TheSamba.com :: View topic - shift speeds don't correlate with speedometer shift marks

Tue May 11, 2004 7:29 am

Hi all,

so i finally got my '67 westy idling closer to correct and drove around the nieghborhood for the first time since i drove the bus home two months ago....

my problem is that my engine (which to the best of my knowledge from previous owner is a mild stroker, like 1650cc, dp) seems to max out in gears 1 and 2 well before the speedometer shift markings...It wants to shift about 5mph before mark #1 and 8mph before mark2...(I haven't gotten it up to mark three yet)

I thought it was a timing issue, but tried with two different dizzys, 009 and single advance vacum, both timed per spec, and noticed no difference when test driving....

the carb i'm using is not perfect (34pict3 with a vacum leak at the butterfly valve bushings...my exhaust sound like popcorn at idle and sound goes away with carb spray)...could this be my problem?....any long term negative effects if i drive the engine this way for 150 miles (want to drive down to VW on the Green in golden colorado next weekend)

I have ordered a new carb, but it will be a bit before i get it....

Any help would be great, thanks

Tue May 11, 2004 9:24 am

sounds like a gearing thing... does your 67 have big (46mm) rear axle nuts, or little nuts? (36mm)...if little that's the reason... it's lower geared that a 67 oughta be. you could borrow a tach to check out where the rpms really are at what speeds in what gears... Ya you can drive it... but probably want to go a little slower rather than winding the piss out of it. I

Tue May 11, 2004 9:34 am

i didn't think of that, but it makes sense...i will check it out....

if that's the case, the lower gearing could be a benefit, since my weekend travels will take me into the mountains (elevation gains upto 7000')...lower gearing would help my brakes out on the way down too!

i will have to search to see what the negatives to the small nuts are if that is the case....thanks, Mark

side thought....if it is smaller nuts, can i go with larger tires?...come to think of it, i should check the size of my tires...that could cause the problem too, i suppose :)

Tue May 11, 2004 10:53 am

Your speedo shift markers are usable if the bus is stock, but once gearing and tire size are not original then its all going to be wrong.

Tue May 11, 2004 11:12 am

marklaken wrote: if that's the case, the lower gearing could be a benefit, since my weekend travels will take me into the mountains (elevation gains upto 7000')...lower gearing would help my brakes out on the way down too!

i will have to search to see what the negatives to the small nuts are if that is the case....thanks, Mark

side thought....if it is smaller nuts, can i go with larger tires?...come to think of it, i should check the size of my tires...that could cause the problem too, i suppose :)

big nut/small nut is simply the size of the axle nuts. it corresponds to the gearing in that 99% of big nut trannies have 1.26:1 reductions and 99% of small nuts have 1.39:1 reductions. that means that small nut trannies go 10% slower (or big nut trannies go 10% faster) so you can put the same tires on either, it makes no difference there.

the negatives on small nuts is that the brakes are smaller and they go slower. the brakes aren't too big of a deal because the fronts do 60-70% of the braking anyway. the slower is nicer for mountains. if you are only traveling in the mountains and you really want to go slow (like 45mph top speed) you can get alpine gears. in fact, there is someone (me) selling an NOS set in the classifieds (shameless plug for the gears I have for sale)

small nut trannies are nice because they are easier to rebuild, but reduction boxes rarely go bad, so that really isn't too much of an issue. if you switch from big nut to small nut, you will need to change your e-brake cables also.

if you need any parts, let me know, I have literally tons of reduction box stuff

Tue May 11, 2004 1:13 pm

Krusher wrote:
"Your speedo shift markers are usable if the bus is stock, but once gearing and tire size are not original then its all going to be wrong."

Side thought: do larger engines still redline at about the same rpm range and thus maintain the same shift speeds (since its all relative to engine rpm going through the transmission in the end).....is a larger engine only going to give more torque and increase accelration...not increase top obtainable speed on, say a flat, windless road?...(i think the answer to that is yes, but not sure)

Lind wrote:
"big nut/small nut is simply the size of the axle nuts. it corresponds to the gearing in that 99% of big nut trannies have 1.26:1 reductions and 99% of small nuts have 1.39:1 reductions. that means that small nut trannies go 10% slower (or big nut trannies go 10% faster) so you can put the same tires on either, it makes no difference there."

