4T60 Final Drive Ratio

This forum is to ask and questions or concerns in converting your Le'Sharo over to G.M.

Re: 4T60 Final Drive Ratio

Unread postby StevenJayne » Fri Mar 23, 2012 12:18 am

Hi Max,
I found several transmission shops advertising differentials on eBay, and I'm sure any local shop can find you one. I don't have the web sites saved, but I could re-find them if you need. These transmission folks are hungry for business, just like everyone else these days (except for the oil companies!) There are many tens of thousands of these cars in the recycling yards, so don't worry about competing for a differential.

I like to drive in 3rd because 4th is really a joke for this heavy machine. It just won't stay locked up! There is not enough power being made below 2500 RPM to pull hills or fight a headwind, so my goal is to keep it between 2500 and 3000. I live in the mountains, so I don't get many chances to see if it locks up in 3rd at 70MPH on the flat, but it should. On the steeper hills I find myself in 2nd gear, running 3500 RPM and about 45MPH. In town, I can't pull a steep hill in 2nd gear and have to shift into first...no fun! The primary reason I want to go to the 3.33 is to move the power band down so that 1st, 2nd and 3rd gears work better in town and up to about 65mph. I'm hoping that 4th will be OK at 70+mph too. Fourth drops the RPM 30%, so I don't know if it will be ideal, but it will certainly be better that what we have now.

My unit is sometimes called an OBD1.5. It has the OBD2 connector, but the software is not fully OBD2.

Since I bought my rig, I have driven close to 1800 miles with no transmission heat issues whatsoever. I don't have a temp gauge on the tranny (yet), but I've never had it slip and my tranny fluid is nice, red and not toasty. One day I drove my rig straight into a 60MPH headwind in Kansas for 6 hours with no issues. I had the thing floored most of the way and got 12MPG, but I made it. My rig has an external transmission cooler and 2 cooling fans that run all the time as soon as I turn the ignition on. My main radiator is out of an El Dorado and is huge, so my engine temp is always solid as a rock. The guy who did this conversion was an engineer and really focused on heat issues.

I would change my tranny fluid NOW if it heated up so much that things started slipping. I would also stay away from putting any additives in the tranny.

Steve
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Re: 4T60 Final Drive Ratio

Unread postby flyingkilt » Fri Mar 23, 2012 12:44 am

Thanks for your reply, Steve,

You are RIGHT about staying away from transmission additives. It COULD have been the Lucas transmission additive I put in just before it heated up and started slipping. I've read some bad reviews about that particular additive since then. I think Lucas oil additive is great, but their THICK automatic transmission additive is not good.

JUST TODAY, my great mechanic -- a hot rodder who knows cars and has helped me on NUMEROUS LeSharo projects now -- changed the transmission fluid, and it looked okay, thank goodness; not a great deal of black clutch material in the bottom of the pan.

I decided to try Royal Purple since it's supposed to cool better. I also changed the coolant, and even added a bottle of "Water Wetter." I think I had a bubble in the coolant system, which contributed to the overheating problem. THEN, we discovered the cooling fans weren't coming on AT ALL, either, and started searching around for the cause, and it turned out to be a failed relay.

Sooooo, with all these improvement combinations under the "WinneBuick's" belt, my wife and I confidently took off this evening from Southern Oregon to the Des Moines, Washington Marina to show Kimberly RV and Marine Wood Stoves during the Des Moines Yacht Club's annual swap meet. This is an important event for our business, and we've had no overheating problems this trip by cruising in 3rd gear only. So far so good, and we've stopped overnight about a third of the way there.

You're right, it WILL NOT lockup in 4th gear, no matter what -- even coming downhill. It STILL runs a little hotter than I'd like, and that Eldorado radiator sofans coming on with the ignition switch. Yes! I LIKE THAT idea! It sounds IDEAL, along with the full-time fans coming on with the ignition switch!

We HAD to stop, tonight, though, as our LeSharo just came out of the paint shop Wednesday smelling to high heaven with lacquer fumes -- http://lesharorv.com/viewtopic.php?f=2&t=1586 -- and also -- http://lesharorv.com/viewtopic.php?f=2&t=1593 -- and it is STILL pretty darn toxic tonight with lacquer fumes. It needs to air out at least another night or two -- meanwhile, we're driving with the windows down and the heater going full-blast sucking in fresh air -- AND we're gonna' stay in motels until the air is safer to breathe in the LeSharo. As it is, we both have headaches tonight, and I think I heard our Jack Russell Terrier, "Mini," complain about her sore head, too . . .
Max Guiley
Chiloquin, Oregon
1985 GM-Converted LeSharo with Buick 3800 V6 and 4T60 FWD Transaxle
1986 All-Wheel-Drive LeSharo on GMC Safari Lifted-Chassis with 350 Chevy V8
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Re: 4T60 Final Drive Ratio

