C6 rebuild for dual purpose trail rig. What C6 mods are mandatory, what ones are overkill? HP frictions or Stock?

[79INA69]

Started the tear down of my C6 as it was making loud whine/ scraping sounds and wanting to slip under load. Found the band was WAY loose for some reason and burnt, leaving a mess in the pan. So the plan is clean and rebuild. It is a 1979 C6 4x4 with the short adapter and 31 spl. It has the aluminum 3 pinion planet and 3 friction front drum with the lower snap ring groove. My question is for those who have run this transmission (which I know is not common in the EB): What are the thoughts on HP frictions (red alto, kolene steels) Super servo's, fitting 4 frictions in the front drum or upgrading the front drum, and what low stall torque converter to run for Ford 400 engine w RV cam, 4:56 gears? (rv, towing, fuel miser?) I already have a b and m shift kit in the VB, Deep aluminum pan, otherwise stock. Just curious if anyone had a solid before and after rebuild, or swap that could chime in. Goals of the trans are not overheating, reliable and stong. Also is there a rec on where the rebuild comes from or brands to stay away from.

 

[Yeller]

For what you’re running there really isn’t a need for anything special, the shift kit is about the only thing it really needs. As for the rebuild, find a reputable local shop with the best warranty, a shop that does shoddy work will not survive if they offer a great warranty.

 

[79INA69]

For what you’re running there really isn’t a need for anything special, the shift kit is about the only thing it really needs. As for the rebuild, find a reputable local shop with the best warranty, a shop that does shoddy work will not survive if they offer a great warranty.

Alright. I have rebuilt 5 C4 transmissions before. All but one have been stock with a shift kit. One of them was fitted with 5 frictions and a slimmer top plate to fit. I have been going back and forth with rebuild this C6 or swap out for the NP435. Cheaper to rebuild the C6 as long as I keep it simple. The local shop wanted $1800 for me to drop off the trans...I would rather spend that $1k somewhere else on the bronco.

 

[Yeller]

If your comfortable, I’d do the rebuild.

 

[bax]

The c6 is the only thing that has lived behind my 400. My rebuild was pretty basic. Upgraded front drum that fit more of the frictions in it (red).The fancy servo and some valve body work. Plus a new planetary set. I did not do the work. I had JW performance transmissions do the work. They are local to me and do all my work since 1980. (Drag racing). Anyway the trans has held up well and I have zero problems with its performance. I do have a leak that I can't seem to fix and it bugs the crap out of me but it works well. I spent about 2K on the work. plus another 800 for the converter. I run pretty much a stock stall converter however it is not a stock converter. It has heavy duty sprag in it with some heat treating on the inside veins. No issues. Yeah I got a lot of money in it but it has lived taking everything the 400 has given it. That SOB is a monster. I run the long shaft model. I found that the front driveshaft was to close to the trans pan (corner) using the short shaft. But with all this said, the c6 is a tough whore and would hold up with the stock internals that it came with. You kill these transmissions by getting them hot. I run a big cooler with a fan.

 

[bax]

Oh and there is no M with a 400. Welcome to the dark side.

 

[79INA69]

Oh and there is no M with a 400. Welcome to the dark side.

Yes I know it is just a 400, the M in my sig, I know. I took the pump apart and the gears look great, no wear in the housing. the frictions and steels in both drums actually look great still, so much less carnage than expected. I would like to fit 4 frictions in the int drum, but is looks like the "Lincoln drum / E40d drum) are not just laying around anymore. I have seen people use the piston side pressure plate on the int drum to fit one more disc and steel, and might go that route. The wider band looks like it takes a new drum or machining to fit. The R style servo looks like a solid upgrade. I want to upgrade the converter to a towing or low stall one. Otherwise it looks like my front band was the only failure. It had no holding when the throttle was above 25%, also felt like the motor was getting loaded down a lot when put into gear. Is this super loose failed intermediate band my smoking gun? I'm going through my doubler set up too (bearings and seals)

 

[Broncobowsher]

I only owned one C6. It was bone stock in a big block truck. Talk about buttery smooth shifts. I can see how that transmission was originally designed for those big engine luxury cars.

The one thing I didn't like about it was the kickdown. When you were almost mashed to the floor, just not buried deep in the carpet, it wasn't positively in kickdown. Sipping half kicked down. Mash it a little harder and it would be a full kickdown. I changed the kickdown design to a small air cylinder triggered off the A/C cut on the Holley Sniper. Not only did it clean up the kickdowns (you could even set the throttle level for the kickdown) it also cleaned up the linkage at the throttle body. Already had the air source since I was running an air horn.

 

[79INA69]

I only owned one C6. It was bone stock in a big block truck. Talk about buttery smooth shifts. I can see how that transmission was originally designed for those big engine luxury cars.

The one thing I didn't like about it was the kickdown. When you were almost mashed to the floor, just not buried deep in the carpet, it wasn't positively in kickdown. Sipping half kicked down. Mash it a little harder and it would be a full kickdown. I changed the kickdown design to a small air cylinder triggered off the A/C cut on the Holley Sniper. Not only did it clean up the kickdowns (you could even set the throttle level for the kickdown) it also cleaned up the linkage at the throttle body. Already had the air source since I was running an air horn.

