1988 LeSabre transmission help?

[Guest 2fit661ca]

My 88 T-Type's transmission is going out and will need to be replaced very soon. As you can see from my signiture, I have a 1991 LeSabre motor and transmission. They both are the same body style and they both have the same SFI 3800 V6. My concern is that the 4T60-E came out in 1991, and based on the information I found through Google, both the H and the C bodies came equiped with it this year. The same source said that the LeSabre also use the THM440T4 (4T60) that year. How would I find out what transmission I have? I had always thought that the 4T60-E was only available with the Series I Tuned Port 3800, which was not available in the 1991 LeSabre.

THANKS!

[Guest Redwind89]

Fit,

look at the front of the 91 transmission(where the transmission cooling lines come out from under it), is there a vacuum regulator? If so then you don't have the 4T60-E.

On a side note you do run the risk of losing the 2.97 final drive gear for the T-types if you drop another transmission in there.

How bad is the 88 transmission? What is it doing? Have you tried replacing the vacuum regulator on it?

[NTX5467]

Considering how some things, however minor, seemed to change from model year to model year to model year back then, it might be advisable to rebuild the trans in the vehicel now rather than trying to cross-breed something.

Sometimes, too, when transmissions sit, they sometimes can acquire internal problems from the non-use. A friend had a THM400 that he'd had freshened for an upcoming Camaro project. It sat on his garage floor for about two years. When he got it installed and such, on the first maiden voyage, the trans that had just been rebuilt suddenly started trying to lock-up when it'd shift into second gear. An internal valve body issue had happened. So, he did make it to the muffler shop in low gear, and home again in low gear, only to have to pull it back out and get it rebuilt AGAIN. On such a rwd car, as the '67 Camaro is, it's quite a bit easier to change the transmission rather than in a fwd car.

Even if your car's trans is not an electronically-controlled unit, there are certain interfaces between the engine, transmission/transaxle, and computer that will need to be fully operational for everything to work correctly. Adapting a computer-controlled valve body transmission to be used in an earlier vehicle could be a much more daunting task than might be suspected.

My recommendation would be to repair the trans currently in the vehicle as that could well be the "path of least and less costly resistance".

Regards,

NTX5467

[JohnD1956]

If you saved the computer and wiring harness that accompanied the 91 motor and tranny then the swap would be less of a challenge. I believe you will want to check the drive axles for compatibility with the older drive line and suspension.

[60FlatTop]

I just had a THM440T4 rebuilt, including a new torque converter, for $900. I tried to find one rebuilt on a shelf somewhere and I considered buying a used one. Ratios became an issue and the used ones had all been sitting a long time. Rebuilding the one I had turned out to be my best choice.

My nephew picks it up tomorrow. We should have the car done in early October. Just in time to test the defrosters, heater, rear window defogger, and traction in snow. We love New York!

[Guest 2fit661ca]

It does have the vacuum modulator, so I know they are the same transmission. The "replacement" came out of the same body of style of car as my T-Type, only it was a 4-door LeSabre Custom. I know the ratios are different, and I do plan on rebuilding the transmission in the near future, but I need the car sooner than that can be done.

THANKS FOR THE HELP, GUYS!

P.S. 60flattop, that's a sweet looking car! I love it when people use this body of LeSabre/Park Avenue for projects.

[Guest Redwind89]

Fit

One more thing to think about.... Make sure to check the wiring pins. I do know that in 1990 or 1991 they changed them again, like they did from 1987 to 1988. If memory serves me right, I think only 88 and 89 are fully inner-changeable. Once again what is the transmission doing that makes you think that its dying? Just trying to help.

[NTX5467]

IF the ratios are different, then the computer will get incorrect signals as to road speed and such. Which means the speedometer will not be accurate, among other things.

Just some thoughts,

NTX5467

[Guest 2fit661ca]

Fit

One more thing to think about.... Make sure to check the wiring pins. I do know that in 1990 or 1991 they changed them again, like they did from 1987 to 1988. If memory serves me right, I think only 88 and 89 are fully inner-changeable. Once again what is the transmission doing that makes you think that its dying? Just trying to help.