Unread postby StevenJayne » Fri Jun 01, 2012 9:53 am

Hi,
I have been super busy as usual, but I have a couple of things to report.
I have not started the project to change the differential, and now I am questioning the wisdom of the idea.
Here's my story:
As you know, I changed the front tires to 205 70 R15's, which is correct for the Buick speedometer and turn a bit faster than the old tires.
We planned a 600 mile trip to Arizona last month, so I did a few things to get the rig ready. I put a can of Seafoam in the gas tank and ran it through by driving around town and several 60 mile trips.
Gas mileage was bad, about 12MPG. Then the engine started to miss badly when accelerating just off idle. I messed with it for a few days and decided I did not have time to fix it before the trip, so I took it to a good mechanic. He found the EGR solenoid/valve was reporting the wrong pintle position to the computer, and they put in a new valve.
We started on the trip and the engine was running normally. We got about 40 miles from home and the transmission slipped out of gear, which scared the crap out of me. I pulled into a Love's and we had a family meeting to decide what to do. The vote was to say "screw it" and keep going. I gassed up and the mileage measured 13MPG.
We got on the freeway and headed West toward Tucson. The transmission performed flawlessly and I got 15 MPG on the leg to Benson, AZ. I noticed that the transmission was locking up in 3rd gear very nicely and it would stay locked up unless we climbed a decent hill. I was driving 65 to 70 and the engine was turning 2500 to 2750 RPM if I remember right.
The next leg was South to a campground near Nogales, and then (2 days later) on to Tombstone, AZ. The engine and transmission worked perfectly and I got 17MPG in spite of some hilly terrain.
The last leg was back to Lordsburg, NM. Again, everything seemed to work very smoothly and I measured 18.5 MPG.
I am thinking that in addition to the EGR valve, something in the fuel system was gummy, plugged or whatever and the Seafoam cleaned it out. The result was that the engine is developing more power and can pull the rig through the air with less effort and better mileage.
Given that, I am pondering the wisdom of going to the 3.33 differential. I am concerned that the new ratio will make 3rd gear to low to run at 70MPH, and 4th gear still to high at 70MPH.
I need to do the math on this before I am sure what I want to do. My rig loves to run between 2500 and 3000 RPM, where it makes really good power. Below 2500 is iffy for anything but flat driving with no wind. Above 3000 RPM is OK, but I think the mileage will suffer.

So, good news is my rig is running better than ever. I am adding a much larger transmission cooler and a transmission temperature gauge next weekend.

Steve
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Re: 4T60 Final Drive Ratio

Unread postby flyingkilt » Fri Jun 01, 2012 12:54 pm

I, too, have been questioning if lowering the final drive ratio is as good of an idea as I first thought, but for a different reason: which pertains to coming down hills under engine braking.

There is one twisty mountain road, in particular -- the Greensprings Highway, Oregon 66 -- that we travel quite often, and our transmission is geared just PERFECTLY for it in its present ratio. This is a dangerous mountain road, and it has so many tight switchbacks, that it requires staying in first gear going up OR down, which gives us a safe 30 to 35 mph climbing or descending, and about 3000 to 3500 RPM.

A lower final drive ratio would slow down our overall climbing and descending speed in first gear, of course, at those same RPMs, and I don't want to turn the engine up any higher, as it starts sounding like its spinning its guts out any higher than 3500.
Max Guiley
Chiloquin, Oregon
1985 GM-Converted LeSharo with Buick 3800 V6 and 4T60 FWD Transaxle
1986 All-Wheel-Drive LeSharo on GMC Safari Lifted-Chassis with 350 Chevy V8
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Re: 4T60 Final Drive Ratio

Unread postby flyingkilt » Fri Aug 24, 2012 11:41 pm

I discovered that my transmission (from an OBD1 1988 Buick Electra Park Avenue) is ACTUALLY a 440T4, which is about the same as a 4T60, and I just had the final drive lowered to 3.33 (from 2.84) and it works GREAT! Here is the link to the early stages of my initial post about it: viewtopic.php?f=6&t=1784

The 3.33 final drive ratio is still in the testing stages, but -- so far -- I LOVE IT! There haven't been any computer issues . . . (yet?) . . .
Max Guiley
Chiloquin, Oregon
1985 GM-Converted LeSharo with Buick 3800 V6 and 4T60 FWD Transaxle
1986 All-Wheel-Drive LeSharo on GMC Safari Lifted-Chassis with 350 Chevy V8
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Re: 4T60 Final Drive Ratio

Unread postby Phasar » Fri Jun 28, 2013 9:18 pm

Steve...

Seafoam is great stuff however you should change your fuel filter out afterwards... at least that's what I've been told.
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Re: 4T60 Final Drive Ratio

Unread postby flyingkilt » Sat Jan 31, 2015 6:55 pm

Here is how I solved the problem of my 3800 conversion coming out of lockup -- the MagnaShift kit solved everything! http://lesharorv.com/viewtopic.php?f=6&t=16498&p=62888#p62888
Max Guiley
Chiloquin, Oregon
1985 GM-Converted LeSharo with Buick 3800 V6 and 4T60 FWD Transaxle
1986 All-Wheel-Drive LeSharo on GMC Safari Lifted-Chassis with 350 Chevy V8
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flyingkilt
 
Posts: 182
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Location: Chiloquin, Southern Oregon


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