LS to AX15

[Ron84cj]

I'm taking much of this info from my build thread. I'll try to clean it up and also add to it as much as possible. I started a pretty nasty rod knock on my 258 back in 2016 right after Sandblast so I needed to make so decisions. I actually had an extra 258 I could have used. It had about 76,000 miles on it. It would have had to be gone through because it was sitting for a VERY long time. I could have gone this route, it would actually make a lot of sense. But I needed more power! So this gave me a good excuse to swap in a chevy 5.3L. I will have a good 100 more horsepower and still should get similar gas mileage. My 04 suburban routinely gets in the neighborhood of 18 mpg. I see no reason my jeep shouldn't get at least that. I bought a 5 3L with 75,000 on it from a local yard. I got the complete motor with the accessories, harness, and starter for $500.

 

[Ron84cj]

I did a ton of research on bolting up a Chevy LS engine to an AX15. There are a few options, if you go the quick lazy way Advance Adapters and Novak will take you well over a $1000 to get you going. Novak requires you to use a stock bellhousing and their adapter plate $319.00(part# GMAX15) to mate to the ax15. Advance Adapters has a whole bellhousing $483.24(part# 712567V) that mates the 2 together. If you go the Novak route, you need a bellhousing that fits an 11 inch clutch/168 tooth flywheel. LS engines only came with a 168 tooth flywheel, so the more common 10 1/2" bellhousing will NOT work.

There are differences with the 4.8, 5.3, and 6.0 that should be noted. The 4.8 and 5.3 use the same block and 3.78" bore, the 4.8 just simply uses a shorter stroke crank. The 6.0L uses its own block for the 4 inch bore. Unless you plan on a rebuild, beware of early 99 blocks. Gm tried to use the same block for all 3 motors! So the cylinder walls were way too thick for the smaller bore 4.8 and 5.3 causing overheating problems. If you find an early 4.8/5.3 for cheap that needs a rebuild, chances are you could simply bore it to 4." to make a 6.0L. Any year 4.8/5.3 you can bore it out to 3.898 to make it a 5.7L. So basically an iron LS1. The 99s and 2000s used iron heads instead of aluminum. The crankshaft on the old GEN 1 engines (350s, etc.) stick out .400" further rearward than LS engines. The 99-2000 4.8 and 6.0L when coupled to a manual trans also stuck out .400" further than the 4.8/5.3/6.0 with automatics. Yes, you read that right. They ran different cranks for the autos and manuals in 99 and 2000. Here is a pic of a 99 flywheel (left) and a 2001 flywheel (right) side by side on the crank mounting surface on 2" blocks for comparison. The location of the starter ring shows the .4" difference.

 

[Ron84cj]

Now, both Novak and Advance adapters will want to sell you a custom flywheel to make up the .4" If you don't, your clutch fork won't work correctly. Also, you will not be able to use a stock LS clutch, it's too tall and won't allow enough room for the throw out bearing. You have to use a Gen 1 11" clutch. So you can either spend around $400 on their "custom" flywheel or simply use a stock LS flywheel and a adjustable pivot ball. McLeod sells the one you need (part #16908).

 

[Ron84cj]

Just a quick comment. Please read all the way through this build thread BEFORE you start buying parts. It will show you what does and does NOT work. I came across some bad info and had to make changes. You'll see what I'm talking about.

 

[Ron84cj]

The flywheel I bought from Autozone is for a 2001 6.0 truck (Duralast part #FW2776). Even though the gen 1 clutch (Duralast part#NU5551) bolt holes line up on the flywheel, you can NOT just simply bolt it up. The gen 1 pressure plate requires 3/8-16 shoulder bolts for proper location. The LS stuff is all metric. It would be horribly imbalanced if you used the metric bolts. No big deal, just have a machine shop drill and tap the holes for you. It's just a 12 5/8 6 point bolt circle. Nothing fancy so I can't imagine it costing too much. If your engine had an auto attached to it, obviously the flexplate bolts will be too short for a flywheel. You need ARP part#330-2802 for the flywheel and ARP part#130-2201 for the pressure plate.

