[maxgig]

Well this weekend I finally took the car on an extended road trip (435 miles total) and got my new mpg's for my locking rearend and 3:55 gears. I took the wife and son with me and with the weight of them and our luggage I found a few new areas that will need attention when the money comes available.

I don't know what you guys get for mpg's but for this trip I averaged about 13.67 mpg's and I only filled up 3x's total compared to 5 before I had the work done. At speeds over 65 mph I can really hear the truetrac rearend making a loud humming noise that drowns out the radio.

I didn't dog it like I usually do because I had the family with me but I did hit 90+ mph a few times on the trip and tried to at least stay with the flow of traffic for the most part. Unfortunately, we all had very sore butts after riding on my O.E. seats for 4 hrs so once we re-locate to Kansas an interior upgrade is going on my list of things to do.

My first fix is going to be getting my rear fenders rolled because with the extra weight in the car my tires rubbed on almost every bump I went over, and this made the wife extremely nervous. I also discovered that my 1980's model alarm system is a piece of crap that has to go. We stayed in a hotel and I basically felt the need to check on my car at least every 2 or 3 hrs during the night because I couldn't sleep.

So if any of you KC KS area guys know of a decent shop I can take it to please send me a pm, thanks.

 

[1969XR7Vert]

A loud humming noise from the rear doesn't sound good or normal. Also, curious what sort of RPM's you had at what speeds with the 3.55's?

 

[Bad69cat]

Yeah - my TT doesn't do that? (or I can't hear it over the headers...) There is a special lubricant that you are supposed to add to that - did you use it? I did have some trouble at first going around corners and have it chattering some. But I added a bit more of the FOMOCO lube and it went away. I'd say mileage wise you are doing about right. Look at your plugs and see what they are telling you.

 

[maxgig]

Yeah - my TT doesn't do that? (or I can't hear it over the headers...) There is a special lubricant that you are supposed to add to that - did you use it? I did have some trouble at first going around corners and have it chattering some. But I added a bit more of the FOMOCO lube and it went away. I'd say mileage wise you are doing about right. Look at your plugs and see what they are telling you.

After my break in period I had the fluid changed at the shop that did the work for me. They used royal purple gear oil but I don't think they used the special additive because they used it when they put the rear end on the car. I'll get some more and add it when I get the car to KS. I'm having it shipped out next Monday, thanks for the reminder.

 

[1969XR7Vert]

Yeah - my TT doesn't do that? (or I can't hear it over the headers...) There is a special lubricant that you are supposed to add to that - did you use it? I did have some trouble at first going around corners and have it chattering some. But I added a bit more of the FOMOCO lube and it went away. I'd say mileage wise you are doing about right. Look at your plugs and see what they are telling you.

I thought (perhaps incorrectly) that since the TrueTrac does not have clutches that friction modifier additive was not needed? Please comment (and anyone else with anything to add, please do as well).

Regards,

Bob

 

[1969XR7Vert]

I thought (perhaps incorrectly) that since the TrueTrac does not have clutches that friction modifier additive was not needed? Please comment (and anyone else with anything to add, please do as well).

Regards,

Bob

I'll reply to myself. Look here:

http://www.eaton.com/ecm/groups/public/@pub/@eaton/@per/documents/content/ct_128482.pdf

Where it says: "The TrueTrac differential is designed to operate in those lubricants recommended by the vehicle/axle
manufacturer for conventional differentials.".

So, according to Eaton, nothing beyond standard gear lube is required.

Regards,

Bob

 

[Jan Ove]

As others have already said, no humming noise is normal on a True Trac, and no additives needed either

 

[Harvey]

still like to hear about the rpm's with that gear ration at highway speed?

 

[Cougrrcj]

still like to hear about the rpm's with that gear ration at highway speed?

That would also depend on what trans he's using and also tire size.

Stock Classic Cougar tire size is approximately 26" (that'd be a 215/70/14). That works out to approximately 780 revs per mile. With 3.55s the engine should be turning somewhere near 2770 rpm with a non-overdrive transmission. There might be some slippage with an outomatic, so the RPMs might be higher. With an AOD (overdrive ratio of .67), the engine RPMs should be ~1860 at 60mph

My car has taller tires (225/70/15) 27.4" tall and 740 rev/mile. With 3.55 rear gears and my WR-AOD (4R70W) overdrive ratio of .70, my engine is turning 1840rpm at 60mph. That's how I can get 15+mpg - out of a 450+hp 393W!

 

[Harvey]

I am not so concerned with the miles per gallon just wouldn't want to gear a car so the engine would be revved to high for highway speeds of 70 or 75 all day long!

 

[mmmeat]

I'd say that is awfully good mileage for a 3:55!

Not to highjack, but what do you guys with a small block 302/289 get with a C-4 and 3.0 rear end? Anybody have any good figures?

I'm a bit weird about Mileage, always trying to get it as good as possible..and I fully intend to be driving a Cougar pretty dang soon on a regular basis, rain or shine!


Thanks for any input.

 

[Copy Cat]

Brian, Mistress gets high 13's as you describe

 

[Bad69cat]

I'll reply to myself. Look here:

http://www.eaton.com/ecm/groups/public/@pub/@eaton/@per/documents/content/ct_128482.pdf

Where it says: "The TrueTrac differential is designed to operate in those lubricants recommended by the vehicle/axle
manufacturer for conventional differentials.".