They are both a 5 - pin connector, and I have the ECM from the 91 as well. If I swap transmissions, I'm probably going to swap engines as well since they are already attached. I know the 59K ran like new and was 10 mpg better on fuel. (17 compared to 27)

And the T-type's transmission slips very badly. When I was driving home from school on Thursday, at speeds above 70, the was an aweful vibration and grinding noise and I have no idea where it came from. I slowed down to a stop at my exit, and when traffic cleared, I proceeded to turn left and drive up the hill into town. It drove throguh first fine, second started to slip, and when it shifted to third, the engine reved up to 4K while my speed droped from 30 to about 25. As the hill started cresting, the speed slowly increased while the RPMs stayed at a consistant 4K. The transmission has actually been slipping mildly for the last 1500 miles or so. For the most part, it would hold a consistant speed such as crusing down the highway, just fine, but it did not like accelerating.

[Guest 2fit661ca]

IF the ratios are different, then the computer will get incorrect signals as to road speed and such. Which means the speedometer will not be accurate, among other things.

Just some thoughts,

NTX5467

I already know the speedometer and odometer are off in the car, or at least I presume. When I drive down the highway with the cruise at 70, on my way to school in the morning, everybody passes me, and according to my trip meter, it is a 54 mile trip from my driveway to my parking spot at school. According to my 97 which has 4 speed sensors, it is 50.00 miles on the dot consistantly (95% freeway driving) and with the cruise at 70, I pass or do the flow of traffic. On top of that, I would still rebuild the transmission, I just can't afford to do it now. It would be much cheaper and easier to put this other transmission in for the time being. (I've pulled many engine/transmissions in these car and I have it down to about 1.5 hours to drive the car in, strip it, pull the motor, and have it sitting on the ground next to the car.)

[Guest Redwind89]

Okay I would say yes, the transmission is dying. I was just wondering. Did you change the pan gasket when you got the car or did you have the fluid flushed? That could have sped up the problem, as the fluid was draining metal filings could have settled in to the teeth on the clutches and stuff. To me, but I could be wrong the high RPMs sound like the torque converter isnt kicking in, which would account for the bad MPG. Also the slipping sounds like the clutches for 3rd gear or the band for 3rd gear are shot. To me thats a little weird. Most of the time with the transmissions with the 2.97 gears, its normally the 2 gear clutches or band that goes (people stomping on the gas and flying though the gears) Also the mileage difference could be from tire size or wheel size. I remember in the pictures you post you still had the factory wheels on the car but what size tire in on there? Did you change them at all? I know more to think about. I would just pull the whole engine and transmission then and drop in the 91 set up. good luck

[Rawja]

I've pulled many engine/transmissions in these car and I have it down to about 1.5 hours to drive the car in, strip it, pull the motor, and have it sitting on the ground next to the car.

WOW! Color me impressed!

[Guest 2fit661ca]

Okay I would say yes, the transmission is dying. I was just wondering. Did you change the pan gasket when you got the car or did you have the fluid flushed? That could have sped up the problem, as the fluid was draining metal filings could have settled in to the teeth on the clutches and stuff. To me, but I could be wrong the high RPMs sound like the torque converter isnt kicking in, which would account for the bad MPG. Also the slipping sounds like the clutches for 3rd gear or the band for 3rd gear are shot. To me thats a little weird. Most of the time with the transmissions with the 2.97 gears, its normally the 2 gear clutches or band that goes (people stomping on the gas and flying though the gears) Also the mileage difference could be from tire size or wheel size. I remember in the pictures you post you still had the factory wheels on the car but what size tire in on there? Did you change them at all? I know more to think about. I would just pull the whole engine and transmission then and drop in the 91 set up. good luck

No, I never bothered with a fluid change in the 4K miles I put on it. Based on what you described, the MPGs being affected by the transmission makes alot of sense. My temp guage reads about 140 when it's completely warmed up, so I thought it might be that, but 10 MPG is pretty big.

