mcguirjf
New member
Well the transplant is complete and I'm happy to say I now own a VJ! Hahaha
The transplant of a 1998 power train into my 1988 YJ chassis is a success! I now have OBD2, fuel injection, an AX15, and a lot more HP. After pulling the nose, old engine, and transmission I found a lot of frame rot that needed to be fixed.
I started on the front and worked my way back. The steering box mount, two of six nut plates for the skid plate, both rear shock mounts, and both rear spring shackle mounts. I also had to transplant the transmission mount section of the skid plate from the TJ onto a 1995 skid plate. I believe I used up three spools of weld wire, and more than a dozen cutoff wheels and grinding disks. The rear spring shackle mounts on the rear of the frame were the trickiest because there was nothing there. I had to bend a strip of steel and tack it into place to recreate the bottom contour of the frame. Then with cardboard make templates of the outer and inner frame.
I also installed a tow hitch which added an additional challenge. Two of the six mounting points for the tow hitch were in the side of the frame that didn't exist. I was worried that if I completely boxed in the frame and install this hitch it would crush the frame. So I used two metal bushings that I had left from a front control arm bushing replacement on my 1995 Dodge Ram and welded them into the frame. Now when I bolt the tow hitch to the frame the bushings support both the outer and inner frame walls.
I also installed the TJ gas tank and I found a lot of back and forth on this discussion and to put an end to it, YES IT FITS! The biggest pain in the rear part of installing the TJ gas tank was creating a filler neck. Using pieces of TJ filler neck hose, eight hose clamps, and pipe fittings from local hardware store spent a few hours installing and removing in trying to create a custom filler neck to interface with the TJ gas tank and the YJ fill opening. I didn?t want to create a hole in the side of my tub to install the TJ gas cap. I will note that the larger diameter for filling the TJ gas tank is switched compared to the YJ gas tank. Please note that my old YJ gas tank did not have an internal fuel pump. I filled the tank and I?m happy to report no issues on filling at the gas station. I used 1? diameter 90 degree black pipe for the filler hose section and a ?? 90 degree pipe for the breather hose.
The exhaust system was pretty simple. I used the TJ exhaust from the manifold to the muffler. Yes use the TJ muffler. Then I used the YJ tail pipe and a section of 2.25 OD to 2.25 ID adapter exhaust pipe about 6 inches long and assembled. The adapter exhaust pipe can be purchased at any local auto parts store.
I will make a note on the skid plate issue. My 1988 skid plate did not have holes to support the use of an AX15. 1995 skid plate I purchased had hole locations for both transmission options, ?but? the TJ AX15 transmission mount is different than the YJ AX15 mount. Now I believe in TJ and YJ AX15 hole patterns are due to the brackets that secure the exhaust down pipe. You will notice that the YJ down pipe uses a ?U? shaped bracket to support the down pipe and the TJ uses a solid round bar. I wanted to use the TJ exhaust bracket so I had to cut the section of the skid plate from the TJ and graft it to the YJ skid plate. This was tricky because I had to support the transmission in the chassis, make sure its aligned, install the skid plate with TJ section, and scribe and outline of the bracket to the skid plate before welding the assembly. Not easy! The caked on road grime on the skid plate helped in scribing and locating the section of TJ skid plate.
The transfer case shifter. So this thing needed some modifying. I had to cut, bend, and re-weld it into shape so the damn thing fit. The shifter ?will? bolt in with the removal of a cast boss on the transmission case. Found out on another forum. ?BUT? the problem I found is that the shifter is badly angled and would hit my right leg. NFG. So cutting, prying, and welding is needed to make the transfer case shifter fit.
Coolant system. You have to use the TJ lower radiator hose to clear the power steering lines. I found out that the output fitting that goes between the heater core and water pump can become brittle over time. Motormite sells a replacement through Autozoo for around $15. You have to remove the water pump to install this pipe. I know I tried. You also have to relocate the fan shroud. It needs to be moved down about an inch.
The TJ throttle cable bolts directly to the YJ gas pedal. You cannot use the YJ throttle cable as it is too short.
Battery and Computer. I used the factory computer mount bracket. It did need to be air chiseled off the firewall of the TJ. I welded it to my YJ?s firewall. I did have to remove the two upper side battery supports. I took three bolts and welded the heads to my YJ battery pan. I then adjusted the nuts on the bolts to control the level of the TJ battery pan. It is very secure.
Power steering lines. The TJ power steering lines fit perfectly into the YJ steering box.
