Truck will not coast

[79Fordpilot]

My project '79 4x4 with automatic transmission seems to shift OK but once I reach cruising speed if I let off the gas the truck does not coast. It doesn't really feel like a down-shift but definately a very noticeable drag. I have driven these trucks when they were new back in the '70s but that was 30+ years ago. I don't remember this being normal operation but maybe it was. Anytime at higher speeds once I let off the gas the truck just seems to bog down. I checked to make sure the hubs are locked out and the transfer is in 2H since I at first thought it might be in 4H. The transfer appears to be shifting in and out of 2x and 4x OK. Rear tires will get scratch in 2H. Front calipers are not rubbing, not sure about the rear drums but nothing is getting hot from friction. Is there a coast clutch in the transmission that might be causing the problem? I'm not sure which transmission I have but can check. Sorry this is so lengthy and any help would be very much appreciated. Thanks!

 

[smokey]

How much drag? These trucks have the areodymanics of a brick.
Jack the truck up and see if the wheels turn free with little to no drag.
Large tires can create a drag also.

 

[79Fordpilot]

Seems like excessive drag to me. Slipping the shifter into neutral at speed takes the drag away. I hope to be able to put the truck on a lift this week. Tires / rims are stock size.

Any additional comments and suggestions are welcome

 

[BKW]

I'm not sure which transmission I have but can check.

It's a C6: 17 trans pan bolt holes.

 

[LEB Ben]

I'd check the rear drums first...beyond that, I lose speed going down slight declines in any dentside I've owned. I'd bet my current rigs lose 10mph over a few hundred feet if I let off the gas at highway speeds.

 

[Mil1ion]

To me the obvious question is what axle ratio do you have ?

4x4's were made for crawling Off-road so I would bet you have tall gears like 4.10/4.11 or 3.73's or at the very least 3.54's which would cause the slow down

 

[79Fordpilot]

Thanks all. Mil1ion I will get gear info and post again. Ben, the truck loses 10 mph immediately and drops from 60 to 40 in about 3 seconds. Just doesn't seem right but may be normal.

 

[79Fordpilot]

Thanks Bill~

 

[mm_0_mm]

and your transmission is definitely shifting into third? maybe the link is not adjusted and you are really only in second gear (which would cause a noticeable engine braking effect). Just throwing it out as a possibility.

 

[BKW]

The AXLE code is stamped on the Warranty Plate, located on the left door face below the latch.

9" = The Ford axle tag is located at approx 5 o'clock, under one of the bolts that retain the carrier (pumpkin) to the housing.

It appears that the hubcaps are retained to the wheels with 3 chrome screws and anchors. If so, these are genuine Ford styled wheels.

 

[79Fordpilot]

Truck is definately shifting from 1st to 2nd to 3rd but that was a good question mm_0_mm. The transmission is a C6 as BKW noted and it has 3.54's.
Still hoping to find a fix for it.

 

[m78]

Take the front drive shaft out and try it.

 

[Jolly Green]

To me the obvious question is what axle ratio do you have ?

4x4's were made for crawling Off-road so I would bet you have tall gears like 4.10/4.11 or 3.73's or at the very least 3.54's which would cause the slow down

This is what I was thinking...now that we know you have 3.54, that seems like a lot of drag though. I say the brakes are hanging up a little.

 

[Mil1ion]

a lot of times people have no idea that the disc brake pistons or rear wheel cylinders are hung up.

Also check the BPPV as they end up seizing and causing brake problems

The only way to check for sure is to jack up the truck and spin the wheels

 

[79Fordpilot]

OK. I hope to be able to put it on a lift next weekend. If all the wheels spin freely then that leaves the gear ratio. Are there options for maybe a higher
3rd gear (or gear set) for the C6 transmission?

 

[mm_0_mm]

does it seem to coast better when you slip the transmission into neutral?

 

[m78]

I have a '87 Bronco II that the rubber (inside) the front break hoses would get hot and swell up, not allowing the pressure to release off of the calipers.
It felt like you discribe is happening to your truck.
After it cooled down it would be fine again.


I haven't figured out what I was thinking on this one. vv

Take the front drive shaft out and try it.

 

[79Fordpilot]

It does seem to get better when I slip it into neutral but It bogs down so fast it is really hard to tell for sure. m78 the front drive shaft actually makes sense if there is something keeping it in 4H, which is actually what it feels like. I'll see if it is worse as truck heats up, could be the hose issue you mentioned. I should get a chance to put it on the rack soon. Thanks!

 

[m78]

I wonder what came of this problem.

 

[79Fordpilot]

Sorry I haven't followed up on this. I have not had a chance to do anything with my truck yet. I need to get more information from the VIN tag but I suspect the cause is 4:11 gears since I found out this truck came out with the factory(?) off-road package. I will post more when I find out. Thanks for your interest Mark.