more than me about this if this gearing sounds like a good fit and secondly if the Explorer rear end seems like a solid way to go. Trying to do this on a budget so this seems a lot more affordable than building a 9" as I can do all the parts for probably under $500. 

at 2000 RPM that should have me about here for what looks like still decent freeway cruising, although honestly I'll miss that under 2000PM freeway cruising I have now :classic_smile:

image.png.63303f9b49f0c03d39cab0f43739f238.png

Here's 3500 RPM

image.png.bbe118e4c3a335f14dcc557fb049edfb.png

And 5,500 RPM 

image.png.7ee6b9e625fec7b120cecd5827b345ec.png

 

 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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Nice to have that 6th gear. In my opinion a cruising speed of 2,000-2,300 rpm is very pleasant, specially if you have the torque. Cruising speed can mean different things to different people. Some may say speed limit, others 10 over, other 90 mph. Whatever is yours try to keep it within that range and you will be good. Now, I don't know if you have a stock engine or one souped up. Mine being a 408 stroker and having 3.5 gears, I can smoke the tires very easily in 1st gear to the point that it is hard to get good launches without spinning. I can only guess that with 4.10 in street tires it will be even harder. Definitely get some type of truetrac type of differential.

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1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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The Explorer rear axle has 31 spline axles and is stronger than the 9-inch with 28 spline axles. Most of them also have Traction-Lok. With a transmission with 0.63 ratio the 4.10 gears will work well, gives you the equivalent of a 2.58 final drive ratio.

Plus, they already have disk brakes.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Perfect, thanks. That's really the confirmation I was looking for. Loads of them in some parts of the country. Around here they get gobbled up for use in jeeps so having a hard time finding that combo. I'll keep looking. Thanks

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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The explorer 8.8s are great. I have beat the snot out of mine for years and it’s still going strong. It is harder to find in 410. Most of them came in 373. Which is what I have. Let me know if you have any questions about the install or just do a search on the forum. It’s been discussed several times. I posted link to a lot of good info on one of the ranger forums also. 

Edited by turtle5353
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Kevin
1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.

 

 

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I would not do the explorer rear due to C clip axles. Look for Lincoln, Granada, Monarch 9' Disc brakes rear much better option. If you are going 297 you have a new worlds record, lol. I do not think explorer is just a bolt in but the 9" is.

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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On 3/27/2021 at 5:58 AM, turtle5353 said:

The explorer 8.8s are great. I have beat the snot out of mine for years and it’s still going strong. It is harder to find in 410. Most of them came in 373. Which is what I have. Let me know if you have any questions about the install or just do a search on the forum. It’s been discussed several times. I posted link to a lot of good info on one of the ranger forums also. 

Thanks. Yeah I'm pretty sold on them and seems like a fairly straight forward install. I'll look up the other links you mentioned. 

On 3/28/2021 at 1:02 PM, Carolina_Mountain_Mustangs said:

I would not do the explorer rear due to C clip axles. Look for Lincoln, Granada, Monarch 9' Disc brakes rear much better option. If you are going 297 you have a new worlds record, lol. I do not think explorer is just a bolt in but the 9" is.

Thanks I like the idea of the bolt in 9", but they are just a lot more money and less plentiful around here anyway so I think the 8.8 should be a big upgrade as it is. And yes, I'm thinking that 297 MPH might be a tiny bit of a stretch for this car. I still haven't had this thing past 90 so I have to think this thing would disintegrate long before that even if I had the power to do it. :classic_smile: 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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  • 3 weeks later...
On 3/27/2021 at 5:58 AM, turtle5353 said:

The explorer 8.8s are great. I have beat the snot out of mine for years and it’s still going strong. It is harder to find in 410. Most of them came in 373. Which is what I have. Let me know if you have any questions about the install or just do a search on the forum. It’s been discussed several times. I posted link to a lot of good info on one of the ranger forums also. 

Hey Kevin,

I've tried searching up and down the forums for details on this but having a hard time as I think it doesn't do well with using 8.8 as a search term, so I'll ask here or if you can point me to some threads I'd appreciate it. 