The transfer case on the TJ does not use a vacuum control switch to engage the front axle in 4WD. You have to remove the electrical switch and transfer the vacuum control switch from the old YJ transfer case. Please note that if you do not remove this switch prior to transfer case removal, it ?WILL? be broken. It is very fragile and the plastic vacuum line fitting are very brittle. Ask me how I know! hahahahaha
Transmission shifter. This is fine as is. The shifter just clears my center console when shifting into 2nd, 4th, and Reverse.
The Hydraulic Clutch assembly. I went with the stock 1998 TJ hydraulic clutch assembly. This is a sealed assembly consisting of the master, slave cylinders, and hydraulic hose all together and pre-bled. The difficulty was the master cylinder mounting to the firewall. I took the original metal bracket that was shipped with the hydraulic clutch assembly and cut it into pieces. I then welded a bracket out of it while on the clutch master cylinder. You must use caution as the master cylinder is plastic and will heat up quickly. I used sheet metal to shield the heat from welding and melting the master cylinder. I then bolted the master cylinder to the firewall.
Now I needed a way of actuating the master cylinder. The rod for the TJ clutch petal is not the same as the YJ. What I did was cut a section of brake line and fitted it between the master cylinder and clutch pedal. I cut the brake line to help me find what length I needed. Please note that the TJ master cylinder has little fingers to secure the rod. If you do not engage those fingers you will wind up with a short clutch rod! I also recommend you push the pedal a few times to ensure the pedal height is accurate. The first time you press the petal the plastic securing strap on the slave cylinder will be broken and excess travel may be noted. I went a step further and made an adjustable rod by taking the TJ section of rod and welding an internally threaded barrel to it. Take the YJ rod and weld a bolt to engage the threaded barrel. You now have an adjustable clutch rod. Use a jamb nut to secure the length!
I noticed that the rear drive shafts were different lengths. I ?believe? I used the TJ drive shaft, but cannot confirm that. I will say that I used the shorter of the two. The front drive shafts look very different, but are length adjustable. The TJ has this funky double U joint on one end. I was told to use the TJ as it is far superior to the old YJ front driveshaft.
To start the engine you need to run a 12 volt positive to pin F10 on black connector C106. This powers up the relays, fuel pump, and computer. Then take a 12 volt positive and touch to F9 pin to engage starter motor. On the end of the engine harness you will have three plugs. Black, Blue, and Yellow.
I still have to hook up my gauges and know there are more issues to follow. I?ll keep this post updated with results.
I hope I can find a way of posting all of these pictures I took. Just reading about this does not do the job justice.
Hope this helps others in performing this task.
The transplant of a 1998 power train into my 1988 YJ chassis is a success! I now have OBD2, fuel injection, an AX15, and a lot more HP. After pulling the nose, old engine, and transmission I found a lot of frame rot that needed to be fixed.
I started on the front and worked my way back. The steering box mount, two of six nut plates for the skid plate, both rear shock mounts, and both rear spring shackle mounts. I also had to transplant the transmission mount section of the skid plate from the TJ onto a 1995 skid plate. I believe I used up three spools of weld wire, and more than a dozen cutoff wheels and grinding disks. The rear spring shackle mounts on the rear of the frame were the trickiest because there was nothing there. I had to bend a strip of steel and tack it into place to recreate the bottom contour of the frame. Then with cardboard make templates of the outer and inner frame.
I also installed a tow hitch which added an additional challenge. Two of the six mounting points for the tow hitch were in the side of the frame that didn't exist. I was worried that if I completely boxed in the frame and install this hitch it would crush the frame. So I used two metal bushings that I had left from a front control arm bushing replacement on my 1995 Dodge Ram and welded them into the frame. Now when I bolt the tow hitch to the frame the bushings support both the outer and inner frame walls.
I also installed the TJ gas tank and I found a lot of back and forth on this discussion and to put an end to it, YES IT FITS! The biggest pain in the rear part of installing the TJ gas tank was creating a filler neck. Using pieces of TJ filler neck hose, eight hose clamps, and pipe fittings from local hardware store spent a few hours installing and removing in trying to create a custom filler neck to interface with the TJ gas tank and the YJ fill opening. I didn?t want to create a hole in the side of my tub to install the TJ gas cap. I will note that the larger diameter for filling the TJ gas tank is switched compared to the YJ gas tank. Please note that my old YJ gas tank did not have an internal fuel pump. I filled the tank and I?m happy to report no issues on filling at the gas station. I used 1? diameter 90 degree black pipe for the filler hose section and a ?? 90 degree pipe for the breather hose.
The exhaust system was pretty simple. I used the TJ exhaust from the manifold to the muffler. Yes use the TJ muffler. Then I used the YJ tail pipe and a section of 2.25 OD to 2.25 ID adapter exhaust pipe about 6 inches long and assembled. The adapter exhaust pipe can be purchased at any local auto parts store.
