Having recently got my Trans Am on the road since buying it, I've noticed that overdrive comes in about 30-40mph. When this happens in the 35-40 speed zones, the rpm's are sitting about 1000 and it seems like the fuel is really being dumped there(Lg4). At 55-65 mph the mileage is great. Should I manually (auto trans) be in Drive not Overdrive at those speeds? Will it burn up my transmission? Should my milelage improve? I have 2.73's and I'm sure that's why the rpm is low.

 

That is normal for that speed with those gears. That is what my '86 did with the same setup. You should be able to cruise at those RPM's but will get better acceleration (and maybe better mileage?) by holding it in D3.

 

I always hold mine in D3 until I get up to about 40-45, otherwise it seems to bog it down if I have it in OD. Besides, like Leo said, you get better acceleration...

KAM

 

not to mention at those speeds is y our lockup threshold, your tranny's converter may get "worn clutch syndrom" (since your stall is about there) and start kicking in and out of lockup. (like mine) dont let it kick into overdrive until about 50 MPH... just words of advice from a sorry 700R4 owner... hellz i went to a Super T-10 manual but the frickin thing blew up behind my 500 horsepower, gota get it rebuilt now.

 

Kingtal0n is right about the wear caused by lugging in od. Od should only be used with speeds above 45 MPH "like anybody really does this." But you should only kick her in to od on the highway 50+MPH.

 

Wait... so you're all saying to keep it in D3 unless/until you get to about 50mph, then manually shift it into OD for the improved performance?

------------------
1985 Camaro SC - 2.8L, auto. Stock.

 

Especially if you have a V-6 (or any low geared 700) since the RPM's are higher the wear and tear on the input sprag is much greater.

 

But manually shifting it into OD from D won't hurt anything? Thats what I was asking.

(or manually shifting it from anything to anything while in-gear and moving for that matter)

 

OK GENERAL RULE OF THUMB:
if your tranny is STOCK or NEAR STOCK AND / OR
YOU do NOT have a manual valve body THEN:
IT's O.K. to go from say, 1st to 2nd, then to 3rd, then to OD... but NOT OK to go from OD to 3rd, or 3rd to second, or 2nd to third UNLESS you can manage to time it perfectly.... but as a rule of thumb, if you dont want to kill your 700R4, dont downshift at ALL EVER.. i made this mistake... dont do it... wear it out to fast!! but upshifting (1st-2nd-3rd-4th) is PERFECTLY fine in FACT i would recommend it ever now and then, just to let your RPMS run up and clean out ure engine without having to WOT it all the time.

 

Hold on now, different people are telling me different things. I know it is ok to upshift the 700r4 but someone told me it was also ok to downshift from OD to D when climbing or descending hills as long as you give it gas to keep the line pressure the same. In fact it was Pro Built Automatics who told me this and I thought he was very knowledgeable about automatic transmissions. Check out this posting https://www.thirdgen.org/messgboard/...ML/002338.html Who do I believe??

[This message has been edited by CAMARORS1991 (edited April 24, 2001).]

 

its ok to downshift from OD to D. i have done it several times. dont worry. and my tranny is stock. but dont get to lower gears while moving its bad.

and you can always up shift no matter! i have a B&M and i upshift all the time!

have fun and if it breaks, blame it on a friend!! just playin

------------------
Jarrad
1990 IROC-Z L98 350 TPI
TH-700R4
G92- 7.5" 10 Bolt 3.23gears
Bright Red Hardtop/ Grey Custom Interior
5,507 IROC's Hardtops/Ttops; 2,415 5.7L IROC's Produced in 1990

DAILY DRIVER: 1991 S10 2.5L/5SPD WITH CAMARO RIMS

 

Manually downshifting to 3rd is no problem. Yes, they are small clutches but they are only meant to hold on deceleration. On acceleration the sprag still does the holding. I have a theory that if the overrun clutches are burnt then you likely have a bad sprag (which will need replacing anyways). I have a high mileage 700 in my '88/V6 that I know is in need of a new sprag (V6's have lower gears=higher RPM=higher stress on the sprag) that I haven't had the time to O/H so whenever I need to KD from 4th to 3rd or lower, I manually downshift to 3rd. The O/R clutches help the sprag to grab and hold. A slipping sprag leads to worn/stripped forward clutches and wildly flared out Sun Shell and Reverse Drum.

 

trust pro-built. Dana is always right about this shi*. I know from experience you shouldn't downshift at all on a stock tranny, no matter what gear its in. Don't do it if it isn't nessessary, it CANT be good for it, even if it isnt bad for it, doesnt mean its GOOD for... as the saying goes. either way, 700R4 is strong, but the less stress the longer it lasts...

 

dam looks like im not down****in from 3rd to 2nd, what if i put a shiftkit in it and a b&m slapshifter, will it still hurt my 700r4 if i keep downshiftin?

 

OK, let's try this again. The question was whether or not to downshift from O/D to DD, right?

I read the pasted post and what I read is about downshifting into even lower gears. Now it is suggested that you need the larger Int/Rev Boost Valve. This is especially true IF you have an early 700 (@'82-'85) since on those you can have lower pressure in Man1 and 2 than what the full line pressure is in Man3 and O/D. On the later versions GM changed the PR system to raise minimum line from @160 to 175 AND they corrected the Man1 and 2 boosted pressures to be @ the same as max line in the normal Drive positions.

That is all well and true BUT, it has nothing to do with the original question. Should he manually downshift from O/D to D. I say yes. The reason is that the sprag, being one of the weakest points durability wise in a 700 will be aided on the reapply. Mention is made in the pasted posts about the band coming on too slow. Again, this has nothing to do with the shift from O/D to D, as the band is ON in 4th and comes OFF in 3rd. It only comes into play if you are talking about going into a LOWER gear (It comes on again in 2nd). This was NOT the question.

There are many reasons why a 700 could have 'blown up' but it likely would have done that anyhow. If you put in a TRUE Shift Kit (TransGo) your trans will last much longer. If the sprag is on the way out (they wear out, due to how they function, sort of like a tire) it won't matter what you do to the trans. This is why I manually shift mine down (not under power, by the way) from O/D to D, I know the sprag/Forward Clutch Teeth can't have much life left. It is the original trans W/@ 132K on it and only a TransGo Shift Kit (not Reprogramming Kit). I would skip the shifter change though. I have seen trannies burn up because of shifter missalignment (OK in one gear position but not in another) caused by universal shifters.