Mark VIII 3.73 Swap - TCCoA Forums
 
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post #1 of 11 (permalink) Old 11-12-2015, 11:10 AM Thread Starter
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Mark VIII 3.73 Swap

I'm back to daily driving my Mark VIII now and the stock 3.08 (3.07's?) gears are getting real old. Sure the gas mileage is great on the highway, but the gearing is all wrong for a high revving DOHC engine with crappy low end torque and no VVT.

I've found a used trak-loc for a great price and will probably get some FRPP 3.73's to go along with it.

Now, I'm finding wildly varying opinions about what's needed to support this swap.

First, I know I'll need a purple speedo gear, but that's easy.

Secondly, I've got a 93 Mark, with the aluminum ds, and zero vibration at highway speeds.

What I'm really concerned about is whether the tranny's tailshaft will be starved or underlubed (I do about 80-90% highway driving, but mostly around 70mph or so) and whether I'll bang into the rev limiter on WOT shifts. I don't track the car FYI and it's just a daily driver with the occasional WOT run.

Some say yes, others say no.

I probably will j-mod the tranny at some point or at least change some springs, but for now it shifts decently and I don't feel like tearing into the tranny.

If going to 3.73's will create a ton of new problems, I'll just live with it, but it'd be nice to hear from others with experience.
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post #2 of 11 (permalink) Old 11-12-2015, 11:31 AM
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Cruising at 70mph with 3.73s should be no problem for your tailshaft. Not that the forced lube mod would be a bad idea anyway, but you shouldn't have any issues at those speeds. As for the shifting and the rev-limiter, without a j-mod you will likely hit the rev limiter on WOT 1-2 shifts, but probably not for 2-3. Either a tune or a j-mod will solve this problem. Also, without a tune, you will likely have a speed limiter kicking in around 90mph or so. Other than that, in my opinion 3.73s are the perfect gear for a daily driver MarkVIII, and are what they should have come with from the factory, so I highly recommend the change.

-91 Cougar LS, coming soon, complete overhaul with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
-98 Mark VIII LSC, Procharger P600b, TR3650 swap and 3.73s.
-90 SC Automatic rustbucket winter beater
-97 Tbird Sport 4.6 Nice weather daily driver
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post #3 of 11 (permalink) Old 11-12-2015, 01:07 PM Thread Starter
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Well, 90mph is not really an issue and might be perfect lol.

BANtario, err I mean Ontario has this 'awesome' speed law that if you get caught doing 50km/h (30mph) over the limit, they call it 'stunt driving/racing' it's a $10k fine, roadside license suspension and roadside vehicle seizure.

Before you get to a Trial. So the cops are judge, jury, executioner.

Needless to say, I won't be doing any high speeds in this car, since it never sees the track.

Anyways, back on topic, Madmikey, since getting the knuckles out of a Mark VIII is a pain vs a t-bird (dumb torx bolts) would I be better off to remove the knuckle/axle on one side and slide the whole pumpkin off to one side? Or maybe there won't be enough room?
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post #4 of 11 (permalink) Old 11-12-2015, 03:10 PM
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It can be done by only dropping one side, but I always found it easier to pull both sides out. The amount of time you spend fighting with the diff to get it out and back in without damaging the axle seal is about the same as what it takes to just pull the other side suspension out.

-91 Cougar LS, coming soon, complete overhaul with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
-98 Mark VIII LSC, Procharger P600b, TR3650 swap and 3.73s.
-90 SC Automatic rustbucket winter beater
-97 Tbird Sport 4.6 Nice weather daily driver
-"Your buddy Mike is INSANE!" -ClintD's dad
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post #5 of 11 (permalink) Old 11-12-2015, 10:26 PM
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Take that time as the time to replace the LCA bushings with delrin, the spring isolators (if you're no longer bagged) with new poly or rubber, and to freshen up the spindle bushings again with Delrin or Poly.

Oh, and the diff mounting bushings in the front and the sway bar end links.

RwP

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post #6 of 11 (permalink) Old 11-13-2015, 02:21 PM Thread Starter
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Quote:
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Take that time as the time to replace the LCA bushings with delrin, the spring isolators (if you're no longer bagged) with new poly or rubber, and to freshen up the spindle bushings again with Delrin or Poly.

Oh, and the diff mounting bushings in the front and the sway bar end links.

RwP
Lucky me, the last owner did most of this stuff lol....

It's got a fairly new coil spring conversion kit (unknown mfr), and I recently replaced a UCA to knuckle bushing with a Mevotech (which was actually made by Tenneco!) it felt like poly, but I suspect it was just higher durometer rubber.

Surprisingly, even the diff and subframe mounts are in great shape - no cracking, no play. The car was garage kept and not winter driven by the first owner for most of its life, so it's pretty well spotless underneath.

My old t-bird on the other hand, well that one had a rough life.

Should I get some new axle seals while I'm at it? They don't leak, but I don't wanna do this twice.
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post #7 of 11 (permalink) Old 11-13-2015, 09:31 PM
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I'll put it this way - "If you have to ask, replace it!" *grins*

I wish I had done that when I did the front rack / PS pump on my Dakota. Today the pressure line blew out and I had to drive 100 miles home.

Wasn't any problem on the interstate, but once I slowed down, it showed that Chrysler wasn't aware it was supposed to be rack and pinion, but instead it's rack and hernia ...

RwP

Fuelly
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post #8 of 11 (permalink) Old 11-14-2015, 02:47 PM
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I put a 373 in my bird this summer from one side only. It went pretty well using a jack with metal wheels it slid right of the axle I did not remove. My problem was the axle seals I got from autozone were the wrong ones for 7-1/2" even though the internet said they were for 8". I'd get those from Ford. My seals are leaking and its going to be a job to replace them after the fact.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.
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post #9 of 11 (permalink) Old 11-15-2015, 09:24 AM Thread Starter
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Quote:
Originally Posted by RalphP View Post
I'll put it this way - "If you have to ask, replace it!" *grins*

I wish I had done that when I did the front rack / PS pump on my Dakota. Today the pressure line blew out and I had to drive 100 miles home.

Wasn't any problem on the interstate, but once I slowed down, it showed that Chrysler wasn't aware it was supposed to be rack and pinion, but instead it's rack and hernia ...

RwP
At least it's not a pressure line on a 4.6 bird lol.

Ever try a Benz without power steering? Some of them run up to 10* of caster! I'm surprised they turn at all.
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post #10 of 11 (permalink) Old 11-15-2015, 09:25 AM Thread Starter
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Originally Posted by gordonm1 View Post
My problem was the axle seals I got from autozone were the wrong ones for 7-1/2" even though the internet said they were for 8". I'd get those from Ford. My seals are leaking and its going to be a job to replace them after the fact.
Good to know. Rockauto says 7.5 and 8.8 are the same... hmmm...this wouldn't be the first time a parts supplier's been wrong about this platform.

Did you have any issues clearing the exhaust that way?
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post #11 of 11 (permalink) Old 11-16-2015, 12:25 AM
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I cut my new exhaust just ahead of the differential to remove the differential. My welding job putting the exhaust back might make you laugh.

I'd like to find a place and parts to section out the exhaust system so working on other areas is not so difficult. I'm just tired of paying four times what I grossed when I was employed to get mediocre satisfaction from mechanics. I'm living with what I have for now.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.
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