 

[b.b.chev]

I've been running a 6.0 with an AX15 since 2011 using Novaks adapter , over 80 thousand miles and still going strong.

 

[Ron84cj]

My pressure plate bolts came in last night so I was able to start on my flywheel. I had to wait so I could measure the shoulder diameter and the depth. First pop out the 2 dowels out of the flywheel. You will no longer need these. I then set up the turntable after work, indicated everything to 0. I didn't have access to the prototrak or cnc at the time, so I went old school (turntable).

What's great is I have the newest mill in the shop. It's from 1981! lol, most of our mills and lathes are 1940s vintage. They just keep on going. Anyways, I went on to center drilling all the holes. The chevy pattern is just a 12.625 6 bolt pattern. So once you have your 0, just move up 6.3125 and turn the turntable every 60 degrees.

drilled all the holes with a 5/16 drill

This is the part that I needed the bolts for. I needed to measure the shoulder diameter for proper fitment. Your pressure plate relies on these for alignment. They were all consistent at .3728. So I reamed all the holes to .373 and .265 deep so the shoulder doesn't bottom out while still retaining as many threads as possible. Then proceeded to tap for the 3/8-16 thread.

 

[Ron84cj]

I've been running a 6.0 with an AX15 since 2011 using Novaks adapter , over 80 thousand miles and still going strong.

You jumped the gun on me here. Please let me finish.

Edit: Going back and re reading I realized I probably sounded like a jerk. Sorry about that, it was not my intention. I was just mid thought at the time with my write up and didn't want to get sidetracked. Lol

 

[Ron84cj]

And the finished product... Everything fits excellent.

I forgot to mention, make sure you drill all the holes all the way thru so you don't upset the balance.
I know most don't have access to this equipment, but overall none of this took that long so a machine shop shouldn't charge that much. Start to finish I only have about an 1 1/2 hours and I was definitely being a poke. There is no reason you should have to pay for more than 1 hour of labor at the shop.

 

[Ron84cj]

Even though I found no evidence of any oil leaks, I wanted to replace the rear main housing gasket and seal, timing cover gasket and seal, and the oil pan gasket. Unlike the old gen 1 motors, the LS stuff has to be properly aligned to work. I went ahead and pulled everything off and cleaned all the gasket surfaces.

GM tells you that you need special tools to install everything, well that kit is over $1000 so I said forget that. For the timing cover and rear housing use a straight edge to align the cover to the oil pan mounting surface. If you measure between the cover and crank with a caliper, you'll find that centers it up and down really well. Just tap the cover side to side until you have it centered. Just double check everything after you tighten everything down to make sure nothing moved on you. The rear of the oil pan needs to be aligned with the bellhousing for the trans to mount up. None of this is hard, just time consuming. A cheap $20 caliper from Menards does just fine for this. They are surprisingly very accurate. I checked mine on some precision gauge blocks at work and it was spot on.

 

[Ron84cj]

Now that I have things back together, I moved on to bolting up the flywheel and clutch and found this...

At first I thought I simply bought the wrong year needed so I tried various different years and had the same results. I read multiple build threads and articles and no one mentions this issue. My bad I guess, I should have noticed this earlier. Maybe it is just fine having a good amount of the friction material hanging off in la la land. But I sure don't trust it. According the www.hotrod.com the gen 3 clutch sits 1 inch taller than a gen 1 clutch. I wanted to compare for myself. So I got one for a 2001 chevy 1500 and it was almost the same height.

I'm a little irritated right now. There is a lot of bad info out there. Before I get to the clutch, I wanted to make sure the pilot bushing was right. According to Novak and several others you need a special bushing that sits in the outer lip of the crank instead of the traditional spot because of the .400 difference. So that's what I bought. I measured with the bellhousing in place and surprise surprise, it's wrong. It does just barely clear the splines. But because of the taper, almost half of the bushing isn't supporting anything. So I need the other bushing that gets installed on the inner part of the crank.

 

[Ron84cj]

Now on to the clutch. I installed the 2001 chevy truck clutch and measured the spline engagement. So again I measured from the bell to beginning of the splines. It has perfect engagement, nothing is hanging off.

