BIG Swap Help

[mpace6a]

Hey all, I'm fairly new to the forum. Been lurkin a while :peek: finally decided to make an account since I bought a 'manche! Thing is, it has a gutless, 2.8 with a bad rod. I'm buying a parts xj this week, and am going to be swapping out the 2.8 for a 4.0, an AX5 for an AW4, and the dash cluster (I hate idiot lights). Wanted to ask to see what I need to change for the swap, anything i might have to buy or fabricate myself for the swap, and see if anyone on here could offer any advice for the swap, maybe tell me things I need to know or consider while doing it? Any and all help is much appreciated!

-Matt

[jimoshel]

If the XJ is complete you shouldn't have to buy anything except maybe new oil, air and transmission filters and fluids..

[Geonovast]

Hello neighbor :waving:

 

A lot of small questions will depend on what years the trucks are. Obviously, being a 2.8, your MJ is an 86. Any year XJ will work, all with about the same amount of work to get it...working. Your MJ is literally going to have to be gutted, and replaced with everything from the XJ. This means all the wiring. Also, IIRC, the 2.8 used a mechanical fuel pump, so you're going to need to find a sender for your tank.

 

You're also going to need a new rear driveshaft, but since your current shaft is longer than you need, it's easy enough to have it shortened. (I'm assuming they are both either 2wd or 4wd).

[mpace6a]

Is the wiring harness on the 2.8 compatable with the 4.0? and is the AW4 longer than the AX5? THe xj is an '88 if that changes anything

[deziped]

Huh! Obiviously you didn't read the last sentence in the thread preceding your last thread. It answers one of the questions in your last thread.

[Pete M]

MJ's have a foot more wheelbase over an XJ so rear shafts do not interchange.

 

nothing in your MJ will help the 4.0 to function. it ALL needs to be swapped, including the radiator and rad support (which necessitates swapping the hood and latches too). it's been done. :thumbsup: oh, and you'll need to splice the XJs rear lighting wires into the MJ harness and the aforementioned fuel pump and whatever changes to the lines it might need.

[Garvin]

The 4.0 rad will not fit unless doing some cutting to the head light buckets, modifying the upper rad support and lowering the frame rails some. You will also run into clearance issues with the header panel if you put it right under the upper rad support.

 

The other thing you will have issues with is the firewall. The firewall was changed in '87 to be pushed back slightly and was flattened out so the 4.0L would fit. You would need to get a BFG and add some love to the firewall to get everything to clearance correctly.

 

To give an idea on the radiator, here's a pic I took while doing my build.

 

 

This is an image of it with the new rad bolted in (crappy picture but only one I really have of the new rad bolted in place).

 

[87Warrior]

If you need a hand in doing any of the big parts of the swap send me a message. If I am free I will certainly make the short drive to help out a fellow MJer. I have never done the 2.8-4.0 swap, but I can pull a dash in no time flat.

[Jerry]

As I understand it there are issues with the firewall too. It needs to be modified to fit a 4.0L. There is another option for you which is replacing your 2.8L block and heads with a Camaro(?) 60 degree 3.4L. All the ancillaries from the 2.8L will swap to the 3.4L. No firewall, wiring or radiator mods.

Please correct if I'm wrong, just repeating info I read here before :wrench:

[Joop]

Been there, done that :ack: If you wish i can snap some pictures of mine and how i made it work, but it will have to wait untill this weekend. Its in a million pieces and parked in my parents garage.

[mpace6a]

Been there, done that :ack: If you wish i can snap some pictures of mine and how i made it work, but it will have to wait untill this weekend. Its in a million pieces and parked in my parents garage.

 

Pics are always great! And I've heard the same about the firewall, but when i measured its exactly the same as a friends '93 XJ?

 

-Matt

[Pete M]

late 86s are reported to have the 87+ firewall.

[mpace6a]

well assuming that the engine will fit, is their anything i really need to do to help the swap along? It'll be my first engine swap, so any advice is useful!

-Matt

[Pete M]

take LOTS of pictures as you go along dismantling the XJ so you'll know where they go in the MJ. :thumbsup:

[A-man930]

As I understand it there are issues with the firewall too. It needs to be modified to fit a 4.0L. There is another option for you which is replacing your 2.8L block and heads with a Camaro(?) 60 degree 3.4L. All the ancillaries from the 2.8L will swap to the 3.4L. No firewall, wiring or radiator mods.

Please correct if I'm wrong, just repeating info I read here before :wrench:

I've heard the same thing. This is the route I would go if I had an '86. The GM 3.4 is a very reliable, simple, and cheap replacement for a 2.8 (which isn't really all that bad to begin with.) You can probably even keep your oe intake/exhaust.

[Dadinator]

The 3.4 is a great swap if you just need a refresh. More power and a bit more reliablity.

 

Now don't take this the wrong way because I absolutely love the 4.0, but if I were going to all the trouble to make it fit an 86, I'd go ahead and step up to a v8. A good small block ford, chebby or mopar will give you more power. (but I'm a power junkie).

 

But that's just me.

 

I understand cooling can be a factor with a V8 in a comanche, but it can be done. As much work as it is likely to take to do the 4.0, that's what I would do.

 

If the 2.5 in the TJ ever gives up the ghost, I think it will be due for a v8. Problem is the dang thing is so reliable that it just keeps going. 175K and still popping.

 

Good luck with whatever you decide.

[mpace6a]

I was thinking about swapping in a 3.4, but from what ive read/heard the ax5 is gutless, and won't hold up as long as i'd like. But on a side note, when i swap in the i6, i was planning on swapping in the xj's axles, but the comanches rear is spring under, and the xj's is spring over, and i was wondering if anyone could give me an estimate of how much lift that will put in the back so i can decide what to do with the front to level it out.

-Matt

[Pete M]

~6". and you'd still need to move the perches since the XJ perches are set outboard of the MJ perches.

 

do you know what gears you have in the comanche?

[ryno56]

Some fabrication is also required to get the XJ rear axle under the MJ. The spring perches are at a different width as well as the shock mounts being different. It might look close, and it will go in, but you'll tear up spring bushings in a hurry.

[ryno56]

Sorry Pete, you beat me to it.

[mpace6a]

I'm pretty sure the comanche has 4.11's in it, and the cherokee has 3.55(?)

-Matt

[Pete M]

need to double check that. I'd much rather have 4.10s than 3.55s.

[mpace6a]

yea, i just need the best possible gas mileage i can get right now, cuz I'm just a poor, unemployed teenager right now :fs1: and i don't plan on doing anything just yet to need the 4.10s

-Matt

[Pete M]

what size tires?

[mpace6a]

for now just stock (26" i think), unless the SOA nets me 6" of lift, then i'll be moving up to the 31"s off dads dodge, he needs new ones, and the 'Manches are bald!