I finally found a 4.10 rear end now and am looking for details on parts needed to complete the job. Any details you have on things like the spring perches, lower leaf spring plate and the axle flange would be a big help.

Thanks

-Will 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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Did you get an 8.8 out of an Explorer?

spring perches I bought from summit racing, they are standard universal perches.  I welded them on to match same pinion angle as the stock 8”  

Lower leaf spring plates I made from 1/4” flat steel. I cut the shock mount ears off stock ones and welded them to the flat plate. Drilled holes properly sized for custom u bolts I had made at spring shop locally. 

Driveshaft was made by same shop that made my u bolts. I used stock drive shaft front half and used rear of the Explorer shaft to bolt to rearend. 

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Kevin
1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.

 

 

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Thanks, that helps a lot.  Yes, it's from a 2000 Explorer. 4.10 gears, trac lock and disc brakes. 

On the perches, I'm thinking of going longer than standard to help with spring wrap. But sounds like the standard ones are working fine for you and you are running a lot more power than I will be so might rethink that. 

I have the stock Explorer U bolts so hopefully those will work for me. Not sure what I'll do on the lower plate just yet, but was thinking of moding the stock lower if possible. I had the driveshaft made for my new trans not that long ago so hoping to make it work with a different flange rather than cutting it again if I can avoid it. 

Thanks again for the feedback. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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The stock lower plates wont work because the size of the axle tube is bigger on the 8.8. That's why I ended up making my own plates and welding the shock mount ears to them.  Also another thing you don't want to forget to do is to weld the axle tubes to the center section with a good stick welded and some 7018 rod. Get a little better penetration than mig welding them, but a mig will work if you have a 220volt and crank her up a bit.  The stock axles tubes on the 8.8 are pressed in and tend to turn under some power. 

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Kevin
1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.

 

 

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Ah that's right on the lower plate. Someone had told me that it can be modded but now I see what you mean. And thanks for the tip on welding the tube. I've seen people do that with 8.8's in rock crawlers, but didn't know if that was needed for our cars. May as well do it since we'll be welding on it anyway. 

Thanks again. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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OK, next question, what did you do about brake lines? Do you recall what hoses and fittings you needed to make that work on the Mustang?

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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Actually the factory mustang hard lines worked fine but they were a little long. Used factory mustang rubber line to the rear end then used the factory hard lines and splitter across the rear end.  I was always going to make new hard line across the rear but never got around to it.  

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Kevin
1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.

 

 

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I do not know about the Explorer 8.8 but in Mustang about 1985 the brake lines went metric, My son broke his in the 84 mustang 5.0 and the one I got out of junk yard was newer model and the old lines would not fit. I am sure if you take calipers to parts house you can get the right fittings.

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When a man is in the woods and talks and no women are there is he still wrong??:P

David

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7 hours ago, turtle5353 said:

Actually the factory mustang hard lines worked fine but they were a little long. Used factory mustang rubber line to the rear end then used the factory hard lines and splitter across the rear end.  I was always going to make new hard line across the rear but never got around to it.  

OK perfect. I was thinking I'd have to rework things. Now looking closer I see the original setup is pretty close, so hopefully this will all just go together. 

4 hours ago, Carolina_Mountain_Mustangs said:

I do not know about the Explorer 8.8 but in Mustang about 1985 the brake lines went metric, My son broke his in the 84 mustang 5.0 and the one I got out of junk yard was newer model and the old lines would not fit. I am sure if you take calipers to parts house you can get the right fittings.

Thanks, I'll verify this isn't metric before trying to wrench things together. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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  • 1 month later...

I'm finally getting this wrapped up. Like every car project I work on it ends up taking ages longer than I initially planned. One thing I ran into was the exhaust. Like literally the drive shaft runs into the exhaust. Since the diff is offset, the driveshaft now hits the exhaust so I had to cut it off up close to the trans. I know there's no magic here as you just need to make it work, but were you able to keep the exhaust running up the tunnel and more or less symmetrical?  Hoping to not have to rebuild the whole exhaust and just reroute the end of this thing, but not sure how that's going to work, especially without it hanging down under lower under the car. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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  • 1 month later...

