Two dumb questions

mmartin

Active Member
I'm realitively new to the desert racing scene, so here are my questions.

1. Why is it that automatic trannies are predomminateley the transmission to use.
It seems for durability and for reliability a standard transmission would be the choice for a long race.
( Don't get me wrong, I put an auto in my mudbogger to shift faster)

2. Do most desert-racing/prerunners use an open rear diff? Why? I personally like locked rear diffs to aid in steering(slides) and traction.

Breakin' the law!
 

Kritter

Krittro Campbell
using a clutch is another thing to think about(which you want to minimize)...the auto trannies use a manual valvebody so they are pretty much a manual without the clutch.

The optimal rear diff is a spool

Kris
<A target="_blank" HREF=http://www.barneysprecision.com/fabproducts.htm> Fab Parts</A>
 

DANKFAB

Well-Known Member
you took the words right out of my mouth:0

"Carpe Diem" Sieze The Day!
 

robert_encinas

Well-Known Member
clutches also dont hold up to the horsepower and torque.
spools are used in live axle rear ends, they lock both axles together for maximum traction with no differentation.
 

WFODAN

Well-Known Member
Actually i wouldn't want an autoimatic in my truck . The chances of me burning out my clutch vs. an automatic burning up the converter are slim to none . I've raced for two years on the same clutch . I take it out and inspect it every race , but it still looks and works great . Once you're use to the third pedal , it is second nature also .


Dan Vance
 

mmartin

Active Member
Cool, by the way I meant spool as "locked rear". But, what do you mean a clutch won't handle the horsepower? I currently drag race and the boys in the "Modified Class"( < 12 seconds) run big horsepower to maximum traction and the clutch is not in most cases the weak link.

p.s. don't most rally cars use a standard?

Enquiring minds want to know.

Thanks for your input.

Breakin' the law!
 

bpthirteen

Well-Known Member
One reason that automatics are used is because of the torque converter. The torque converter can absorb shock. I remember the Nissan TT that Vessals drove briefly had a manual transmission with a torque converter added for this reason. The reason a clutch is good for lower horsepower vehicles is because it is more efficient. Also, no coolers or plumbing (extra weight). If you have plenty of power, you don't mind losing a little in the torque converter. If you do choose an automatic, invest in a really good trans cooler.

http://www.prepbyjake.com
 

AllwaysRcn

Well-Known Member
re: "clutches also dont hold up to the horsepower and torque."

They make clutches that hold 1000+ hp. It's the transmission behind it that usually fails. Marking's car is probably the highest hp car with a manual (Mendeola 4 spd). Still trying to improve it's reliability. Lot's of big v6 class 1's with DG-N (Fortin 5 speeds or 4 speeds). Problem is you have to have at least 2, since you've always got one at the shop.
 

martininsocal

Well-Known Member
The other reason many use auto's is the fact that the torque converter can multiply torque for better low end performance. It allows the trans to spin at a slower speed while the engine is in its higher revving power band.

If your gonna go, go BIG
 

ESB4130

Well-Known Member
id say on 4 cyls...its all about manual. gotta manipulate that power the best you can. with bigger higher hp motors like a v8, an auto is cool cuz you just stand on the gas and go, even in shifts. and offroad...its all about a spool for sure. a locker is cool if your going on and offroad..but a spool is the best traction. yes....ralleys run manual trannies..but thats a different type of driving. dan is the exception here...but most people dont like shiftin a manual trans in the middle of a whoop section while hold the steering wheel avoidin rocks and boucing all over the place.
 

jeff

Moderator
The pro WRC rally cars use a sequential gearbox - they only use the clutch to start the vehicle in motion. After they are rolling it's just click - click - click. And sometimes they go boom. Most of the pro WRC teams replace those transmissions whenever they can as the amount of abuse they see makes them a wear item.

There are plenty of manual transmission equipped off-road race vehicles - I think it's safe to say that if you someone examined all the vehicles currently racing off-road that the manual transmission is still the dominant transmission of choice.

Aloha
 

Dave_G

Well-Known Member
Jeff,
The key to keeping the sequential shift trans as wear free as possible has everything to do with how good the software is. If the computer looks for a very low matching RPM before shifting, the drive dogs and shift cam will live a lot longer. You have to remember that the gears don't move and engage like a manual trans. They stay stationary and the dogs do all the moving and slamming.

Dave

"I started out with nothing and still have most of it left"
 

desertracer

Well-Known Member
I think that transmission in pic is John Markings 4 speed medeola for his class 1 Jimco with the 600 or 700 hp v8. Doesn't that thing have like a 13'' r&p. Looks like an impressive transmission none the less.

MDR Class 1
#112
 

Attachments

dunerking

Well-Known Member
Is that transmission one of the Mendeola HD?That thing is massive,the R&P is huge.Looks like a big investment.

hit it hard
 

FABRICATOR

Well-Known Member
Overall, automatic type transmissions apply more tractive effort to the ground. All gears are in constant mesh which reduces wear and tear. Unless a vehicle is too heavy or the trans setup is poor, an automatic type transmission will live a long time.

Front engined race trucks use locked rears. Prerunners use both, depending on pavement duty. Mid and rear engined cars with IRS often have open type diffs.

<font color=blue>"A Ship in the harbor is safe, but that's not what ships are built for"</font color=blue>
 

martininsocal

Well-Known Member
How does an automatic apply more tractive effort to the ground? ALL autos have slippage at all times, it is part of their design. Manual transmissions are either in gear or out, the only factor determining the amount of horsepower to the rear wheels is what shape the clutch is in. And power to the ground and tractive effort is more related to differential type than trans when the rubber meets the rocks/sand/silt.

If your gonna go, go BIG
 

tedmales

Well-Known Member
automatics, the newer one anyway, lock the torque converter after shifts, and when in overdrive to keep from overheating

life is too short to be small
 
Top