That sounds rad! I would like to see how you set that up. I have a sniper set up on this motor.

 

[Broncobowsher]

That sounds rad! I would like to see how you set that up. I have a sniper set up on this motor.

This and this and I was running a fairly low pressure air tank for the air horn. Maybe 60 PSI? Never took pictures of the linkage, it was simple.

 

[bax]

Thats pretty fancy. Good thinking. Now I want to go do it to mine.

 

[brewchief]

I used power packs that use thinner clutches and steels to add more clutches. Looking back it was probably overkill. I added an R servo, get the superior brand as the sonnex has a problem with the o ring groove not cut deep enough. The apply lever should compliment the servo, E is max with an R servo, the F can put to much band pressure and break the case supposedly. I did the rear sprag upgrade with the e4od sprag and added a thrust bearing there instead of a washer.
I run a broader reverse manual valve body, a few clearances needed to be set slightly different from stock.

I run a loose converter that builds a lot of heat, even with 2 coolers fed with -8 lines it ran a bit hot until I added a deep aluminum pan, I don't know exactly how but it dropped temps by up to 30-40 degrees at the sand dunes.

I run a 205 with the short adapter and pan clearance was very tight, I found a 1310 cv yoke that was like 5/8 shorter and still had to grind the corner of the pan and take all the weights off the stock driveshaft so it didn't rub.

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[Madgyver]

The Dark Side...

 

[79INA69]

I used power packs that use thinner clutches and steels to add more clutches. Looking back it was probably overkill. I added an R servo, get the superior brand as the sonnex has a problem with the o ring groove not cut deep enough. The apply lever should compliment the servo, E is max with an R servo, the F can put to much band pressure and break the case supposedly. I did the rear sprag upgrade with the e4od sprag and added a thrust bearing there instead of a washer.
I run a broader reverse manual valve body, a few clearances needed to be set slightly different from stock.

I run a loose converter that builds a lot of heat, even with 2 coolers fed with -8 lines it ran a bit hot until I added a deep aluminum pan, I don't know exactly how but it dropped temps by up to 30-40 degrees at the sand dunes.

I run a 205 with the short adapter and pan clearance was very tight, I found a 1310 cv yoke that was like 5/8 shorter and still had to grind the corner of the pan and take all the weights off the stock driveshaft so it didn't rub.

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So on your direct clutch (high clutch) I have 3 frictions with .076 steels. When running 4 thinner steels and frictions, will this allow the stock location of the snap ring? I would be fine with 4 in direct and 5 in forward. On the fence about the r servo. I have an N stock, and have not confirmed what lever ratio I have. My direct frictions are toast. The drum might be okay. For sure I want to put the plastic cage roller sprag, one piece case bushing, torrington bearing roller clutch center, and full rebuild with either high energy or power pack. I was wondering about the cooling lines: Did you drill out and re tap? My stock lines are 5/16". Up the side to 3/8" should help right?

 

[brewchief]

So on your direct clutch (high clutch) I have 3 frictions with .076 steels. When running 4 thinner steels and frictions, will this allow the stock location of the snap ring? I would be fine with 4 in direct and 5 in forward. On the fence about the r servo. I have an N stock, and have not confirmed what lever ratio I have. My direct frictions are toast. The drum might be okay. For sure I want to put the plastic cage roller sprag, one piece case bushing, torrington bearing roller clutch center, and full rebuild with either high energy or power pack. I was wondering about the cooling lines: Did you drill out and re tap? My stock lines are 5/16". Up the side to 3/8" should help right?

With the power packs I think I ended up with 6 or 7 in each, I used an extra pressure plate flipped over to gain one in one of them.

The power packs are more expensive and it might make more sense to find one of the drums that hold more stock or one that was machined to allow it.

For cooler lines I found some adapters from straight pipe thread to -8 on ebay. I have 2 large stacked plate coolers, one in front of radiator and one mounted underneath basically below the drivers seat, I have a 3500 stall converter so it builds a ton of heat but it works well at the dunes for me.

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[79INA69]

C6 UPDATE: For those who care: I rebuilt the trans with a full kit from transparts warehouse using full thickness alto green high energy frictions and steels. 5 in the low reverse set at .070" clearance. 5 in the forward using one .090" steel to get .035" clearance. 4 frictions in the direct using a Broader performance stepped top plate, one .090" steel to get .031" clearance. E40d larger plastic cage one way roller. Machined one way roller race and #9 thrust replaced with torrington. Sonnax one piece rear case bushing. Superior billet R servo. Stock style replacement converter from TransStar Industries 1800-2200 stall range. The new converter drops right in 3 clicks and turns freely both directions. When I removed it, it was hard to turn counter clockwise and had tension clock wise. For what thats worth. Im assuming the converter was damaged or the failed band was binding it up. Moving on to the 205 doubler while its out. Rebuild it and be done with the heavy lifitng.