Don't like my full throttle upshift RPM - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 5 (permalink) Old 07-17-2010, 02:27 AM Thread Starter
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Don't like my full throttle upshift RPM

I just completed my 6.2L diesel swap into a 1993 Suburban 2wd, complete with a 700-R4. I like the smoothness of the drivetrain, and the ease of acceleration (I was pleasantly surprised), and the effortless way it cruises at highway speeds (I might even want to re-gear to a taller ratio). My only concern is that the transmission on full throttle just doesn't want to upshift. It lingers forever near the governed RPM and then bumps into the next gear. It does that on WOT 1-2 and 2-3 (I don't have the nerve to see the 3-4!). I don't rocket around at WOT all that much but it would be nice to have an upshift a few hundred RPM lower. I wanted to know if there are any heavier weights available for these governors so I can try and lower the WOT upshift points a few hundred revs. I'd really like to get WOT upshifts at about 3,500 RPM instead of GM's recommended 3,800 calibration. I know that there are two primary and two secondary weights, and a pair of secondary weight springs, which the primary weights use to exert force on the secondary weights, which then act on the governor valve. While I am not transmission expert, I do have a GM factory training manual for the 700-R4 which does a good job of explaining how the governor works, and it would seem that heavier weights are the answer. I also know that backing off the T.V. cable to get earlier shifts is a bad idea, so recalibrating the governor is the only practical solution. I know easing off the throttle works, but I just want this thing to shift right at all throttle angles. Besides, it would seem that earlier part throttle upshifts would be advantageous with the way this engine likes to run. For what it's worth, it's currently geared with 3.73:1 gears, but I might see about swapping them for a set of 3.42s when I get a chance. This rig is purely a family car (I built it with long highway sprints in mind) and will not be used to tow anything more substantial than a 2,500lb pop up camper, because I have a truck for that. I am even considering a set of 3.08:1 gears, but I might just hedge my bets ad go with 3.42s. Anyhow, what can anyone recommend about the governor weights?
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post #2 of 5 (permalink) Old 07-20-2010, 02:34 AM
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Is the 700R4 from a gas engine or a diesel? If so that could be your problem. The gas transmission use different governors, as well as a different torque converter.

From wht you've described, I doubt thats your problem though. From another one of your threads, you said the 6.2L came out of an 1984 C2500. I'm guessing thats where you got your tranmission from too. So, my guess is your TV cable is out of alignment. Adjust it back to factory spec and you should be good.


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post #3 of 5 (permalink) Old 07-20-2010, 05:32 PM Thread Starter
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I have adjusted the TV cable so it is tight at WOT, but not limiting throttle travel. I adjusted it all the way in and stomped the pedal to snap it into place. Also, I know I have a three bolt converter. My question is this: did they use six bolt converters in the early to mid 80s? the converter doesn't stall very high (I briefly stall tested the converter with my Snap On timing meter hooked up, and it leveled out at appx. 1300 RPM after 5 seconds). At light throttle it shifts fine, at moderate throttle, it's ok, but at heavy to full throttle it just upshifts too late. I suppose it's possible it is a gas 700 with a low stall converter. The PO of the 84 suburban I got the transmission from said that he had gotten the transmission rebuild about 8,000 miles prior (and had an invoice to prove it), but that doesn't mean that the trans shop necessarily built it for a diesel, especially if they swapped a bad one for a good one (as some shops are known to do). This Suburban is not intended for any heavy labor. It's primary purpose is family car, with the possibility of someday pulling a small pop up camper (2-3000 lbs max) on a family vacation. The engine was built to maximize fuel economy, and as such, probably would not be a good puller anyway. I have my F-150 for heavy use, like pulling derelict Suburbans home to scavenge parts off of. I may try swapping the governor out and see what happens. Despite the light duty application I intend to use this Suburban for, I do in fact have a big honking auxiliary trans cooler on it (Hayden 18,000 lb GVW) in conjunction with the stock radiator mounted one. I don't know tons about automatics, but I do know the like keeping cool.

1993 Suburban 2wd 6.2L Diesel Conversion "Andromeda":
3.73:1 gears, THM 700-R4 transmission, and
J-code 6.2L diesel from a 1984 C2500 Suburban
1996 Ford F-150 4x4 300ci Inline 6 "The Argo"
327,000 miles and climbing
1992 Caprice Wagon 5.0L TBI "Enterprise-D"
Quote:
Originally Posted by Mater View Post
Ah ha ha ha! I swear! Tractors is so dumb!
Quote:
Originally Posted by General Nazca View Post
The Argo? That ridiculous pile of scrap metal!

Last edited by argo; 07-20-2010 at 05:35 PM.
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post #4 of 5 (permalink) Old 07-20-2010, 09:03 PM
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To answer your question, yes, they did use 6 bolt converters. I had a 6.2L 85' Suburban and it was a 700R4 with a 6 bolt converter. As far as your transmission, I dont know what else to say. Its impossible to know what they shop did if they rebuilt it. Good luck brother.

-Robert.

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2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A

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post #5 of 5 (permalink) Old 07-24-2010, 03:56 AM Thread Starter
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The 80% solution

I ordered a B&M Governor recalibration kit from Summit. I was discouraged to find that it's heaviest weights were LIGHTER than the weights on my governor. However, it's springs (even the light ones) were tighter than the factory ones. I used the kit's two heaviest springs to re-calibrate the governor and took a test drive. This truck runs substantially better, and will even full throttle upshift from first gear without much hesitation. I emphasize the word much because just as the engine starts to wheeze, it hits second. the 2-3 WOT upshift still requires me to lift, but just barely. It also stays in TCC lockup much longer, doesn't downshift from overdrive as readily, and will go into TCC lockup and overdrive at 35 MPH. In addition, part throttle and light throttle driving is smoother and also quicker, because keeping the revs down really helps the engine pull. This is a substantial improvement. I wonder though, now that I have this problem 80% licked, if my fan isn't the other 20% of the problem. I have read that with the clutch fully locked up the fan I am using (the "super duty" cooling fan that uses the 6 bolt fan clutch) can suck up to 30 HP. The problem is, it seems to stay engaged all the time, even though it's a new clutch (I know about the problem with aftermarket HD clutches, but I didn't know that until I had already bought this one, so I decided to give it a go with the AutoZone clutch anyway, since I already had it). I am sure that with the conservative way I built this engine, the fan is putting allot of drag on the engine as the RPMs close in on the WOT shift point. If I'm only making 130 HP to begin with, then perhaps that is part of the problem? I think that at 58MPH and higher I am faintly detecting some fan roar, so that is probably going to negatively affect my fuel economy as well, so I guess the next step is to loose the AutoZone clutch and buy a GM or Kennedy clutch, or go to a lighter duty fan and clutch and supplement it with an auxiliary electric fan.

1993 Suburban 2wd 6.2L Diesel Conversion "Andromeda":
3.73:1 gears, THM 700-R4 transmission, and
J-code 6.2L diesel from a 1984 C2500 Suburban
1996 Ford F-150 4x4 300ci Inline 6 "The Argo"
327,000 miles and climbing
1992 Caprice Wagon 5.0L TBI "Enterprise-D"
Quote:
Originally Posted by Mater View Post
Ah ha ha ha! I swear! Tractors is so dumb!
Quote:
Originally Posted by General Nazca View Post
The Argo? That ridiculous pile of scrap metal!

Last edited by argo; 07-24-2010 at 04:06 AM.
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