HELP! My husband and I own a '78 F250 super cab, 460, 4" lift on 35's. We recently had our c-6 transmission rebuilt with an RV torque converter and shift kit. 20 miles into our tow the transmission went! We are towing a 5500 lb trailer (mostly up hill). Now the "transmission guy" is telling us it could be all these different things: transmission cooler (we recently put in a brand new perma-cool), chassis problem, pinched line (even though it passed the flow test). Are we asking too much of this truck? What could be the problem and what can we do to fix it?

 

Did whoever installed the rebuilt tranny, flush all the lines to the cooler and the radiator?
A lot of metal and nasty stuff ends up there when a tranny goes out. They make special cans of cleaner just for this purpose.

 

The lines were flushed when it was installed, if the transmission guy doesn't know what is wrong with it, how are we supposed to know. A few people have said it may be the pump in the transmission?

 

I also want to add this is the 2nd transmission blown in 30 days!!!!!

 

When you say the transmission "went" what exactly did it do?

If it is the second tranny that has blown something is probably wrong extrnal to the transmission or your use is way out of it's capabilities as built. This is strange due to the fact that a C6 can handle 800HP if set up properly, -the operative word is properly. There is a limit on how long the transmission can tow uphill without a cooldown period. I would also suggest a transmission temp gage for this application. Test the sender in some boiling water to check accuracy.

A standard tranny is still best for towing.

 

When i say it went, it slowed way down to low gear, 30 mph is the maximum it would do. It started smoking then it went to billowing smoke, we pulled off to check it and the truck would not start again until it sat for about 20 minutes. even though it wouldn't move after that. We are towing to the desert which is a good 60 miles all uphill, will this truck ever be able to do that? We have been considering a brand new f250 diesel with an allison transmission but that is a lot of $$$. We have put so much $$ into the '78 we were hoping we could make it work.

 

I pull a 5,500 pound Airstream with my 1977 F-250 SuperCab. It has a 460 engine and 460,000 miles on it. All original except for the power steering pump and the starter motor. I have never had a problem towing the trailer. I can barely feel the transmission shift.

 

We have no problems towing it either......on flat ground. But the trip we take it on is 60 miles up to 4000 ft and then it drops back down again. The truck is not making the tow past 20 miles.

 

I'm in Washington State. There are many hills I often tow through the mountain passes.

 

it is constant uphill, i am just trying to find out what the problem could be. It is a hard trip and there is no downhill until you reach the top, so basically the truck is pulling 5500 lbs non-stop uphill for a solid hour maybe hour and a half. I need to talk to someone who really knows if this truck is capable of doing this

 

You haven't said what Rear Axle Ratio you have in this truck, and I don't thimk you probably Know!!!......TO TOW THAT TRAILER under the conditions that you have described you NEED a 4:11 rear axle ratio which means you're Fuel milage isn't going too be very good. You need to find another tranny shop that Knows how to really Enhance the C6 that is in your truck. For every 1,000 feet of elevation you get ABOVE about 3,000 feet your engine is going to LOOSE approximately 4% of it's rated horsepower\Torque output Because of the Decreasing Air density which means it won't pull as good at 5,000 feet as it would at Sea Level. fd.............Another thought....if pulling this trailer is more important than driving around on Oversize tires you might want to consider Going Back to the Correct size of tires that the Truck was designed to PULL with.....the "35's" are Creating a Tremendous Workload for the engine and the Tranny and All that additional work is Generating Lots Of Un-necessary Heat which is Probably what is Killing Your tranny!!!!!Get those big , tires OFF your truck , and have a 4:11 axle ratio installed and your Good to Go.....fd

 

The most important question is: Did you break in the transmission BEFORE towing that pile of wheels?? You shouldn't be towing at 20 miles!!

Break the new transmission in. You can begin towing as early as 1000 miles.

And install a transmission filter when the trans gets rebuilt. You won't believe how much metal shavings could go through that filter!

Install a 10,000 pounds minium transmission cooler!

Go easy on the new transmission!

 

Oooh, cool....this is like trying to solve a Court Room Drama mystery on TV!

The big clue for me was the "billowing smoke" from the trans.

This tells me that one of the clutch packs is not holding pressure mayb due to a cut, twisted or improper Square "O" ring install on a pressure piston. Another possibility is that the huge Belville spring washer is either broken or very weak and letting a clutch pack not return, also causing lots of heat to be generated.

Something is allowing one of the clutch packs to slip BADLY, genetate LOTS of heat and vaporizing the trans fluid. Yes, low line pressure could cause it, but it was stated that line pressure was good. Based on what's been written by the owner "cbears".... this trans is probably toast.

Are we SURE we're using the correct fluid? C-6's that year should be Dextron/Mercon and not Type "F".

Also get the rebuilder to verify they used the correct clutch discs, and (I assume) Master Rebuild Kit for this year/make/model. I've had the parts folks hand me the wrong items in the "right" box many times before. Any rebuilder shuld be savvy enough to check what he's got before installing it.

There's much merit to the earlier post too about the gear ratio and oversized tires, but I honestly think that would be a slower process to failure than the catastrophic failure(s) we're seeing here.

Please let us know what the final fix is!

John

 

Was your engine running hot? They affect each other through the radiator. A hot engine will heat a tranny and vice versa.

 

ok, my 2 cents, firstly get rid of the huge tires, put p235's back on there or w/e it's designed for. secondly if you just rebuilt the tranny, dont overwork it, break it in slowly

also dont drive so slow uphill. the tranny is shifting between 1st and 2nd too much

get a new tranny shop,

just my 2 cents