There are two chevy throwout bearings that I'm aware of, long and short. I got the short one for a 1977 chevy 305 truck. It measures about 1.25". I think the tall one is around 1.875", so it's easy to tell them apart. With the bearing in place there is plenty of room behind it. Also plenty of clearance between the fork and pressure plate, at least .75". The only thing I feel I need to address is the snout. The bearing is going to be REALLY close to the end of the snout. So I will either shim it or just make a new snout. Not sure yet. Besides that, once I get the right pilot bushing I should have everything I need. I really don't see why any of this won't work unless I'm not seeing something?

 

[Ron84cj]

I was a bit nervous about the amount of travel on the snout, I didn't want the throw out bearing to go right to the edge or over the edge. So I made a 1/4" thick spacer. Maybe this wasn't needed, but it gives me a piece of mind. The snout fits in a 1/8" deep pocket in the adapter plate, but it's not really needed to locate the snout because of the countersunk bolts. They locate it just fine, I simply got longer ones to make up the 1/4" difference. Once installed I double checked the clearance and all is good.

I switched out the pilot bushing on the outer lip for one that mounts in further. I now have full engagement on the input shaft for proper support.
Before

After

Now I could finally assemble everything for good. I got thread locker on all the bolts, adjusted the pivot ball, and mounted up the clutch slave. The slave is for an 86-91 Mazda RX7. My buddy swapped in a LT1 with a Pontiac Solstice trans (basically the same as AX15) into his RX7 and bought an entire kit for the swap. He went with an internal slave so he gave me the bracket. Even if he didn't it wouldn't be hard to make one out of some angle iron. The RX7 bore size is 3/4" which is the same as the 75-80 toyota land cruiser slave that advance adapters uses for their swap. So either one should work just fine.

 

[Ron84cj]

I finally got my motor in! The trans had to be moved forward about 1.5" the the engine wouldn't be against the firewall. Well it looks like I'll have to change the driveshafts...again

As far as the mounts go, I had some Gen 1 laying around so I used those. All I had to do was make an adapter plate. Sorry I forgot to take pics of the plate, I basically did the same thing as Randy. I could have offset the plates a bit more for clearance for the exhaust manifolds, but it clears fine. Of course my kids were out jeepin while I'm working on this.

Dimensions for the plate... I have no idea why it tells you to drill the outer holes to .5625. The bolts aren't that big. I don't know if they changed sizes through the years so just check what you have and drill accordingly.

 

[Ron84cj]

I made my exhaust flanges too. You can buy them online for like $60, but all these little purchases add up quickly. So if it's something I can make, I will.

I got the grill back on to figure out what to do for hoses. I'm running an aftermarket aluminum radiator for a 6 cylinder. I called radiatorexpress (where I got it from) and they assured me it would be fine for a Chevy 5.3L. After making a few trips back and forth to auto zone I found some that work. Sorry, I don't remember the part #s anymore. If someone needs them I could probably figure them out. I ran 2 separate hoses for the lower and made a simple bracket in the middle to prevent them from bouncing around. I had just bought the radiator earlier that year which is the only reason I did this. For anyone else you are better off just buying one for a Chevy conversion.

 

[Ron84cj]

For my wiring needs I worked on my own harness. I followed the write up on LT1swap.com. Most of the info is on there. I did get the rest on here but honestly I don't remember anymore. I know Randyzzz helped but beyond that sorry guys

Now that I have it running and driving, I can definitely tell you what works and what doesn't with clutch master and slaves. When the master is bigger than the slave the pedal is stiffer with a short travel distance to disengage. When the master is smaller you have an easier pedal, but the travel distance is longer. First I tried a factory cj clutch master cylinder which is a 13/16 bore. The pedal is way too stiff. This doesn't work at all unless you are Hercules. Then I tried using Novaks recommendation to use a master from an 87-90 yj which is a 11/16 bore. The pedal went to the floor and wouldn't even disengage the clutch. The factory cj clutch pedal is lower than the brake pedal. So I cut and rewelded the pedal so they are both the same height. I did not want it higher than the brake pedal.
Before

After

The pedal was much easier to push, but it would disengage the clutch JUST off the floor. I had to take out my floor mat to drive it. I didn't like this at all so I bought a universal Wilwood master that was a 3/4 bore.

