Team Chevelle banner
1 - 20 of 20 Posts

·
Registered
Joined
·
617 Posts
Discussion Starter · #1 · (Edited)
'morning all. Spend the weekend changing weights but have a number of questions! :)

1) Why is there only one of each weight? The documentation says it's ok even to have only one inner weight but surely this causes imbalance? Driving the car today, it does have a high frequency vibration when I go above 75mph, could this cause it? I'm afraid I'll knacker the transmission driving with different sized weights

2) I can't find any clear explanation about the difference between changing weights and springs. All the documentation and Google says is weights changes the shift point and springs changes how far they are apart. ?? What? Ok, example:

Before changing the weight (only one changed), 2-3 shift was at 4400. I changed one weight and left the spring and now it changes at 1-2 - 3900 and 2-3 - 4200. So what will a lighter weight do? Change one? Both?

So when the 2-3 shift currently is later than the 1-2, will a stiffer sping cause 2-3 to go lower compared to 1-2? Or have I misunderstood?

3) If I currently have 3900 and 4200 what should I change to get 5500 and 5300? And are those even good shift points when peak power is at 4800?

EDIT:

4) What determines at what RPMs it will kickdown?

Thanks for any advice
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #2 ·
No-one? :confused: :(

Does someone at least have an opinion about the vibrations with uneven weights?

I've ordered a second kit now (it's the B&M one) so I can put the same weights in, I just feel they're mis-selling it claiming you only need one.
 

·
Premium Member
Joined
·
291 Posts
On mine the shift was too soon. Changed the weights don't remember which way and the shift point was higher than I wanted. Don't even know where. At 6K I backed off so it would shift. Weighed all the weights on a scale and determined a middle ground between the two settings. Works great now. 5700 to 5800 full throttle and 4600 to 4800 part throttle. Just cruising shifts are much lower. Just some trial and error and keep track of where you are and where you have been. Could be more of an exact science from a trans guy, but that I am not. So experimenting worked for me.
 

·
Lifetime Founding Member
Joined
·
14,758 Posts
On mine both shift points were way too soon due to the trans originally being from a car with a much higher (lower numerically) rear gear than mine. I experimented with different springs to get it right. Didn't touch the weights.
 

·
Premium Member
Joined
·
7,278 Posts
On my TH400, I left the springs alone and used the #3 and #4 weights from the B&M kit. Both shifts are now about 5600.
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #7 ·
Thanks for this input, looks like experimenting will be the way to go but it's a pig getting that cover on and off!

I don't understand the rear gearings influence and six months ago I had mine changed from a 2:73 to a 3:42 but that didn't change the shift points.
 

·
Premium Member
Joined
·
7,278 Posts
I don't understand the rear gearings influence and six months ago I had mine changed from a 2:73 to a 3:42 but that didn't change the shift points.
I don't think Von is saying that rear gearing affects shift points. I think he is saying that the factory calibrates the governor to shift at lower rpms with 2.73 gears, for example, and calibrates the governor to shift at higher rpms with 3.73 gears, for example.
 

·
Lifetime Founding Member
Joined
·
14,758 Posts
Well I was assuming my low shift points (speeds) were due to the trans coming from a car with a 2.56 rear gear (per speedo gears) and mine has a 3.36. If a car with a 2.56 shifts to 2nd at say 15 mph at a certain rpm, with a 3.36 gear the speed will be much lower at the same rpm. Also, since shifts are controlled by line pressure, which is affected by both the governor and the vacuum modulator, a lower vacuum signal in a car with lower numerical gears could cause an earlier shift. Mike could be right though.
 
G

·
Von,
You are correct. These trans are calibrated differently for differing rear ratios. The governor (and shift points) is affected by the rear ratio since it is driven by the output shaft.
The trans doesn't know the input rpm, it has no way of sensing it.
 

·
Premium Member
Joined
·
7,278 Posts
My bad, I didn't stop to consider that the governor is driven off the output shaft.
 

·
Premium Member
Joined
·
7,278 Posts
Wait, I've confused myself again...the output shaft is upstream of the ring & pinion, so the governor senses output speed, not road speed. I would not think that changing rear gears would affect shift points.
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #13 ·
Right, I replaced one weight without knowing what the stock weights compare to in the B&M kit, with a #4 which dropped the RPMs. I've ordered another kit and will put 2 #5 in instead.