My tire size is the stock P215/60R15 (maybe 65; I don't remember, all I know is it's right)

again, THANKS FOR THE HELP! I'd be lost without you guys!

[Guest Thomas Lord]

2fit661: I certainly hope your 17 mpg fuel mileage from the T-type hasn't always been that poor. I've owned four 88-89 LeSabre T-types and they all routinely achieved 29-31 mpg on the interstate. Combined city/hwy for me was 25-27. I will admit I drive very conservitively.

I had a 1990 LeSabre Limited for six years as a work/winter car, and that returned basically the same mpg as the T-types on any highway trip. About two years ago, I took it to a friend's wedding, a 300+ mile round trip in August (car had over 195K at the time). When I arrived back home and topped the tank off, I was surprised to find the mpg was only 26. It should have been 30+. I suspected the torque convertor lock-up or fourth gear had stopped functioning, but because the car did not have a tachometer I didn't notice.

Shortly afterwards, I discovered the ATF fluid was 1.5 - 2 quarts low.:eek: I suspect this had caused the malfunctioning in the trans but cannot prove it. I changed the fluid and filter, then changed them again a year later. It seemed to revive the lock-up/overdrive function, but I don't know for sure, as the majority of driving was 'around town' in that car.

The '91 drive train swap sounds like a good plan. I would not be very concerned about the difference in axle ratio.

Edited September 22, 2011 by Thomas Lord (see edit history)

[Guest Thomas Lord]

Okay I would say yes, the transmission is dying. Did you change the pan gasket when you got the car or did you have the fluid flushed? That could have sped up the problem, as the fluid was draining metal filings could have settled in to the teeth on the clutches and stuff.

I presume you mean that flushing is a potential bad thing for automatic transmissions.

I would not want people getting the idea that simply draining the fluid would risk harm. Draining old & putting in new ATF fluid is always good for the transmission.

BTY: After I changed the fluid and screen on my '90 Limited, the chronic 'banging' into reverse actually went away. It was starting to gradually come back in the last several months that I had that car. It was stolen this past June.

It still had the numbers matching transmission with 215K miles. I don't know if it was ever rebuilt before I bought it with 156K on it.

Tom

[Guest Redwind89]

I know of a lot of places that wont touch transmissions with over 100k for fear of flushing them will cause a failure. If the fluid has never been changed and the car has high miles places are saying to leave it alone. The problem being that the old fluid is thicker and hides the floating metal filings and other stuff, where as the new fluid is thinner and the stuff settles out of it. In fact I did a transmission flush on my 84 Chevy Celebrity and with in two weeks the transmission was slipping and starting to fail. So its not always a good thing. Just my two cents.

[NTX5467]

The converter lockup function is handled by an electric solenoid in the valve body. It should not "come and go" with fluid condition. Their usual failure mode is "engaged", so when you come to a stop sign, the brakes work against the engine just as if it was a manual transmission and you didn't push in the clutch at the stop sign. It is modulated, typically, by both the vehicle speed sensor and a manifold vacuum switch, plus the brake light switch.

When the lockup function of the torque converter goes away, every time the converter tries to lockup, you'll get a major shudder situation, especially if it happens going up a hill at the magic, lockup mph. Backing out of the throttle will make the shudder go away as the vehicle slows and is below the designated lockup mph. The way around this, or any other "hunting" situation with converter lockup is to back out of the throttle, let the speed drop a little, then use heavier throttle (to keep the converter unlocked), get past the previous lockup mph, then back out of the throttle and let the converter lockup "not under power". It'll usually lockup in that unstressed situation, lockup solidly, and then you can proceed in normal fashion.

In the world of flush machines, there are some BIG variations in how the machines work. In some of the earlier ones, it took an attendant to manually monitor the extraction of the old fluid AND the simultaneous replacement with the new fluid. In others, the fluid coming out modulates the fluid going in. They usually use the trans cooler line attachments under the hood for their flush machine hookups. If not enough fluid goes in as the old fluid comes out, front pump longevity can be greatly influenced!