This worked really well but the pedal got stiffer again. A bit too much for my liking. So the clutch was to blame. This is what Novak and Advance Adapters told me. They told me it wouldn't work and damn near laughed at me for even trying it. So I took the kick in the nuts and bought the $350 custom flywheel they told me I just had to have. Got a Gen 1 11inch clutch again and changed everything over. Only to find out..........it barely made a difference!!! I was so pissed. If I knew that I would've just left it. I was done dealing with it and decided I just needed to get used to it. Now after driving it all summer, it's really not that bad. I like the travel distance and the stiffer feel doesn't bother me as much anymore.

 

[FLCJ8]

This is invaluable information...
Thanks for taking the time to post.

 

[Ron84cj]

I don't think I mentioned this but at first I used a cj pedal, drilled it, and used a shoulder bolt. This works fine, but I found that the shoulder bolt wears out quick. After I replaced a few of them I eventually just swapped in a YJ pedal. I can't count the number of times people have told me there is a difference between the CJ and YJ pedal. THERE IS NONE. I compared them side by side. The height and angle is exactly the same. The only difference is that the YJ pedal has the little stub for the master cylinder.

 

[ag4ever]

I don’t think there is a difference in the pedals, but there IS a difference in master cylinders between CJ / Early YJ and Late YJ.

Master cylinder bracket.

 

[Ron84cj]

So, here is the basic list of what I used. IT DOES 100% work...
-Early YJ clutch pedal along with the support bracket for the firewall. Mine was from an 89.
-Wilwood 3/4" bore Clutch Master to basic off the shelf brake line (don't remember the thread)
-The brake line then connects to a brake hose from a Ford Escape (I think from an 06)
-The Ford Escape brake hose is a decent length and is the correct fitting/thread for the slave
-The slave is from an 89 Mazda RX7
-The mount for the slave can very easily be made from angle iron. Nothing fancy
-Chevy Bell for 11" clutch NOT the bell for 10.5" clutch (VERY IMPORTANT)
-Chevy 11" clutch from 77 Chevy 305 C10 Pickup. It should come with correct throw out bearing (1.25 tall). The spacer plate I mentioned earlier is not needed.
-Pilot bearing/bushing from Novak. There are two available. I needed the inner one even though Novak told me the outer one is what I needed. So measure what you actually have to make sure you get the right one. DO NOT just go by what they tell you.
-Exhaust manifolds from C6 Corvette. (The truck manifolds won't work)
-Shifter from a YJ. I added a little to the top to make it taller just for comfort.
-AX15 to DANA 300 clocking ring (I bought mine on ebay for like $40)
-AX15 tailshaft seal from a 94 V6 Dodge Dakota 4x4. The Wrangler version will NOT work and no, you don't need that expensive double lip seal. The Dakota seal works perfect.
-I mounted the trans using a factory cj mount and bracket. I just simply drilled new holes to match the AX15 mounting holes. I also drilled new holes in the factory skid plate since it is now further back than the T176 that it replaced.
-Obviously you will need your driveshaft lengths changed. I actually used a rear drive shaft for the front and rear. The fatter drive shaft does comfortably clear everything INCLUDING the factory truck oil pan. No need for an F body oil pan.
-There is an oil level sensor on the side of the pan directly in the way of the driveshaft. Simply plug it off.
-Speed sensor, Dakota Digital makes one to go inline with your cable driven speedo. I don't remember the signal it sends but make sure when you send out your computer they change it to match. Believe it or not, I have yet to hook mine up and have had absolutely zero issues.
-Send out your factory computer to turn off the antitheft crap and anything else you delete out of the harness. Any dyno shop can do this for you.
-I used the factory clutch fan, works great. Even with no shroud I have had zero overheating problems in 100+ degree stop and go traffic. I would still highly recommend a shroud though. I have just been lazy and haven't gotten to it yet.