View Full Version : 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?
john8662
07-19-2010, 12:35
A few things come to mind here...
The engine isn't being fueled in the upper RPM's due to a plugged fuel filter or air filter, so the engine can't generate the power necessary to reach the 3800 RPM shift point quickly.
The injection pump may need to be recalibrated, perhaps it was calibrated for a lower RPM. These pump should all go to 4100 with no load. You WILL need a tach to get this right though.
The transmission governor, yes 3800 is the right number, You could lower it, but I'd keep it and conentrate on why it's taking a long time.
Does it do this in all gears? How is the 1-2 WOT shift. Since 1st gear is so low it should do this quickly and easily, if not look at the fuel/air system.
John
ok how can u tell the difference in the 6.2 and 6.5 i have a 92 k1500 so says from the previous owner it has the 6.5l but i did a vin check and the original motor is 6.2l i have a banks turbo kit installed on it and as far i can see banks only has it for the 6.2's this is my first diesel so excuse me if i sound completely stupid lol
A few things come to mind here...
The engine isn't being fueled in the upper RPM's due to a plugged fuel filter or air filter, so the engine can't generate the power necessary to reach the 3800 RPM shift point quickly.
The injection pump may need to be recalibrated, perhaps it was calibrated for a lower RPM. These pump should all go to 4100 with no load. You WILL need a tach to get this right though.
The transmission governor, yes 3800 is the right number, You could lower it, but I'd keep it and conentrate on why it's taking a long time.
Does it do this in all gears? How is the 1-2 WOT shift. Since 1st gear is so low it should do this quickly and easily, if not look at the fuel/air system.
John
It does in in all gears. I used my Snap On timing meter to read the unloaded max RPMs and it was just a smidge above 4,000, but not quite 4,100. I also thought it was fuel related, so I replaced both fuel filters (I am running a Raycor 10 Micron fuel filter/water separator and the Stanadyne Model 80) but it ran just the same. I also have loads of fuel flow from my lift pump. I am using a GM solenoid type pump for the 6.5L engine. Through both filters, it will flow about a quart a minute. To be fair, I don't know what RPM the trans is shifting at during WOT. I have no tach and I am afraid of damaging the timing meter by leaving it hooked up and driving it. The trans came with the diesel engine, as it was with the engine in the 1984 C2500 Suburban I took the engine from. It is absolutely possible it was originally for a gas engine. That's why I was wondering if there are weight kits for these governors. I could play with this one until it felt right. Otherwise, I am very happy with it.
ok how can u tell the difference in the 6.2 and 6.5 i have a 92 k1500 so says from the previous owner it has the 6.5l but i did a vin check and the original motor is 6.2l i have a banks turbo kit installed on it and as far i can see banks only has it for the 6.2's this is my first diesel so excuse me if i sound completely stupid lol
Not stupid at all. If the engine was replaced, it may have been with a 6.5L, since that was the defacto replacement engine once the 6.2L left production. So even though the VIN says it's a 6.2L, it could be a 6.5L. If you look on the back side of the engine (where a gas Chevy V8 has it's distributor) you should see a casting number and either a 6.2 or a 6.5 cast in it. I know they have these markings elsewhere, but I can't think of where they might be off the top of my head.
convert2diesel
07-19-2010, 19:21
Argo:
Two things here. Yes the govenor for the diesel is different then the gasser. Not expensive ($40.00???) and quick to replace. Also, check the torgue convertor. It is common for these installation to find that the PO, not knowing diesels, installed a gasser torgue convertor. That little extra slip might be a contributor. Check to see if you have six mounting bolts. If you only have three then the torque has been replaced and may have been replaced with a gasser. You can get a three bolt one spec'd for 1,200 RPM stall assuming the PO, or his tranny guy knew what he was doing but I have seen the opposite too many times.
Something else you might look at is the TV cable adjustment. If it is not right on, it will seriously effect shift points. Another easy fix and a required one. If these are not adjusted right they will take out the tranny in short order.
Bill
WhiteTruck
07-19-2010, 20:30
A little theory will be helpful here. Since you have the factory manual, take another peek at this part. Let's say that the only shift control is the governor. This would mean that the shifts would always occur at the same speed, regardless of throttle position. This wouldn't work so well, since you want more rpm when towing or if you want to accelerate quickly.
The same thing holds true of line pressure. You would need max line pressure all the time without a T.V. cable (or vacuum modulator on a trans that used them) to make sure that you didn't get a slip under full throttle. So far we have a trans that always shifts quickly into OD and has harsh shifts since we have max line pressure.
Adding the T.V. cable and the valve it controls gives us a much better shift quality, since we can vary the line pressure and a shift speed that increases as we accelerate harder.
I will only comment about the shift speeds next, since that is your concern. There are more components in the valve body that modify other aspects of the shifts, but for our discussion here, this will be enough.