Getting all of the old fluid out of the trans and cooler assy is good, BUT you still have a dirty filter/screen in the trans. Not everybody who sells "trans flushes" acknowledges that. Most of them have some sort of chemical package that also goes into the fluid, which can include seal conditioners, additional detergents, or whatever else.

Obviously many places have been snake-bit by flushing an older, higher mileage trans. Probably a little over-zealous in their sales techniques? But what they might have sold, instead, was a traditional fluid/filter change where the pan is removed, cleaned, and a new filter/screen installed. It might not be a complete oil change for the trans, but if you do it again soon thereafter, then that'll further decrease the amount of old (now diluted somewhat) fluid in the system. BUT, if they'd looked at the fluid before they did the flush, AND did a road test of the vehicle, they might have backed away from selling a flush rather than a fluid/filter change. Be that as it may . . .

Just some thoughts,

NTX5467

[Guest Lesabre_]

I have a 91 buick lesabre, and I need a tcc solenoid, is there any way to do it without removing the side cover of the trans and if the switch by the brake is the cause.

Thanks

[60FlatTop]

It is interesting that this string has come up again. Dealing with the incredible lack of knowledge around these cars has been as frustrating as it has been incredible.

I purchased my car with a knocking engine and no transmission action. I bought an old stock quality rebuilt engine, had the transmission rebuilt with a new torque converter, and pretty much provided a blank check.

The transmission is quiet until I put it in Drive or Reverse. Then the pump whines very loud. It has been back to the rebuild shop twice. The first time was when it would not upshift when first installed. The fluid was badly carbonized and I figured they just threw the valve body aside and never cleaned it internally. It was fixed in a day. Then the whine started and it was returned again. When I called for an update I was told I better talk with my engine mechanic. Supposedly the engine vacuum was too high and causing the modulator valve to pull out too far and make the pump "overpump" beyond its capacity and whine. I asked how low the vacuum was supposed to be to avoid this and did not get an answer. I gave my nephew instructions to remove my car from the transmission shop property and not enter into a discussion with them. Apparently I am supposed to tune the engine in some manner that reduces the vacuum. Give me a break. Sometime before spring I will take it to another shop and have it done right. I will probably have to get in the car and put it in gear, then raise my voice above the whine and loudly say "Make that whine stop." I imagine it will cost another $1,000.

It is interesting that it comes right after totaling over $1200 in the new exhaust for my '60 Electra. That started out as a complete "factory" replacement system from a well known pipe bender in Buick circles. The only parts left from the original purchase are the tailpipes. Everything else, front and intermediate pipes and muffler (it did not muffle) are in my nephew's scrap metal pile; just junk and the labor for trying to make it fit right.

Oh, and then there were the new points and condenser I put in the '60 Buick just for general principle after nine years. One week later the wire fell out of the condenser and the car had to be flat-bedded home.

I am being very careful about who I deal with for any service or parts. Next year the garage will be expanded and the cars will be cut back to 1960's or older. Parts that have taken boat rides will be excluded from the shelves. Only original old stock will be allowed.

Well, let's see if I have a quiet convertible next year. And if I have to fix it myself.

Bernie

Edited October 22, 2012 by 60FlatTop (see edit history)

[Guest Lesabre_]

Hello,

i have a problem, don't know if it can be answered, I have a 1991 buick lesabre limited with automatic autodrive. My check engine light comes on when idling in the morning, probably five minutes after startup. The light doesn't go away, until I depress the brake pedal, then it goes away. While driving it comes on but if I press the brake, it will go away, and if I leave my foot on the brake, it will never come on. What could be causing this check engine light to disappear every time I press the break? Any help and answers would help me a lot, thank you

[Ben Bruce aka First Born]

Take the car to someone with a code scanner, a garage or auto parts store, have them check it. The scanner will tell you what the problem is. Most parts stores will do this free.

Ben