Replace rear-end in a MK II

[RJF9301]

I have a MK II Roadster with a solid axle 8.8 Ford rear end with a 273 ratio. The problem is constant shifting between 3rd and 4th gears and 5th gear is useless below 85-90 mph and only 1st gear does not bog below 2100 rpm. I would prefer fifth gear to become effective in the 60-65 mph range. I am contemplating a Mustang replacement with either a 345 or 355 ratio built between 1986 and 1993 with a solid axle length of 59 and 11/44 inches. Do I have this correct? My transmission ratios are: of 3.35:1; 1.99:1; 1.33:1; 1.00:1; and, 0.675:1. If there is something better than the above replacement, if so,what would it be?
Bob

[michael everson]

You can just change the gears in the 8.8 you have. Any competent shop can do it for you. Most people like the 3:55 ratio.
Mike

[David Hodgkins]

You can just change the gears in the 8.8 you have. Any competent shop can do it for you. Most people like the 3:55 ratio.
Mike

^^^^This. You will be happy with 355s

:)

[mburger]

Ditto on the 3:55. It’ll feel like a new motor was swapped in.

[RJF9301]

Thanks for the positive comments on choosing a 355 ratio. However, swapping gears on a Ford 8.8 is inconsistent with what I have been told by two different mechanics, one of whom for years was with Porsche Racing. Because the 8.8 is not a bumpkin gear box and has a solid axle, the gears cannot be swapped, rather the entire axle and gear box unit must be replaced. So my questions are: is that true? Secondly, if true, do I have the axle length correct (59 and 11/44 inches) for an MK II? I would add a third question, do I want a limited slip unit or non-limited slip unit?

Bob

[David Williamson]

Yes the gears can be changed in the 8.8 axle, I changed mine myself from 2.73 to 3.27 in my garage. Yes you want a limited slip and the clutches for it are independent of the gears so they just stay inplace when the gears are changed.
David W

[RJF9301]

David

Yes that is true, but I understand that a special, unique tool is required to set the pinion and ring which few people have and is not cost justifiable for a single use. If the pinion is not accurately set, eventually whining and premature wearing will occur.

Thanks for the answer on limited, non-limited slip differential.

Bob

[David Williamson]

No special tools that a mechanic won't have. You need to set the pinion bearing pre-load using a beam style torque wrench. Check the back lash with a dial indicator. Check the gear pattern with thin grease. Most times if you use Ford gears the shims from the old gears will be good for the new ones. Like I said I did it in my garage except for using a bearing puller at work (big chemical company) so just basic tools. I wanted the shim from the old pinion to use on the new pinion. I did do it before putting the axle in the car but many have done it on an assembled car. I heated the ring gear in the oven while my wife was away :-)
David W

[luvaz]

To the OP-

Yes, you can do this yourself w/the proper tools, or have a shop specializing in drivelines do it for you. A few years back, there was a video produced by a Ford Master Tech that went by Bad Shoe Productions. He sold a video made specifically for DIY 8.8 ring & pinion swaps, start to finish. Like others, I too have done the swap from 2.73 to 3.27. It took the better part of a day to do it. Doing it right requires a deflecting beam-style torque wrench to measure drag torque when crushing the pinion collar. If you look around, they are out there. Although it may be overkill, I chose to have a 'companion flange holding tool' (it's a Ford-specific tool) made at a local machine shop (it cost me a whole case of beer, LOL). Many have done the gear swap w/o the tool, though. I understand it is less complicated to do if you use Ford gears in the swap. Again, Bad Shoe Productions has the DIY video to walk you through it!

ON another note, I understand the 3.55's are known to wake up a stock 5.0 (and others), but you should consider your specific set up (engine size, cam, etc.) to help guide you w/the better (none are perfect- it's all a compromise) ring & pinion choice. I went w/a 3.27 as I have a 427 stroker, for example.

Whereabouts are you located? Perhaps another owner/builder lives nearby....

HTH,
Will

[Just puttering]

Calculate your current setup and then look at the ratio you want to go to. https://www.tremec.com/calculadora.php

1. replacing the axle housing will be harder than replacing the gears, and you can put any ratio made in the housing you have (as stated below).

2. get an install kit so you have a selection of shims. Actually, you could try and use the shims from yours and see if you luck out and they work. If needed it would not take long to get them. just consider you may not be able to finish this in one day. FORD probably has individual shims on the shelf if you find you need one!

2. a bearing puller is needed for the pinion and case bearings! the pinion bearing may need to come off several times to change the shims to set the pinion depth. You need to be able to install the bearings also.

3. when setting the pinion depth DO NOT use the crush sleeve, it is used at the final install not during setup, also wait on the pinion seal, less chance of damaging it.

4. be very careful when installing the bearing races, there are race driver tools but you can get away without them if you are careful. Same with the pinion seal

5. If you are going to have the differential apart, put in a POSI!!!!

6. If I was going to have a shop fix it, I might consider pulling the rear axle and taking it to them ???

I found a nice chart of 8.8 parts, ratios and etc.
https://www.differentials.com/ford-8-8-differential-parts-3/


Here is a nice write up on changing gears
https://www.motor.com/magazinepdfs/102015-8.pdf

[RJF9301]

Will

Thanks for you excellent and informative response, which I am happy to learn sync's with what my mechanic has been saying. We have opted for a complete axle replacement using a 355. Lastly, I am located in Strasburg, VA, which is in the extreme NW corner of VA.

Bob

[RJF9301]

Moderator

Thanks for you excellent and informative response; however, we have opted for a complete axle replacement using a 355.

Bob

[Just puttering]

What rear suspension do you have?

Where are you getting the 3.55 one?

Please post your swap over process. I do not remember seeing a swap out the rear axle thread before, And dont forget to add a few pictures.

A first drive video would be great, i bet the 3.55's will make a big difference!!!