4+3 Trans

[Lucs_Vette]

Hi Folks,

i've just ordered a new filter and gasket for my 85 4+3 tranny. any thing special i should consider before, during or after the oil and filter change? any thing i should look for, any adjustments while the pan is off?

Any help would be appreciated .. thanks .. Luc

 

[tnovot]

If you do a search of this forum, you will find more info on this topic.
One thing I remember someone saying is that some who have used the cork gasket which comes with the filter have experienced fluid leaks. The advice was to use black RTV which I did a couple of years ago and have had absolutely no leaks.
You should clean the sealing surface of the pan well and also any sludge from the bottom of the pan. Check the pan lip for straightness for good sealing. You should also check the inside of the pan for any pieces of clutch material or metal fragments which could indicate trouble. You will need some type of pump with the trans fluid bottle to add fluid to the OD unit after the pan is reinstalled. I used an 6-8" piece of tygon tubing over the tip of an plastic squeeze bottle which worked fairly well to add the fluid.
Terry

 

[o2bnkc]

What was a 4+3 tranny? This is one I never have figured out. Thanks.

 

[wallyknoch]

What was a 4+3 tranny? This is one I never have figured out. Thanks.

Doug Nash made them for GM. They have a overdrive built on the back a Muncie 4 speed case. Very good trans if you take care of them. Otherwise expensive to repair.

 

[CharlesBrown]

4+3 transmission

Doug Nash made them for GM. They have a overdrive built on the back a Muncie 4 speed case. Very good trans if you take care of them. Otherwise expensive to repair.

My C4 has one with 15K on the clock. Very interested in your comment re the subject tranny. Please define "take care of." Thanks
PS My man @ Just Corvettes says they are "weak."

 

[JonM]

My C4 has one with 15K on the clock. Very interested in your comment re the subject tranny. Please define "take care of." Thanks
PS My man @ Just Corvettes says they are "weak."

Absolutely, Positively, change the fluid every ten thousand miles, and it will last a long time.

 

[c4cruiser]

Hope you didn't buy the $20+ version from the typical accessory catalogs. The filter is the same one used in the Ford FMX tranny that came on many V8-powered Cougars, F150's and mid-sized cars. CarQuest has them for around $7 or so.

Clean the pan rails and the tranny case mounting surface making sure to get any old gastet material off. Then use a good black RTV sealant making sure you get coverage around the bolt holes in the pan. Straighten the pan rails and tighten the bolts evenly. No need to use a lot of torque on the pan bolts.

To get all of the old fluid out, disconnect one of the cooler lines and use a pump to push out the old fluid. You should need a couple quarts of Dexron II or III fluid

What was a 4+3 tranny? This is one I never have figured out. Thanks.

The 4-speed portion of the tranny is really a Borg-Warner Super T10 that has had the case and output shaft modified to accept the 2-speed OD unit. Doug Nash built the tranny for GM. It's a pretty stout tranny and was used behind the RPO B2K 87 Callaway twin turbo motors that generated 345 +HP and 465 ft-lbs of torque.

Here's a link that shows how the 4+3 operates: http://www.5speeds.com/43table.htm They do operate slightly differently based on the year of the car.

 

[o2bnkc]

Well, I guess that answers my question. Thanks again.

 

[WhalePirot]

My man @ Just Corvettes says they are "weak."

From what Paul, at 5speeds told me, the O/D is very strong. First gear is the weak link.

 

[muddywaters]

4+3 Transmission

Just my 2 cents, My 88 has the D/N 4+3, when I serviced the car I use a filter and gasket from Ecklers, I dressed the pan, took usual pains to avoid leaks and with the gasket it leaked, after a short time I dropped the pan, changed the filter again and used silicone this time with no leaks. The one thing I didn't like about the 4+3 was how the O/D came in, from first to second it would come in and you had to cancel it, after it was cancelled the computer would bring it in, I jumpered the rear most switch on the tranny and now the O/D doesn't come in until you hit 4th gear, cancelling it then eliminates the O/D until you ask for it w/ shifter button. Much better drivability and your eliminating wear and tear on the O/D unit by not calling for it until you want it. I was told the stock set up was for EPA mileage balony, but I found it to be a pain. For a simple no cost jumper wire I enjoy my 4+3 much more while eliminating wear and tear with unneeded O/D usage. Works for me. Muddywaters

 

[CharlesBrown]

Great!!! I thought I was stuck with the automatic up-shift to O/D from 2 thru 4. I'll try your fix. Always thought 2,3,and 4 O/D were to weak for the job. Great tip. Thanks.

 

[muddywaters]

4+3 Transmission

Charlie, Just make sure you jump the switch, not the wires to it. It didn't make sense to jump the switch, so I jumped the wires to it, lost speedo. Put it back to stock, jumped switch at the tranny, rear switch and the O/D comes in when you hit 4th gear. Must be continuity threw tranny somehow. Your basiclly just putting a loop on the switch. Like I said, it worked for me. Muddywaters

 

[muddywaters]

4+3 Transmission

Charlie, disconnect battery FIRST. Muddywaters

 

[r1junky]

my wife and i are looking at purchasing a '85 vette (never owned a vette before), with a 4+3 tranny. how exactly does the 4+3 trany work? my understanding is that in 2nd through 4th, the car will electronically "shift" to OD, based on amount of throttle being used. is this correct?

 

[JonM]

r1junky

Linkage

 

[r1junky]

thanks jon. i did see that link, just wasnt 100% clear. for '85 model, 2nd and 3rd "no throttle kickdown" is different than the other years. is there a real difference in how the car performs in these 2 gears?

 

[CharlesBrown]

You are right. WOT from 2nd on will void the OD up shift. Given a choice I'd stay away from this tranny. Seems there is a new and old version with the new starting some time in '88. The new is better, but 2 and 3 OD in many caces just doesn't have enough umph. Per other posts here I see that you can do some switch changes to solve this problem. My Corevtte mech. is looking into this. I'll let you know what he comes up with

 

[muddywaters]

4+3

r!junky, Yes and it's a pain in the a$$. I went with the jumpered switch, now I only get O/D in 4th gear and when you cancel it via shift knob button, it doesn't come back until you ask for it. Saves wear and tear on O/D unit also. Muddywaters

 

[r1junky]

thanks for the replys folks. its really helpful. i'm still interested in the '85 even if it does have an odd tranny. should find out today about the car. if we get it, i'll be in touch with you muddy about modifiying the switch!!

 

[steveb]

thanks for the replys folks. its really helpful. i'm still interested in the '85 even if it does have an odd tranny. should find out today about the car. if we get it, i'll be in touch with you muddy about modifiying the switch!!

If it's an early '85 with the OD switch on the console and not the shifter, you can leave the OD off and it will stay off until you flip the switch. I drive mine like a regular 4 speed in town and flip the OD switch for the highway.

--sb--