1991 RMW - First tow with new trailer - Advice?

[happygene]

Hi All,

I've just put the first tow on my 1991 Roadmaster Estate Wagon (w/~150k miles, never used to tow before) pulling a 6x14x6 1/2' tall enclosed trailer (aluminum frame, ~1600# empty). I had fixed a bunch of maintenance things and had a trans cooler installed. I had a class III/IV receiver and brake controller installed too...

I picked the trailer up about 4 1/2 hours away and pulled it home, primarily on interstate. First off, I was a little shocked at how hard the engine had to run relative to no trailer...more specifically how hard I had to mash the gas pedal. I got a calf cramp then let the cruise handle the heavy lifting (pressing?). I also note that if I released the CC, the accelerator pedal sprang back pretty severely...I suspect this linkage load is not good for the cruise either...

On fuel economy... $30 to get to the trailer... ~$110 in gas to get back home! :O

I also consumed a fair amount of oil. Around town I probably need to make up about 1/2 quart per tank full. Pulling the trailer it was probably 1 quart per tank. I had the rocker cover gaskets replaced because they were leaking pretty bad, but did not have the rocker housing gaskets changed yet. I doubt I am blowing this much oil across the external leak, but would be curious what other owners have experienced.

Terminal velocity was around 70 MPH with AC on in the flats.

I have the GU2 (2.73?) rear end.

Questions:
Should I get a different rear end gear?
Can I get a softer throttle spring?
Do I need to change any programming? (and who could do that for me?)
What else should I pay attention to? (for drivability, durability and performance)

I did a search on this forum for Roadmaster towing and looked through the first 10 pages of results or so and did not find this specific line of concern discussed. If there are good links that answer my questions please share...

thanks,
gene

 

[buickwagon]

Honestly, my advice would be to get another engine. The 305 in the 91 just doesn't have enough torque to tow anything substantial. A 92 Roadmaster with towing package will have the 350 roller cam motor and lower rear end gearing, making it a much better tow vehicle.

But if that ain't in the cards, then yes, lower gearing will help. I remember having to tow in 2nd gear with my old 81 Electra 5L. Keeping the speed down to 55mph on the highway will also help a lot. A trailer that size is going to have a lot of wind drag.

 

[happygene]

Honestly, my advice would be to get another engine. ....

But if that ain't in the cards, then yes, lower gearing will help. ...

Yes, for the moment this is the car and engine I have.

To me it looks like the 3.08 rear end should help alot. I've got the gear and install kit, but I'm coming up slim on information about the speedo gear. I assume I need to put a new speedo gear to match the 3.08. Do you happen to know which gear I need? (# teeth and color are how they are described on the GM parts page)

Do I need to get anything changed in the ECM/ECU or any other controller once I get the speedo gear?

thank you!
gene

 

[gmgold]

I've changed from a 2.56:1 to a (Richmond) 3.08:1 on a large Buick. It made the car a lot snappier, but it still wouldn't do for highway towing with the low horsepower engine. If you really want to keep the Roadmaster wagon, probably the best bet would be both find an LT1 (350 cid) from a late Roadmaster ('94 - '96) and switch the axle to at least a 3.08:1, maybe even a 3.23:1. With those two changes, you'll find everyday driving to be a lot more enjoyable. Still, it's not going to be something you want to pull with at (high altitude or steep grades) and high (70+) speeds. If neither high altitude or steep grades, you might be okay with those two changes.

 

[gmgold]

Forgot to add: If you do change engine, consider finding a '96 wreck and pulling the tranny out also. The tranny you have now behind the 305 won't have as many plates in each clutch pack as you'd find in the tranny mated to the LT1 350. You might end up with short tranny life with the existing tranny and the higher rated engine.

 

[CarbonBlackCXS]

That's actually a fairly light trailer and most of the drag is due to wind resistance not weight. I have a similar sized trailer I pull on occasion behind my '12 Ram and it too will use much more gas despite having 400HP. Changing out the rear end wouldn't make much difference for you. (Been there done that on an old van). What you have is a tired engine. If you must, put the cash into a better engine or rebuild that one.

 

[gmgold]

That's actually a fairly light trailer and most of the drag is due to wind resistance not weight. ... What you have is a tired engine. If you must, put the cash into a better engine or rebuild that one.

Absolutely. The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed. (old quote, not mine) The frontal area and thus wind resistance of the trailer at 6.5' high is a real problem at 70 mph requiring plenty of horsepower at driven RPM. Not going to happen with the 305. The steeper axle ratio will get the engine RPMs up slightly to a higher hp level, a help, but that won't be enough.
While you're noticing a problem with the empty trailer, the amount of future weight inside the trailer might become a factor also. BTW, if you really have a heavy load being pulled by your RMW, you want to pull in direct, not overdrive.

 

[happygene]

Here's an update... I've had a few issues getting the rear end ratio changed, it's still not "right" and will need further work, maybe...

#1 The options sticker lists GU2 which should be a 2.73 differential, but the differential gears turned out to be a 2.56. I am skeptical this was an aftermarket differential change, so I just find this strange.
#2 I've been to 2 shops to try to get the rear end set up correctly, neither was able to get the whine out... now I'm reading 2.56 is the carrier break so maybe the problem is I needed a different carrier or spacer or thick gears?
#3 Since I'm looking at even more $$ to get the rear end fixed, I went ahead and pulled the trailer to see if the 3.08 helped...it did help...alot! ... I would just be very happy to have a working reliable 3.08 in this car... it would do what I need...

I've looked at this
buickforums.com/forums/threads/27048-Differential-Gear-Options
and this
http://www.crawlpedia.com/thick_gears.htm
even found this:
http://www.drivetrainshop.com/Ring_Gear_Spacer_p/mrg908a.htm

Any guidance?
--gene

 

[gmgold]

Whose gears did you use? If Richmond, yeah, you're going to get some axle whine. But they make real strong gears.
Make sure shimmed correctly.

If listed on sticker as GU2, it should have been built with 2.73:1 gears. I can't imagine anyone willingly pulling 2.73s from a 91 RMW to put in 2.56:1 gears. No wonder it didn't like pulling your little trailer.

 

[happygene]

Whose gears did you use? If Richmond, yeah, you're going to get some axle whine.

It's not just whine, I'm pretty sure the ring gear is walking. On power it sounds OK, but if you go neutral throttle or engine breaking it really howls. The 256 gear required a Series 2 carrier. The local shops did not understand that the ring gear carrier for a 256 should not just be shimmed... apparently if you shim for the carrier difference (the difference from Series 2 for 2.56 and down to Series 3 for 2.73 and up is 0.210 inch) plus whatever is needed to get alignment, it puts the ring gear above the ID pilot on the carrier and the stack of shims tends to slip leading to instability.

I've ordered a new series 3 carrier, a new 308 ring and pinion and a new ABS reluctor for the 308 (that I missed first time). Probably overkill, probably could have re-used first 308, but do not trust it since it's not been running properly.

I can't imagine anyone willingly pulling 2.73s from a 91 RMW to put in 2.56:1 gears.

Yeah, this has me stumped...