I will make a note on the skid plate issue. My 1988 skid plate did not have holes to support the use of an AX15. 1995 skid plate I purchased had hole locations for both transmission options, ?but? the TJ AX15 transmission mount is different than the YJ AX15 mount. Now I believe in TJ and YJ AX15 hole patterns are due to the brackets that secure the exhaust down pipe. You will notice that the YJ down pipe uses a ?U? shaped bracket to support the down pipe and the TJ uses a solid round bar. I wanted to use the TJ exhaust bracket so I had to cut the section of the skid plate from the TJ and graft it to the YJ skid plate. This was tricky because I had to support the transmission in the chassis, make sure its aligned, install the skid plate with TJ section, and scribe and outline of the bracket to the skid plate before welding the assembly. Not easy! The caked on road grime on the skid plate helped in scribing and locating the section of TJ skid plate.
The transfer case shifter. So this thing needed some modifying. I had to cut, bend, and re-weld it into shape so the damn thing fit. The shifter ?will? bolt in with the removal of a cast boss on the transmission case. Found out on another forum. ?BUT? the problem I found is that the shifter is badly angled and would hit my right leg. NFG. So cutting, prying, and welding is needed to make the transfer case shifter fit.
Coolant system. You have to use the TJ lower radiator hose to clear the power steering lines. I found out that the output fitting that goes between the heater core and water pump can become brittle over time. Motormite sells a replacement through Autozoo for around $15. You have to remove the water pump to install this pipe. I know I tried. You also have to relocate the fan shroud. It needs to be moved down about an inch.
The TJ throttle cable bolts directly to the YJ gas pedal. You cannot use the YJ throttle cable as it is too short.
Battery and Computer. I used the factory computer mount bracket. It did need to be air chiseled off the firewall of the TJ. I welded it to my YJ?s firewall. I did have to remove the two upper side battery supports. I took three bolts and welded the heads to my YJ battery pan. I then adjusted the nuts on the bolts to control the level of the TJ battery pan. It is very secure.
Power steering lines. The TJ power steering lines fit perfectly into the YJ steering box.
The transfer case on the TJ does not use a vacuum control switch to engage the front axle in 4WD. You have to remove the electrical switch and transfer the vacuum control switch from the old YJ transfer case. Please note that if you do not remove this switch prior to transfer case removal, it ?WILL? be broken. It is very fragile and the plastic vacuum line fitting are very brittle. Ask me how I know! hahahahaha
Transmission shifter. This is fine as is. The shifter just clears my center console when shifting into 2nd, 4th, and Reverse.
The Hydraulic Clutch assembly. I went with the stock 1998 TJ hydraulic clutch assembly. This is a sealed assembly consisting of the master, slave cylinders, and hydraulic hose all together and pre-bled. The difficulty was the master cylinder mounting to the firewall. I took the original metal bracket that was shipped with the hydraulic clutch assembly and cut it into pieces. I then welded a bracket out of it while on the clutch master cylinder. You must use caution as the master cylinder is plastic and will heat up quickly. I used sheet metal to shield the heat from welding and melting the master cylinder. I then bolted the master cylinder to the firewall.
Now I needed a way of actuating the master cylinder. The rod for the TJ clutch petal is not the same as the YJ. What I did was cut a section of brake line and fitted it between the master cylinder and clutch pedal. I cut the brake line to help me find what length I needed. Please note that the TJ master cylinder has little fingers to secure the rod. If you do not engage those fingers you will wind up with a short clutch rod! I also recommend you push the pedal a few times to ensure the pedal height is accurate. The first time you press the petal the plastic securing strap on the slave cylinder will be broken and excess travel may be noted. I went a step further and made an adjustable rod by taking the TJ section of rod and welding an internally threaded barrel to it. Take the YJ rod and weld a bolt to engage the threaded barrel. You now have an adjustable clutch rod. Use a jamb nut to secure the length!
I noticed that the rear drive shafts were different lengths. I ?believe? I used the TJ drive shaft, but cannot confirm that. I will say that I used the shorter of the two. The front drive shafts look very different, but are length adjustable. The TJ has this funky double U joint on one end. I was told to use the TJ as it is far superior to the old YJ front driveshaft.
To start the engine you need to run a 12 volt positive to pin F10 on black connector C106. This powers up the relays, fuel pump, and computer. Then take a 12 volt positive and touch to F9 pin to engage starter motor. On the end of the engine harness you will have three plugs. Black, Blue, and Yellow.
I still have to hook up my gauges and know there are more issues to follow. I?ll keep this post updated with results.
I hope I can find a way of posting all of these pictures I took. Just reading about this does not do the job justice.
Hope this helps others in performing this task.
