6bt in 71 chev longhorn

[dlefebvre]

I am seriously thinking of putting a 5. 9 ctd in my 71 chev 3/4 ton this spring. The truck currently has a 402 bb and a custom built 700r4 auto made for pulling(extreme duty clutch packs,etc)Does anyone have any info on conversion kits,etc to do this job?The donour engine is from a 89 - stock 160 hp, 400 ftlbs torque. I would really like to use the automatic I had built. Any advice or steering in the right direction would be greatly appreciated! Thanks, Dean

 

[CyberRanger]

There is no conversion kit for this swap.



Believe it or not, there is a bellhousing adapter available to fit your conversion. Here in Colorado & Wyoming many Chevy Stepvans (older G30) use a B3. 9 tied to a TH400. These local delivery vans are used & are bein' phased out of use by Rainbow Bread & Frito Lay. As far as I've been able to ascertain the B3. 9 & the B5. 9 use exactly the same bellhousing adapter.



The only person I know of who has done a 5. 9 conversion into a '67-'72 Chevy is Ron Savage, a long time TDR member. He isn't a computer user & you won't likely find him here on the forum. That said, both his & my conversion (mine is planned, but on hold for the moment) are into 4x4 Chevys. Ron's 5. 9 is a 12 valve & he simply lifted the Dodge crossmember along w/ the engine & modified it to fit his Chevy. Unlike your truck or mine, his was heavily modified for competition pulling (major frame beefing). He is now running a Browning 14-speed in it (or was last time I talked to him) which required a 6" body lift. You should be able to remove the engine cradle crossmember & use a modified Dodge crossmember. He said it was far easier to do that than try to modify the Chevy, besides the fact the Chevy crossmember isn't stout enough for the Cummins. Here is a link to my webpage about Ron's truck which includes some awesome photos.



What rear end do you have in your Longhorn? If its the Eaton-made "Corporate" GM rear end, it should survive fine behind the 5. 9. The Corporate rear-end has a drop-out 3rd member, like a Ford 9". If its the Dana 60 (somewhat squared looking cover w/ 10 bolts & a "60" cast into the side of the pumpkin), it'll have to be swapped out or it won't last long. (You probably already know all this!)

 

[1stgen4evr]

5.9 to 71 Chevy

Squeeze it. It will go. May take a little whack here or there on the firewall. If you don't have overdrive, you will be very slow. I don't know what the 700 is but OD is a must for highway speed. We have done a couple of newer Chevys (the boxy ones) but can't tell you about frame strength on yours. We wound up with the complete Dodge drive line from a donor truck.



As CyberRanger commented there are lots of the 4bts in bread/cracker trucks. The back of the engines are the same. The adapter to the 400 transmission is a three piece set with a connecter for the converter, a plate to tie the engine to the transmission and a crank spacer to make the setup couple correctly.



Seems like I remember that some of the 3/4 and one ton Chevys had dana axles that may be 70s in that time period. If it is a 60, you had best drive with a very light foot.



1stgen4evr

James

 

[towner]

A dana 60 is very durable diff... I'd take one any day of the week over a 14 bolt... . I've had a 60 front and rear in my landcruiser with 40's for three seasons with more multiplied torque than any cummins ever dreamed of... yes a 70 a geat diff but compare carrier size and tooth engagement over a 60 and there hardly any difference... I'd be more concerned a 700r4 holding up... . you'll waste more money adapting that trans up to the cummins... . find a worthy trans and sell all you stuff.....

 

[CyberRanger]

I have to differ w/ ya on that towner. The 60 is a great diff for lighter applications, but my Chevy, w/o the Cummins in it runs nearly 6000lbs empty & his Longhorn is pretty close to that. A Dana 60 in heavier vehicle has a tendency to spin the carrier bearings on the diff carrier after some miles & when that occurs the races frequently spin in the housing--you end up w/ a junk axle. I used to work in a 4x4 shop & we saw this frequently. This is why you find few good 60s in 3/4 ton trucks. I was lucky on my truck. The bearings spun on the carrier, but the races didn't spin in the axle housing. The 14-bolt GM axle is sturdier than the Dana 60, but not the Dana 80. I plan to swap a shortened Dodge Dana 80 into my Chevy behind my 6bts/NV5600 & NP205. Unless I'm mistaken, dlefebvre should have the big Eaton-made "Corporate" GM axle, the same one that was in all the 1 tons. The Longhorn was basically a 3/4 ton front half & a 1 ton back half w/ an extended wheelbase & bed.



