TH350 Problems - 2004r Recommendations

[DavidOrr]

Tranmissions are not my area of expertise, so please excuse the rudementary questions.

I'm having problems with a TH350, my ultimate goal is to replace the 350 with a 2004r. However, I am experiencing problems with the 350 that I think are not directly related to the actual tranmission and will exist even after a conversion.

I was having issues with a clogged exhaust system that appeared to be also affecting the tranmission. The tranmission was unable to hold 3rd gear. 1-2 was fine, 2-3 had problems. Usually I could manully shift and force it to 3rd, however it would not hold, typically it would slip back to second. I began to belive I had a heat problem as a result of the exhaust system, so I popped the plug out of the catalytic converter (opening a 1.5" diameter exhaust lead) and took it for a 50 mile test drive without problems. Put a plug back into the cat and begin to experience problems within 2 blks of a test drive. Again my thought was heat, due to the malifunctioning exhaust.

Put headers on the car, which by the way is a 79 corvette, had a new exhaust system installed - hoping this would help with the trans problems. The problem still exists however it gets dramatically worse as the car heats up. Now I am having delayed shifts from 1-2, slipping from 2-1, If I make it to 3rd it will quickly fall back to 2.

Again thinking it was heat, I replaced the metal cooler lines, which were close to the headers, with rubber lines - running them as far from the exhaust as possible. Still having problems.

Drained fluid, replaced filter, replaced vacuum modulator - still having problems.

So am I fighting a heat issue, did my transmission finally give up, if I put a new tranmission in am I going to have the same problems?

2004r - when I do the conversion, is there a specific model/year that I should look for. Initially I will be on a budget - my goal would be to find a used unit and use it for a while then rebuild it later. I have a midly modified 350 small block, we'll say less than 300hp with 3:55 rear end gearing.

Thanks -David

 

[MeanBuicks]

The first thing to check is the governor and it's bore in the case. Measure the OD of the governor shaft. At no point should it measure smaller than 0.799". Also, run your finger in the bore to check for roughness or wear. An internal leak here will cause a world of problems.

Next, make sure that the spool valve inside the governor shaft is free and not sticking. I would also take a look at the vacuum modulator system.

Be sure that your vacuum line from the intake to the modulator is in top shape with no kinks or leaks. It should be a metal line with a couple inches of rubber hose on each end for connections. The modulator itself contains a vacuum diaphram. Make sure the diaphram doesn't leak.

If all this stuff looks good, it'd be best to have a line pressure check done on the transmission.

As far as 200-4R recommendations, use the search function here first as this type thing is discussed with regularity in this forum.

 

[HOTTOGO]

Good 200-4R's...

Code Model
BRF 86-87 Grand National Servo casting # = 94 Lipseal servo w/
strongest spring
TAF* 89 Anniversary T/A Servo casting # = 94 Lipseal servo w/
strongest spring
CZF/CRF 86-87 Monte Carlo SS Servo casting # = 92 Lipseal servo w/ 2nd
strongest spg
OZF/KZF 85-7 442 , 83-4 Hurst Olds Servo casting # = 92 Lipseal servo w/
2nd strongest spg
Only buy transmissions produced after 1/84; avoid 88 models; 90 models from Caddies

The most common "good" ones are the ones in Monte Carlo SSs. The reason the 90 models are good is because they have all the technical upgrades, including the best GM input shaft and the 690 front pump.

 

[WE4]

The 350 guys problem is vacuum related. Gaurenteed!

Vaccuum is his problem. one way or the other.

 

[HOTTOGO]

If I wasn't so gun shy...

that was my guess, choked exhaust = bad vacuum, right? Check for other leaks as well as to the modulator. When did problems start? Any changes made to eng. prior to that?

 

[DavidOrr]

HOTTOGO a better question might be what has not changed. Put a new cam in, ran for a couple of weeks. Carb was running real lean, fouling plugs and compounding my exhaust issues. Driving home one day, fouled number 3 - then I started experiencing transmission problems.

Replaced carb with a Holley Street Avenger, new fuel pump, edelbrock performer intake, holley competition headers, new true dual exhaust.

Now the tranmission is worse, cold it runs fine - once warm it gets progressively worse.

Last time I checked vacuum - couple of wees ago - I was pulling 12 at idle - roughly 18 under @ 3k rev.

Bruce, HOTTOGO what should I be pulling at the modulator?

Took it by a tranny shop last night, they wanted me to take it someplace else - not even interested in touching it.

 

[HOTTOGO]

Originally posted by DavidOrr
HOTTOGO a better question might be what has not changed. Carb was running real lean, fouling plugs and compounding my exhaust issues. Driving home one day, fouled number 3 - then I started experiencing transmission problems.

Carb running lean won't foul the plug, blister or crack it maybe.

Now the tranmission is worse, cold it runs fine - once warm it gets progressively worse.

May be due to eng. warming up causing prob. not trannie. maybe carb/mani gasket leak, try spraying starting fluid around them and see if rpm's pick-up.

Last time I checked vacuum - couple of wees ago - I was pulling 12 at idle - roughly 18 under @ 3k rev.

very low @ idle for a mild eng. should be a min. 17, 18-20 better. Higher rpm and load should equal lower vac. 7-10, yours is just the oppisite? May have something to do w/prob.

Bruce, HOTTOGO what should I be pulling at the modulator?

Same as manifold vac.

I'll give it some more thought.

 

[88MCSS]

avoid 88 models;

Why do you say to avoid 88 models?

John

 

[GNVAIR]

Re: Good 200-4R's...

Originally posted by HOTTOGO

Only buy transmissions produced after 1/84; avoid 88 models; 90 models from Caddies

The most common "good" ones are the ones in Monte Carlo SSs. The reason the 90 models are good is because they have all the technical upgrades, including the best GM input shaft and the 690 front pump.

I am curious as to what is wrong with the 88 model transmissions. I have the original CZF behind the turbo 6 in my father's car and it seemed to work fine.
What is your reasoning to avoid the 88's?

 

[HOTTOGO]

YIKES!!!

I did not write the statement, it was a copied quote I recieved from the person that actually turned me on to this fourm, I didn't even really ? that point myself. Didn't mean to open a can of worms. BRUCE HELP! any truth to that statement

 

[HOTTOGO]

I have a possible answer?

Originally posted by WE4
No accumulator was changed in 1987 but only the housing in preparation for the big change in late 88 which Buicks never saw. It was on a couple of late Montes and all caddys and of course the tta. If on a TTA you mod the accumulator the way we do on GN's , you will burn up L/R clutch and possibly the High clutch if you try to drive through it once. One time is all it will take to fry. But the housing change and the TTa change had zero effect , as far as gaskets and or anything else for that matter. Just NEVER remove the ck ball if working on a late late one.

 

[WE4]

Phooey!!!!

The input shaft and 690 pump thing is true however. They are better but the only ones to avoid are 82-83 big car trans'. Some hard parts are ok but in essence they are weaker. Thats it.