So, according to Eaton, nothing beyond standard gear lube is required.

Regards,

Bob

Thanks Bob - now ya tell me! ;>) I don't know why it was chattering then? It went away! Anybody want half a bottle of friction modifier!

 

[maxgig]

That would also depend on what trans he's using and also tire size.

Stock Classic Cougar tire size is approximately 26" (that'd be a 215/70/14). That works out to approximately 780 revs per mile. With 3.55s the engine should be turning somewhere near 2770 rpm with a non-overdrive transmission. There might be some slippage with an outomatic, so the RPMs might be higher. With an AOD (overdrive ratio of .67), the engine RPMs should be ~1860 at 60mph

My car has taller tires (225/70/15) 27.4" tall and 740 rev/mile. With 3.55 rear gears and my WR-AOD (4R70W) overdrive ratio of .70, my engine is turning 1840rpm at 60mph. That's how I can get 15+mpg - out of a 450+hp 393W!

I'm running the same size tires (225/70/15) but I have a C4 transmission, I may go the AOD route later on down the road.

 

[Art]

Well this weekend I finally took the car on an extended road trip (435 miles total) and got my new mpg's for my locking rearend and 3:55 gears. I took the wife and son with me and with the weight of them and our luggage I found a few new areas that will need attention when the money comes available.

I don't know what you guys get for mpg's but for this trip I averaged about 13.67 mpg's and I only filled up 3x's total compared to 5 before I had the work done. At speeds over 65 mph I can really hear the truetrac rearend making a loud humming noise that drowns out the radio.

That's not the Tru-trac. Someone missed the mark when they set your gears up.

I didn't dog it like I usually do because I had the family with me but I did hit 90+ mph a few times on the trip and tried to at least stay with the flow of traffic for the most part. Unfortunately, we all had very sore butts after riding on my O.E. seats for 4 hrs so once we re-locate to Kansas an interior upgrade is going on my list of things to do.

My first fix is going to be getting my rear fenders rolled because with the extra weight in the car my tires rubbed on almost every bump I went over, and this made the wife extremely nervous. I also discovered that my 1980's model alarm system is a piece of crap that has to go. We stayed in a hotel and I basically felt the need to check on my car at least every 2 or 3 hrs during the night because I couldn't sleep.

So if any of you KC KS area guys know of a decent shop I can take it to please send me a pm, thanks.

I'd say that is awfully good mileage for a 3:55!

Not to highjack, but what do you guys with a small block 302/289 get with a C-4 and 3.0 rear end? Anybody have any good figures?

I'm a bit weird about Mileage, always trying to get it as good as possible..and I fully intend to be driving a Cougar pretty dang soon on a regular basis, rain or shine!


Thanks for any input.

16.5 is about the best I could ever get. Some report unreal numbers that I question.

Bad69cat-You're cornfusing an aftermarket tru-trac with a OEM trac-lock

 

[Scott Gregory]

Loud Humming noise? Before you condemn the Tru-trac, I suggest you check the axle bearings. Does the noise get louder proportionally the faster you go? Does it change in pitch when you change lanes on the highway? In most cases if the noise increases/changes like this you will find a bad axle bearing. Another good tell-tale "may" be a leaking axle seal.

Conversely, if the noise gets louder upon deceleration I would check the rear for a bad pinion bearing(s) and or carrier bearings. If you rear housing has drain plug, drain the lube into a clean pan and check it for excessive metal. It will always have a slight metallic look but it should not have an excessive amount. You can strain the lube through a tee-shirt and reuse it if looks ok.

 

[old wood]

I agree with Art.Whoever did your rear end might not have it shimmed properly.

 

[maxgig]

Loud Humming noise? Before you condemn the Tru-trac, I suggest you check the axle bearings. Does the noise get louder proportionally the faster you go? Does it change in pitch when you change lanes on the highway? In most cases if the noise increases/changes like this you will find a bad axle bearing. Another good tell-tale "may" be a leaking axle seal.

Conversely, if the noise gets louder upon deceleration I would check the rear for a bad pinion bearing(s) and or carrier bearings. If you rear housing has drain plug, drain the lube into a clean pan and check it for excessive metal. It will always have a slight metallic look but it should not have an excessive amount. You can strain the lube through a tee-shirt and reuse it if looks ok.

It doesn't get louder when I slow down it actually goes away. Unfortunately we're moving out of state next week and I can't take it back to the shop that did the work. I'll live with it for now and get it checked out in Kansas, thanks for the ideas.

 

[1969XR7Vert]

It doesn't get louder when I slow down it actually goes away. Unfortunately we're moving out of state next week and I can't take it back to the shop that did the work. I'll live with it for now and get it checked out in Kansas, thanks for the ideas.

Which most likely means either the ring and pinion were not set up properly or the gears are of poor quality. Do you know what brand gears were used? And were they new or used? There are only a few good gear makers and the inexpensive white-box chinese-crap ones from places like Summit are a big no-no.

 

[posidude]

Pinion depth and proper bearing preload is also important in order to get a good gear pattern.