Another update: I finally have this thing running and driving more or less normally. Took me a while to get someone to redo the right side exhaust that I cut off to make this fit. 

One big problem I ran into is the flange on diff was running into the corner of the floor / tunnel. Basically as soon as I'd step on the gas at all, the diff would grind hard into the floor. Up and down 20 times beating the tunnel and floor and I got it so it would only happen over very big bumps or when I stomp on the gas, but that's about as good as I could get with hammers. 

Long story short, I finally ended up doing something I hate for this car and put giant ass shackles on the back to deal with this for now. That isn't what I have in mind for this car as if anything I want it lower and not taller so that was a painful choice. At some point, I'll need to bite the bullet and cut a hole in that corner and put in a patch to get more clearance.  Just hate doing that to rust free original floors. I was OK with beating on it, but not excited about cutting it away. 

Now on the plus side, boy is this car a lot better mannered now and drives like it was supposed to. I was worried that 4:10's would be too much, but if anything I could see going even lower. This should get even better once I get some more reasonable size wheels and tires on this thing.

 

 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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Traction bars will help the spring wrap on acceleration and keep the differential pointed ahead instead of up.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Well that's an interesting idea. I'll have to think about that. I've never loved the look of the big ones that clamp onto the spring. Are there more modern designs that aren't that expensive? Since I'm just looking to try this out, I'd hate to spend a bunch on it to experiment. 

Thanks

 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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To be honest I forgot all about the clearance on the tunnel. I apologize.  I do remember now that you mentioned it. I clearanced mine with a hammer and a long solid rod. My car does have shackles in the back and sits pretty high. So that maybe why mine didn’t rub as bad.  

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Kevin
1971 Mach 1

408C Stroker - C4 w/3,000 stall - 8.8" Rear w/3.73's - Disc brakes all way around.

 

 

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Each car is different, and honestly a little relieved that you had do so some of that as well. It was really bad at first. I didn't have a good angle to see it and didn't catch that there was going to be a clearance problem once the suspension is down. With the new shackles and probably 1.5" of lift, it's not hitting most of the time. I hit a big bump yesterday and it touched but at least didn't bash into the floor like it was. I had the same idea of trying to use a rod of some kind and a hammer to make some room, but haven't been able to come up with the right rod and a way to do that in the driveway. Going to see if I can get it on a lift and beat the crap out of it a bit. 

My car has giant tires on it right now (tall and wide), so being that high doesn't look terrible I think as the wheel wells are still pretty full. At the moment, just glad to be able to drive it and see how this rear end works. 

 image.png.c5a82cdc270542869e213815ec368140.png   72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed, FiTech EFI, 8.8 / 4.10 LSD Rear end, discs all around. Fancy rattle can paint job. 

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Sitting stationery, how much clearance do you have? If you go to smaller wheels and shorter shackles, how much worse will it likely be?

I've considered getting an 8.8 as well for when I get around to my car. Probably a 3.55, but 3.73 is more common. 

What year Explorer did yours come from? I intended on getting one with disc brakes and from a leaf spring Explorer. 

After reading about the offset, I figured on shortening the long side so the diff was centered to avoid the 'clunk' and exhaust clearance issues. Seems like it would be easy enough when moving the spring perches around.

Also, I know aftermarket aluminum driveshafts are available for the Fox and later Mustangs. Depending on the trans, I thought about an AOD or T5, then a lighter driveshaft becomes an option, too.

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I'm running a 408, 5 speed (.82), 3:89's with a 27" tire. 1st gear is pretty useless. I'm running nitto 555R II's and can blow the tires away with ease at the top of 2nd. Haven't tried 3rd yet. I don't race the car but it is fun to drive around town. 

www.puregemdetailing.com

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