7.3 in a bronco? - Diesel Forum

Seijirou · 05-24-2007, 12:43 PM

I searched the forums and found a few people who did this with a 6.9 I believe. I have access to an old Uhaul truck with a 7.3, non turbo motor, and scrambled eggs for a transmission.

I have an 88 Bronco, 351w with a C6 (not overdrive) transmission.

I've considered the idea of putting the 7.3 diesel in the Bronco.
I'm familiar enough with most of the processes involved, what I don't know however is if the 351W C6 transmission will bolt to a 7.3 diesel block.

I've searched alot but I havn't found any yesses or nos.

I'm pretty sure the answer is no, but you guys are the experts not me!

Any insight?
Thanks!

EDIT: The Uhaul truck is a 1990 if that matters.

Mr_Roboto · 05-24-2007, 12:56 PM

The only trans that will bolt to the diesel is a diesel C6 or a diesel E4OD. The bolt pattern is unique to the diesel.

Keep in mind that if that U-Haul has an E4OD (overdrive) trans you are looking at a couple grand to replace it. Plus assuming the Bronco is 4x4 you're going to need a 4x4 trans to bolt up to the transfer case.

Then there is the matter of how long a 8.8" rear axle will stand up to the diesel's torque. This I don't know one way or the other.

Seijirou · 05-24-2007, 01:00 PM

[ QUOTE ]
The only trans that will bolt to the diesel is a diesel C6 or a diesel E4OD. The bolt pattern is unique to the diesel.

Keep in mind that if that U-Haul has an E4OD (overdrive) trans you are looking at a couple grand to replace it.

[/ QUOTE ]

I found out I was wrong, I have a C6 not a C4. However, Are the bellhousings removable with the C6 transmission?

Primarily I'm a mustang/manual guy, I don't know much about these autoboxes [img]/ubbthreads/images/graemlins/smile.gif[/img]

agnem · 05-24-2007, 01:33 PM

The bell housing is part of the trans, so you don't get to swap them around. Your best bet is to have a 4X4 F-250 or F-350 diesel as a parts truck. If the U-haul is one of those, fine, but if it's 2WD you'll have to give up 4X4, or rebuilt the trans in a different case. If it is an S-1600, then your not going to be able to use the trans that is in it regardless. My parts truck was a 2wd F-350, so I needed to source a different C6 which I did. You will need the front coils out of a 2WD F-250 or F-350, so really you need both a 4X4 and 2WD parts truck. [img]/ubbthreads/images/graemlins/tongue.gif[/img] There is no problems with the Bronco rear axle, however for consistency sake with my fleet, I intend to upgrade my Bronco to 8 lug stuff.

Seijirou · 05-24-2007, 01:42 PM

[ QUOTE ]
The bell housing is part of the trans, so you don't get to swap them around. Your best bet is to have a 4X4 F-250 or F-350 diesel as a parts truck. If the U-haul is one of those, fine, but if it's 2WD you'll have to give up 4X4, or rebuilt the trans in a different case. If it is an S-1600, then your not going to be able to use the trans that is in it regardless. My parts truck was a 2wd F-350, so I needed to source a different C6 which I did. You will need the front coils out of a 2WD F-250 or F-350, so really you need both a 4X4 and 2WD parts truck. [img]/ubbthreads/images/graemlins/tongue.gif[/img] There is no problems with the Bronco rear axle, however for consistency sake with my fleet, I intend to upgrade my Bronco to 8 lug stuff.

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The Uhaul is 2wd, I'll have to see if the transfer case is divorce mated or part of the tailshaft. If it's part of the tailshaft I might be able to use it on an otherwise 2wd transmission, but even if not I think giving up 4x4 in the meantime for a 7.3 diesel would be worthwhile [img]/ubbthreads/images/graemlins/smile.gif[/img]

Something in these transmissions would have to come apart though, if not the bellhousing, wouldn't it then be the tailshaft? I don't know how'd you rebuild them otherwise! [img]/ubbthreads/images/graemlins/confused.gif[/img]

You mention rebuilding the trans in a different case. Which brings up a question. I have a perfectly good 4x4 c6 SBF transmission.

Could I use the internals from that trans in the Diesel case?
I know the cases are different, but how different are the internals.

Input shaft, etc.

Thanks for all the advice/information/help!

Mr_Roboto · 05-24-2007, 02:21 PM

[quote
The Uhaul is 2wd, I'll have to see if the transfer case is divorce mated or part of the tailshaft. If it's part of the tailshaft I might be able to use it on an otherwise 2wd transmission, but even if not I think giving up 4x4 in the meantime for a 7.3 diesel would be worthwhile [img]/ubbthreads/images/graemlins/smile.gif[/img]

The only difference between a 2wd and a 4wd trans is the length of the taishaft, and of course the 4wd trans does not have a tailhousing.

Something in these transmissions would have to come apart though, if not the bellhousing, wouldn't it then be the tailshaft? I don't know how'd you rebuild them otherwise! [img]/ubbthreads/images/graemlins/confused.gif[/img]

The front pump comes out then all the guts come out behind it. Most automatics are cast with the bellhousing and case as one piece.

You mention rebuilding the trans in a different case. Which brings up a question. I have a perfectly good 4x4 c6 SBF transmission.

Could I use the internals from that trans in the Diesel case?
I know the cases are different, but how different are the internals.

Input shaft, etc.