Does this mean that you do not get any extra torque at the wheels from a small nut tranny? (if you did get more torque, wouldn't you arguably be able to run a larger size tire with that extra torque...not planning to do this, just want to understand a little better)

thanks all, Mark[/quote]

Tue May 11, 2004 7:14 pm

Mark- I know this bus is new to you, but how new are you to the aircooled scene? Reason I ask is until you get used to it a bus sounds like it's gonna fly apart from high rpms, even when you are still at a relative low rpm. Put a tach on the engine and see where you are, it might be as simple as a frame of reference. Or see if anyone else w/ a split near you can let you take a spin. might be enlightening.

Tue May 11, 2004 7:32 pm

marklaken wrote: Does this mean that you do not get any extra torque at the wheels from a small nut tranny? (if you did get more torque, wouldn't you arguably be able to run a larger size tire with that extra torque...not planning to do this, just want to understand a little better)

It's not a torque issue, it's a issue of them fitting under the wheel wells...

Wed May 12, 2004 7:10 am

fasster-laster...
this is my second bus...first was a '77 2.0 liter fatchick, bought in '98...this is my first experience with the 1600cc dual port....man i love that type4 engine!

back to my situation...
the engine won't go any faster when i shift and yeah, it's loud as hell...in other words, i shift when the speedometer quits moving and the speedo quits moving several mph's before shift point.....when i do shift, the next gear does not lug the engine, it smoothly continues to accelerate (i'll double check that my accelerator cable is taut, but i am certain it is)....

as for the torque question, let me rephrase it....does the small nut redux box result in more torque? (would be useful when the pavement ends and i still have miles to go....)

people that bajaify busses ussually look for more torque to turn giant tires (and yes, they cut the wheel wells out to fit them in...not my intent, just wondering if a small nut setup might suit my purposes better...i would be better of with more torque rather than a higher top speed, since i will always be going up or down big hills...don't really anticipate speeds over 45-50 mph in the twisty canyons and passes out here....

Mon May 17, 2004 6:57 am

okay, so i checked my nuts and damn they are big!..... :)

after a couple more test drives, my thinking has changed to a slipping clutch being the main culprit....logical?.....any other places i could be experienceing a slipping in the drivetrain?.... any quick remedies?...engine was too hot to see where wingnut was on linkage...if i have thread, will tightening the wingnut solve my problem?

thanks for all the help....mark

Mon May 17, 2004 10:14 pm

Hello Mark, the 1600cc is definetly not a 2.0 litre like a bay! Torque is related to displacement, the more you have, the more torque available. The reduction gears are there to multiply torque from a rather small displacement engine, allowing a bus to carry a heavy load - rather slowly. To check if your clutch is slipping, engage the emergency brake, put the bus in fourth gear with the engine running and clutch in. Next slowly let the clutch out. Does the engine die? Does it keep running? If engine lugs and then dies -- clutch good. If engine keeps running -- clutch bad, or way out of adjustment. Good Luck, Jeff

Tue May 18, 2004 6:36 am

alright so i took the engine out last night (i have an overheating issue due to incorrect tin, plus just curious to see what's all stuffed in there)...looked at clutch and previous owner had the wing nut tightened all the way down!...

clutch is about 50% worn...and the pressure plat metal is blue for heat I assume...still flat and straight when putting it on formica counter top.....

so i figured i'd just let that wign nut out and put it all back in there....only thing i noticed is that that the throwout shaft return spring does not pull the throwout arm all the way back to the furthest out position that the arm can move too....do i need a new one?....are there any other things i should look at?...

i gotta get up and running by thursday, but i am making a list of parts to order for the next time i take the engine out....

thanks, mark

Tue May 18, 2004 7:38 am

It sounds like there are many variables invloved here, but I've found that I always shift a bit before the shift marks. Not way before, but a few miles an hour before each mark. I treat each mark as a red line (partly because they are red).

-Taylor