Changing weights shouldn't affect part throttle shift, should it?
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #14 ·
I really, really wish someone could give me a pointer. I've spent a week on this now and I'm sick of getting under the car getting that cover on and off all the time.

I have the problem that whatever combination of weights I use it shifts at either 4000rpm or never. I'm aiming for low to mid 5000rpm but no matter what I do I just get 4000rpm or never.

There's no help on the Internet. Nothing about which weights does what approximately. And I can't find anywere explaining exactly how the governor works. I can see the basic principle but... I assume the hydraulic pressure comes in the middle slot, varies with rpm (?), and that's what keeps the weights in?

What about inner and outer weights and the springs? I'm trying to get my head round when the outer weights would go out, what effect this has on the plunger with different springs, when the inner weights would go out... Again, no-where can I find conclusive descriptions of what the inner, outer weights and springs actually do. The governor senses output speed right, but the pressure against it is input speed but modulated by manifold vacuum? My head's spinning!

If some-one could just say "If you put weight this and that in you'll get roughly early 5000rpm" I'd be so happy. I can't email B&M because they're old fashioned and don't use email and it's expensive calling from the UK if they're going to spend 20 minutes explaining to me. I guess if no-one can help I'll just have to spend the money on a call...

Thanks for any bit of advice given.
Henrik
 

·
Lifetime Founding Member
Joined
·
14,758 Posts
I don't have a cut and dried answer but I was able to get my shift points where I want them just by experimenting with gov springs. My trans came out of a car with 2.56 rear gears but mine has 3.36. The springs came in a $15 Trans-Go shift improver kit called the "No Yo Yo" kit. I got it at www.bulkpart.com. I believe you must also have your kickdown linkage adjusted properly for correct WOT shift points. The kickdown linkage must be fully extended (pulled away from trans) at the same point as the carb reaches wide open throttle position. Also be sure the vacuum modulator is good and getting full manifold vacuum with no vacuum leaks.
 

·
Premium Member
Joined
·
7,278 Posts
I have used the B&M weight/spring kit on two TH350's and one TH400, and it was fairly easy on all three to zero in on the weights/springs needed for a 5500 RPM shift. I'm wondering if von is closing in on the problem...make sure your kickdown and vacuum modulator are working properly.
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #17 ·
How do I find out? I adjusted the cable when installing a new carb recently and it kicks down fine. How do I test the modulator? It seems to shift fine depending on load but I'll go double check the vacuum hose.
 

·
Lifetime Founding Member
Joined
·
14,758 Posts
On the kickdown, first make sure your carb linkage is adjusted properly by having someone push down the accelerator pedal all the way while you see if the carb throttle shaft will move any further open. Then disconnect the kickdown cable at the carb and open the carb to WOT while pulling the kickdown cable all the way extended out of the trans. See if the connector matches up to the attachment point at the carb. If not, adjust the kickdown cable at its attaching bracket til it does. For the modulator and vacuum line, disconnect the line at the modulator and put a vacuum gage on the line while the engine is running or disconnect the line at the intake manifold while not running and put a vacuum pump on it to see if the line and modulator hold vacuum. If any trans fluid runs out of the line or modulator when you disconnect the line at the modulator the modulator is bad. Make sure the modulator holds vacuum.
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #19 ·
Right, I give up! Makes no bloody sense!

To add to the injury I just poured a bottle of old ATF in there that had all sorts of dirt and crap in it. How bad is this? Can I get away with flushing the fluid or do I need a new filter as well? I only drove it up on the ramps after realising.

Anyway, kick down cable and modulator are fine, to answer previous posts.
 

·
Registered
Joined
·
617 Posts
Discussion Starter · #20 ·
Well, I gave up back then after having spent almost $400 trying to get this to work, but went racing a couple of weekends ago and going again tomorrow so really wanted to give this another shot.

This time I cut my existing weights instead. Stock shift points were 4400/4200.

Cut a corner of one weight and got 5000/4600! Result! Was aiming for 5500/5200 so that was exactly half. Cut an identical corner of the other weight, NO CHANGE! Cut one more corner of the first weight, again NO CHANGE!

*sigh* This governor actually doesn't follow the laws of physics, how did GM manage that?

I'll try changing springs now but don't have much hope.
 
1 - 20 of 20 Posts
Top