'85 4+3 - trans and rear end limits?

[craig0ry]

I keep trying to find a reliable source that can tell me what the 4+3 trans and rear end on an '85 l98 is good for as far as power levels. I am confident that the l98, with the compression ratio it has, can easily hit 350-400 hp and comparable torque levels without too much risk if done with the correct mods. I am not so sure that the 4+3 will be able to handle that, nor do I think the rear end will (what is it, dana 44?). Can anyone voice in and tell me?

At this point in time it is purely benchracing, but! I found what may turn out to be a tentative sweet deal on an 85. My friend and I were discussing modifications today and we both realized we had no clue what the rest of the drivetrain could handle...

 

[Hib Halverson]

85 was the first year for the D44. The weak link in the Doug Nash 4+3 is the overdrive unit. I'd make sure it is in good condition and is lubricated by synthetic ATF. The gearbox section of the Nash ought to handle the torque as long as you don't drag race a lot with sticky tires.

When the OD finally goes out, Richmond Gear has a really nice kit that replaces the 4+3 with a six-speed.

 

[WhalePirot]

The Dana 44 came on manual trans cars probably starting in '85, as Hib says. the 36 was used on other cars and had early and late designs. You are smart to consider the drivetrain as Ken and I have found. (we both broke our Dana rears.) My '84 Z-51 had an early-design Dana36, which had been changed from the stock 3.08 to a USG 3.73 ratio. I believe Ken has a 44. I never BEAT my car, but drove aggressively at times (okay--a lot).

My Nash '+3' was rebuilt by 4 speeds, of Boca Raton (ops since sold) {see link in C4Cruiser's post below} who did the Callaway O/Ds. Paul, there, claimed that I'd never break the Nash, but after 105k, with a mostly stock L-83, my T-10 gears were scrap, with numerous cracks and worn-thru surface hardening, despite exclusive use of synthetic gear lube.

My cars are maintained to the highest levels and my overdrive was working just fine when I had the shop go through it. As I was building a very strong engine, I wanted to ensure the drivetrain would handle the power.

Many may argue otherwise, but this is what I saw in my car, with the best professional mechanics I consulted. I believe that most of the O/D issues were from improper maintenance and/or misunderstanding of the details of how and when the unit worked (all of which was bandied about in an old, searchable, thread).

Know too, that the '85 (similar to the '84) was a one-off year in some regards, which can be a real problem if you need certain parts. The ECM was unique as were certain other emissions and accessory parts.

It all depends on the restrictions you have and your intentions for the car.

 

[Ken]

I didn't break mine like Mike broke his though. This is Mike's:

Mine was more of a wear issue. ​

 

[c4cruiser]

The 84 and early 85 cars had some issues with the 4+3 and wear was an issue with seals and bearings. The Borg-Warner T-10 tranny is a strong unit but the main issue (like any other tranny) is proper maintenance. Change the OD fluid to a high quality synthetic ATF and then change it at least every 12-15K miles. Use a quality gear oil in the T-10. You should have the tranny rebuilt with quality HP parts. At the very least, get a small parts kit that should include bearings, synchros and seals. Have the components inspected for excessive wear and replace as necessary. Carefully inspect the case for any signs of craking or wear.

This page may help with some information: http://www.5speeds.com/dne.htm
I believe the 87 Z51 and Callaways got a slightly beefier version of the 4+3 with a .62 final drive ratio compared to the standard .67. The Callaway delivered 350HP or so and 460+ ft-lbs of torque so the 4+3 had to stand up to that level of power.

If you are going to go beyond 375HP or so, look at the Richmond Gear 6-speed as they have a bolt-in version for Vettes. You might also contact Keisler Automotive Engineering to see how they are progressing on their C4 version of a T56 Tremec 5-speed and 6-speed. http://www.keislerauto.com/home.html

 

[WhalePirot]

Good advice.

The Richie 6er is described as quite noisy and requires cutting the tranny tunnel for installation. It is also described as virtually bulletproof and was my choice until 1) I was promised the O/D was strong enough, saving me the cutting, etc. and 2) of uninstalls of some Ritchies, due to noise, by a Vette shop in San Diego.