TheSamba.com :: View topic - Type 1 transmission HP limits and best upgrades

Sat Feb 22, 2014 11:48 am

so im still using the standard beetle transaxle in my 69 baja, and i have a 1983 datsun/nissan 1500cc 4 cylinder with a custom adapter plate. the motor is stock and rated to make 75-80 hp and about 60 pounds of torque. already, although rarely, it will pop out of reverse gear but it did this pretty much as soon as i was test driving it, and mileage on the gearbox is unknown. how much power have people often used with this stock tranny? i realize the breakage and wear rate has much to do with how its treated, and i drive nicely as possible but being offroad sometimes i have to romp on it to get out of situations. so again, my question is what would be a reasonable estimation of how much hp these can handle while stock? i dont want to go to a bus transaxle cause i do alot of highway driving, my second question is what type of modifications are best for prolonging the life of these if i was to get one professionally built for more strength? (id probably also change 4th gear slightly for running bigger tires)

Sat Feb 22, 2014 2:13 pm

should handle 140 ft-lb forever no problem. Torque kills, not HP

If it is ACTUALLY a 69' model trans then it will have the weaker diff compared to mid-70's trans, so if rebuilt then get the later stronger diff and "welded" 3rd and 4th gears

the later model SSC trans has been known to handle 180 ft-lb and sometimes over 200 HP without modification. Reverse is even weaker tho.

The key is either your clutch or your tires have to slip, if nothing slips then you will break things. Don't run a clutch stronger than you need.

Sat Feb 22, 2014 3:46 pm

It;s the weak fine tooth 4th gear that usually lets go first in the late IRS boxes with torque.

I had mine rebuilt with the coarse tooth bus 3rd and 4th for strength and better gearing just recently but prior to that I put over 100k on it in totally stock format.
My engine was 167ft-lb when stock, with the mods it has now who knows but it never broke my stock box which now has over half a million KMs on it.

All that aside, what size tyres are you running?
I know you said you dont want a bus box but they are well suited to bajas.

Sat Feb 22, 2014 5:12 pm

What size rear tires?

Sat Feb 22, 2014 8:49 pm

the stock transaxles are relatively strong, but you can kill one pretty easy. drag race starts (dumping the clutch) on pavement is hard on them, and you mentioned offroad so shock loads will kill one in a hurry.

if your offroad, and you have the tires spinning (mud, sand, and such) and then you hit something hard (rock, root, and such) the tires will stop quickly. this is a huge shock load and it will kill transaxles, axles, and all kinds of stuff.

i used to build rockcrawlers. you can have the biggest baddest axles out but a good shock load from a stock motor will kill them.

point is, good driving and a stock transaxle will hold up fine, bad driving and even the best will die a horrible painful death.

Sun Feb 23, 2014 5:18 pm

ahh well they are much stronger then i thought though to be handling that much power. i guess my concerns are somewhat ungrounded then but i totally hear you guys about abuse versus being used properly. i never do clutch dumps or speed shift without using the clutch, the most concerning treatment i give my car is some heavy throttling in 1st gear sometimes to get through rough stuff (snow and mud lately if you must know, much fun) , but for a young kid i dont think i drive it too hard, not as bad as others anyway. i have a pair of 29"x10.5's tsl thornbirds that i run on the back and when i do i have to hit really high rpm's in 3rd and then 4th gear gathers speed really slowly. lately ive been using my 195's on the back because ive mostly been on the highways and streets and those tires work much better in 4th gear, and better mileage. if something ever happens to my transaxle ill probably just get another stock one. what is the advantage of having 3rd and 4th welded?

Sun Feb 23, 2014 5:40 pm

With 29" tires you should get a 4.37 R&P gear. With the 4.12 you have is why it accelerates real slow in 3rd & 4th. The stock 3/4 gears are pressed on their hub which is fine for the stock 60 HP engine they came with. When you increase the engine HP then you can slip them on the hubs. They weld them and stop this.

Sun Feb 23, 2014 8:19 pm

With your tiny engine I'd think you'd want lower gears.

If fourth gear is your only issue then sure you could switch to 1.00 or 1.04 or 1.12 fourth, but seems like you'd be better off to bring all the gears down.

Sun Feb 23, 2014 9:33 pm

I'm running a 2054cc with a stock gearbox and transaxles. Have taken it down the 1/4 mile a few times, just no burnouts or hard launches. My 4th gear has always popped out but an occy strap holds it for me on the highway. I plan to upgrade my gearbox and transaxles but until then i'll take it easy.

Mon Feb 24, 2014 1:37 am

huh.. food for thought perhaps after this tranny goes ill get the next one built with a different R and P gear ratio and welded gears, but the classic maxim is if it aint broke dont fix it right? thanks for the advice fellas much appreciated but hey dont call my engine tiny :shock: try getting almost 40 mpg with the vw aircooled motor and seeing how they had 36 hp stock i make more then double that while getting better gas mileage.. but hey im not trying to be rude and we were talking about tranny's anyway i really appreciate the speedy responses, and i know a modified vw engine makes far more power with the stroker combo's but hey im trying to be modest

Mon Feb 24, 2014 2:08 am

youngMattinson wrote: try getting almost 40 mpg with the vw aircooled motor and seeing how they had 36 hp stock i make more then double that while getting better gas mileage.

My 1904cc singleport actually does qualify :wink:

I only mean tiny in comparison to most. People bolt v-6, and quad four, and pintos, and corvairs, and ford SHO engines on there, your trans has it easy!

Mon Feb 24, 2014 2:08 am

double

Mon Feb 24, 2014 2:35 am

ahh that makes much more sense in such context.. some people do ask that much from their trans but im trying for reliability in a budget, not buying a mendola to match my +500 hp engine thats gonna smoke my ten thousand dollar tranny first time out anyway, lol. but again i really should judge good day to all with outrageous horsepower im more or less just jealous anyways, cheers!!

Mon Feb 24, 2014 7:37 am

I would rebuild the trans now before it breaks. Good cores are getting harder and harder to find. In a few years it's gonna be tough finding the parts to rebuild them.