Not sure if the parts will physically interchange, but you are best off buying a short tailshaft and rebuilding the existing trans. The SB guts will not stand up to the diesel.

Thanks for all the advice/information/help!

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Casey_1 · 05-24-2007, 02:25 PM

The cases are the same between the 4x4 and 4x2. The output shafts and extension housings are different. To change a 4x2 to a 4x4 you need to completely tear down the trans, change the output shaft, and put it all back together. Then bolt on the 4x4 extension and you're ready to go.

The trans internals come out through the front, through the non-removeable bellhousing. You remove the pump, and that leaves a big hole to remove all the parts.

You could use the internals from the SBF trans in the diesel case, but I expect that the diesel would tear those up in a pretty short time. You need a diesel trans to live behind a diesel engine.

Seijirou · 05-24-2007, 02:37 PM

[ QUOTE ]
The cases are the same between the 4x4 and 4x2. The output shafts and extension housings are different. To change a 4x2 to a 4x4 you need to completely tear down the trans, change the output shaft, and put it all back together. Then bolt on the 4x4 extension and you're ready to go.

The trans internals come out through the front, through the non-removeable bellhousing. You remove the pump, and that leaves a big hole to remove all the parts.

You could use the internals from the SBF trans in the diesel case, but I expect that the diesel would tear those up in a pretty short time. You need a diesel trans to live behind a diesel engine.

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Yes the survivability of the SBF guts behind a diesel does concern me, but for the purposes of function I may do it until I can get ahold of some diesel guts on the cheap. A bronco isn't exactly heavy, and normal driving down the road wouldn't require any more power than the 351 is making now anyway.

Do these motors use a mechanical initial fuel pump or electric (internal/external?)

I imagine the stock fuel pump is going to give the injection pump way too much initial pressure. I could try replacing the stock pressure regulator with one designed for a carb. perhaps. 6-8 psi about right for the injection pump?

Another question if I may. I've read that the 6.9 basically bolts in (physcially speaking) where the 5.8 was with minor fitment changes, no attachment issues. Are 7.3's similiar in that manner?

agnem · 05-24-2007, 04:06 PM

Everything will be the same for the 7.3 as it was for the 6.9. It will just drop in. Your gasser C6 will be geared wrong. I imagine 1st will be unusable and 2nd bearly there. Keep in mind that the diesel will rarely need to turn over 2500 and maxes out at 3300, where as the gas engine could go amost twice that. Yes the EFI frame mounted fuel pump will be too strong. Just bypass it, and let the engine mounted lift pump do the work. The little pump in the fuel tank is of no consequence, but you will need to let it run to keep fuel flowing. You CAN start and run a diesel on a single battery in warm climates, so you can keep your front clip. The bigger challenge is the cooling. Unless you put the diesel radiator in there, you'll be charting new territory, and the diesel DOES NOT tolerate overheating. Most of these engines only overheat once, before going into the shop, and the 7.3 is more prone to overheat than the 6.9.

Seijirou · 05-24-2007, 04:27 PM

[ QUOTE ]
Everything will be the same for the 7.3 as it was for the 6.9. It will just drop in. Your gasser C6 will be geared wrong. I imagine 1st will be unusable and 2nd bearly there. Keep in mind that the diesel will rarely need to turn over 2500 and maxes out at 3300, where as the gas engine could go amost twice that. Yes the EFI frame mounted fuel pump will be too strong. Just bypass it, and let the engine mounted lift pump do the work. The little pump in the fuel tank is of no consequence, but you will need to let it run to keep fuel flowing. You CAN start and run a diesel on a single battery in warm climates, so you can keep your front clip. The bigger challenge is the cooling. Unless you put the diesel radiator in there, you'll be charting new territory, and the diesel DOES NOT tolerate overheating. Most of these engines only overheat once, before going into the shop, and the 7.3 is more prone to overheat than the 6.9.

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Cool deal. Cooling capacity can always be expanded [img]/ubbthreads/images/graemlins/smile.gif[/img]

Thanks to everybody for all the helpful information and advice.

aceohearts · 05-24-2007, 07:11 PM

[ QUOTE ]
Another question if I may. I've read that the 6.9 basically bolts in (physcially speaking) where the 5.8 was with minor fitment changes, no attachment issues. Are 7.3's similiar in that manner?

[ QUOTE ]
Everything will be the same for the 7.3 as it was for the 6.9. It will just drop in.

[/ QUOTE ]

[/ QUOTE ]

The 7.3 is the same as the 6.9 however they don't "bolt right in" where a gas motor was mounted...

Going from the 351 to a diesel you will have to change the mount towers (where the motor mount attaches to the frame). The diesel mounts aren't much more than a plate bolted to the crossmember, whereas the gasser mounts rise up about 3-4" above the crossmember. The crossmember (I believe) is already drilled for the bolts on the diesel mounts, but I'm almost sure at least one of your gasser mounts will be riveted in. Don't know why Ford does that, [img]/ubbthreads/images/graemlins/shrug.gif[/img] but they will bolt side and rivet the other...

typefour · 05-24-2007, 08:47 PM

The only major internal differences in the c6 gas and diesel is the diesel has more forward and direct clutches, planetary ratios are the same. The hot ticket is to use a e4od gearset for more strength and a little lower ratio. Valve body is a little different but I have swapped them back and forth with no problems. I build literally dozens of c6's at work every year from I6 to diesels, parts are starting to get scarce.