6bt mated to a thm400 gm???

[BAnsley]

I have a 87 v30 454/thm400/np205. Wanting to swap in a 93 6bta,Ihave the parts to bolt in the cummins, but was wondering if thm 400 handles a stock 6bt. I plan on overhauling the trans and installing a shift kit. I have seen a mechanical modulator for diesel application. But how is the p30 vans setup?





Thanks Brian

 

[DogDiesel]

THM-400 Modulation

The transmissions used in the P30 vans are actually THM-475, which is the T400 with diesel converter and maxxed out clutches.



The P30 transmission uses a fixed modulator, a spring with solidly adjusted set-screw bolt and nut. I removed my modulator and installed the cable modulator from a THM-400 Hummer. At low throttle it shifter fine, but gouge on the throttle and your teeth get loose on each shift. After one extended road-test, where no adjustment was satisfactory, I promptly re-installed the bolt-nut modulator.



4BT in early Bronco. 3:50 gears, with 35" tires = 2:78-1 overall ratio.



The problem simply is my transmission has the hardest damn clamping pressures I've seen on a T400 series. I have my 4BT/THM-475 set to shift at 1400 RPM and for the most part, it shifts like glass. It accelerates nicely, and I get smooth shifts. Firm, no slop, but I keep my teeth. If I turn it up mildly, to say 2100 RPM, it will snatch a shift so hard, my rear end jumps sideways and rubber scratches on each shift, to include high gear. I have locking rear gears. Now, I am not talking throwing you back in the seat acceleration, just bone snapping, teeth loosening, u-joint destroying hard, jerking and damn annoying shifts.



I just purchased a low-mileage 120HP 4BTA that was mated to a THM-475. The set-up took the pinion bearings out of the P30 van rear end. Ironic, isn't it?



So the question is: WILL the THM hold up to a 6BT?

Stock, yes. Very likely.

 

[DogDiesel]

Thm-475

BTW - the guy I bought the van from has the THM-475 for sale -- STILL.

He wants $300. I have the GM adapter & flywheel.

Wayne

 

[BAnsley]

I plan on machining the clutch pistons to accept another clutch and and probly add a upgraded sprag unit. does any know what i need exactly to switch my gas th 400 to a fixed modulator? do I have get a new modulator spool valve, and is the stall speed the same as a gm ''low stall'' diesel unit. Where do go to buy a new fixed modulator valve?







Thanks Brian

 

[Speedo]

The transmissions used in the P30 vans are actually THM-475, which is the T400 with diesel converter and maxxed out clutches.

The P30 transmission uses a fixed modulator, a spring with solidly adjusted set-screw bolt and nut. I removed my modulator and installed the cable modulator from a THM-400 Hummer. At low throttle it shifter fine, but gouge on the throttle and your teeth get loose on each shift. After one extended road-test, where no adjustment was satisfactory, I promptly re-installed the bolt-nut modulator.



4BT in early Bronco. 3:50 gears, with 35" tires = 2:78-1 overall ratio.



The problem simply is my transmission has the hardest damn clamping pressures I've seen on a T400 series. I have my 4BT/THM-475 set to shift at 1400 RPM and for the most part, it shifts like glass. It accelerates nicely, and I get smooth shifts. Firm, no slop, but I keep my teeth. If I turn it up mildly, to say 2100 RPM, it will snatch a shift so hard, my rear end jumps sideways and rubber scratches on each shift, to include high gear. I have locking rear gears. Now, I am not talking throwing you back in the seat acceleration, just bone snapping, teeth loosening, u-joint destroying hard, jerking and damn annoying shifts.



I just purchased a low-mileage 120HP 4BTA that was mated to a THM-475. The set-up took the pinion bearings out of the P30 van rear end. Ironic, isn't it?



So the question is: WILL the THM hold up to a 6BT?

Stock, yes. Very likely.

Actually the TH-475 is a heavy duty version of the TH-400 and was used with gas engines. Some of the ones that I have seen came without a park pawl and a drum style park brake on the the tailshaft housing. They came with 6 friction discs in the fwd. clutch housing and straight cut gears in the planetaries, which makes for a definite whine in low range.



Gus