The governor is responsible for the minimum speed at which each shift will occur. The main difference in the weights was to calibrate these speeds based on the axle ratio used and the type of engine. The trans output speed, and accompanying governor speed are different with the axle ratios, so the springs were different for this reason.
The T.V. system modifies line pressure based on throttle position, and also modifies governor pressure acting on the shift valves. This is what is mainly responsible for your WOT shift points. The calibration you are after are the different springs used in the valve body itself. The valve body for a gas engine is calibrated for higher rpm shifts, so if you have a gas valve body, this is your problem, for example.
This is why your shift speeds drop when you back off the T.V. cable. You have less T.V. pressure modifying the governor pressure - lower pressure, earlier shifts.
Changing the weights will change the shift points too, but I just wanted you to see that there is more to it. Are the minimum shift speeds where they should be?? If they are all late, then you would gain by working with the governor. If they are where they should be, then the valve body calibration is what I would look at.
In reading through this thread, I see loads of good info.
To cover some issues again and reenforce them.
The 700R4 came in many incarnations over the years depending on the application/engine.
The governor is specific for the use with a diesel. Most good tranny shops can get you the proper governor for the 6.2 application.
The Gassers rev a lot higher than the diesel and the wrong governor will certainly keep the RPM band way above what the diesel is happy with.
As mentioned, the converter is also an integral part of the equation too.
The gasser converters are much "Looser" with a higher stall speed.
There is a specific conveter for use with the diesel.
Valve body calibration is also different. (Shift valve springs and a few other items)
A transgo shift kit has specific calibrations for the diesel engine application.
The TV cable on these trannies is literally their lifeline.
To adjust the TV properly (With all the stock brackets installed properly)
Slide the adjustment ratchet slider assembly all the way to the rear and then with the engine OFF press the throttle all the way to the floor mat, then let off.
This procedure will properly set the TV cable/valve adjustment.
To test the TV setting, drive the rig (warmed up) on a flat level roadway and so a very very light throttle application and allow the tranny to do the 1-2 upshift. As soon as the 1-2 shift happens (15-20 + -) mat the throttle, the tranny should drop right back to 1st gear. If the tranny does not drop to 1st there is an issue with not enough TV pressure.
Unless the tranny has issues or the TV cable/ brackets have issues (Been damaged or modified) things generally work fine.
The governor on the diesel has considerably heavier weights.
The governor and the TV system work against each other. The governor tries to allow an upshift and the TV ballances against the governor system.
Together this allows the system to properly sense when the shift needs to occur.
The newer trannies use the TPS, the input and output speed sensors, Map sensor readings and a few other bits of information all fed to the computer to do the job of the TV and the governor.
The electronic trannies have the pressures controlled by the computer.
The 700R4 had one of the worst track records for troubles with the TV system of any GM tranny ever built.
The transgo Kits have over the years fixed the issues and allowed the 700R to become a fairly good "LITTLE" tranny.
Other little knows facts about the 700R
The units used in the V6 applications were very light duty with minimal clutch plates as compared to the V8 and diesel units.
The early 700R from 82 (first year in a truck) up to about 86 were very prone to snapping input shafts.
The later "K" case (has a big K cast into the bell housing area of the tranny) units were much better and are the desired box to build for a truck application.
If you lined up all the service bulletins for the 700R on a shelf, it will fill a spot about 6 feet long. :eek:
The aftermarket has done a marvelous job of getting the 700R from being a third rate Junk box up to being a very dependable unit capable of handling some respectable power.
If towing any real loads is the game, this tranny is not the player.
A small lake boat or little tent trailer and such is fine. Using a 700R in a rig thats going to see a larger utility trailer or a larger travel/camp trailer being pulled any distance is trouble waiting to happen.
A 700R4 thats really well built is an expensive tranny.
The last one I did and installed all the good stuff, cost me in the $1500 range ( I did the bench work)
Check your governor and or replace it with a known diesel governor.
Be sure the TV is set properly.
If the speeds are still way too high then some look see at the converter and or the VB calibrations are in order.
Missy
Depending on the casting numbers on the block, you may not be able to tell if the engine is a 6.2 or 6.5
The late 6.2 used the 599 block (same as early 6.5) The later 6.2 also used the same crank as the 6.5 (one piece rear main)
Other than looking to see the bore size, really tough if at all possible to tell unless you look at the Julian date on the casting. If the casting date is far enough back (before 92 intro of the 6.5) the engine is likely a 6.2
Really makes no difference. The Banks stuff works fine on either engine as they are almost identical (except for the Bore diameter)
Hope this helps the ????
Allot of good information here. I do in fact have the T.V. cable adjusted properly, as it is very tight at WOT. I also know that it is 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.:rolleyes:
Tranny shops will mix and match parts as they see fit.
The governor for the diesel is different (fly weights are heavier)
Check out the governor and get the one that is for the diesel. Its easy to remove the cover and swap them out.
Missy
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.
Take the fan off and go for a (short!) drive to see if it makes a big difference...
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions Inc. All rights reserved.