[Socrates]

Howdy,

I broke the input/drive gear on my TH400 and I'm attempting to replace the gears in the pump. In my haste to open up the front pump I didn't carefully look to see which direction the drive gear goes back in, with the tangs that engage the converter either up or down with respect to the front half of the pump.

Put another way, does the half of the drive gear with the 2 tangs sit with the tangs closest to the converter and a space behind the tangs looking into the pump from the front, or do the tangs sit all the way back with respect to the converter?

On the subject of the pump gears, I'm told there are different sized gears. I'd like to buy new gears, so what do I need to look for regarding the different sizes? Would the size differences in the gears be obvious? The trans I'm fixing is a Switch Pitch TH400, so just getting a new front pump isn't such a simple or cheap matter, and I'd rather conserve and rebuild whenever possible.

Thanks so very much!

[Half-Inch Stud]

Tangs least engaged.
Tangs further from Converter.
Tangs up in Pump cover.
Tangs score the Pump Back cover.
Converter disengages from tangs easiest.

All saying the same ting.

[67 Lamnas]

Place the gear in the pump housing so the tangs are AWAY from the convertor.

The stock gears are more than adequate for most all applications.......just check the gears for wear......

With the large gear on the bench, drop the small gear inside so the teeth engage......if you can't pull the drive gear teeth out of engagement of the driven gear teeth, they're fine.

[vidguy]

I just sweated this too. I removed my pump to do something..

Here's a link to the Google Book result.
http://books.google.com/books?id=iU-...um=6&ct=result

[Socrates]

Thanks so much for the quick replies!

Anyone have a source for new quality pump drive gears? Even a heavy duty set, maybe? Can I order gears from Napa or other local chain or is it more a specialty item?

I'm not making offensive power with my E-head'd 428, though it was enough to break the tangs, nonetheless. The trans shops I called on this previously that built the trans (PAE in Texas) said it's likely just a quality control issue and regular replacement gears would suffice, as breaking the tangs are extremely rare, though if a HD set exists and don't cost too much, why not, right?

[67 Lamnas]

Originally Posted by Socrates

Thanks so much for the quick replies!

Anyone have a source for new quality pump drive gears? Even a heavy duty set, maybe? Can I order gears from Napa or other local chain or is it more a specialty item?

I'm not making offensive power with my E-head'd 428, though it was enough to break the tangs, nonetheless. The trans shops I called on this previously that built the trans (PAE in Texas) said it's likely just a quality control issue and regular replacement gears would suffice, as breaking the tangs are extremely rare, though if a HD set exists and don't cost too much, why not, right?

This place carries standard pump gears....looks like you have to measure the old ones.....

You WILL be replacing the pump bushing.....right??

http://www.tsr-racing.com/shop/TH400/TH400pricelist.php

[jakeshoe]

Standard pump gears are fine, even at the 1500 HP level. They don't get broken unless you have an improper converter installation, too tight pump clearances and they bind when they get hot, or something goes through them.

I can get pump gears for you, they are relatively inexpensive, $15 or so, but I would try to get a set from a local trans shop. A reman pump is also not too expensive, might be a good investment, new pump and stator bushings.

And yes they are different thicknesses, .721 is the standard thickness IIRC, but I hand fit them. Get the closest size I can and sometimes flat sand them to get the perfect clearance.

[TTS]

Originally Posted by Socrates

The trans shops I called on this previously that built the trans (PAE in Texas) said it's likely just a quality control issue and regular replacement gears would suffice, as breaking the tangs are extremely rare, though if a HD set exists and don't cost too much, why not, right?

I haven't seen a HD set. Aftermarket TH pump gears have been poor quality forever. GM gears aren't available, so we have to buy what's available.

An engine miss can break the drive lugs off very quickly.

Visit your local transmission shop, tell them you want a .727" gear set. Don't pay more than $15.

[stevep]

Aren't the Switch-Pitch pump gears thinner than .727?

[jakeshoe]

SP used the same gears as the others as best as I can remember, the pump is obviously different. I have a SP400 with a GV in my '69 Chevelle SS.

.721" is std thickness I'm almost certain but you can flat sand a thicker set down, but if you are taking off more than a thousandths or two, have fun

[vidguy]

transmissionpartsusa.com
Like $12.00, that's where I got mine.

[Half-Inch Stud]

Switch-Pitch Pump gears are SAME. Pump castings are "similar" , Switch-Pitch Front pump neck quite different.

[TTS]

Originally Posted by stevep

Aren't the Switch-Pitch pump gears thinner than .727?

I didn't read that part.

I haven't seen a SP pump in so long, I don't know if they're different. As far as I know they're all .727"