[see my post below]



The 700R4 is just a TH400 w/ an overdrive or simply a non-computer controled 4L80E. Like 1stgen4evr said, they built 1000s of the Chevy G30s with a 4bts & a TH400 in it, in fact I'm gonna get one for a 4bts for my 71 CJ-5 conversion & I'll have a TH400 that'll bolt up to a Cummins that I'll have to sell. The TH400 stood up well behind a 4bts that was run hard day in & day out. If he uses the 160hp 6bts, the 700R4 should do just fine.



If we really wanted to overkill we could do like Ron Savage & put in a 22,000 lb Eaton from a KW!!!

 

[britannic]

FYI: The TH700R4 is the TH350 redesigned with a . 70 OD, in stock form these transmissions are very light duty and utterly dependent on the TV cable being adjusted to factory spec or you almost guarantee instant failure. I have a TH700R4 that's been built to 1/4 mile race specifications, but it still won't handle more than 650HP/650Tq.



The 4L80E is the computer version of the TH400 with OD and the 4L60E is the computer version of the TH700R4.



A 4L80E on steroids with an aftermarket computer to tune the shifts and HD TCC would be reasonable choice behind the Cummins. In my case however, I'm too nervous to go that route and have decided to convert to an NV4500 and NP205.

Originally posted by CyberRanger

I have to differ w/ ya on that towner. The 60 is a great diff for lighter applications, but my Chevy, w/o the Cummins in it runs nearly 6000lbs empty & his Longhorn is pretty close to that. A Dana 60 in heavier vehicle has a tendency to spin the carrier bearings on the diff carrier after some miles & when that occurs the races frequently spin in the housing--you end up w/ a junk axle. I used to work in a 4x4 shop & we saw this frequently. This is why you find few good 60s in 3/4 ton trucks. I was lucky on my truck. The bearings spun on the carrier, but the races didn't spin in the axle housing. The 14-bolt GM axle is sturdier than the Dana 60, but not the Dana 80. I plan to swap a shortened Dodge Dana 80 into my Chevy behind my 6bts/NV5600 & NP205. Unless I'm mistaken, dlefebvre should have the big Eaton-made "Corporate" GM axle, the same one that was in all the 1 tons. The Longhorn was basically a 3/4 ton front half & a 1 ton back half w/ an extended wheelbase & bed.



The 700R4 is just a TH400 w/ an overdrive or simply a non-computer controled 4R80E. Like 1stgen4evr said, they built 1000s of the Chevy G30s with a 4bts & a TH400 in it, in fact I'm gonna get one for a 4bts for my 71 CJ-5 conversion & I'll have a TH400 that'll bolt up to a Cummins that I'll have to sell. The TH400 stood up well behind a 4bts that was run hard day in & day out. If he uses the 160hp 6bts, the 700R4 should do just fine.



If we really wanted to overkill we could do like Ron Savage & put in a 22,000 lb Eaton from a KW!!!

 

[CyberRanger]

Oops! Auto trannies aren't my strength!

Originally posted by britannic

FYI: The TH700R4 is the TH350 redesigned with a . 70 OD, in stock form these transmissions are very light duty and utterly dependent on the TV cable being adjusted to factory spec or you almost guarantee instant failure. I have a TH700R4 that's been built to 1/4 mile race specifications, but it still won't handle more than 650HP/650Tq.



The 4L80E is the computer version of the TH400 with OD and the 4L60E is the computer version of the TH700R4.



A 4L80E on steroids with an aftermarket computer to tune the shifts and HD TCC would be reasonable choice behind the Cummins. In my case however, I'm too nervous to go that route and have decided to convert to an NV4500 and NP205.

Thanks britannic!



You are both absolutely right on the trannies. I had to go back & look in my old transmission manual to get it straight in my head. The 700R4 will stand up to high horsepower for short periods, but not high torque like the Cummins makes. Chevy did put the 700R4 in many of its trucks when it came out, which led me to think it was the update for the TH400. I was forgetting that the engines, even in the trucks, at that time were pathetic & in no danger of damaging even a wimpy transmission.



Yes, I'd sell your 700R4 & get a newer 4L80E.